# Patent

## Title
Systems and methods of radiometrically determining a hot-spot temperature of tissue being treated

## Abstract

According to some embodiments, systems for energy delivery to targeted tissue comprise a catheter with an ablation member, a radiometer configured to detect temperature data from the targeted tissue, a processor configured to determine a calculated temperature (e.g., an extreme temperature, such as a peak or trough temperature) within the tissue by applying at least one factor to the temperature data detected by the radiometer, the processor configured to compare the calculated temperature to a setpoint and an energy source configured to energize the ablation member and to regulate delivery of ablative energy to the targeted tissue of the subject based at least in part on the comparison. In some embodiments, the factor depends on at least one characteristic of the targeted tissue. Information regarding a tissue characteristic can be provided using information from an imaging set (e.g., intracardiac echo) or an electrical signal of the subject (e.g., electrocardiogram).

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent application Ser. No. 13/418,136, filed on Mar. 12, 2012, the entirety of which is hereby incorporated by reference herein.
The entireties of U.S. Pat. No. 8,206,380, filed as U.S. patent application Ser. No. 12/483,407 on Jun. 12, 2009 and issued on Jun. 26, 2014, U.S. Publication No. 2012/0035603, filed as U.S. patent application Ser. No. 13/142,865 on Sep. 16, 2011 and published on Feb. 9, 2012, U.S. Publication No. 2013/0204240, filed as U.S. patent application Ser. No. 13/368,112 on Feb. 7, 2012 and published on Aug. 8, 2013, and U.S. Publication No. 2013/0324993, filed as U.S. patent application Ser. No. 13/486,889 on Jun. 1, 2012 and published on Dec. 5, 2013, are all hereby expressly incorporated by reference herein and made a part of the present application.


FIELD
This application generally relates to ablation devices, systems and methods, and more specifically, to devices, systems and methods for measuring and controlling temperature during tissue ablation.
BACKGROUND
Tissue ablation may be used to treat a variety of clinical disorders. For example, tissue ablation may be used to treat cardiac arrhythmias by destroying (e.g., at least partially or completely ablating, interrupting, inhibiting, terminating conduction of, otherwise affecting, etc.) aberrant pathways that would otherwise conduct abnormal electrical signals to the heart muscle. Several ablation techniques have been developed, including cryoablation, microwave ablation, radio frequency (RF) ablation, and high frequency ultrasound ablation. For cardiac applications, such techniques are typically performed by a clinician who introduces a catheter having an ablative tip to the endocardium via the venous vasculature, positions the ablative tip adjacent to what the clinician believes to be an appropriate region of the endocardium based on tactile feedback, mapping electrocardiogram (ECG) signals, anatomy, and/or fluoroscopic imaging, actuates flow of an irrigant to cool the surface of the selected region, and then actuates the ablative tip for a period of time and at a power believed sufficient to destroy tissue in the selected region.
Although commercially available ablative tips may include thermocouples and/or other sensors (such as thermistors, other conventional temperature-measurement devices, e.g., devices that merely detect or measure a temperature at or near the temperature measure device, etc.) for providing temperature feedback via a digital display, such thermocouples typically do not provide meaningful temperature feedback during irrigated ablation. For example, the thermocouple or other sensor only measures surface temperature, whereas the heating or cooling of the tissue that results in tissue ablation may occur at some depth below the tissue surface. Moreover, for procedures in which the surface of the tissue is cooled with an irrigant, the thermocouple will measure the temperature of the irrigant, thus further obscuring any useful information about the temperature of the tissue, particularly at depth. As such, the clinician has no useful feedback regarding the temperature of the tissue as it is being ablated or whether the time period of the ablation is sufficient. Because the clinician lacks such information, the clinician furthermore cannot regulate the power of the ablation energy so as to heat or cool the tissue to the desired temperature for a sufficient period of time.
Accordingly, it may only be revealed after the procedure is completed—for example, if the patient continues to experience cardiac arrhythmias—that the targeted aberrant pathway was not adequately interrupted. In such a circumstance, the clinician may not know whether the procedure failed because the incorrect region of tissue was ablated, because the ablative tip was not actuated for a sufficient period of time to destroy the aberrant pathway, because the ablative tip was not touching or sufficiently touching the tissue, because the power of the ablative energy was insufficient, or some combination of the above. Upon repeating the ablation procedure so as to again attempt to treat the arrhythmia, the clinician may have as little feedback as during the first procedure, and thus potentially may again fail to destroy the aberrant pathway. Additionally, there may be some risk that the clinician would re-treat a previously ablated region of the endocardium and not only ablate the conduction pathway, but damage adjacent tissues.
In some circumstances, to avoid having to repeat the ablation procedure as such, the clinician may ablate a series of regions of the endocardium along which the aberrant pathway is believed to lie, so as to improve the chance of interrupting conduction along that pathway. However, there is again insufficient feedback to assist the clinician in determining whether any of those ablated regions are sufficiently destroyed.
Despite the promise of precise temperature measurement sensitivity and control offered by the use of radiometry, there have been few successful commercial medical applications of this technology. One drawback of previously-known systems has been an inability to obtain highly reproducible results due to slight variations in the construction of the microwave antenna used in the radiometer, which can lead to significant differences in measured temperature from one catheter to another. Problems also have arisen with respect to orienting the radiometer antenna on the catheter to adequately capture the radiant energy emitted by the tissue, and with respect to shielding high frequency microwave components in the surgical environment so as to prevent interference between the radiometer components and other devices in the surgical field.
Radiofrequency ablation techniques have developed a substantial following in the medical community, even though such systems can have severe limitations, such as the inability to accurately measure tissue temperature at depth, e.g., where irrigation is employed. However, the widespread acceptance of RF ablation systems, extensive knowledge base of the medical community with such systems, and the significant cost required to changeover to, and train for, newer technologies has dramatically retarded the widespread adoption of radiometry.
SUMMARY
According to some embodiments, a method of facilitating energy delivery to a targeted tissue during a procedure (e.g., an ablation procedure) comprises activating a radiofrequency electrode to deliver radiofrequency energy to the targeted tissue, receiving a signal from a radiometer, the signal being indicative of temperature data of the targeted tissue, determining a calculated temperature within the targeted tissue by, at least in part, applying at least one factor (e.g., scaling factor, such as an estimation or correlation factor) to the temperature data received from the radiometer, receiving a setpoint temperature, comparing the calculated temperature to the setpoint temperature and regulating (e.g., automatically regulating) the radiofrequency energy delivered to the electrode based on, at least in part, a comparison between the calculated temperature and the setpoint temperature. In some embodiments, all or some of the steps are performed, at least in part, by a processor or other controller.
According to some embodiments, regulating (e.g., automatically regulating) a delivery of radiofrequency energy comprises attaining or maintaining the calculated temperature at or near the setpoint temperature (e.g., a temperature, a temperature range, a setpoint curve, etc.). In one embodiment, the calculated temperature comprises a peak temperature within the targeted tissue. In some embodiments, the at least one scaling factor comprises an estimation factor, the estimation factor depending on, at least in part, at least one characteristic of the targeted tissue (e.g., a thickness of the targeted tissue, whether the targeted tissue is “thick” or “thin,” a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue, a characteristic of the subject being treated, etc.). According to some embodiments, wherein the at least one factor depends on at least one additional input, the at least one additional input comprises a characteristic of the subject being treated (e.g., a subject's age, a subject's gender, a subject's height, a subject's weight, a condition or disease of the subject, etc.).
According to some embodiments, the method additionally comprises receiving information regarding the at least one characteristic of the targeted tissue via a user input device. In some embodiments, the method further comprises receiving information (e.g., automatically or manually) regarding the at least one characteristic of the targeted tissue via imaging data or electrical signal data of the subject. In some embodiments, information regarding a tissue characteristic can be provided using information from an imaging set (e.g., intracardiac echo) or an electrical signal of the subject (e.g., electrocardiogram). In some embodiments, information regarding the characteristics of the targeted tissue is provided manually. In some embodiments, the least one scaling factor is determined, at least in part, theoretically and/or experimentally.
According to some embodiments, a method of facilitating energy delivery to a targeted tissue during an ablation procedure comprises delivering energy (e.g., ablative energy, other energy, etc.) to the targeted tissue by activating an energy delivery member (e.g., an ablation member, such as a radiofrequency electrode, a microwave emitter, an ultrasound transducer, a cryoablation member, etc.), receiving temperature data of the targeted tissue using, at least in part, a radiometer, determining a calculated temperature within the targeted tissue by, at least in part, applying at least one factor (e.g., scaling factor, such as an estimation or correlation factor) to the temperature data received from the radiometer, receiving a setpoint temperature, comparing the calculated temperature to the setpoint temperature and regulating (e.g., automatically or manually) a delivery of ablative energy to the ablation member based on, at least in part, a comparison between the calculated temperature and the setpoint temperature. In some embodiments, all or some of the steps are performed, at least in part, by a processor or other controller.
According to some embodiments, regulating (e.g., automatically regulating) a delivery of energy (e.g., ablative energy) comprises attaining or maintaining the calculated temperature at or near the setpoint temperature, the setpoint temperature comprising a target ablation temperature, a temperature range or a set curve. In some embodiments, the at least one factor comprises an estimation factor, the estimation factor depending on, at least in part, at least one characteristic of the targeted tissue (e.g., a thickness of the targeted tissue, whether the targeted tissue is “thin” or “thick,” a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue, a characteristic of the subject being treated, etc.). In some embodiments, the calculated temperature relates to an extreme temperature (e.g., a peak or hot spot temperature, a trough or cold spot temperature, etc.) within the targeted tissue.
According to some embodiments, the ablative energy (e.g., ablative energy) delivery using the ablative member is configured to heat the targeted tissue and the extreme temperature comprises a peak temperature. In some embodiments, the energy (e.g., ablative energy) delivery using the ablative member is configured to cool the targeted tissue and the extreme temperature comprises a trough temperature. In one embodiment, the at least one characteristic of the targeted tissue is received via at least one of imaging data and electrical signal data of the subject. In some embodiments, information regarding a tissue characteristic can be provided using information from an imaging set (e.g., intracardiac echo) or an electrical signal of the subject (e.g., electrocardiogram). In some embodiments, information regarding the characteristics of the targeted tissue is provided manually. In some embodiments, the least one scaling factor is determined, at least in part, theoretically and/or experimentally.
According to some embodiments, a method of energy delivery to a targeted tissue during an ablation procedure comprises receiving temperature data of the targeted tissue using, at least in part, a radiometer, determining a calculated temperature within the targeted tissue by, at least in part, applying at least one factor (e.g., scaling factor, such as an estimation or correlation factor) to the temperature data received from the radiometer and regulating (e.g., automatically or manually) a delivery of ablative energy to the targeted tissue based, at least in part, on the calculated temperature. In some embodiments, the calculated temperature relates to an extreme temperature (e.g., peak or trough temperature, hot or cold spot temperature, etc.) within the targeted tissue; and wherein the at least one factor depends on, at least in part, at least one characteristic of the targeted tissue. In one embodiment, the at least one characteristic of the targeted tissue comprises a thickness of the targeted tissue, a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue, a characteristic of the subject being treated and/or the like. In some embodiments, all or some of the steps are performed, at least in part, by a processor or other controller.
According to some embodiments, a system for energy delivery to a targeted tissue of a subject comprises a catheter, probe or other medical instrument comprising a radiofrequency electrode, a radiometer configured to detect temperature data from the targeted tissue, a processor configured to determine a calculated temperature within the targeted tissue by applying at least one scaling factor to the temperature data detected by the radiometer, the processor being configured to compare the calculated temperature to a setpoint temperature, and an energy source configured to energize the radiofrequency electrode and regulate delivery of ablative energy to the targeted tissue of the subject based at least in part on a comparison between the calculated temperature and the setpoint temperature. In some embodiments, the calculated temperature relates to a peak (e.g., hot spot) temperature within the targeted tissue.
According to some embodiments, the at least one scaling factor comprises an estimation factor, the estimation factor depending on, at least in part, at least one characteristic of the targeted tissue (e.g., a thickness of the targeted tissue, whether the targeted tissue is “thick” or “thin” tissue, a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue, a characteristic of the subject being treated and/or the like). In one embodiment, the at least one factor further depends on at least one additional input, the at least one additional input comprises a characteristic of the subject being treated (e.g., a subject's age, a subject's gender, a subject's height, a subject's weight, a condition or disease of the subject and/or the like).
According to some embodiments, information related to the at least one characteristic of the targeted tissue is provided manually by a user (e.g., via a touchscreen, keypad, other input device, etc.). In some embodiments, information related to the at least one characteristic of the targeted tissue is provided using at least one of imaging data and electrical signal data of the subject. In some embodiments, information regarding a tissue characteristic can be provided using information from an imaging set (e.g., intracardiac echo) or an electrical signal of the subject (e.g., electrocardiogram). In some embodiments, information regarding the characteristics of the targeted tissue is provided manually. In some embodiments, the system further includes an input device (e.g., a touchscreen, keypad, other input device, etc.) configured to receive the setpoint temperature, the setpoint temperature comprising a target ablation temperature or temperature range of the targeted tissue, a set curve and/or the like. In some embodiments, the energy source is configured to regulate the delivery of energy to the radiofrequency electrode by comparing the calculated temperature to the setpoint temperature. In one embodiments, the at least one scaling factor is determined, at least in part, theoretically or experimentally.
According to some embodiments, a system for energy delivery to a targeted tissue of a subject includes a processor configured to determine a calculated temperature within the targeted tissue by adjusting temperature data received by a radiometer using at least one factor and an ablation energy source configured to energize an ablation member to deliver energy to the targeted tissue of the subject based on, at least in part, the calculated temperature. In some embodiments, the calculated temperature relates to an extreme temperature (e.g., a peak or hot spot temperature, a trough or cold spot temperature, etc.) within the targeted tissue. In one embodiment, the system additionally comprises an input device (e.g., a touchscreen, keypad, other input device, etc.) configured to receive a setpoint, the setpoint comprising a target ablation temperature of the targeted tissue or a set curve, wherein the energy source is configured to regulate delivery of energy to targeted tissue by comparing the calculated temperature to the setpoint. In some embodiments, the at least one factor comprises an estimation factor, the estimation factor depending on, at least in part, at least one characteristic of the targeted tissue (e.g., a thickness of the targeted tissue, a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue, a characteristic of the subject being treated, etc.).
According to some embodiments, the ablation member (e.g., radiofrequency electrode, ultrasound transducer, microwave emitter, etc.) is configured to heat the targeted tissue when energized and the extreme temperature comprises a peak temperature within the targeted tissue. In other embodiments, the ablation member (e.g., cyroablation emitter) is configured to cool the targeted tissue when energized and the extreme temperature comprises a trough temperature within the targeted tissue. In some embodiments, information related to the at least one characteristic of the targeted tissue is provided using at least one of imaging data and electrical signal data of the subject or is provided manually by a user.
According to some embodiments, a system for energy delivery to a targeted tissue of a subject comprises a processor configured to determine a calculated temperature within the targeted tissue by adjusting temperature data received by a radiometer using at least one factor (e.g., scaling factor, such as an estimation or correlation factor) and an energy source configured to deliver energy to an energy delivery member to deliver energy to the targeted tissue of the subject based on, at least in part, the calculated temperature. In some embodiments, the at least one factor comprises an estimation factor, the estimation factor depending on, at least in part, at least one characteristic of the targeted tissue (e.g., a thickness of the targeted tissue, a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue, a characteristic of the subject being treated, etc.). In one embodiment, the calculated temperature relates to an extreme temperature within the targeted tissue, the extreme temperature comprising a peak or hot spot temperature or a trough or cold spot temperature.
According to some embodiments, systems, devices or apparatuses and/or methods are disclosed that permit radiometric measurement of temperature at depth in tissue, and permit use of such measurements to control the application of ablation energy in an ablation treatment, e.g., a hyperthermia or hypothermia treatment, particularly in an automated fashion so as to maintain a target region of tissue at a desired temperature for a desired period of time. In some embodiments, such systems, devices and/or methods are configured to detect a “hot spot” or localized peak temperature of tissue being treated. The determination of such a hot spot temperature can, in some embodiments, depend, among other things, on the type of tissue being treated (e.g., the thickness or approximate thickness of the anatomical tissue to which energy (e.g., radiofrequency) is being directed or applied, other characteristics of the targeted tissue (e.g., type, composition, etc.) and/or the like). In some embodiments, the hot spot or peak temperature is calculated based on experimental or empirical models or approximations.
According to some embodiments, apparatuses, systems and/or related methods are disclosed herein that employ microwave radiometer components that can be readily constructed and calibrated to provide a high degree of measurement reproducibility and reliability. In some embodiments, apparatuses, systems and/or related methods permit radiometric temperature measurement and control techniques to be introduced in a manner that is accessible (e.g., readily accessible) to clinicians trained in the use of previously-known RF ablation catheters (e.g., with a minimum of retraining). In some embodiments, apparatuses, systems and/or related methods permit radiometric temperature measurement and control techniques are configured to be readily employed with or otherwise incorporated into existing RF electrosurgical generators, thereby increasing the efficacy of the systems, improving the safety of the systems, reducing the capital costs needed to implement such new techniques and/or the like.
In some embodiments, it further would be desirable to provide apparatus and methods that employ microwave radiometer components that can be readily constructed and calibrated to provide a high degree of measurement reproducibility and reliability.
In some embodiments, it also would be desirable to provide apparatus and methods that permit radiometric temperature measurement and control techniques to be introduced in a manner that is readily accessible to clinicians trained in the use of previously-known RF ablation catheters, with a minimum of retraining.
In some embodiments, it still further would be desirable to provide apparatus and methods that permit radiometric temperature measurement and control techniques to be readily employed with previously-known RF electrosurgical generators, thereby reducing the capital costs needed to implement such new techniques.
In some embodiments, it would be desirable to provide apparatus and methods for treating living tissue that employs a radiometer for temperature measurement, and a temperature control subsystem that uses feedback from the radiometer to regulate the power of ablation energy being applied to the tissue. In accordance with one aspect of the invention, systems and methods are provided for radiometrically measuring temperature during RF ablation, i.e., calculating temperature based on signal(s) from a radiometer. Unlike standard thermocouple techniques used in existing commercial ablation systems, a radiometer may provide useful information about tissue temperature at depth—where the tissue ablation occurs—and thus provide feedback to the clinician about the extent of tissue damage as the clinician ablates a selected region of the heart muscle. Furthermore, the temperature control subsystem may automatically regulate the power of the ablation energy applied to the tissue based on the tissue temperature, so as to maintain the tissue at the desired temperature and for the desired amount of time to achieve sufficient ablation.
In one embodiment, the present invention comprises an interface module (system) that may be coupled (e.g., reversibly coupled, irreversibly coupled/integrated) to a previously-known commercially available ablation energy generator, e.g., an electrosurgical generator, thereby enabling radiometric techniques to be employed with reduced capital outlay. In this manner, the conventional electrosurgical generator can be used to supply ablative energy to an “integrated catheter tip” (ICT) that includes an ablative tip, a thermocouple, and a radiometer for detecting the volumetric temperature of tissue subjected to ablation. The interface module is configured to be coupled (e.g., reversibly coupled, irreversibly coupled/integrated) between the conventional electrosurgical generator and the ICT, and to coordinate signals therebetween. The interface module thereby provides the electrosurgical generator with the information required for operation, transmits ablative energy to the ICT under the control of the clinician, and displays via a temperature display the temperature at depth of tissue as it is being ablated, for use by the clinician. The displayed temperature may be calculated based on signal(s) measured by the radiometer using algorithms such as discussed further below. The interface module further includes a temperature control subsystem configured to interface with the power control of the electrosurgical generator. The temperature control subsystem stores a setpoint temperature to which the tissue is to be heated, and regulates the power control of the electrosurgical generator based on the setpoint temperature and on the calculated temperature of the tissue so as to bring the calculated tissue temperature to the setpoint temperature and maintain it at that value for a desired period of time.
In some embodiments, the interface module includes a first input/output (I/O) port that is configured to receive a digital radiometer signal and a digital thermocouple signal from the ICT, and a second I/O port that is configured to receive ablative energy from the electrosurgical generator. The interface module also includes a processor, a patient relay in communication with the processor and the first and second I/O ports, and a persistent computer-readable medium. The computer-readable medium stores operation parameters for the radiometer and the thermocouple, as well as instructions for the processor to use in coordinating operation of the ICT and the electrosurgical generator.
The computer-readable medium preferably stores instructions that cause the processor to execute the step of calculating a temperature adjacent to the ICT based on the digital radiometer signal, the digital thermocouple signal, and the operation parameters. This temperature is expected to provide significantly more accurate information about lesion quality and temperature at depth in the tissue than would a temperature based solely on a thermocouple readout. The computer-readable medium may further store instructions for causing the processor to cause the temperature display to display the calculated temperature, for example so that the clinician may control the time period for ablation responsive to the displayed temperature. The computer-readable medium may further store instructions for causing the processor to close the patient relay, such that the patient relay passes ablative energy received on the second I/O port, from the electrosurgical generator, to the first I/O port, to the ICT. Note that the instructions may cause the processor to maintain the patient relay in a normally closed state, and to open the patient relay upon detection of unsafe conditions.
In some embodiments, the interface module further includes a temperature control subsystem that regulates the power of the ablative energy based on the calculated temperature.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematic illustration of a first embodiment of an arrangement including an interface module, temperature control subsystem, and power control interface according to one aspect of the present invention, including a display of the front and back panels of, and exemplary connections between, the interface module, temperature control subsystem, power control interface, a previously known ablation energy generator, e.g., electrosurgical generator, and an integrated catheter tip (ICT).
FIG. 1B is a schematic illustrating exemplary connections to and from the interface module, temperature control subsystem, and power control interface of FIG. 1A, as well as connections among other components that may be used with the same.
FIG. 1C is a schematic illustrating exemplary connections to and from an alternative embodiment of an interface module, temperature control subsystem, and power control interface, as well as connections among other components that may be used with the same.
FIG. 1D is a schematic illustrating exemplary connections to and from another alternative embodiment of an interface module, temperature control subsystem, and power control interface, as well as connections among other components that may be used with the same.
FIG. 1E is a schematic illustrating exemplary connections to and from yet another alternative embodiment of an interface module, temperature control subsystem, and power control interface, as well as connections among other components that may be used with the same.
FIG. 2A is a schematic illustrating internal components of the interface module of FIG. 1A-1B.
FIG. 2B schematically illustrates additional internal components of the interface module of FIG. 2A, as well as selected connections to and from the interface module.
FIG. 2C is a schematic illustrating internal components of the temperature control subsystem of FIGS. 1A-1B.
FIG. 2D illustrates a perspective view of an exemplary temperature control subsystem, power control interface, and interface module coupled to each other and to a previously-known ablation energy generator in accordance with the embodiment illustrated in FIGS. 1A-1B and 2A-2C.
FIG. 3A illustrates steps in a method of using the interface module and temperature control subsystem of FIGS. 1A-2D during tissue ablation.
FIG. 3B illustrates steps in a method of calculating radiometric temperature using digital signals from a radiometer and a thermocouple and operation parameters.
FIG. 3C illustrates steps in a method of controlling an ablation procedure using a temperature calculated based on signal(s) from a radiometer using the interface module and temperature control subsystem of FIGS. 1A-2D.
FIGS. 4A-4F illustrate data obtained during exemplary ablation procedures performed using the interface module, temperature control subsystem, and power control interface of FIGS. 1A-1B and 2A-2D operated in accordance with the methods of FIGS. 3A-3C.
FIG. 5A illustrates a plan view of an exemplary patient interface module (PIM) associated with an integrated catheter tip (ICT) for use with the interface module, temperature control subsystem, and power control interface of FIGS. 1A-2D.
FIG. 5B schematically illustrates selected internal components of the PIM of FIG. 5A, according to some embodiments of the present invention.
FIGS. 6A-6B respectively illustrate perspective and exploded views of an exemplary integrated catheter tip (ICT) for use with the interface module, temperature control subsystem, and power control interface of FIGS. 1A-2D and the PIM of FIGS. 5A-5B, according to some embodiments of the present invention.
FIG. 7 schematically illustrates an ablation system according to one embodiment.
FIGS. 8A-8C schematically illustrate embodiments of a catheter tip of an ablation system contacting tissue of a subject.
FIGS. 9A and 9B schematically illustrate embodiments of radiometer reception patterns for different targeted tissues of the subject.
FIG. 10 illustrates a chart that correlates actual temperature change at the “hot spot” obtained experimentally against temperature change measured by a radiometer to assist in the determination of the temperature at a “hot spot” or extreme (e.g., peak or trough) temperature location of a tissue volume being treated, according to one embodiment.
FIG. 11 illustrates one embodiment of an image depicting a portion of a subject's anatomy obtained by an imaging technique together with corresponding electrical activity signals of the heart.
FIG. 12 illustrates a block diagram of a temperature control scheme for an ablation procedure, according to one embodiment.
FIG. 13 illustrates a block diagram of an algorithm for automatic determination of tissue thickness, according to one embodiment.



