Patent Publication Number: US-11647908-B2

Title: Systems and methods for intracavitary temperature measurement and monitoring

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/583,798, filed May 1, 2017, now U.S. Pat. No. 10,702,163, which claims the benefit of priority of U.S. Provisional Patent Application No. 62/331,362, filed on May 3, 2016, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD OF USE 
     This application generally relates to systems and methods for measurement and monitoring intracavitary tissue temperature. 
     BACKGROUND 
     Atrial fibrillation (AF) is a major cause of stroke and the most common arrhythmia that is clinically significant, with prevalence rates of 3.8% in individuals 60 years of age or older and 9.0% in individuals over 80 years of age. In 2001, the prevalence of AF was projected to increase 2.5-fold by 2050 due to the rapidly growing elderly population. One surgical treatment method for AF is called the maze procedure, which was developed in 1991 by Cox. In this procedure, incisions are made directly into the atrium of the heart during major, open heart surgery. While successful, due to the procedure&#39;s long operative time and morbidity rate, most clinicians have adopted a variation of the procedure which uses percutaneous radiofrequency ablation (RFA) to create transmural lines of electrically inactive scar tissue within the left atrium (LA), endocardially. As a result, there has been an increase in RFA techniques to treat paroxysmal and persistent atrial fibrillation. The approach to RFA changed dramatically in 1998 with the discovery by Haïssaguerre and associates that the majority of ectopic atrial beats originated somewhere within 1 or more of the 4 pulmonary veins (PVs) due to the extension of muscular bands from the LA into the PVs. Following this discovery, mapping and ablation of arrhythmogenic foci of both the PVs and the LA have been performed, with today&#39;s procedures showing success rates of 60-90%. 
     Although RFA has been effective at treating atrial fibrillation, complications have been reported, the most serious of which is a left atrial-esophageal fistula that forms secondary to thermal esophageal injury. Atrio-esophageal fistula is the most dreadful and lethal complication among all others related to AF catheter ablation. Patients with an atrio-esophageal fistula may be presented with a variety of signs and symptoms such as chest pain, heartburn, dysphagia, anorexia, and hematemesis immediately after or also late after the index procedure. Usually death occurs because of cerebral or myocardial air embolism, endocarditis, massive gastrointestinal bleeding and septic shock. New esophageal late gadolinium enhancement has been shown to be present in almost one-third of patients after AF ablation, suggesting some form of esophageal injury. This finding is irrespective of the type of catheter ablation (irrigated vs. not-irrigated tip) used during the procedure, of ablation time, of anatomical location of the esophagus compared with the left atrium, of the size of left atrium cavity or of the timing of cardiac magnetic resonance study after pulmonary vein isolation. 
     As demonstrated by computed tomography, cardiac magnetic resonance, and intracardiac echocardiography, the strict anatomic relationship between the left atrium and the esophagus together with the delivery of radiofrequency energy on the posterior wall of the left atrium are the principal causes leading to the occurrence of atrio-esophageal fistula or, more generally, of esophageal injury. 
     Since radiofrequency energy exerts a rise in local temperatures, it is common practice now to monitor the esophageal temperature with an esophageal probe to titrate the radiofrequency energy application on the areas at potential risk of esophageal injury and to stop radiofrequency energy delivery when a rapid elevation of the esophageal internal temperature is recorded. However, a problem with current systems and methods for measuring and monitoring intracavitary tissue temperature is poor correlation between esophageal internal temperature and total radiofrequency energy delivery. 
     For example, in U.S. Patent Pub. No. 2014/0012155 to Flaherty, a device having a plurality of sensors is used to monitor temperature of esophageal tissue while actively ablating target tissue to reduce risk of injury to untargeted tissues. The device may be positioned within the esophagus with positioning elements. However, the accuracy of esophageal temperature monitoring to estimate the esophageal heating and then anticipating the formation of the esophageal injury is uncertain. For example, particles, fluids and gases traversing the esophagus may obstruct the field of view of the sensors, resulting in inaccurate temperature measurements. 
     It would therefore be desirable to provide improved systems and methods for measuring and monitoring intracavitary tissue temperature. 
     Specifically, it would be desirable to provide systems and methods for measuring and monitoring intracavitary tissue temperature using a device tailored for optimal introduction to, positioning at, and having an optimum, unobstructed field of view of, the target tissue. 