DETAILED DESCRIPTION
Embodiments of the present invention provide systems and methods for radiometrically measuring temperature during ablation, in particular cardiac ablation, and for automatically regulating the power of ablation energy based on same. As noted above, commercially available systems for cardiac ablation may include thermocouples for measuring temperature, but such thermocouples may not adequately provide the clinician with information about tissue temperature. Thus, the clinician may need to make an “educated guess” about whether a given region of tissue has been sufficiently ablated to achieve the desired effect. By comparison, calculating a temperature based on signal(s) from a radiometer is expected to provide accurate information to the clinician about the temperature of tissue at depth, even during an irrigated procedure. Furthermore, a temperature control subsystem may be employed that monitors the calculated temperature, and automatically regulates or controls the power of ablation energy provided to the tissue so as to maintain the tissue at a desired temperature and for a desired time to achieve sufficient ablation. A “retrofit” solution that includes, in several embodiments, an interface module that works, for example, with existing, commercially available ablation energy generators, such as electrosurgical generators, or as described herein, as an integrated portion to a designed generator or other part of the system. In accordance with one aspect of the present invention, the interface module displays a tissue temperature based on signal(s) measured by a radiometer and includes, or is connected to, a temperature control subsystem that controls or regulates the power of ablation energy based on same via a power control interface, such that a clinician may perform ablation procedures with significantly better accuracy than can be achieved using only a thermocouple for temperature measurement.
The various systems, devices and/or related methods disclosed herein can be used to at least partially ablate and/or otherwise heat or cool one or more portions of a subject's anatomy, including without limitation, cardiac tissue (e.g., myocardium, atrial tissue, ventricular tissue, valves, etc.), a bodily lumen (e.g., vein, artery, airway, esophagus or other digestive tract lumen, urethra and/or other urinary tract vessels or lumens, other lumens, etc.), sphincters, other organs, tumors and/or other growths, nerve tissue and/or any other portion of the anatomy. The selective ablation and/or other heating of such anatomical locations can be used to treat one or more diseases or conditions, including, for example, atrial fibrillation, mitral valve regurgitation, other cardiac diseases, asthma, chronic obstructive pulmonary disease (COPD), other pulmonary or respiratory diseases, including benign or cancerous lung nodules, hypertension, heart failure, denervation, renal failure, obesity, diabetes, gastroesophageal reflux disease (GERD), other gastroenterological disorders, other nerve-related disease, tumors or other growths, pain and/or any other disease, condition or ailment.
In any of the embodiments disclosed herein, one or more components of an interface module, including a processor, computer-readable medium or other memory, controllers (e.g., dials, switches, knobs, etc.), displays (e.g., temperature displays, timers, etc.) and/or the like are incorporated into and/or coupled with (e.g., reversibly or irreversibly) one or more modules of the generator, the irrigation system (e.g., irrigant pump, reservoir, etc.) and/or any other portion of an ablation system.
One embodiment of an integrated module 800 that includes components of both an interface module and a generator is schematically illustrated in FIG. 7. As shown, the module 800 can comprise an energy generator or energy delivery device or component 810 that is configured to selectively activate or energize a tissue modification member, such as an ablation member (e.g., RF electrode, microwave emitter, ultrasound transducer, etc.) located along the distal end of a catheter 880 (e.g., on or near an ICT 890). In some embodiments, one or more electrical cables, wires or other conductive connectors are routed from the module 800 to the ablation member (e.g., via a lumen or other interior portion of the catheter 880) in order to electrically couple the ablation member to the integrated module 800. The module 800 can comprise a coupling or other adapter 804 that is sized, shaped and/or otherwise configured to receive a corresponding proximal portion (e.g., coupling) of the catheter 880. In some embodiments, the proximal end of the catheter 880 is removably secured to the coupling 804 using a standard or non-standard connection so as to advantageously permit for relatively easy and quick connection and disconnection of the catheter 880.
With continued reference to FIG. 7, the integrated module 800 can further include one or more memory devices, computer-readable media 850, a temperature control subsystem and/or the like. As discussed in greater detail herein, such memory devices 850 can be used to store operation parameters for the system. For example, operation parameters can be related to the signals of the radiometer, the thermocouple or other temperature sensor or temperature-measurement device, etc. in order to calculate or determine a temperature at depth of a subject's tissue volume being treated. Further, a memory device 850 of the module 800 can be used to store one or more algorithms that help determine the hot spot or peak temperature of the tissue volume being treated (e.g., by utilizing experimental or empirical models that take into consideration the type of tissue being heated, the depth or approximate depth of such tissue, the amount of contact force being applied to the tissue during an ablation procedure and/or the like). Additional details regarding contact force determination and/or measurement are provided in U.S. Pat. No. 8,206,380, filed on Jun. 12, 2009 and issued on Jun. 26, 2012, and U.S. Publication No. 2013/0324993, filed as U.S. patent application Ser. No. 13/486,889 on Jun. 1, 2012 and published on Dec. 5, 2013, the entireties of both of which are incorporated by reference herein and made a part of this specification.
In some embodiments, as depicted schematically in FIG. 7, the integrated system or module 800 additionally comprises a processor 860 or other control module that is operatively coupled to other components of the module (e.g., the computer-readable medium or other memory device, the generator or energy delivery device, etc.). The processor 860 can be configured to regulate the operation of the generator or energy delivery device 810 to control the activation of the ablation member (e.g., RF electrode) located along the distal end of the catheter (e.g., ICT 890). For example, as discussed in greater detail herein, the processor 860 can regulate energy delivery from the generator, energy source (e.g., ablative energy source) or other energy delivery device 810 to the ablation member of the ICT 890 based on one or more real-time temperature measurements sensed or determined by the ablation system (e.g., radiometer feedback, thermocouple or other temperature sensor feedback, calculation of temperature of a volume of tissue at a depth, calculation of a peak temperature of a volume of tissue being heated or hot spot temperature, etc.). The processor 860 can regulate the delivery of power to the ablation member using one or more additional parameters or factors, such as, for example, elapsed time, the manipulation of controllers (e.g., dials, knobs, switches, etc.) by a physician or other user, contact force applied by the catheter tip to the subject tissue (and/or confirmation of contact between the catheter tip and targeted tissue) and/or like, either in lieu of or in addition to temperature feedback, as desired or required.
With continued reference to FIG. 7, an integrated module 800 can further include a display or other output (or input/output) device 820, one or more controllers 840 and/or any other component or feature. For example, the display 820 can be configured to provide a sensed temperature (e.g., hot spot temperature, other radiometrically-determined temperature of the subject's tissue at a depth, temperature of a thermocouple or other sensor configured to detect localized temperature, etc.). In some embodiments, the display 820 can provide other data and information (e.g., patient information, elapsed time, etc.), either in lieu of or in addition to temperature data. The display 820 can comprise a touchscreen display 820 that provides a customizable graphic user interface. Thus, in such a configuration, the display 820 can provide information and other data to the user and permit the user to enter instructions and/or information to the integrated module 800 through the same display device 820.
In some embodiments, the integrated module 800 can comprise, at least partially, one or more components of an irrigation system. For example, an irrigant pump and/or an irrigation fluid reservoir can be incorporated into a housing of the integrated module. Alternatively, one or more components of the irrigation system can be separate from the integrated module 800, but operatively and/or physically coupled to the module, as desired or required. For example, even in embodiments where components of the irrigation system are included in a separate housing or module from the integrated module 800, the irrigation system components (e.g., the irrigation pump, its controller, power supply and other electronic components, the reservoir, etc.) can be, at least partially, operatively coupled to the integrated module 800. In some embodiments, the integrated module 800 and components of the irrigation system are operatively coupled (e.g., placed in data communication with one another) using one or more hardwired or wireless connection methods or devices. Thus, the integrated module 800 can advantageously control one or more aspects of the irrigation system (e.g., flowrate of irrigation fluid) during an ablation procedure or other treatment protocol.
First, high level overviews of the interface module, including the connected or integrated temperature control subsystem and power control interface, and connections thereto are provided. Then, further detail on the internal components of the interface module, temperature control subsystem, and power control interface, alternative embodiments thereof, and related methods of calculating radiometric temperature and controlling an ablation procedure using the same, are provided. Data obtained during experimental procedures also is presented. Lastly, further detail on components that may be used with the interface module, temperature control subsystem, and power control interface is provided.
FIG. 1A illustrates plan views of one embodiment of an interface module 110, temperature control subsystem 119, and power control interface, which are constructed in accordance with the principles of some embodiments of the present invention. As described in greater detail below, in some embodiments, the temperature control subsystem 119 is in communication with the power control functionality of electrosurgical generator 130, and is configured to control the power of ablation energy generated by generator 130 responsive to the temperature calculated by interface module 110, by sending appropriate control signals to power control interface 290 that adjusts the power generated by generator 130. Temperature control subsystem 119, power control interface 290, and interface module 110 may be separate from one another and connected by appropriate cabling as illustrated in FIGS. 1A-1B, or alternatively may be integrated into one or more modules (e.g., wherein one, some or all components are reversibly or irreversibly coupled or integrated into one or more modules) having combined functionality, e.g., as described in greater detail below with reference to FIGS. 1C-1E and FIG. 7. In some embodiments, the temperature control subsystem 119, power control interface 290 and/or interface module 110 are reversibly or irreversibly coupled with or integrated into the generator 130 or a system that includes the generator 130.
As illustrated in FIG. 1A, front panel 111 of interface module 110 may be connected to a catheter 120 that includes patient interface module (PIM) 121 and/or integrated catheter tip (ICT) 122. Catheter 120 optionally is steerable, or may be non-steerable and used in conjunction with a robotic positioning system or a third-party steerable sheath (not shown). In some embodiments, the ICT 122 is positioned by a clinician (optionally with mechanical assistance such as noted above), during a procedure, within subject 101 lying on grounded table 102. ICT 122 may include, among other things, an ablative tip, a thermocouple and/or any other temperature sensor or temperature-sensing device, and a radiometer for detecting the volumetric temperature of tissue subjected to ablation. The ICT 122 optionally includes one or more irrigation ports, which in one embodiment may be connected directly to a commercially available irrigant pump.
In embodiments in which the ablation energy is radiofrequency (RF) energy, the ablative tip may include an irrigated ablation electrode, such as described in greater detail below with reference to FIGS. 6A-6B. ICT 122 further may include one or more electrocardiogram (ECG) electrodes for use in monitoring electrical activity of the heart of subject 101. In some embodiments, the interface module 110 receives signals from the thermocouple, radiometer, and/or optional ECG electrodes of ICT 122 (e.g., via PIM 121). Interface module 110 provides to ICT 122, (e.g., via PIM 121), power for the operation of the PIM, the sensors (thermocouple, radiometer, ECG electrodes, etc.), ablation energy to be applied to subject 101 via the ablative tip and/or any other electronic components of the ablation system. In some embodiments, as discussed herein, components of the interface module (e.g., the processor, the computer-readable medium that stores operation parameters, the temperature control subsystem, etc.) are integrated with or coupled to the generator so as to form a single or combined module, thereby eliminating the need for a separate interface module. Therefore, in some embodiments, the generator or energy generating/delivery device is not an off-the-shelf device, and instead, is specifically designed to include one or more other components of the system, such as, for example, a processor, a computer-readable medium or other memory device, a temperature control subsystem, a controller, a display and/or the like.
In embodiments where the interface module 110 is separate from the generator 130, the back panel 112 of interface module 110 may be connected via connection cable 135 to a commercially available previously-known ablation energy generator 130, for example an electrosurgical generator 130, such as a Stockert EP-Shuttle 100 Generator (Stockert GmbH, Freiburg Germany) or Stockert 70 RF Generator (Biosense Webster, Diamond Bar, Calif.). In some embodiments, e.g., where the electrosurgical generator 130 is a Stockert EP-Shuttle or 70 RF Generator, the generator 130 includes display device 131 for displaying temperature and the impedance and time associated with application of a dose of RF ablation energy; power control knob and/or other controller (e.g., dial, switch, foot pedal, etc.) 132 for allowing a clinician to manually adjust the power of RF ablative energy delivered to subject 101; and start/stop/mode input 133 for allowing a clinician to initiate or terminate the delivery of RF ablation energy. Start/stop/mode input 133 also may be configured to control the mode of energy delivery, e.g., whether the energy is to be cut off after a given period of time. However, in other embodiments, as discussed herein, the energy-generating device or energy generator is not a commercially available or previously-known device, and is instead, a device that is specifically designed to be used with one or more the configurations of the ablation systems and methods disclosed herein. As such, the energy-generating device can be incorporated into a single housing or integrated module with other components of the ablation system, including, without limitation, the processor, the computer readable medium or other memory device, the temperature control subsystem, etc. Thus, in some embodiments, the various components of the interface module (e.g., the processor, the computer readable medium or other memory device, the temperature control subsystem, etc.) are reversibly or irreversibly coupled or integrated into one or more modules with a generator or other energy-delivery device.
Although generator 130 may be configured to display temperature on display device 131, that temperature is based on readings from a standard thermocouple. As noted above, however, that reported temperature may be inaccurate while irrigant and ablative energy are being applied to tissue. In some embodiments, the interface module 110 provides to generator 130, via connection cable 135, a thermocouple signal for use in displaying such a temperature, and signals from the ECG electrodes; and provides via indifferent electrode cable 134 a pass-through connection to indifferent electrode 140. Interface module 110 receives from generator 130, via connection cable 135, RF ablation energy that module 110 controllably provides to ICT 122 for use in ablating tissue of subject 101.
As noted above, temperature control subsystem 119 is configured to control the power of ablation energy provided to ICT 122. In the illustrated embodiment, temperature control subsystem 119 is coupled to interface module 110 via temperature control cable 136, or alternatively may be an internal component of interface module 110 as described below with reference to FIG. 1D. Temperature control subsystem 119 is coupled to power control interface 290 which is operatively coupled to the power control of generator 130, e.g., is mechanically coupled to power control knob 132, and is configured to regulate ablation power based on the tissue temperature calculated by interface module 110, for example using a stepper motor 291 as described below with reference to FIG. 2D. In the illustrated embodiment, power control interface 290 is coupled to temperature control subsystem 119 via power control cable 137. However, it should be understood that temperature control subsystem 119 and power control interface 290 may be integrated into a single unit, i.e., disposed within a single housing, such as described below with reference to FIG. 1C. Moreover, it should further be understood that temperature control subsystem 119, power control interface, and interface module 110 may be integrated into a single unit, i.e., disposed within a single housing, for example as illustrated and discussed herein with reference to FIGS. 1E and 7.
In the embodiment illustrated in FIG. 1A, back panel 112 of interface module 110 includes data ports 114 that are configured to output one or more signals to temperature control subsystem 119, via control cable 136, for use in automatically regulating the power of ablation energy generated by electrosurgical generator 130. Such signals may include, for example, the tissue temperature calculated by interface module 110, and the power of ablation energy that interface module 110 receives from generator 130. As described in greater detail below, temperature control subsystem 119 stores a target temperature (setpoint) to which the tissue temperature is to be raised, and also includes a processor that calculates a power at which the ablation energy is to be provided to ICT 122 through interface module 110. The temperature control subsystem 119 sends control signals to power control interface 290, via cable 137, that cause the power control interface to mechanically manipulate the power control knob 132 of generator 130 such that the ablation energy is provided at this power. Other methods of controlling the power of ablation energy of generator 130 also may be used, for example by instead transmitting an appropriate control signal to generator 130 to cause generator 130 to output ablation energy at a desired power. In either embodiment, the coupling between temperature control subsystem 119, power control interface 290, and generator 130 preferably is configured such that a clinician may manually override the automated power control at any time during an ablation procedure.
As will be familiar to those skilled in the art, for a monopolar RF ablation procedure, a clinician may position an indifferent electrode (IE) 140 on the back of subject 101 so as to provide a voltage differential that enables transmission of RF energy into the tissue of the subject. In the illustrated embodiment, IE 140 is connected to interface module 110 via first indifferent electrode cable 141. Interface module 110 passes through the IE signal to second indifferent electrode cable 134, which is connected to an indifferent electrode input port on electrosurgical generator 130. Alternatively, the IE may be connected directly to that port of the electrosurgical generator 130 via appropriate cabling (not shown).
It should be understood that electrosurgical generators other than the Stockert EP-Shuttle or 70 RF Generator suitably may be used, e.g., other makes or models of RF electrosurgical generators. Alternatively, generators that produce other types of ablation energy, such as microwave generators, cryosurgical sources, or high frequency or other types of ultrasound generators, may be used, and the power of ablation energy generated by such generators may be suitably regulated using an appropriate mechanism (e.g., by mechanically adjusting a control knob via control interface 290 or by providing a control signal via appropriate cabling). Ablation energy generator 130 need not necessarily be commercially available, although as noted above it may be convenient to use one that is. It should also be appreciated that the connections described herein may be provided on any desired face or panel of interface module 110, and that the functionalities of different connectors and input/output (I/O) ports may be combined or otherwise suitably modified.
Front panel 111 of interface module 110 includes temperature display 113, e.g., a digital two or three-digit display device configured to display a temperature calculated by a processor internal to interface module 110, e.g., as described in greater detail below with reference to FIGS. 2A-2B and 3A. Other types of temperature displays, such multicolor liquid crystal displays (LCDs), touchscreen displays (e.g., that are configured to provide data to the user and to also receive input from the user) and/or the like alternatively may be used. Front panel 111 also includes connectors (not labeled) through which interface module 110 is connected to ICT 122 via PIM 121, and to the IE 140 via indifferent electrode cable 141.
Back panel 112 of interface module 110 includes connectors (not labeled) through which interface module 110 is connected to electrosurgical generator 130, via indifferent electrode cable 134 and connection cable 135. The data ports 114 of interface module 110, which as noted above provide information to temperature control subsystem 119, also may be configured to output one or more signals to a suitably programmed personal computer or other remote device, for example an EP monitoring/recording system such as the LABSYSTEMTM PRO EP Recording System (C.R. Bard, Inc., Lowell, Mass.). Such signals may, for example, include signals generated by the thermocouple, radiometer, and/or ECG electrodes of the ICT, the tissue temperature calculated by interface module 110, the power of ablation energy being provided to ICT 122, and the like.
Referring now to FIG. 1B, certain non-limiting connections to and from interface module 110, externally coupled temperature control subsystem 119, and externally coupled power control interface 290 of FIG. 1A, as well as connections among other components, are described. Examples of alternative configurations for partially or fully integrated combinations of interface module 110, temperature control subsystem 119, and power control interface are described below with reference to FIGS. 1C-1E.
In FIG. 1B, interface module 110 is in operable communication with catheter 120 having an integrated catheter tip (ICT) 122 that includes a radiometer, ablative tip, a thermocouple or other reference temperature sensor (TC), and optionally also includes ECG electrodes and/or irrigation ports(s), via patient interface module (PIM) 121. In the illustrated embodiment, the interface module 110 is in operable communication with temperature control subsystem 119 via temperature control cable 136, is in operable communication with electrosurgical generator 130 via connection cable 135, and is in operable communication with indifferent electrode 140 via indifferent electrode cable 141, such as discussed above with reference to FIG. 1A. Temperature control subsystem 119 is in operable communication with power control interface 290 via power control cable 137. Power control interface 290 is in operable communication with power control 132 of ablation energy generator 130 via stepper motor 291 described further below with reference to FIG. 2D.
As illustrated in FIG. 1B, electrosurgical generator 130 optionally is in operable communication with electrophysiology (EP) monitoring/recording system 160 via appropriate cabling 161, or alternatively via data ports 114 of interface module 110 and appropriate cabling. EP monitoring/recording system 160 may include, for example, various monitors, processors, and the like that display pertinent information about an ablation procedure to a clinician, such as the subject's heart rate and blood pressure, the temperature recorded by the thermocouple or other reference temperature sensor on the catheter tip, the ablation power and time period over which it is applied, fluoroscopic images, and the like. EP monitoring/recording systems are commercially available, e.g., the MEDELECTM Synergy T-EP-EMG/EP Monitoring System (CareFusion, San Diego, Calif.), or the LABSYSTEMTM PRO EP Recording System (C.R. Bard, Inc., Lowell, Mass.).
If the ICT 122 includes irrigation port(s), then one convenient means of providing irrigant to such ports is irrigation pump 140 associated with electrosurgical generator 130, which pump is in operable communication with the generator and in fluidic communication with the ICT via connector 151. For example, the Stockert 70 RF Generator is designed for use with a CoolFlowTM Irrigation pump, also manufactured by Biosense Webster. Specifically, the Stockert 70 RF Generator and the CoolFlowTM pump may be connected to one another by a commercially available interface cable, so as to operate as an integrated system that works in substantially the same way as it would with a standard, commercially available catheter tip. For example, prior to positioning ICT 122 in the body, the clinician instructs the pump to provide a low flow rate of irrigant to the ICT, as it would to a standard catheter tip; the ICT is then positioned in the body. Then, when the clinician presses the “start” button on the face of generator 130, the generator may instruct pump 150 to provide a high flow rate of irrigant for a predetermined period (e.g., 5 seconds) before providing RF ablation energy, again as it would for a standard catheter tip. After the RF ablation energy application is terminated, then pump 150 returns to a low flow rate until the clinician removes the ICT 122 from the body and manually turns off the pump. As noted herein, in some embodiments, one or more components of the irrigation system can be incorporated into and/or otherwise coupled (e.g., physically, operatively, etc.) to an integrated module.
As noted above, the functionalities of interface module 110, temperature control subsystem 119, and/or power control interface 290 optionally may be integrated with one another. For example, FIG. 1C illustrates an embodiment in which alternative temperature control subsystem 119c and alternative power control interface 290c are integrated with one another, e.g., located within the same housing with one another. Integrated temperature control subsystem/power control interface 119c, 290c may be connected to interface module 110 via temperature control cable 136, and may be connected to power control 132 of ablation energy generator 130 via stepper motor 291 described further below with reference to FIG. 2D. Other connections may be substantially the same as described above with reference to FIGS. 1A-1B.
Or, for example, FIG. 1D illustrates an embodiment in which interface module 110d and alternative temperature control subsystem 119d are integrated with one another, e.g., located within the same housing with one another. Integrated interface module/temperature control subsystem 110d/119d may be connected to catheter 120 via PIM 121, may be connected to ablation energy generator 130 via connection cable 135, and may be connected to power control 132 of ablation energy generator 130 via power control cable 137, power control interface 290, and stepper motor 291. Other connections may be substantially the same as described above with reference to FIGS. 1A-1B.
As still another example, FIG. 1E illustrates an embodiment in which alternative interface module 110e, alternative temperature control subsystem 119e, and alternative power control interface 290e are integrated with one another, e.g., located within the same housing (e.g., integrated module) with one another. Integrated interface module/temperature control subsystem/power control interface 110e, 119e, 290e may be connected to ablation energy generator 130 via connection cable 135, and may be connected to power control 132 of ablation energy generator 130 via stepper motor 291. Other connections may be substantially the same as described above with reference to FIGS. 1A-1B.
Referring now to FIGS. 2A-2D, further details of internal components of interface module 110, temperature control subsystem 119, and power control interface 290 of FIGS. 1A-1B are provided. It should be understood that such components suitably may be modified to alternatively configure module 110, subsystem 119, and interface 290 in partially or fully integrated modules such as shown in FIGS. 1C-1E.
FIG. 2A schematically illustrates internal components of one embodiment of interface module 110. Interface module 110 includes first, second, third, and fourth ports 201-204 by which it communicates with external components. Specifically, first port 201 is an input/output (I/O) port configured to be connected to catheter 120 via PIM 121, as illustrated in FIG. 1A. Port 201 receives as input from catheter 120 digital radiometer and digital thermocouple (TC) signals, and optionally ECG signals, generated by ICT 122, and provides as output to catheter 120 RF ablation energy, as well as power for circuitry within the ICT 122 and the PIM 121. Second port 202 is also an I/O port, configured to be connected to electrosurgical generator 130 via connection cable 135 illustrated in FIG. 1A, and receives as input from generator 130 RF ablation energy, and provides as output to generator 130 a reconstituted analog thermocouple (TC) signal and raw ECG signal(s). Third port 203 is an input port configured to be connected to indifferent electrode (IE) 140 via indifferent electrode cable 134 illustrated in FIG. 1A, and fourth port 204 is an output port configured to be connected to generator 130 via indifferent electrode cable 141 illustrated in FIG. 1A. As shown in FIG. 2A, interface module 110 acts as a pass-through for the IE signal from IE 140 to generator 130, and simply receives IE signal on third port 203 and provides the IE signal to generator 130 on fourth port 204.
In some embodiments, the interface module 110 also includes processor 210 coupled to non-volatile (persistent) computer-readable memory 230, user interface 280, load relay 260, and patient relay 250. Memory 230 stores programming that causes processor 210 to perform steps described further below with respect to FIGS. 3A-3C, thereby controlling the functionality of interface module 110. Memory 230 also stores parameters used by processor 210. For example, memory 230 may store a set of operation parameters 231 for the thermocouple (and/or other reference temperature sensor) and radiometer, as well as a temperature calculation module 233, which processor 210 uses to calculate the radiometric temperature based on the digital TC and radiometer signals received on first I/O port 201, as described in greater detail below with respect to FIG. 3B, algorithms used to determine the extreme temperature (e.g., peak or “hot spot” temperature or trough or low temperature of a volume of tissue being treated during a particular procedure (e.g., as discussed herein with reference to FIGS. 8A-13B) and/or any other module or algorithm. The operation parameters 231 may be obtained through calibration, or may be fixed. Memory 230 also stores a set of safety parameters 232 that processor 210 uses to maintain safe conditions during an ablation procedure, as described further below with respect to FIG. 3C. Memory 230 further stores decision module 234 that processor 210 uses to control the opening and closing of patient relay 250 and load relay 260 based on its determinations of temperature and safety conditions, as described further below with reference to FIGS. 3A-3C. When closed, patient relay 250 passes ablative energy from the second I/O port 202 to the first I/O port 201. When closed, load relay 260 returns ablative energy to the IE 140 via dummy load D (resistor, e.g., of 120Ω resistance) and fourth I/O port 204.
As illustrated in FIG. 2A, interface module 110 further includes user interface 280 by which a user may receive information about the temperature adjacent ICT 122 as calculated by processor 210, as well as other potentially useful information. In the illustrated embodiment, user interface 280 includes digital temperature display 113, which displays the instantaneous temperature calculated by processor 210. In other embodiments (not shown), display 113 may be an LCD device that, in addition to displaying the instantaneous temperature calculated by processor 210, also graphically display changes in the temperature over time for use by the clinician during the ablation procedure. User interface 280 further includes data ports 114, one or more of which are connected to temperature control subsystem 119 to provide the calculated temperature and/or ablation energy power to subsystem 119. Data ports 114 also optionally may be connected to a computer or EP monitoring/recording system 160 by appropriate cabling 161 as noted above, and which may output digital or analog signals being received or generated by interface module 110, e.g., radiometer signal(s), a thermocouple signal, the ablation energy power, and/or the temperature calculated by processor 210.
So as to inhibit potential degradations in the performance of processor 210, memory 230, or user interface 280 resulting from electrical contact with RF energy, interface module 110 may include opto-electronics 299 that communicate information to and from processor 210, but that substantially inhibit transmission of RF energy to processor 210, memory 230, or user interface 280. This isolation is designated by the dashed line in FIG. 2A. For example, opto-electronics 299 may include circuitry that is in operable communication with first I/O port 201 so as to receive the digital TC and radiometer signals from first I/O port 201, and that converts such digital signals into optical digital signals. Opto-electronics 299 also may include an optical transmitter in operable communication with such circuitry, that transmits those optical digital signals to processor 210 through free space. Opto-electronics 299 further may include an optical receiver in operable communication with processor 210, that receives such optical digital signals, and circuitry that converts the optical digital signals into digital signals for use by processor 210. The opto-electronic circuitry in communication with the processor also may be in operable communication with a second optical transmitter, and may receive signals from processor 210 to be transmitted across free space to an optical receiver in communication with the circuitry that receives and processes the digital TC and radiometer signals. For example, processor 210 may transmit to such circuitry, via an optical signal, a signal that causes the circuitry to generate an analog version of the TC signal and to provide that analog signal to the second I/O port. Because opto-electronic circuitry, transmitters, and receivers are known in the art, its specific components are not illustrated in FIG. 2A.
With respect to FIG. 2B, additional internal components of interface module 110 of FIG. 2A are described, as well as selected connections to and from the interface module. FIG. 2B is an exemplary schematic for a grounding and power supply scheme suitable for using interface module 110 with an RF electrosurgical generator, e.g., a Stockert EP-Shuttle or 70 RF Generator. Other grounding and power supply schemes suitably may be used with other types, makes, or models of electrosurgical generators, as will be appreciated by those skilled in the art. In some embodiments, such grounding and power supply schemes can be incorporated into an integrated module, which, as discussed herein, can comprise, for example, a generator or energy-delivery device, a processor, a memory, a temperature control subsystem and/or the like.
By way of example, as illustrated in FIG. 2B, interface module 110 includes isolated main power supply 205 that may be connected to standard three-prong A/C power outlet 1, which is grounded to mains ground G. Interface module 110 also includes several internal grounds, designated A, B, C, and I. Internal ground A is coupled to the external mains ground G via a relatively small capacitance capacitor (e.g., a 10 pF capacitor) and a relatively high resistance resistor (e.g., a 20 MΩ resistor) that substantially prevents internal ground A from floating. Internal ground B is coupled to internal ground A via a low resistance pathway (e.g., a pathway or resistor(s) providing less than 1000Ω resistance, e.g., about 0 Ω/resistance). Similarly, internal ground C is coupled to internal ground B via another low resistance pathway. Internal ground I is an isolated ground that is coupled to internal ground C via a relatively small capacitance capacitor (e.g., a 10 pF capacitor) and a relatively high resistance resistor (e.g., a 20 MΩ resistor) that substantially prevents isolated ground I from floating.
Isolated main power supply 205 is coupled to internal ground A via a low resistance pathway. Isolated main power supply 205 is also coupled to, and provides power (e.g., ±12V) to, one or more internal isolated power supplies that in turn provide power to components internal to interface module 110. Such components include, but are not limited to components illustrated in FIG. 2A. For example, interface module 110 may include one or more isolated power supplies 220 that provide power (e.g., ±4V) to processor 210, memory 230, and analog circuitry 240. Analog circuitry 240 may include components of user interface 280, including temperature display 113 and circuitry that appropriately prepares signals for output on data ports 114. Data ports 114, as well as analog circuitry 240, are coupled to internal ground B via low resistance pathways, while processor and memory 210, 230 are coupled to internal ground C via low resistance pathways. Interface module also may include one or more isolated power supplies 270 that provide power (e.g., ±4V) to ICT 122, PIM 121, and RF circuitry 290.
RF circuitry 290 may include patient and load relays 250, 260, as well as circuitry that receives the radiometer and thermocouple signals and provides such signals to the processor via optoelectronic coupling, and circuitry that generates a clock signal to be provided to the ICT as described further below with reference to FIG. 5B. RF circuitry 290, ICT 122, and PIM 121 are coupled to isolated internal ground I via low resistance pathways.
As shown in FIG. 2B, power supply 139 of RF electrosurgical generator 130, which may be external to generator 130 as in FIG. 2B or may be internal to generator 130, is connected to standard two- or three-prong A/C power outlet 2. However, generator power supply 139 is not connected to the ground of the outlet, and thus not connected to the mains ground G, as is the isolated main power supply. Instead, generator power supply 139 and RF electrosurgical generator 130 are grounded to internal isolated ground I of interface module 110 via low resistance pathways between generator 130 and PIM 121 and ICT 122, and low resistance pathways between PIM 121 and ICT 122 and internal isolated ground I. As such, RF circuitry 290, PIM 121, IE 140, and generator 130 are all “grounded” to an internal isolated ground I that has essentially the same potential as does ICT 122. Thus, when RF energy is applied to ICT 122 from generator 130 through interface module 110, the ground of RF circuitry 290, PIM 121, ICT 122, IE 140, and generator 130 all essentially float with the RF energy amplitude, which may be a sine wave of 50-100V at 500 kHz.
As further illustrated in FIG. 2B, the ±12V of power that isolated main power supply 205 provides to isolated processor/memory/analog power supply 220 and to isolated ICT/RF power supply 270 may be coupled by parasitic capacitance (pc, approximately 13 pF) to A/C power outlet 1, as may be the ±4V of power that such power supplies provide to their respective components. Such parasitic coupling will be familiar to those skilled in the art. Note also that the particular resistances, capacitances, and voltages described with reference to FIG. 2B are purely exemplary and may be suitably varied as appropriate to different configurations.
FIG. 2C schematically illustrates components of temperature control subsystem 119, which as noted above may be connected to one or more data ports 114 of interface module 110 via control cable 136 (FIGS. 1A-1B), or alternatively may be included within the housing of interface module 110 (FIGS. 1D-1E). In the illustrated embodiment, temperature control subsystem 119 includes input port(s) 212, processor 211, memory 235, user input 285, and display 286. Temperature control subsystem 119 is connected to power control interface 290 via power control cable 137, although power control interface 290 alternatively may be integrated with temperature control subsystem 119 and/or interface module 110 (FIGS. 1C, 1E and 7). Note that the functionalities of processor 210 of interface module 110 and processor 211 of temperature control subsystem 119 optionally may both be provided by a single processor, particularly (but not necessarily) in embodiments where interface module 110 and temperature control subsystem 119 are integrated with one another (FIGS. 1D-1E). Additionally, or alternatively, the functionalities of memory 230 of interface module 110 and memory 235 of temperature control subsystem 119 may both be provided by a single memory, particularly (but not necessarily) in embodiments where interface module 110 and temperature control subsystem 119 are integrated with one another (FIGS. 1D-1E and 7).
As illustrated in FIG. 2C, temperature control subsystem 119 receives on input port(s) 212, from data port 114, the temperature calculated by processor 210 based on signal(s) from the radiometer, as well as the power of the ablation energy being transmitted to the ICT 122 via first I/O port 201 of interface module 110. An appropriate ablation energy power meter may be provided within interface module 110 for such purpose.
Memory 235 of temperature control subsystem 119, which may be any suitable persistent, computer-readable medium, stores setpoint 281, ablation time 282, feedback parameters 283, and temperature control module 284. In some embodiments, as discussed in greater detail herein, the memory can store or more algorithms or modules that are configured to calculate or estimate the extreme temperature (e.g., hot spot temperature or peak temperature or trough or low temperature) of a tissue volume being heated or cooled by the ablation system. For example, as discussed below, the memory can include algorithms that determine such a hot spot or other extreme temperature based on empirical or experimental models, which take into consideration one or more parameters or inputs, such as, for example, tissue type, tissue thickness, contact force applied by the catheter tip to the tissue and/or the like. Setpoint 281 is a target temperature at which a region of tissue is to be ablated during an ablation procedure, e.g., 55° C. for a cardiac hyperthermia ablation procedure. Ablation time 282 is a target time for which the region of tissue is to be ablated once the target temperature is reached, e.g., 60 seconds for a cardiac hyperthermal ablation procedure performed at 55° C. Note that appropriate setpoints and times may vary depending on the particular type of ablation being performed (e.g., hypothermia, hyperthermia), as well as the location in the heart where the ablation is being performed. Setpoint 281 and/or ablation time 282 may be pre-determined, or alternatively may be input by a clinician via user input 285. Ablation time 282 alternatively may be omitted from temperature control subsystem 119, and the ablation time controlled via ablation energy generator 130 as described above. Temperature control subsystem 119 may display to the clinician the calculated temperature, the power of ablation energy, setpoint 281, and/or ablation time 282 via display 286, which may be a single-color or multi-color digital display such as an LCD or LED.
Feedback parameters 283 define the feedback characteristics of the power regulation that temperature control subsystem 119 provides. For example, parameters 283 may include a slope with which the power is to be ramped, as well as under-shoot/over-shoot parameters that prevent the power from being ramped to too low or too high a power due to delays in the temperature as the tissue responds to the applied ablation energy. Optionally, one or more of parameters 283 may be adjusted by the clinician via user input 285 and/or displayed to the clinician via display 286. Temperature control module 284 contains a set of instructions that cause processor 211 to regulate the power of ablation energy based on the setpoint 281 and feedback parameters 282 stored in memory 235 and the calculated temperature and ablation energy power signals received on input port(s) 212 from data ports 114. Such instructions may include steps such as described further below with respect to FIGS. 3A and 3C.
Temperature control subsystem 119 further is in operable communication with power control interface 290 via power control cable 137. Power control interface 290 is configured to be operably coupled to an adjustable power control of electrosurgical generator 130. For example, electrosurgical generator 130 may include an I/O port (not illustrated) through which generator 130 may receive suitable control signals that define a power at which the generator outputs ablation energy, and power control interface 290 may include a control signal generator that generates suitable control signals and passes those control signals to the generator via an I/O port connected to the port of the generator. In some embodiments, as discussed in greater detail herein, the temperature control subsystem 119, the electrosurgical generator, one or more components of the interface module (e.g., the processor, memory, etc.), controllers and/or other system components or devices are coupled (e.g., reversibly coupled, irreversibly coupled/integrated) in a single integrated module.
Alternatively, as illustrated in FIG. 1A, electrosurgical generator 130 may include a power control knob 132 that, during a conventional procedure, a clinician uses to manually adjust the ablation energy power. In some embodiments, the power control interface 290 of temperature control subsystem 119 may include a suitable mechanism for mechanically controlling the ablation energy power via such a power control knob 132. For example, as illustrated in FIG. 2D, power control interface 290 may include stepper motor 291, which is coupled to power control knob 132 (not visible in FIG. 2D) of generator 130 via spring-loaded knob adjuster 292, and which is coupled to temperature control subsystem 119 via power control cable 137. Stepper motor 291 and spring-loaded knob adjuster 292 may be held in place by bracket 293. Stepper motor 291 includes an on-board mini-controller (not shown) that, responsive to instructions from processor 211 provided via cable 137, rotates knob adjuster 292. Knob adjuster 292 is spring-loaded so as to apply pressure to the face of knob 132, such that rotation of knob adjuster 292 causes knob 132 to rotate and thus to increase or decrease the ablation energy power by an amount determined by processor 211 based on the above-noted inputs and parameters. Preferably, knob 132 also may be manually adjusted even when power control interface 290 is in place, such that a clinician may rapidly intervene and manually adjust the ablation energy power as needed during an ablation procedure. Note that although FIG. 2D depicts interface module 110, temperature control subsystem 119, and power control interface 290 as being separate elements from one another connected via appropriate cabling, consistent with FIGS. 1A-1B, such elements alternatively may be partially or fully integrated with one another such as described above with reference to FIGS. 1C-1E and 7.
Referring now to FIG. 3A, method 300 of using interface module 110, temperature control subsystem 119, and power control interface 290 of FIGS. 1A-2D during a tissue ablation procedure is described. The clinician may couple the integrated catheter tip (ICT) 122 and indifferent electrode (IE) 140 to respective I/O ports of interface module 110 (step 301). For example, as shown in FIG. 1A, ICT 122 may be coupled to a first connector on front panel 111 of interface module 110 via patient interface module (PIM) 121, and IE 140 may be coupled to a third connector on front panel 111 via indifferent electrode cable 141. The first connector is in operable communication with first I/O port 201 (see FIG. 2A) and the third connector is in operable communication with third I/O port 203 (see FIG. 2A).
In FIG. 3A, the clinician may couple temperature control subsystem 119 to interface module 110 and power control interface 290, and may couple power control interface 290 to the power control of electrosurgical generator 130 (step 302). For example, as illustrated in FIGS. 1A and 2D, temperature control subsystem 119 may be coupled to data port(s) 114 of interface module 110 via temperature control cable 136 and may be coupled to power control interface 290 via power control cable 137. Power control interface 290 may be coupled to power control knob 132 of electrosurgical generator 130. Note that if interface module 110, temperature control subsystem 119, and/or power control interface 290 are partially or fully integrated with one another, then the clinician need not separately provide connections between them. Additionally, if electrosurgical generator 130 accepts suitable control signals to adjust the ablation energy power, then the power control interface 290 may be coupled to the generator via appropriate cabling, rather than by a mechanical interface such as stepper motor 291. In some embodiments, however, as discussed herein with reference to, e.g., FIGS. 1C, 1E and 7, the elements or components may be partially or fully integrated with one another (e.g., in a single housing or integrated module).
In FIG. 3A, the clinician may couple electrosurgical generator 130 to I/O port(s) of interface module 110 (step 303). For example, as illustrated in FIG. 1A, electrosurgical generator 130 may be coupled to a second connector on back panel 112 of interface module 110 via connection cable 135, and also may be coupled to a fourth connector on back panel 112 via indifferent electrode cable 134. The second connector is in operable communication with second I/O port 202 (see FIG. 2A), and the fourth connector is in operable communication with fourth I/O port 204 (see FIG. 2A).
In FIG. 3A, the clinician initiates flow of irrigant, positions ICT 122 within the subject, e.g., in the subject's heart or other targeted tissue, and positions IE 140 in contact with the subject, e.g., on the subject's back (step 304). Those skilled in the art will be familiar with methods of appropriately positioning catheter tips relative to the heart of a subject in an ablation procedure, for example via the peripheral arterial or venous vasculature.
Interface module 110 receives digital radiometer, digital thermocouple, and/or analog ECG signals from ICT 122, and receives ablation energy from generator 130 (step 305), for example using the connections, ports, and pathways described above with references to FIGS. 1A-2D. Preferably, generator 130 may provide such ablation energy to interface module 110 responsive to the clinician pressing “start” using inputs 133 on the front face of generator 130 (see FIG. 1A).
Interface module 110 calculates and displays the temperature adjacent to ICT 122, based on the radiometer and thermocouple signals (step 306). In some embodiments, as discussed in greater detail herein with reference to FIGS. 8A-13B, the system can be configured to determine (and optionally display) an extreme temperature (e.g., hot spot, peak, low or trough temperature) of the tissue volume being heated. Such calculations may be performed, for example, by processor 210 based on instructions in temperature calculation module 233 stored in memory 230 (see FIG. 2A). Exemplary methods of performing such a calculation are described in greater detail below with respect to FIG. 3B.
In method 300, interface module 100 also actuates patient relay 250 so as to provide ablation energy to ICT 122 for use in tissue ablation (step 307). For example, processor 210 maintain patient relay 250 illustrated in FIG. 2A in a normally closed state during operation, such that ablation energy flows from electrosurgical generator 130 to ICT 122 through interface module 110 without delay upon the clinician's actuation of the generator, and may open patient relay 250 only upon detection of unsafe conditions such as described below with respect to FIG. 3C. In an alternative embodiment, processor 210 may maintain patient relay 250 in a normally open state during operation, and may determine based on instructions in decision module 234 and on the temperature calculated in step 305 that it is safe to proceed with the tissue ablation, and then close patient relay so as to pass ablation energy to the ICT. In either case, after a time period defined using input 133 on the front face of generator 130, the supply of ablation energy ceases or the clinician manually turns off the supply of ablation energy.
Interface module 110 also generates an analog version of the thermocouple signal, and provides the ECG and analog thermocouple signals to generator 130 (step 308). Preferably, step 308 is performed continuously by the interface module throughout steps 304 through 307, rather than just at the end of the ablation procedure. For example, as will be familiar to those skilled in the art, the Stockert EP-Shuttle or 70 RF Generator may “expect” certain signals to function properly, e.g., those signals that the generator would receive during a standard ablation procedure that did not include use of interface module 110. The Stockert EP-Shuttle or 70 RF generator requires as input an analog thermocouple signal, and optionally may accept analog ECG signal(s). The interface module 110 thus may pass through the ECG signal(s) generated by the ICT to the Stockert EP-shuttle or 70 RF generator via second I/O port 202. However, as described above with reference to FIG. 2A, interface module 110 receives a digital thermocouple signal from ICT 122. In its standard configuration, the Stockert EP-Shuttle or 70 RF generator is not configured to receive or interpret a digital thermocouple signal. As such, interface module 110 includes the functionality of reconstituting an analog version of the thermocouple signal, for example using processor 210 and opto-electronics 299, and providing that analog signal to generator 130 via second I/O port 202.
In FIG. 3A, temperature control module 119 then regulates the power of ablation energy provided to ICT 122 based on the calculated temperature and on a setpoint, e.g., a target ablation temperature (e.g., a mean temperature of the tissue volume being treated, an extreme temperature of tissue being treated, such as a peak or hot spot or trough or low temperature of tissue being treated, etc.), via power control interface 290 (step 309). For example, as discussed above with respect to FIGS. 2C-2D, temperature control module 119 receives calculated temperature and ablation energy power signals from interface module 110, e.g., via data port(s) 114. Based on the received signals, stored setpoint 281, stored ablation time 282, stored feedback parameters 283, and instructions in temperature control module 284, processor 211 of subsystem 119 determines a power and time at which ablation energy should be provided to the tissue, for example using PI (proportional-integral) or PID (proportional-integral-derivative) control loop feedback algorithms such as known in the art. Then, processor 211 causes power control interface 290 to regulate the ablation energy power generated by generator 130 so as to achieve the power, e.g., by generating an appropriate control signal or by mechanically adjusting the power knob on the face of generator 130. Responsive to the regulation of the ablation energy power, the tissue temperature may change, resulting in changes to the digital radiometer and/or digital thermocouple signals from the ICT (step 305). The new temperature may be calculated based on the changed signals (step 306) and the ablation energy power provided to the ICT regulated based on the new temperature (step 309). As such, the ablation energy power may be dynamically and automatically controlled during the ablation procedure so as to substantially continuously maintain the tissue temperature at or near the setpoint (e.g., hot spot or peak temperature of the subject's tissue volume being treated) for a desired amount of time, e.g., using PI or PID control loop feedback algorithms.
Turning to FIG. 3B, the steps of method 350 of calculating radiometric temperature using digital signals from a radiometer and a thermocouple and operation parameters is described. The steps of the method may be executed by processor 210 based on temperature calculation module 233 stored in memory 230 (see FIG. 2A). While some of the signals and operation parameters discussed below are particular to a PIM and ICT configured for use with RF ablation energy, other signals and operation parameters may be suitable for use with a PIM and ICT configured for use with other types of ablation energy. Those skilled in the art will be able to modify the systems and methods provided herein for use with other types of ablation energy.
In FIG. 3B, processor 210 of interface module 110 obtains from memory 230 the operation parameters for the thermocouple (TC) and the radiometer (step 351). These operation parameters may include, for example, TCSlope, which is the slope of the TC response with respect to temperature; TCOffset, which is the offset of the TC response with respect to temperature; RadSlope, which is the slope of the radiometer response with respect to temperature; TrefSlope, which is the slope of a reference temperature signal generated by the radiometer with respect to temperature; and F, which is a scaling factor (e.g., coefficient factor, estimation factor, other adjustment parameter, etc.). A coefficient or estimation factor or other scaling factor can be used to adjust a temperature determination using a radiometer in any embodiments disclosed herein. In some embodiments, for example, a scaling factor (e.g., estimation or coefficient factor) can be used to approximate or otherwise determine the extreme temperature (e.g., hot spot or peak temperature and/or cool spot or trough temperature) within a volume of tissue being treated. The scaling factor can include a factor that accounts for one, two, three or more tissue characteristics, including but not limited to, tissue thickness, tissue-type, etc.
Processor 210 then obtains via first I/O port 201 and opto-electronics 299 the raw digital signal from the thermocouple, TCRaw (step 352), and calculates the thermocouple temperature, TCT, based on TCRaw using the following equation (step 353):




  TCT
  =
  
    
      TCRaw
      TCSlope
    
    =
    TCOffset
  




Then, processor 210 causes temperature display 113 to display TCT until both of the following conditions are satisfied: TCT is in the range of 35° C. to 39° C., and ablation energy is being provided to the ICT (e.g., until step 307 of FIG. 3A). There are several reasons to display only the thermocouple temperature TCT, as opposed to the temperature calculated based on signal(s) from the radiometer, until both of these conditions are satisfied. For example, if the temperature TCT measured by the thermocouple is less than 35° C., then based on instructions in decision module 234 the processor 210 interprets that temperature as meaning that ICT 122 is not positioned within a living human body, which would have a temperature of approximately 37° C. If ICT 122 is not positioned within a living human body, then it would be unsafe to provide power to the radiometer circuitry, as it may rapidly burn out if powered on in air as opposed to blood.
Processor 210 then provides ablation energy to ICT 122, e.g., in accordance with step 307 described above, and receives via second I/O port 202 two raw digital signals from the radiometer: Vrad, which is a voltage generated by the radiometer based on the temperature adjacent the ICT; and Vref, which is a reference voltage generated by the radiometer (step 355). Processor 210 calculates the reference temperature Tref based on Vrefusing the following equation (step 356):




  Tref
  =
  
    
      Vref
      TrefSlope
    
    +
    TrefOffset
  




Processor 210 also calculates the radiometric temperature Trad based on Vrad and Tref using the following equation (step 357):




  Trad
  =
  
    
      Vrad
      RadSlope
    
    =
    
      RadOffset
      +
      Tref
    
  




During operation of interface module 110, processor 210 may continuously calculate TCT, and also may continuously calculate Tref and Trad during times when ablation power is provided to the ICT (which is subject to several conditions discussed further herein). Processor 210 may store in memory 230 these values at specific times and/or continuously, and use the stored values to perform further temperature calculations. For example, processor 210 may store in memory 230 TCT, Tref, and Trad at baseline, as the respective values TCBase, TrefBase, and TradBase. The processor then re-calculates the current radiometric temperature TradCurrent based on the current Vrad received on second I/O port 202, but instead with reference to the baseline reference temperature TrefBase, using the following equation (step 358):




  TradCurrent
  =
  
    
      Vrad
      RadSlope
    
    -
    RadOffset
    +
    TrefBase
  




Processor 210 then calculates and causes temperature display 113 to display a scaled radiometric temperature TSrad for use by the clinician based on the baseline thermocouple temperature TCBase, the baseline radiometer temperature TradBase, and the current radiometer temperature TradCurrent, using the following equation (step 359):

TSrad=TCBase+(TradCurrent−TradBase)×F 

In this manner, interface module 110 displays for the clinician's use a temperature calculated based on signal(s) from the radiometer that is based not only on voltages generated by the radiometer and its internal reference, described further below with reference to FIGS. 6A-6B, but also on temperature measured by the thermocouple.
With respect to FIG. 3C, method 360 of controlling an ablation procedure based on a temperature calculated based on signal(s) from a radiometer, e.g., as calculated using method 350 of FIG. 3B, hot spot or other extreme temperature determination (e.g., in accordance with the disclosure of FIGS. 8A-13B), etc., and also based on safety parameters 232 and decision module 234 stored in memory 230 of interface module 110 (FIG. 2A) and setpoint 281, ablation time 282, feedback parameters 283, and instructions in temperature control module 284 stored in memory 235 of temperature control subsystem 119, will now be described.
In method 360 of FIG. 3C, a slow flow of irrigant is initiated through ICT 122, and the ICT is then positioned within the subject (step 361). For example, in embodiments using a Stockert 70 RF Generator 130, the generator may automatically initiate slow irrigant flow to catheter tip 122 by sending appropriate signals to a CoolFlow irrigant pumping system 150 associated with the generator, responsive to actuation of the generator by the clinician.
The clinician presses a button on generator 130 to start the flow of ablation energy to ICT 122; this may cause the generator to initiate a high flow of irrigant to the ICT and generation of ablation energy following a 5 second delay (step 362). Interface module 110 passes the ablation energy to ICT 122 via patient relay 250, as described above with respect to step 307 of FIG. 3A.
Based on the calculated and displayed temperature (see methods 300 and 350 described above with respect to FIGS. 3A-3B), the clinician determines the temperature of the tissue volume that is being ablated by the ablation energy (step 363). As discussed herein, in some embodiments, the system can be configured to advantageously determine the extreme temperature (e.g., hot spot or peak temperature and/or cool spot or trough temperature) of the tissue volume that is being ablated (e.g., via the delivery or removal of heat from said tissue). By comparison, temperature measured by a thermocouple alone would provide little to no useful information during this stage of the procedure.
Then, based on the calculated temperature (e.g., extreme temperature, such as the hot spot or trough temperature), the power of ablation energy is automatically regulated so as to achieve the setpoint temperature, e.g., using temperature control subsystem 119 and power control interface 290 (step 364). Based on such regulation, the tissue temperature may change, which change is measured at step 363; the power of ablation energy may further be regulated based on such changes in the calculated tissue temperature.
Interface module 110 (or related components incorporated or coupled together with other system components or devices, e.g., generator, processor, etc., into an integrated module) further may use the calculated radiometric temperature (e.g., mean temperature of the tissue volume being treated, extreme temperature of the tissue volume being treated, etc.) to determine whether the ablation procedure is being performed within safety parameters (e.g., such that the targeted temperature does not exceed an upper threshold temperature or a lower threshold temperature). For example, processor 210 may obtain safety parameters 232 from memory 230. Among other things, these safety parameters may include a cutoff temperature above which the ablation procedure is considered to be “unsafe” because it may result in perforation of the cardiac tissue being ablated, with potentially dire consequences. The cutoff temperature may be any suitable temperature below which one or more unsafe conditions may not occur, for example “popping” such as described below with respect to FIGS. 4E-4F, or tissue burning, but at which the tissue still may be sufficiently heated. One example of a suitable cutoff temperature is 85° C., although higher or lower cutoff temperatures may be used, e.g., 65° C., 70° C., 75° C., 80° C., 90° C., or 95° C. Instructions in decision module 234, also stored in memory 230, cause processor 210 to continuously compare the calculated radiometric temperature to the cutoff temperature, and if the radiometric temperature exceeds the cutoff temperature, the processor may set an alarm, open the patient relay, and close the load relay so as to return power to the IE via I/O port 204, thereby cutting off flow of ablation energy to the ICT (step 365 of FIG. 3C). Otherwise, the processor may allow the ablation procedure to proceed (step 365).
The ablation procedure terminates (step 366), for example, when the clinician presses the appropriate button on generator 130, or when the generator 130 automatically cuts of ablation energy at the end of a predetermined period of time.
Referring now to FIGS. 4A-4F, illustrative data obtained during ablation experiments using interface module 110, optionally with temperature control subsystem 119, and power control interface 290 constructed and operated in accordance with some embodiments of the present invention will now be described. This data was obtained using an unmodified Stockert EP Shuttle Generator with integrated irrigation pump, and a catheter including the PIM 121 and ICT 122 described further below with reference to FIGS. 5A-6B.
FIG. 4A illustrates one embodiment of the change over time in various signals collected during an ablation procedure in which ICT 122 was placed against exposed thigh tissue of a living dog, and the Stockert EP Shuttle generator manually actuated so as to apply 20 W of RF energy for 60 seconds. A Luxtron probe was also inserted at a depth of 3 mm into the dog's thigh. Luxtron probes are considered to provide accurate temperature information, but are impractical for normal use in cardiac ablation procedures because such probes cannot be placed in the heart of a living being. In this procedure, temperature control subsystem 119 and power control interface 290 were not used, but the data is explained with the intention of orienting the reader as to signals that may be generated during an ablation procedure performed using interface module 110; data obtained during temperature-controlled procedures, in which temperature control subsystem 119 and power control interface 290 were used with interface module 110 is provided further below with reference to FIGS. 4B-4C.
In FIG. 4A, signal 401 corresponds to scaled radiometric temperature TSrad; signal 402 corresponds to the thermocouple temperature; signal 403 corresponds to a temperature measured by the Luxtron probe; and signal 404 corresponds to the power generated by the Stockert EP Shuttle Generator. As can be seen from FIG. 4A, power signal 404 indicates that RF power was applied to the subject's tissue beginning at a time of about 40 seconds and ending at a time of about 100 seconds. Radiometric temperature signal 401 indicates a sharp rise in temperature beginning at about 40 seconds, from a baseline in region 405 of about 28° C. to a maximum in region 406 of about 67° C., followed by a gradual fall in region 407 beginning around 100 seconds. The features of radiometric temperature signal 401 are similar to those of Luxtron probe signal 403, which similarly shows a temperature increase beginning around 40 seconds to a maximum value just before 100 seconds, and then a temperature decrease beginning around 100 seconds. This similarity indicates that the calculated radiometric temperature 401 has similar accuracy to that of the Luxtron probe 403. By comparison, thermocouple signal 402 shows a significantly smaller temperature increase beginning around 40 seconds, followed by a low-level plateau in the 40-100 second region, and then a decrease beginning around 100 seconds. The relatively weak response 402 of the thermocouple, and the relatively strong and accurate response of the calculated radiometric temperature 401, indicate that an unmodified Stockert EP Shuttle Generator successfully may be retrofit using interface module 110 constructed in accordance with the principles of at least some of the embodiments of the present invention to provide a clinician with useful radiometric temperature information for use in an ablation procedure.
FIG. 4B illustrates one embodiment of signals obtained during a similar experimental procedure performed in the thigh of a living dog, but in which temperature control subsystem 119 and power control interface 290 configured illustrated in FIGS. 1A-1B and 2C-2D were coupled to interface module 110 and used to automatically regulate the ablation power provided to the animal's tissue to a setpoint (target ablation temperature) of 80° C. for about 80 seconds. In FIG. 4B, signal 411 corresponds to scaled radiometric temperature TSrad; signal 412 corresponds to the thermocouple temperature; signal 413 corresponds to a temperature measured by the Luxtron probe; signal 414 corresponds to the power generated by the Stockert EP Shuttle Generator; signal 415 corresponds to the measured tissue impedance; and signal 416 corresponds to Vrad.
In FIG. 4B, beginning around 19 seconds, power signal 414 may be seen to increase to a maximum of approximately 42 watts as the scaled radiometric temperature signal 411 increases from about 36° C. to about 84° C., and the Luxtron probe signal 413 increases from about 29° C. to about 84° C., while the thermocouple temperature 412 does not significantly change. Oscillations 417 may be seen between about 25 and 40 seconds in power signal 414 and correspond to rapid adjustments that temperature control subsystem 119 makes to the ablation power, via power control interface 290, responsive to changes in the scaled radiometric temperature signal 411. Between about 40-120 seconds, power signal 414 then decreases to and stabilizes at about 25 watts, representing the reduced power required to maintain the tissue near the setpoint temperature (rather than to heat the tissue to that temperature, which requires additional power). During the same time period, scaled radiometric temperature signal 411 may be seen to stabilize at about 80° C., and Luxtron probe signal 413 to stabilize at around 82° C. At around 120 seconds, the ablation power is reduced to zero with concomitant reduction in power signal 414, and thereafter the scaled radiometric temperature signal 411 and Luxtron probe signal 413 may be seen to gradually decrease back to body temperature. Impedance signal 415 may be seen to increase and then stabilize during application of ablation power between about 19-120 seconds, while Vrad signal 416 may be seen to decrease during this time period.
FIG. 4C illustrates signals obtained during a similar experimental procedure performed in the beating of a living dog, and in which temperature control subsystem 119 and power control interface 290 configured illustrated in FIGS. 1A-1B and 2C-2D were coupled to interface module 110 and used to automatically regulate the ablation power provided to the animal's tissue to a setpoint (target ablation temperature) of 80° C. for about 60 seconds. In FIG. 4C, signal 421 corresponds to scaled radiometric temperature TSrad; signal 422 corresponds to the thermocouple temperature; signal 424 corresponds to the power generated by the Stockert EP Shuttle Generator; signal 425 corresponds to the measured tissue impedance; and signal 426 corresponds to Vrad. A Luxtron probe was not used during this procedure because it was performed in a beating heart.
In FIG. 4C, beginning around 18 seconds, power signal 424 may be seen to increase to a maximum of approximately 30 watts as the scaled radiometric temperature signal 421 increases from about 40° C. to about 85° C., while the thermocouple temperature 422 does not significantly change. Oscillations 427 may be seen between about 25 and 45 seconds in power signal 424 and correspond to rapid adjustments that temperature control subsystem 119 makes to the ablation power, via power control interface 290, responsive to changes in the scaled radiometric temperature signal 421. Between about 45-78 seconds, power signal 424 then decreases to and stabilizes at about 17 watts, representing the reduced power required to maintain the tissue near the setpoint temperature (rather than to heat the tissue to that temperature, which requires additional power). During this same time period, scaled radiometric temperature signal 421 may be seen to stabilize at about 80° C. At around 78 seconds, the ablation power is reduced to zero with concomitant reduction in power signal 424, and thereafter the scaled radiometric temperature signal 421 may be seen to gradually decrease back to body temperature. Impedance signal 425 may be seen to increase and then stabilize during application of ablation power between about 18-78 seconds, while oscillating as a result of the beating of the heart, while Vrad signal 426 may be seen to decrease and oscillate during this time period.
Additional experimental data obtained during other procedures in which temperature control subsystem 119 and power control interface 290 were not used will now be described with reference to FIGS. 4D-4F, so as to more fully explain the functionality of interface module 110. It will be appreciated that coupling interface module 110 to temperature control subsystem 119 and power control interface 290 may provide additional enhanced functionalities, including temperature control, such as described further above.
FIG. 4D illustrates one embodiment of signals obtained during an experimental procedure similar to that described above with reference to FIG. 4A, and in which two Luxtron probes were implanted into the thigh tissue of a living dog, the first at a depth of 3 mm and the second at a depth of 7 mm. The Stockert EP Shuttle generator was activated, and the RF power was manually modulated between 5 and 50 W using power control knob 132 on the front panel of the generator. In FIG. 4D, the scaled radiometric temperature signal is designated 431, the 3 mm Luxtron signal designated 432, and the 7 mm Luxtron designated 433. The scaled radiometric temperature signal 431 and the 3 mm Luxtron signal 432 may be seen to have relatively similar changes in amplitude to one another resulting from the periodic heating of the tissue by RF energy. The 7 mm Luxtron signal 433 may be seen to have a slight periodicity, but far less modulation than do the radiometric temperature and 3 mm Luxtron signals 431, 432. This is because the 7 mm Luxtron is sufficiently deep within the tissue that ablation energy substantially does not directly penetrate at that depth. Instead, the tissue at 7 mm may be seen to slowly warm as a function of time, as heat deposited in shallower portions of the tissue gradually diffuses to a depth of 7 mm.
FIGS. 4A-4F illustrate data obtained during a series of cardiac ablation procedures that were also performed in living humans using the experimental setup described above with respect to FIG. 4C, but omitting temperature control subsystem 119 and power control interface 290. The humans all suffered from atrial flutter, were scheduled for conventional cardiac ablation procedures for the treatment of same, and consented to the clinician's use of the interface box and ICT during the procedures. The procedures were performed by a clinician who introduced the ICT into the individuals' endocardia using conventional methods. During the procedures, the clinician was not allowed to view the temperature calculated by the interface module. As such, the clinician performed the procedures in the same manner as they would have done with a system including a conventional RF ablation catheter directly connected to a Stockert EP-Shuttle generator. The temperature calculated by the interface module during the various procedures was made available for the clinician to review at a later time. The clinician performed a total of 113 ablation procedures on five humans using the above-noted experimental setup.
FIG. 4E illustrates the change over time in signal 441 corresponding to the scaled radiometric temperature TSrad, as well as the change over time in the signal 442 corresponding to the thermocouple temperature, during the tenth ablation procedure performed on the individual. During the procedure, about 40 W of RF power was applied to the individual's cardiac tissue for 60 seconds (between about 20 seconds and 80 seconds in FIG. 4E), and the clinician had a target temperature 445 of 55° C. to which it was desired to heat the cardiac tissue so as to sufficiently interrupt an aberrant pathway causing the individual's atrial flutter. It can be seen that the scaled radiometric temperature signal 441, which was subjected to data smoothing in FIG. 4E, varied between about 40° C. and 51° C. while RF power was applied and manually controlled by the clinician via control knob 132. By comparison, as expected, the thermocouple temperature 442 provided essentially no useful information about the tissue temperature during the procedure. Notably, the clinician's target temperature 445 of 55° C. was never reached during the procedure, even though the clinician believed based on his or her perceptions of the procedure that such temperature had been reached by manually adjusting the RF power via control knob 132. Because the target temperature 445 was not reached, the tissue was insufficiently heated during the procedure to interrupt an aberrant pathway. The failure to reach the target temperature may be attributed to insufficient contact and/or force between the ablative tip of the ICT and the individual's cardiac tissue, the condition of the cardiac surface, insufficient power, and the like.
FIG. 4F illustrates one embodiment of the change over time in signal 451 corresponding to TSrad, as well as the change over time in signal 452 corresponding to the thermocouple temperature, during the eleventh ablation procedure performed on the same individual as in FIG. 4E. During this procedure, again about 40 W of RF power was applied to the individual's cardiac tissue for 60 seconds (between about 20 seconds and 80 seconds in FIG. 4E), and the clinician again had a target temperature 455 of 55° C. It can be seen that the scaled radiometric signal 451, again subject to data smoothing, varied between about 55° C. and 70° C. while RF power was applied and manually controlled by the clinician via control knob 132, while the thermocouple temperature 452 again provided essentially no useful information. Here, the clinician attributed the higher temperature tissue temperature achieved during the ablation to better contact between the ablative tip of the ICT and the individual's cardiac tissue. However, it can be seen that even while RF power was being applied to the tissue, the temperature varied relatively rapidly over time, e.g., from about 70° C. at about 35 seconds, to about 56° C. at 40 seconds, which may be attributed to variations in the quality of contact between the ICT and the individual's cardiac tissue.
The results of the ablation procedures performed on the five individuals are summarized in the following table:















% of Total



Total
Ablation


















Number of patients
5



Number of ablations
113


Number of ablations that did not reach target
50
44%


temperature of 55° C.


Number of ablations that reach high temperature
13
12%


cutoff of 95° C.


Number of pops
3
 3%


Number of successful treatments of atrial flutter
5
100% 









As can be seen from the above table, 44% of the ablation procedures did not reach the clinician's target tissue temperature of 55° C. As such, it is likely that this percentage of the procedures resulted in insufficient tissue heating to interrupt aberrant pathway(s). However, although many of the ablation procedures failed, the clinician repeated the ablation procedures a sufficient number of times to achieve 100% treatment of the individuals' atrial flutter. It is believed that displaying the calculated temperature to the clinician during ablation procedures would enable the clinician to far more accurately assess the quality of contact between the ablative tip of the ICT and the individual's cardiac tissue, and thus to sufficiently heat the tissue above the target temperature for a desired period of time, and thus reduce the clinicians' need to repeatedly perform numerous ablation procedures on the same subject so as to achieve the desired treatment. Moreover, it is believed that automatically controlling the ablation power during ablation procedures would provide the clinician with greater control over lesion formation, thus improving the percentage of effective lesions and reducing the incidence of pops and burns.
As shown in the above table, 12% of the ablation procedures triggered the high temperature cutoff such as illustrated in FIG. 3C. Here, the cutoff temperature was defined to be 95 C. However, it was observed that at this cutoff temperature, “pops” formed during three of the ablation procedures. A “pop” occurs when the blood boils because of excessive localized heating caused by ablation energy, which results in formation of a rapidly expanding bubble of hot gas that may cause catastrophic damage to the cardiac tissue. It is believed that a lower cutoff temperature, e.g., 85° C., may inhibit formation of such “pops.”
Additional components that may be used in conjunction with interface module 110, temperature control subsystem 119, and power control interface 290 of the various systems disclosed herein, e.g., a PIM 121 and ICT 122 of catheter 120, are now briefly described with reference to FIGS. 5A-6B.
In FIG. 5A, patient interface module (PIM) 121 that may be associated with the integrated catheter tip (ICT) described further below with respect to FIGS. 6A-6B is described. PIM 121 includes interface module connector 501 that may be connected to front panel 111 of interface module 110, as described with reference to FIG. 1A; PIM circuitry 502, which will be described in greater detail below with reference to FIG. 5B; ICT connector 503 that may be connected to catheter 120; and PIM cable 504 that extends between interface module connector 501 and PIM circuitry 502. PIM 121 is preferably, but not necessarily, designed to remain outside the sterile field during the ablation procedure, and optionally is reusable with multiple ICT's.
FIG. 5B schematically illustrates internal components of PIM circuitry 502, and includes first I/O port 505 configured to be coupled to catheter 120, e.g., via ICT connector 503, and second I/O port 506 configured to be coupled to interface module 110, e.g., via PIM cable 504 and interface module connector 501.
PIM circuitry 502 receives on first I/O port 505 an analog thermocouple (TC) signal, raw analog radiometer signals, and analog ECG signals from catheter 120. PIM circuitry 502 includes TC signal analog-to-digital (A/D) converter 540 that is configured to convert the analog TC signal to a digital TC signal, and provide the digital TC signal to interface module 110 via second I/O port 506. PIM circuitry 502 includes a series of components configured to convert the raw analog radiometer signals into a usable digital form. For example, PIM circuitry may include radiometric signal filter 510 configured to filter residual RF energy from the raw analog radiometer signals; radiometric signal decoder 520 configured to decode the filtered signals into analog versions of the Vref and Vrad signals mentioned above with reference to FIG. 3B; and radiometric signal A/D converter 530 configured to convert the analog Vref, Vrad signals into digital Vref, Vrad signals and to provide those digital signals to second I/O port for transmission to interface module 110. PIM circuitry 502 also passes through the ECG signals to second I/O port 506 for transmission to interface module 110.
On second I/O port 506, PIM circuitry 502 receives RF ablation energy from generator 130 (e.g., a Stockert EP-Shuttle or 70 RF Generator) via interface module 110. PIM circuitry 502 passes that RF ablation energy through to catheter 120 via first I/O port 505. PIM circuitry 502 also receives on second I/O port 506 a clock signal generated by RF circuitry within interface module 110, as described further above with reference to FIG. 2B, and passes through the clock signal to first I/O port 505 for use in controlling microwave circuitry in ICT 122, as described below.
Referring now to FIGS. 6A-6B, an exemplary integrated catheter tip (ICT) 122 for use with the interface module 110, temperature control subsystem 119, and power control interface 290 of FIGS. 1A-2D and the PIM of FIGS. 5A-5B is described. Further detail on components of ICT 122 may be found in U.S. Pat. No. 7,769,469 to Carr, the entire contents of which are incorporated herein by reference, as well as in U.S. Patent Publication No. 2010/0076424, also to Can (“the Can publication”), the entire contents of which are incorporated herein by reference. The device described in the aforementioned patent and publication do not include a thermocouple or ECG electrodes, which preferably are included in ICT 122 configured for use with interface module 110.
As described in the Can publication and as depicted in FIGS. 6A-6B, ICT 122 includes an inner or center conductor 103 supported by a conductive carrier or insert 104. Carrier 104 may be formed from a cylindrical metal body having an axial passage 106 that receives conductor 103. Upper and lower sectors of that body extending inward from the ends may be milled away to expose passage 106 and conductor 103 therein and to form upper and lower substantially parallel flats 108a and 108b. Flat 108a may include coplanar rectangular areas 108aa spaced on opposite sides of conductor 103 near the top thereof. Likewise, flat 108b may include two coplanar rectangular areas 108bb spaced on opposite sides of conductor 103 near the bottom thereof. Thus, carrier 104 may include center segment 104a containing the flats and distal and proximal end segments 104b and 104c, respectively, which remain cylindrical, except that a vertical groove 107 may be formed in proximal segment 104c. 
Center conductor 103 may be fixed coaxially within passage 106 by means of an electrically insulating collar or bushing 109, e.g. of PTFE, press fit into passage 106 at distal end segment 104b of the carrier and by a weld to the passage wall or by an electrically conductive collar or bushing (not shown) at the carrier proximal segment 104c. This causes a short circuit between conductor 103 and carrier 104 at the proximal end of the carrier, while an open circuit may be present therebetween at the distal end of the carrier. In the carrier center segment 104a, the walls 106a of passage 106 may be spaced from center conductor 103. This forms a quarter wave stub S, as described in greater detail in U.S. Pat. No. 7,769,469 and U.S. Patent Publication No. 2010/0076424. Conductor 103 includes distal end segment 103a which extends beyond the distal end of carrier 104 a selected distance, and a proximal end segment 103b which extends from the proximal end of ICT 122 and connects to the center conductor of cable 105 configured to connect to PIM 121.
As illustrated in FIG. 6B, mounted to the upper and lower flats 108a and 108b of carrier 104 is a pair of opposed, parallel, mirror-image, generally rectangular plates 115a and 115b. Each plate 115a, 115b may include a thin, e.g. 0.005 in., substrate 116 formed of an electrically insulating material having a high dielectric constant. Printed, plated or otherwise formed on the opposing or facing surfaces of substrates 116 are axially centered, lengthwise conductive strips 117, preferably 0.013-0.016 mm wide, which extend the entire lengths of substrates 116. Also, the opposite or away-facing surfaces of substrates 116 are plated with conductive layers 118, e.g. of gold. The side edges of layers 118 wrap around the side edges of the substrates.
When the ICT is being assembled, plate 115a may be seated on the upper flat 108a of carrier 104 and the lower plate 115b is likewise seated on the lower flat 108b so that the center conductor 103 is contacted from above and below by the conductive strips 117 of the upper and lower plates and the layer 118 side edges of those plates contact carrier segment 104a. A suitable conductive epoxy or cement may be applied between those contacting surfaces to secure the plates in place.
At least one of the plates, e.g. plate 115a, functions also as a support surface for one or more monolithic integrated circuit chips (MMICs), e.g. chips 122 and 124. The chip(s) may include a coupling capacitor connected by a lead (not shown) to center conductor 103 and the usual components of a radiometer such as a Dicke switch, a noise source to provide a reference temperature, amplifier stages, a band pass filter to establish the radiometer bandwidth, additional gain stages if needed, a detector and buffer amplifier. Due to the relatively small profile of the present ICT 122, the above circuit components may be arranged in a string of four chips. The chip(s) may be secured to the metal layer 118 of plate 115a by a suitable conductive adhesive so that that layer which, as described above, is grounded to the insert 104 may function as a ground plane for those chips. The plates also conduct heat away from the chips to conductor 103 and carrier 104. Various leads (not shown) connect the chips to each other and other leads 125b extend through carrier slot 107 and connect the last chip 124 in the string, i.e. the radiometer output, to corresponding conductors of cable 105 leading to PIM 121.
A tubular outer conductor 126 may be slid onto carrier 104 from an end thereof so that it snugly engages around the carrier with its proximal and distal ends coinciding with the corresponding ends of the carrier (not shown). The conductor 126 may be fixed in place by a conductive epoxy or cement applied around the carrier segments 104b and 104c. 
ICT 122 also may include an annular dielectric spacer 137, e.g. of PTFE, which is centered on the distal end of carrier 104 and surrounds the conductor segment 103a. The spacer may have a slit 137a enabling it to be engaged around that conductor segment from the side thereof. The spacer 137 may be held in place by a conductive collar 136 which encircles the spacer and is long enough to slidably engage over a distal end segment of outer conductor 126. The collar 136 may be press fit around that conductor and carrier segment 104b to hold it in place and to electrically connect all those elements.
The distal end of the ICT 122 may be closed off by conductive tip 142 which, in axial section, may be T shaped. That is, the tip 142 may have discoid head 142a that forms the distal end of the ICT and an axially extending tubular neck 142b. The conductor segment 103a is sufficiently long to extend beyond the distal end of the spacer 137 into the axial passage in neck 104b. The tip may be secured in place by conductive adhesive applied around the distal end of conductor segment 103a and at the distal end or edge of collar 136. When the tip is in place, the conductor segment 103a and tip 104 form a radiometric receiving antenna, as described in greater detail in U.S. Pat. No. 7,769,469 and U.S. Patent Publication No. 2010/0076424.
ICT 122 may further include dielectric sheath 144 which may be engaged over the rear end of outer conductor 126 and slid forwardly until its distal end 144a is spaced a selected distance behind the distal end of tip 142. The conductors 103 and 126 of ICT 122 form an RF transmission line terminated by the tip 104. When the ICT 122 is operative, the transmission line may radiate energy for heating tissue only from the uninsulated segment of the probe between tip 104 and the distal end 144a of the sheath 144. That segment thus constitutes an RF ablation antenna.
The proximal ends of the center conductor segment 103b, outer conductor 126 and sheath 144 may be connected, respectively, to the inner and outer conductors and outer sheath of cable 105 that leads to PIM 121. Alternatively, those elements may be extensions of the corresponding components of cable 105. In any event, that cable 105 connects the center conductor 103 to the output of a transmitter which transmits a RF heating signal at a selected heating frequency, e.g. 500 GHz, to the RF ablation antenna.
As illustrated in FIG. 6A, ICT 122 further may include first, second, and third ECG electrodes 190 disposed on the outside of sheath 144, as well as a thermocouple 191 positioned so as to detect the temperature of blood or tissue in contact with ICT 122. Signals generated by electrodes 190 and thermocouple 191 may be provided along cable 105 connected to PIM 121.
If desired, cable 105 further may include probe steering wire 145 whose leading end 145a may be secured to the wall of a passage 146 in carrier segment 104c. 
Preferably, helical through slot 147 is provided in collar 136 as shown in FIGS. 6A-6B. The collar material left between the slot turns essentially forms helical wire 148 that bridges spacer 137. Wire 148 is found to improve the microwave antenna pattern of the radiometric receiving antenna without materially degrading the RF heating pattern of the RF ablation antenna.
The inner or center conductor 103 may be a solid wire, or preferably is formed as a tube that enables conductor 103 to carry an irrigation fluid or coolant to the interior of probe tip 142 for distribution therefrom through radial passages 155 in tip head 142a that communicate with the distal end of the axial passage in tip neck 142b. 
When plates 115a and 115b are seated on and secured to the upper and lower flats 108a and 108b, respectively, of carrier 104, conductive strips 117, 117 of those members may be electrically connected to center conductor 103 at the top and bottom thereof so that conductor 103 forms the center conducts for of a slab-type transmission line whose ground plane includes layers 118, 118.
When ablation energy is provided to ICT 122, a microwave field exists within the substrate 116 and is concentrated between the center conductor 103 and layers 118, 118. Preferably, as noted here, conductive epoxy is applied between conductor 103 and strips 117 to ensure that no air gaps exist there because such a gap would have a significant effect on the impedance of the transmission line as the highest field parts are closest to conductor 103.
Plates 115a, 115b and conductor 103 segment together with carrier 104 form a quarter wave (λR/4) stub S that may be tuned to the frequency of radiometer circuit 124, e.g. 4 GHz. The quarter wave stub S may be tuned to the center frequency of the radiometer circuit along with components in chips 122, 124 to form a low pass filter in the signal transmitting path to the RF ablation antenna, while other components of the chips form a high pass or band pass filter in the signal receiving path from the antenna to the radiometer. The combination forms a passive diplexer D which prevents the lower frequency transmitter signals on the signal transmitting path from antenna T from reaching the radiometer, while isolating the path to the transmitter from the higher frequency signals on the signal receiving path from the antenna.
The impedance of the quarter wave stub S depends upon the K value and thickness t of substrates 116 of the two plates 115a, 115b and the spacing of center conductor 103 from the walls 106a, 106a of passage 106 in the carrier center segment 104a. Because the center conductor 103 is not surrounded by a ceramic sleeve, those walls can be moved closer to the center conductor, enabling accurate tuning of the suspended substrate transmission line impedance while minimizing the overall diameter of the ICT 122. As noted above, the length of the stub S may also be reduced by making substrate 116 of a dielectric material which has a relatively high K value.
In one working embodiment of the ICT 122, which is only about 0.43 in. long and about 0.08 in. in diameter, the components of the ICT have the following dimensions:











Component
Dimension (inches)







Conductor 103
0.020 outer diameter



0.016 inner diameter (if hollow)


Substrate 116 (K = 9.8)
0.065 wide; thickness t = 0.005


Strips
0.015 wide


Air gap between 103 and each 106a
0.015









Thus, the overall length and diameter of the ICT 122 may be relatively small, which is a useful feature for devices configured for percutaneous use.
Targeted Ablation with Enhanced Temperature Detection and Control Features
According to some embodiments, any of the ablation devices, systems and methods disclosed herein, or equivalents thereof, can be configured to radiometrically detect a temperature of a volume of a subject's tissue being treated (e.g., heated, cooled, otherwise ablated or modified, etc.). In some embodiments, as discussed in greater detail below, the extreme temperature (e.g., peak temperature or trough or low temperature) within the volume of treated tissue can be advantageously determined (e.g., approximated, estimated, etc.). This can help ensure that the temperature of the “hot spot,” “cool spot” or other extreme temperature point within a volume of tissue is maintained within a desired range (e.g., below a maximum threshold, above a minimum threshold, at or near a setpoint temperature or range, etc.). Thus, the extreme temperature that is calculated or otherwise determined in accordance with the present disclosure can be used in a control scheme for any of the ablation devices, systems and methods disclosed herein to ensure that proper heating or cooling is achieved within the subject target tissue, while reducing the likelihood of overheating, overcooling and/or other undesirable damage to the targeted tissue.
According to some embodiments, it may be desirable or helpful to determine and/or control the extreme (e.g., peak or trough) temperature in the tissue in order to create a clinically-effective lesion without overtreating (e.g., overheating or overcooling) the targeted and/or surrounding tissue of the subject. For example, overheating, overcooling and/or other overtreatment could undesirably result in damaging targeted and/or non-targeted tissue of the subject. As discussed in greater detail herein, conventional temperature measurement schemes, e.g., schemes that incorporate thermocouples and/or other temperature sensing devices that detect temperatures at or near a point of catheter contact are not capable of accurately measuring or estimating the extreme (e.g., hot spot or trough) temperature and/or location relative to the tissue surface.
As disclosed with reference to other embodiments herein, tissue being treated or otherwise targeted by the ablation or other tissue modification devices and systems can include, without limitation, cardiac tissue (e.g., myocardium, atrial tissue, ventricular tissue, valves, etc.), a bodily lumen (e.g., vein, artery, airway, esophagus or other digestive tract lumen, urethra and/or other urinary tract vessels or lumens, other lumens, etc.), sphincters, other organs, tumors and/or other growths, nerve tissue and/or any other portion of the anatomy. The selective ablation and/or other heating of such anatomical locations can used to treat one or more diseases or conditions, including, for example, atrial fibrillation, mitral valve regurgitation, other cardiac diseases, asthma, chronic obstructive pulmonary disease (COPD), other pulmonary or respiratory diseases, including benign or cancerous lung nodules and lymphatic nodes, hypertension, heart failure, renal failure, denervation, obesity, gastroesophageal reflux disease (GERD), other gastroenterological disorders, other nerve-related disease, cancers, tumors or other growths, pain and/or any other disease, condition or ailment.
As noted above, in some embodiments, an ablation system can be used to radiometrically determine an extreme temperature (e.g., a “hot spot” or peak temperature and/or a “cool spot” or trough or low temperature) within a volume of tissue being treated. This can result in enhanced precision in the amount of energy (e.g., RF, microwave, ultrasound, cryogenic energy, etc.) that is delivered to the subject's tissue during a treatment procedure, and can help maintain the extreme temperature within a particular range (e.g., at, near or below a desired upper threshold, at, near or above a desired lower threshold, etc.). Accordingly, upon implementation of a control scheme that regulates the delivery of power to an ablation member (e.g., RF electrode, microwave emitter, ultrasound transducer, cryogenic emitter, other emitter, etc.) located along the distal end of a medical apparatus (e.g., catheter, probe, etc.), the target level of treatment can be accomplished without negatively impacting (e.g., overheating, over-treating, etc.) the subject's tissue (e.g., within and/or adjacent a treatment volume). As discussed herein, in some embodiments, when, for example, cryoablation is performed, the systems, devices and/or methods disclosed herein can be used to determine the “cool spot”, trough or lowest temperature point, within the ablation volume. In some embodiments, technologies that cool tissue face similar clinical challenges of controlling the tissue temperature within an efficacious and safe temperature range. Consequently, the various embodiments disclosed herein can be used with technologies that either cool or heat targeted tissue. Accordingly, the term extreme temperature, as used herein, can include either a peak or high temperature (e.g., “hot spot” temperature) or a trough or low temperature (e.g., “cool spot” temperature). As a result, determination of the extreme (e.g., peak temperature or hot spot temperature or trough or cool spot temperature) within targeted tissue can result in a safer, more efficient and more efficacious treatment procedure.
In some embodiments, the creation of a lesion and/or confirmation of an extreme temperature within the targeted tissue can be facilitated with the use of radiometry, in accordance with the various embodiments described and/or illustrated herein. For example, as discussed in greater detail herein, targeted tissue (e.g., cardiac tissue) can be ablated or otherwise heated, cooled, modified or otherwise impacted by activating one or more ablation members (e.g., RF electrodes, microwave emitters, ultrasound transducers, cryogenic emitters, etc.) located along or near a distal end of a catheter or other medical apparatus or instrument. In some embodiments, for instance, as illustrated and described herein with reference to FIGS. 6A and 6B, a single RF electrode is located along an integrated catheter tip of an intraluminal ablation system. The electrode can be configured to deliver RF energy radially outwardly (e.g., toward and through the adjacent wall of a lumen) when the electrode is electrically activated. In other embodiments, however, the type, quantity, shape, orientation, location and/or other details of the energy delivery member can be different than discussed herein. For example, other types of ablation members and/or other energy-delivery devices can be incorporated into the catheter tip, such as, for example, emitters that use microwave, laser, ultrasonic, cryogenic and/or other types of energy. Further, a catheter tip can include two or more (e.g., 2, 3, 4, 5, 6, more than 6, etc.) ablation members, as desired or required. Such electrodes and/or other emitters can be located along different portions of the catheter tip. For example, they can be staggered (e.g., axially or longitudinally, radially, etc.). Regardless of the type and/or other details of the ablation members incorporated into a particular ablation system, the system can advantageously include a radiometer or other temperature sensing device configured to detect temperature of the tissue being heated or otherwise treated by the ablation system at a particular depth (e.g., distance relative to the ablation member, a tissue surface adjacent the ablation member, etc.). Thus, the temperature within the tissue volume being treated can be more accurately determined.
Once activated, the one or more ablation members or other energy delivery devices of the system can be configured to deliver energy toward targeted tissue being treated. Depending on the type of ablation member being used, the targeted tissue of the subject may be heated or cooled, thereby creating a desired heating or cooling profile in the targeted tissue. In some embodiments, the relatively elevated density of energy delivery located near the catheter tip (e.g., adjacent and/or near the ablation member) creates a concentration of energy (e.g., which, in some embodiments, results in heat delivery or removal) along the adjacent tissue of the subject.
For any ablation systems that are configured for heat transfer away from the catheter tip (e.g., using an irrigation system, other active or passive cooling system, etc.), tissue that contacts and/or is otherwise near or adjacent the ablation member or other energy delivery device can be selectively cooled or otherwise thermally conditioned. Accordingly, in some embodiments, the greatest amount of heating or treatment impact occurs at a particular depth beneath the surface of tissue that is immediately adjacent the ablation member of the catheter. For example, in some embodiments, the tissue immediately adjacent the catheter can be at least partially cooled using an irrigation system, another cooling device, the subject's natural cooling system (e.g., blood flow) and/or the like. In addition, energy delivered to tissue will dissipate or will be less intense (e.g., and thus, less impactful) with increasing distance from the ablation member (e.g., RF electrode, ultrasound transducer, microwave emitter, laser, other emitter, etc.). As a result, for systems that are used to deliver heat to targeted tissue, the hot spot or peak temperature point within the volume of tissue being treated will be at a distance away from the tissue surface (e.g., away from the portion of the tissue adjacent or near the ablation member). Alternatively, however, for systems that are used to remove heat away from targeted tissue (e.g., to cryogenically treat tissue), the various embodiments disclosed herein can be used to estimate or otherwise determine the cool spot or trough temperature point within the volume of tissue being treated. The various systems, devices and methods disclosed herein help determine (e.g., accurately approximate) the temperature of that extreme (e.g., peak or low) temperature point in order to provide for improved therapeutic results and/or other benefits during an ablation or other tissue modification procedure. For example, as noted herein, the determination of such an extreme temperature within the tissue volume can help reduce the like likelihood of incidental damage to adjacent tissue as a result of overheating, overcooling or other overexposure to the ablation member's energy.
In some embodiments, the resulting heating or cooling profile (e.g., and thus, the location of the hot spot or highest degree of heating or cool spot or highest degree of cooling relative to the catheter and/or the tissue surface adjacent the catheter) can vary depending on the type of tissue being targeted. For example, the resulting heating or cooling profile can be impacted, at least in part, by the properties (e.g., the type of tissue being treated, composition of the tissue being treated, thickness of the tissue being treated, the presence of tissues, organs and/or other members adjacent the targeted tissue, etc.), the amount of energy being delivered to the tissue, the manner in which energy is delivered to the ablation member (e.g., continuously, intermittently, frequency of delivery, etc.), whether the ablation member (and/or other energy delivery device) contacts the targeted tissue, and if so, the amount of force imparted by the ablation member on the tissue, the distance between the ablation member and the tissue and/or one or more other factors or considerations.
In some embodiments, for example, the temperature of hot or cool spot within a volume of tissue being treated can be estimated or otherwise determined by considering one or more characteristics of the tissue being treated, either alone or in combination with one or more other factors or considerations. For example, in some embodiments, the system is able to approximate the hot spot temperature using the radiometer signals and the thickness (or approximate thickness) of the tissue being ablated. Accordingly, as discussed in greater detail herein, temperature data received by a radiometer can be adjusted using one or more scaling factors (e.g., estimation factor, coefficient factors, etc.) to approximate or otherwise determine the hot spot or cool spot temperature within the volume of targeted tissue being treated.
By way of example, in some embodiments, the location of the hot spot or peak temperature (or cool spot or trough temperature) can occur at a depth (e.g., relative to the tissue surface) of 1 to 3 mm, 2 to 3 mm, 2 to 4 mm (e.g., 1.0-1.2, 1.2-1.4, 1.4-1.6, 1.6-1.8, 1.8-2.0, 2.0-2.2, 2.2-2.4, 2.4-2.6, 2.6-2.8, 2.8-3.0, 3.0-3.2, 3.2-3.4, 3.4-3.6, 3.6-3.8, 3.8-4.0 mm, depths between the foregoing ranges, etc.). In other embodiments, the hot spot occurs at a depth less than 1 mm or greater than 4 mm (e.g., 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 mm, greater than 10 mm, etc.) relative to the tissue surface being contacted by and/or being adjacent to the catheter tip. In some embodiments, tissues in which the location of the hot spot or peak temperature occurs at a depth of 1 to 3 mm, 2 to 3 mm and/or 2 to 4 mm can be considered relatively “thick” tissues. Such tissues can include, without limitation, ventricular tissue, myocardium, organs (e.g., livers, kidneys, lungs, stomach, etc.), certain muscle tissue, tumors, bone and/or the like.
In other embodiments, the ablation system is used to treat tissue having a relatively smaller thickness. Such “thin tissues” include, without limitation, atrial tissue, veins (e.g., pulmonary veins), arteries (e.g., aorta, renal arteries, etc.), other vessels or lumens (e.g., trachea, other airways, esophagus, lumens of the urinary tract system, etc.), valves, other cardiac and/or non-cardiac tissue, etc. Thus, in some embodiments, the location of the extreme temperature (e.g., hot spot or cool spot) can occur at shallower depths relative to the tissue surface. For example, in some embodiments, the location of the hot spot or peak temperature (or cool spot or trough temperature) can occur at a depth of 0.5 to 1.0, 0.5 to 1.5 mm, 1 mm, 0 to 1 mm, 0 to 2 mm (e.g., 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 mm, depths between the foregoing ranges, etc.).
FIG. 8A schematically illustrates one embodiment of an ablation system 1000 comprising a catheter tip 1020 that has been advanced (e.g., intraluminally) to a desired anatomical location of a subject. For example, as discussed herein, the catheter can be advanced through a subject vasculature to reach a subject's cardiac tissue, a lumen (e.g., vein, artery, etc.) and/or any other anatomical location, as desired or required by a particular treatment protocol or use. As discussed above, the depth, composition or type and/or other properties of the targeted tissue can vary. For example, in the embodiment illustrated in FIG. 8A, the catheter tip 1020 is positioned adjacent and is in contact with tissue that is relatively thick (e.g., ventricular tissue of a subject).
Alternatively, as schematically depicted in FIG. 8B, the catheter tip 1020 can be positioned adjacent relatively thin tissue of the subject (e.g., atrial tissue, a vein, artery, other lumen, etc.). As discussed in greater detail above, the determination of the extreme temperature (e.g., hot spot or peak temperature, cool spot or trough temperature) using a radiometer can depend on, among other things, the type of tissue being treated, the thickness (or approximate thickness) of the targeted tissue and/or other properties of the targeted tissue. Thus, the thickness, approximate thickness, relative thickness characteristics and/or any other qualitative or quantitative metric can be used by an ablation system (e.g., one or more processors, memories and/or logical components of an ablation system) to determine the peak or hot spot temperature within a volume of tissue being treated.
By way of example, relative thickness characteristics can include a set of qualitative levels of thickness, e.g., thin tissue, intermediate tissue, thick tissue and/or the like. In other embodiments, relative thickness characteristics comprise two or more quantitative levels of thickness, e.g., Level 1, Level 2, Level 3, Level 4, Level 5, etc. For example, each thickness level in such a configuration can be representative of a particular thickness range, a particular target tissue and/or the like. In yet other arrangements, as discussed in greater detail herein, the thickness of the targeted tissue can be calculated, approximated and/or otherwise determined, e.g., manually by the user, automatically by the system and/or another device to which the system is operatively coupled, etc.
Regardless of how a targeted tissue is characterized with respect to thickness, such thickness data or other information can be advantageously used, together with a radiometer signal (e.g., temperature data related to a radiometer signal), to determine (e.g., approximate, predict, estimate, etc.) the extreme temperature (e.g., hot spot or cool spot) of a treated tissue volume during an ablation procedure, either alone or in conjunction with one or more factors or considerations.
With continued reference to FIGS. 8A and 8B, in some embodiments, the reception pattern 1030 of the radiometer, which may be at least partially located or incorporated within the tip 1020 of the catheter, extends beyond the volume 1050 of tissue that is heated by the ablation member of the tip 1020, regardless of the thickness of the tissue being treated. Thus, the radiometer can advantageously detect signals generated by the heated or cooled tissue along the entire treatment volume 1050, allowing for accurate measurement of the temperature of the tissue volume. As shown in FIG. 8C, in some embodiments, the catheter tip 1020 can comprise an omni-directional antenna so the reception pattern of the radiometer is not affected by the orientation of the catheter tip relative to the targeted tissue. Thus, the temperature of the treated tissue volume 1050, and in accordance with the disclosure below, the extreme temperature (e.g., hot spot or peak temperature or cool spot or low temperature) of the volume 1050 can be determined regardless of the exact orientation of the catheter tip 1020 relative to the tissue.
In FIGS. 8A-8C, the extreme (e.g., hot spot or peak) temperature region 1054 is schematically represented by a smaller volume within the larger tissue volume 1050. As is discussed in greater detail herein, in some embodiments, the temperature of the hot spot or cool spot temperature region 1054 can be determined by applying a scaling factor (e.g., estimation factor or function, a coefficient factor, etc.), for example, such as a correlation coefficient representative of the target tissue being treated. Such a scaling factor (e.g., an estimation function or factor) can depend on, one or more factors or inputs, such as, for example and without limitation, the thickness of targeted tissue, the amount of energy that is being delivered by the ablation member, the contact force, if any, applied by the catheter tip to the tissue and/or the like. In one embodiment, however, the estimation or correlation factor depends only on the thickness (or some thickness characteristic, e.g., quantitative or qualitative characteristic or metric) of the tissue being treated. Additional details regarding the use of an estimation or correlation factor to determine the temperature of the hot spot or peak temperature location within the treatment volume are provided below.
In some embodiments, as illustrated in FIG. 9A, a radiometer that is at least partially incorporated into a catheter tip 1020, can include a reception pattern 1100A around at least a portion of the tip 1020 (e.g., along or near an antenna). Depending on the thickness and/or other characteristics of the subject's tissue being targeted, the radiometer's reception pattern 1100 can vary. For example, the pattern 1100 illustrated in FIG. 9A is created when the tip 1020 is positioned against and/or adjacent relatively thick tissue TA of the subject. A change in the reception pattern 1100B can occur, as schematically depicted in FIG. 9B, when the catheter tip 1020 is positioned along relatively thin tissue TB. For example, the targeted tissue in FIG. 9B can include atrial tissue or the wall of a pulmonary vein or other vessel or bodily lumen.
According to some embodiments, the antenna of the radiometer included within a particular catheter tip 1020 and/or other portions of the ablation system is configured to receive and detect noise (e.g., Johnson-Nyquist noise) and/or another type of emitted signal from the targeted tissue that is being heated or cooled. Such noise and/or other signals can be proportional and/or can otherwise be correlated to the temperature of the tissue within the volume of tissue being treated by the ablation system. Depending on the shape, range and/or other characteristics of the radiometer's reception pattern 1100A, 1100B, noise and/or other signals detected by the radiometer can include contributions from the various points within the area covered by the particular reception pattern. In some embodiments, the noise or signals received by the radiometer antenna are dependent (e.g., directly or indirectly proportional, linearly or non-linearly, etc.) to the magnitude of the noise or signals at each point within the pattern. Accordingly, in some embodiments, the radiometer output can be calculated in accordance with Equation 1.

Tradiometer=ΣTtissue(i)·ωi  (Equation 1)

With reference to Equation 1, Ttissue(i) includes the temperature at the ith tissue component of the assumed tissue configuration and ωi is the weight assigned to the ith tissue component. In some embodiments, the summation, in accordance with Equation 1, takes place over the entire measurement volume (e.g., reception pattern) for a specific radiometer. In some arrangements, the assigned weight (e.g., ωi) depends on the proximity of the respective tissue component to the radiometer antenna, the fractional volume of such tissue and/or one or more considerations, as desired or required.
According to some embodiments, in order to construct a model of the radiometer temperature response, the weights (ωi) assigned to various tissue components are determined experimentally, empirically, theoretically and/or using some combination thereof. For example, in some embodiments, the weight (ωi) is smaller for a thicker tissue treated relative to a thinner tissue of similar composition and other characteristics. For example, in relatively thick tissues, the volume of tissue being treated (including the hot spot or cool spot temperature region or volume within than larger volume) is likely farther away from the antenna. Thus, the respective weight of tissue components contributing to the tissue response in such embodiments can be relatively lower (e.g., compared to thinner tissue). Alternatively, in relatively thin tissues, the volume of tissue being treated (including the hot spot or cool spot temperature region or volume within than larger volume) is likely closer to the antenna. Thus, the respective weight of tissue components contributing to the tissue response in such embodiments can be greater.
Equation 2 below is indicative of one embodiment of a simple radiometric model, in accordance with Equation 1, that is configured to receive and detect noise or other signals from different tissue types within the radiometer antenna reception pattern. For example, in the embodiment represented by Equation 2, three different tissue components contribute to the signals received by the antenna. These can include, for example, the tissue targeted for treatment (e.g., myocardium, atrial tissue, ventricular tissue, pulmonary vein, other vessels or body lumens, etc.), blood, air, muscle, tissue adjacent to the targeted tissue and/or the like. In other embodiments, depending on where the treatment procedure is occurring, the characteristics of the radiometer (e.g., the reception pattern of the radiometer antenna, the frequency and power of the radiometer, etc.) and/or one or more other factors, the radiometer model can include more or fewer that three tissue components (e.g., 1, 2, 3, 4, 5, 6, 7, 8, more than 8, etc.), as desired or required. By way of example, in the embodiment of Equation 2, the three types of tissues contributing to the noise or signals received by the antenna comprise targeted cardiac tissue, tissue adjacent to the cardiac tissue (e.g., lung tissue) and blood (e.g., adjacent the catheter tip and located within the chamber or vessel in which the tip is positioned). In reference to FIGS. 8A-8C, in some embodiments, the targeted tissue (e.g., cardiac tissue) can be along region 1050, e.g., around the extreme temperature location (e.g., hot spot, cool spot) 1054.

Tradiometer=(Ttarget·ωtarget)+(Tadj—tissue·ωadj—tissue)+(Tblood·ωblood)  (Equation 2)

With continued reference to Equation 2, each tissue or other anatomical component (e.g., cardiac tissue, adjacent tissue, blood, etc.) includes its own contribution to the noise or signal received by the radiometer antenna. Further, as discussed herein, each component can be assigned its own weight (ω). In certain embodiments, the temperature of certain types of tissues or other anatomical components, such as, for example, blood, air, non-targeted adjacent tissue, etc., remains constant or substantially constant. Accordingly, by manipulating Equation 2, the change in the temperature of the targeted tissue (e.g., cardiac tissue) can be determined as indicated in Equation 3 below.

ΔTtarget=(1/ωtarget)·(ΔTradiometer)  (Equation 3)

Thus, with reference to Equation 3, the change in the temperature detected by the radiometer (ΔTradiometer) can be used together with a weight factor value (ωtarget) assigned to the tissue being treated to advantageously determine the change in the temperature of the targeted tissue at the extreme (e.g., peak or trough) temperature volume during an ablation procedure. Thus, in some embodiments and in accordance with Equation 3, a linear relationship exists between the change in peak or trough temperature (ΔTtarget) within a volume of tissue being treated and the change in volumetric temperature (ΔTradiometer) provided by the radiometer. The weight factor for various targeted tissues (ωtarget) can be determined experimentally or empirically, theoretically and/or using any other model or method (e.g., finite element models, other mathematical or predictive models, etc.), as desired or required. In some embodiments, weight factors (ωtarget) are obtained for various tissues that may be targeted using an ablation system or method. This can allow for determination of extreme temperature (e.g., peak or trough temperature) within a treatment volume based on the procedure being performed.
One embodiment of a graph comprising experimental data used for the determination of a weight factor (ωtarget) for a specific target tissue (e.g., of a specific type, thickness, etc.) is provided in FIG. 10. As shown, the graph plots experimentally measured changes in tissue temperature (e.g., on the y axis) against a change of temperature measured by the radiometer (e.g., on the x axis). In some embodiments, the experimentally measured changes in tissue temperature are detected at a depth where the likely hot spot or cool spot volume is likely to be located, such as, for example, at a depth of 2 to 4 mm, e.g., 3 mm (e.g., 2-2.2, 2.2-2.4, 2.4-2.6, 2.6-2.8, 2.8-3.0, 3.0-3.2, 3.2-3.4, 3.4-3.6, 3.6-3.8, 3.8-4.0 mm, values between the foregoing ranges, etc.) relative to the surface adjacent the ablation member (e.g., below the surface of the ablation member). In other embodiments, the actual change in tissue temperature is measured at a depth less than 2 mm (e.g., 0-0.2, 0.2-0.4, 0.4-0.6, 0.6-0.8, 0.8-1.0, 1.0-1.2, 1.2-1.4, 1.4-1.6, 1.6-1.8, 1.8-2.0 mm, values between the foregoing ranges, etc.) or greater than 4 mm (e.g., 4-4.5, 4.5-5, 5-6, 6-7, 7-8, 8-9, 9-10 mm, values between the foregoing ranges, greater than 10 mm, etc.). The depth used to detect the actual change in tissue temperature can vary, depending on the type of tissue, its overall thickness and/or one or more other factors or considerations.
Accordingly, a correlation factor (e.g., based on the slope or approximate slope of the line that approximates the plotted data) can be determined and used in models for determining the change in temperature along the extreme temperature location (e.g., hot spot, cool spot, etc.) of the tissue volume being treated. By way of example, in the depicted arrangement, the slope of the linear line that approximates the plotted data was determined to be 4.283 for the specific tissue being tested. In some embodiments, the slope of the line in FIG. 10 comprises the estimation factor or function and comprises the scaling factor (1/ωtarget), e.g., estimation or correlation factor, used in the determination of the change in the extreme (e.g., peak or trough) temperature in accordance with Equation 3. In other embodiments, however, the estimation factor or function can be non-linear (e.g., curved, logarithmic, exponential, irregular, sinusoidal, etc.) for a specific tissue type, thickness and/or the like.
According to some embodiments, an estimation or other scaling factor (1/ωtarget) of 2 to 5 (e.g., 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, value between the foregoing, etc.) can be used for relatively thick tissue being treated (e.g., ventricular tissue, myocardium, tumors, other thick wall organs, etc.). In other embodiments, the estimation or correlation factor (1/ωtarget) for relatively thick tissue can be below 2 (e.g., 1-1.5, 1.5-2, values between the foregoing, etc.) or greater than 5 (e.g., 5-5.5, 5.5-6, 6-7, 7-8, values between the foregoing, greater than 8, etc.).
According to some embodiments, a scaling (e.g., estimation or correlation) factor (1/ωtarget) of 1 to 4 (e.g., 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, value between the foregoing, etc.) can be used for relatively thin tissue being treated (e.g., atrial tissue, pulmonary veins, other veins, arteries, vessels or other bodily lumens, etc.). In other embodiments, the estimation or correlation factor (1/ωtarget) for relatively thin tissue can be below 1 (e.g., 0-0.2, 0.2-0.4, 0.4-0.6, 0.6-0.8, 0.8-1.0 values between the foregoing, etc.) or greater than 4 (e.g., 4-4.5, 4.5-5, 5-6, 6-7, values between the foregoing, greater than 7, etc.).
In some embodiments, the user manually enters the scaling (e.g., estimation or correlation) factor (1/ωtarget) into the system to permit the processor and/or other system components to more accurately determine the extreme (e.g., hot spot or cool spot) temperature within the tissue volume being treated. For example, the scaling factor (1/ωtarget), e.g., estimation or correlation factor or function, can be entered into an input device co target), (e.g., a keypad, a touchscreen, etc.) of an integrated module or housing of the ablation system. In some embodiments, the input device allows the user to select one or a number of target tissues (e.g., “left atrium,” “right ventricle,” “myocardium,” “pulmonary vein,” “renal artery,” “trachea,” “downstream airway,” etc.), each of which includes an estimation or correlation factor (1/ωtarget). Such scaling factors can be prestored in the system (e.g., the memory of a generator or integrated module) or can be entered by user according to the user's own correlation factor determination.
In some embodiments, the ablation system can be configured to receive additional information regarding the subject to be treated, the targeted tissue of the subject and/or the like. Such information can be used (e.g., together or in lieu of information related to tissue thickness) to facilitate an accurate determination of the hot spot or peak temperature during an ablation procedure. In some embodiments, the system is configured to receive certain clinical information about the subject, such as, for example, age, gender, height, weight, etc. Such information can be used to determine a typical or normal thickness of the targeted tissue of the subject. Thus, the scaling factor (1/ωtarget), e.g., the estimation factor or function, can be adjusted accordingly to assist with a more accurate determination of the hot spot temperature.
In some embodiments, the system is configured to receive information regarding diseases or other conditions of the subject, especially diseases or conditions that may have an impact on the thickness and/or other characteristics of the subject's targeted tissue, either in addition to or in lieu of receiving other information regarding the subject (e.g., age, gender, height, weight, etc.). For example, if a subject suffers from heart failure or left ventricular hypertrophy (LVH), the subject's left ventricular wall is likely to be enlarged (e.g., may be thicker) relative to a subject who does not suffer from such diseases, while the subject's right ventricular wall may have a normal thickness or may be slightly thinner than normal. In some embodiments, for instance, subjects that suffer from LVH may have a left ventricular wall that is relatively thick (e.g., having a thickness greater than about 2 cm, e.g., 2-2.5, 2.5-3 cm, thickness between the foregoing values, etc.), while the subject's right ventricular wall has a thickness of about 5 mm or less (e.g., 0-1, 1-2, 2-3, 3-4, 4-5, 5-6 mm, thickness between the foregoing values, etc.). By way of comparison, for example, a normal thickness of a subject's left ventricular wall may be approximately 1 cm (e.g., 0.5-1, 1-1.5 cm, etc.). Thus, as with providing basic information regarding the subject to the system, additional information regarding diseases or other conditions affecting the subject (e.g., especially those that may impact the structure, composition, thickness and/or other details of the targeted tissue) may be helpful in obtaining a more accurate determination of the extreme (e.g., peak or trough temperature).
According to some embodiments, the scaling factor, e.g., estimation or correlation factor, (1/ωtarget) can be adjusted using one or more adjustment factors related to the subject. One embodiment of how the correlation factor can be modified is represented by the Equation 4 below, where adjustment factor (α) accounts for modifications to the correlation factor as a result one or more additional factors or considerations regarding the subject, as noted herein (e.g., age, gender, height, weight, diseases/conditions affecting the subject, duration and/or severity of such disease or condition, environmental or occupational considerations, etc.). In some embodiments, the adjustment factor (α) can collectively represent the consideration or combination of two or more factors, as desired or required.

(1/ωtarget)=(1/ωtarget)·(α)  (Equation 4)

In some embodiments, the system (e.g., via one or more of the system components, such as, the processor, the computer-readable medium or other memory, etc.) is configured to automatically recognize and utilize information regarding the targeted tissue of the subject in the determination of the hot spot or peak temperature. For example, in some embodiments, the system uses data and/or other information obtained from imaging technology (e.g., ultrasound, intracardiac echo, fluoroscopy, x-ray, etc.) regarding the targeted tissue (e.g., tissue type, composition, thickness, etc.). In some embodiments, the ablation system is operatively coupled to one or more imaging devices or systems. In such configurations, the ablation system and the imaging device or system can be physically connected to each other or can be physically separate from each other, as desired or required. For example, an integrated module of the ablation system (e.g., a module that includes a generator or other energy delivery device, a processor, a computer-readable medium or other memory, etc.) can include a port or other connector for a hardwired connection to an imaging device or system. In other arrangements, an integrated module and an imaging device or system are configured to communicate with one another wirelessly and/or through an intermediate device of system (e.g., the internet, a computer network, another computing device, etc.).
In some embodiments, however, imaging information is obtained by a separate imaging system that is not operatively coupled to the ablation system. Thus, in some arrangements, a physician or other user manually enters information obtained from an imaging device (e.g., target tissue thickness, tissue density, etc.) into an input (e.g., keypad, touchscreen, etc.) of the ablation system to provide for a more accurate determination of the hot spot or peak temperature.
According to some embodiments, information regarding the targeted tissue that may be used in selecting an appropriate scaling factor (1/ωtarget), e.g., estimation factor or function, is obtained by using electrocardiogram and/or electrogram data. In some embodiments, as illustrated in FIG. 11, an intracardiac echo image 1210 can be used to visually confirm the location of the ablation system's catheter tip C relative to the target tissue of the subject. Once the catheter tip has been properly positioned relative to the subject's targeted tissue, electrogram data can be obtained and used to determine one or more characteristics of the tissue, such as, for example, tissue thickness, tissue type, tissue density, exact tissue location and/or the like. As noted herein, such information can be used in the calculation (or modification) of the estimation or correlation factor (1/ωtarget) used by the ablation system to help determine the temperature of the hot spot or peak temperature point within the volume of tissue being treated. In some embodiments, the thickness of target cardiac tissue can be determined using the offset in the timing of the two electrical activity signals of the heart, such as, for example, the offset in the timing between an intracardiac electrogram signal 1226 and a surface electrocardiogram signal 1224, as illustrated in FIG. 11. For example, as shown in FIG. 11, in some embodiments, the timing of the intracardiac electrogram 1226 corresponds to the P wave seen in the electrocardiogram 1224. Consequently, confirmation can be provided that the tip of the catheter C lies in the left atrium. As a result, an estimation or other correlation factor suitable for thin-tissue models would be automatically selected.
FIG. 12 illustrates a flow chart of one embodiment of a control scheme 1300 that can be used to regulate the delivery of energy to the catheter tip of an ablation system (and thus, to the targeted tissue of the subject). In accordance with embodiments disclosed herein, the control scheme 1300 can be configured to determine the extreme (e.g., peak or trough) temperature within a volume of targeted tissue of a subject.
As shown in the flowchart of FIG. 12, a physician or other user of the ablation system can select a temperature setpoint 1350. In some embodiments, the temperature setpoint can include the target extreme temperature (e.g., hot spot or cool spot temperature) to be achieved in the targeted tissue volume (e.g., a lesion of the targeted tissue), as discussed herein. For example, the temperature setpoint (e.g., the hot spot or peak temperature within the tissue volume being targeted) can be between 55 and 90° C. (e.g., 55-60, 60-65, 65-70, 70-75, 75-80, 80-85, 85-90° C., temperatures between the foregoing, etc.), depending on the targeted tissue and desired result. In other embodiments, however, the setpoint can include a temperature range or a general temperature setting (e.g., Level 1, Level 2, Level 3, etc.). In other embodiments, the setpoint can be a set curve, which changes its values in the range provided above, according to, for example, known thermodynamic parameters, such as tissue response time. For example, the set curve may start at temperature of 60° C. and increase its value by 5° C. every 10 s until a plateau value of 75° C. is reached. Regardless of what form the temperature setpoint is provided in, such information can be entered (e.g., via a keypad, touchscreen, etc.) directly into a component of the ablation system (e.g., an integrated module, an interface module, a separate input device, etc.) or indirectly using a device or system that is operatively coupled to the ablation system (e.g., a computer, a separate computing device, etc.).
With continued reference to FIG. 12, the temperature setpoint information entered into the system can be used by the system's processor (e.g., PID controller) to regulate the amount of energy that is delivered by the generator or other energy delivery device to the ablation member along the distal end of the catheter. For example, in one embodiment, a radiofrequency (RF) power setting of the RF generator is regulated (e.g., activated, deactivated, modulated, etc.) to selectively control the amount of power that is provided to the ablation member by the RF power generator 1320. Thus, the system can automatically control the amount of heating provided by the ablation member to the targeted tissue to ensure that the temperature setpoint is maintained (e.g., not exceeded). In other embodiments, cryogenic cooling rates can be controlled in a manner consistent with maintaining tissue temperatures within a safe and efficacious cryoablation therapeutic range (e.g. −60 to −75° C., for example, −60 to −65, −65 to −70, −70 to −75° C., temperatures between the foregoing, etc.).
As energy is delivered to the targeted tissue and the tissue is heated or cooled, noise (e.g., Johnson-Nyquist noise) and/or other signals from the tissue can be detected by the radiometer antenna 1362. In some embodiments, such temperature data can be used by the radiometer 1330 of the ablation system to determine a temperature value of the radiometer 1366. As discussed herein, the radiometer temperature values can be adjusted (e.g., using an estimation or other scaling factor (1/ωtarget)) target)) to determine the temperature of the extreme (e.g., hot spot or peak temperature location or cool spot or low or trough temperature location) within the tissue volume being treated 1374. In some embodiments, the appropriate adjustment 1340 of the radiometer temperature (e.g., using a scaling factor, e.g., an estimation or correlation factor) is accomplished, at least in part, by providing to the system information regarding the subject and/or information regarding the targeted tissue of the subject 1370. As discussed herein, such data and/or other information regarding the subject, the target tissue and/or the like can be provided manually by the physical or other user (e.g., by having the user select the targeted tissue, enter a thickness of the targeted tissue, etc.) and/or automatically (e.g., with the assistance of imaging, electrocardiograph data, etc.). In some embodiments, a touchscreen or other input device of the system can provide one or more pull down or other selection menus to the physician or other user. Such menus can guide the physician through the various possible inputs regarding the subject, the targeted tissue and/or the like can could be entered to help in more accurately determining the extreme (e.g., hot spot or cool spot) temperature.
By way of example, the user can indicate to the system 1370 that the treatment procedure is intended to ablate tissue of (e.g., and thus, create a lesion within) the right ventricle of the subject. Accordingly, under those circumstances, a model indicative of thicker tissue can be used to determine the temperature of the hot spot. In some embodiments, the system can also be configured to allow for the input of information regarding the subject, such as, for example, the subject's age, gender, height, weight, medical condition and/or the like. Such factors can be used by the system to advantageously adjust the determination of the hot spot temperature to provide more accurate results. For example, the user can indicate that the subject suffers from left ventricular hypertrophy, which is usually associated with a thickening of the ventricular wall. Therefore, the system can adjust the model used to determine the hot spot temperature accordingly. One or more other inputs and/or other considerations can be used to adjust the model that is used to determine the temperature of the hot spot, either in addition to or in lieu of those mentioned above, as desired or required for a particular protocol or procedure.
FIG. 13 illustrates an alternative embodiment for determining the extreme temperature (e.g., hot spot or cool spot) temperature 1374A. Such an embodiment can be incorporated into the control scheme 1300 depicted in FIG. 12. As shown in FIG. 11 and discussed in greater detail above, the step of determining the hot spot temperature by module 1340A can be facilitated by the automatic recognition by the system of certain characteristics of the targeted tissue 1370A. For example, the system can be configured to automatically detect the type or location of tissue being targeted, the thickness of the targeted tissue, the density, composition and/or other physical or biological characteristics of the targeted tissue and/or the like. In reference to FIG. 11, signals 1224 and 1226 or echo image 1210 can be used to automatically determine the heart chamber where the ablation member has been deployed. As a result, in some embodiments, a proper selection of the scaling factor (e.g., estimation factor or function) can be performed automatically by module 1340A. Accordingly, the system can determine the extreme temperature (e.g., peak or trough temperature) by applying the appropriate scaling factor (e.g., estimation or correlation factor, other adjustment, etc.) to the temperature data of the radiometer 1366A.
In some embodiments, power control schemes for an ablation system, such as, the scheme schematically depicted in FIGS. 12 and 13, can be configured to regulate the delivery energy to the subject by taking into account one or more considerations, e.g., thermal inertia, thermal response time (e.g., for the electrode-blood-tissue system), etc. For example, if the controller (e.g., PID controller) senses that the temperature of the targeted tissue (e.g., the peak or trough temperature of the volume) is increasing at a rate faster than a threshold value, the controller can decrease the applied power. This can occur even though the target temperature for the tissue (e.g., the setpoint temperature) has not yet been attained. This can help ensure that the setpoint temperature will not be inadvertently exceeded (e.g., as a result of overshooting the setpoint by a faster than expected rise in temperature during a treatment procedure). In other embodiments, the system can be configured to limit the power than can be provided to the ablation member. As an additional safeguard for the subject, the system can be configured to cease (or greatly reduce) the delivery of power to the ablation member when the temperature of the targeted tissue (e.g., the determined hot spot temperature) exceeds the setpoint temperature by a pre-determined amount.
While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made herein without departing from the invention. For example, although the interface module has primarily been described with reference for use with an RF electrosurgical generator and the PIM and ICT illustrated in FIGS. 5A-6B, it should be understood that the interface module suitably may be adapted for use with other sources of ablation energy and other types of radiometers. Moreover, the radiometer may have components in the ICT and/or the PIM, and need not necessarily be located entirely in the ICT. Furthermore, the functionality of the radiometer, ICT, and/or PIM optionally maybe included in the interface module. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the inventions.
To assist in the description of the disclosed embodiments, words such as upward, upper, bottom, downward, lower, rear, front, vertical, horizontal, upstream, downstream have been used above to describe different embodiments and/or the accompanying figures. It will be appreciated, however, that the different embodiments, whether illustrated or not, can be located and oriented in a variety of desired positions.
Although several embodiments and examples are disclosed herein, the present application extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and modifications and equivalents thereof. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combine with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.
While the embodiments disclosed herein are susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the inventions are not to be limited to the particular forms or methods disclosed, but, to the contrary, the inventions are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the various embodiments described and the appended claims. Any methods disclosed herein need not be performed in the order recited. The methods disclosed herein include certain actions taken by a practitioner; however, they can also include any third-party instruction of those actions, either expressly or by implication. For example, actions such as “advancing a catheter” or “delivering energy to an ablation member” include “instructing advancing a catheter” or “instructing delivering energy to an ablation member,” respectively. The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. Numbers preceded by a term such as “about” or “approximately” include the recited numbers. For example, “about 10 mm” includes “10 mm.” Terms or phrases preceded by a term such as “substantially” include the recited term or phrase. For example, “substantially parallel” includes “parallel.”

## Claims

1. A system for energy delivery to a targeted tissue of a subject, comprising:
a catheter comprising a radiofrequency electrode;
a radiometer configured to detect temperature data from the targeted tissue;
a processor configured to determine a calculated temperature within the targeted tissue by applying at least one scaling factor to the temperature data detected by the radiometer, the processor being configured to compare the calculated temperature to a setpoint temperature; and
an energy source configured to energize the radiofrequency electrode and regulate delivery of ablative energy to the targeted tissue of the subject based at least in part on a comparison between the calculated temperature and the setpoint temperature.

2. The system of claim 1, wherein the calculated temperature relates to a peak temperature within the targeted tissue.

3. The system of claim 1, wherein the at least one scaling factor comprises an estimation factor, the estimation factor depending on, at least in part, at least one characteristic of the targeted tissue.

4. The system of claim 3, wherein the at least one characteristic of the targeted tissue comprises at least one of: a thickness of the targeted tissue, a type of the targeted tissue, a location of the targeted tissue and a density of the targeted tissue and a characteristic of the subject being treated.

5. The system of claim 4, wherein information related to the at least one characteristic of the targeted tissue is provided manually by a user.

6. The system of claim 4, wherein information related to the at least one characteristic of the targeted tissue is provided using at least one of imaging data and electrical signal data of the subject.

7. The system of claim 1, wherein the at least one factor further depends on at least one additional input, the at least one additional input comprises a characteristic of the subject being treated, the characteristic of the subject being treated comprising at least one of: a subject's age, a subject's gender, a subject's height, a subject's weight and a condition or disease of the subject.

8. The system of claim 1, further comprising an input device configured to receive the setpoint temperature, the setpoint temperature comprising a target ablation temperature of the targeted tissue or a set curve.

9. The system of claim 8, wherein the energy source is configured to regulate the delivery of energy to the radiofrequency electrode by comparing the calculated temperature to the setpoint temperature.

10. The system of claim 1, wherein the at least one scaling factor is determined, at least in part, theoretically or experimentally.