     SUMMARY 
     The present invention overcomes the drawbacks of previously-known systems by providing systems and methods for measuring and monitoring intracavitary tissue temperature using a device having an expandable structure that provides optimal field of view of the target tissue, resulting in accurate and early indicators of tissue injury. For example, the intracavity tissue may be tissue at the inner wall of a body lumen such as the esophagus so that the systems and methods permit measuring and monitoring tissue temperature at the inner wall of the body lumen. 
     In accordance with one aspect of the present invention, a system for intracavitary tissue temperature measurement and monitoring is provided. The system may include an introducer device sized and shaped to be positioned adjacent to an intracavitary tissue and software that runs on a computer operatively coupled to the introducer device. 
     The introducer device may include a catheter shaft having a distal end, a longitudinal axis, a lumen extending therethrough, and an opening at the distal end along the longitudinal axis such that at least a portion of the lumen is exposed. The catheter shaft may have a circuit board at least partially disposed in the opening at the distal end of the catheter shaft, wherein the circuit board has an array of infrared sensors disposed thereon. The circuit board may be rotated within the catheter shaft to alter a field of view through the opening of the catheter shaft. The sensors of the array of infrared sensors may each have circuitry integrate therewith that is programmed to generate a signal indicative of temperature of the intracavitary tissue. 
     The introducer device may also include an expandable structure formed from an infrared transmissive material and disposed on the catheter shaft proximal to the opening at the distal end to surround the array of infrared sensors, providing a field of view through the opening. The expandable structure may be a restrained or unrestrained inflatable bladder providing an optimum viewing distance between the array of infrared sensors and the intracavitary tissue. Alternatively, the introducer device may have a transmissive foil glued or sealed to the edges of the opening of the catheter shaft, thereby providing the array of infrared sensors a field of view through the opening. 
     The non-transitory computer readable media has instructions stored thereon that, when executed by a processor operatively coupled to the circuit board, cause a graphical user interface to display information indicative of temperature of the intracavitary tissue based on the signal from the array of infrared sensors. The instructions stored on the non-transitory computer readable media may also cause, when executed by the processor, the graphical user interface to trigger an alarm if the generated signal indicative of temperature of the intracavitary tissue exceeds a predetermined threshold to alert the patient&#39;s clinician. Accordingly, the clinician may cease or adjust the application of RF ablation to nearby tissue to thereby prevent esophageal injury. 
     In accordance with another aspect of the present invention, a method for measuring and monitoring intracavitary tissue temperature using the system described above is provided. First, the clinician positions the introducer device adjacent to an intracavitary tissue such that the opening of the catheter shaft is oriented toward the intracavitary tissue. The clinician then inflates the bladder to provide a field of view through the opening and an optimal viewing distance between the array of infrared sensors and the intracavitary tissue. The clinician optionally may rotate, either manually or by a motor, the circuit board within the lumen of the catheter shaft to achieve a desired field of view of the intracavitary tissue. 
     Next, the clinician instructs the array of infrared sensors to detect infrared radiation emitted by the intracavitary tissue. The circuitry integrated with each sensor of the array of infrared sensors then processes the detected infrared radiation to generate a signal indicative of temperature of the intracavitary tissue. Processing the detected infrared radiation may include amplifying the signal, filtering the signal, performing compensation for local actual temperature of the one or more infrared sensors, and converting the signal to a digital serial stream for convenient use by the clinician&#39;s computer. 
     Finally, the processed information indicative of temperature of the intracavitary tissue based on the generated signal is displayed on a graphical user interface. In addition, the graphical user interface may trigger an alarm if the generated signal indicative of temperature of the intracavitary tissue exceeds a predetermined threshold to alert the clinician so that the clinician may cease or adjust the application of RF ablation to nearby tissue to thereby prevent esophageal injury. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a schematic view of an exemplary embodiment of a system constructed in accordance with the principles of the present invention.  FIG.  1 B  is a schematic view of an alternative embodiment of a system constructed in accordance with the principles of the present invention. 
         FIG.  2    illustrates the circuit board of  FIG.  1 A . 
         FIG.  3 A  shows a front cross-sectional view of an alternative embodiment of the introducer device of  FIG.  1 A . 
         FIG.  3 B  shows a front cross-sectional view of an alternative embodiment of the introducer device of  FIG.  3 A  having a restrained bladder element. 
         FIG.  3 C  shows a front cross-sectional view of the introducer device of  FIG.  3 B  disposed within an esophagus. 
         FIGS.  4 A and  4 B  show an alternative embodiment of the introducer device of  FIG.  1 A , where  FIG.  4 A  is a schematic view and  FIG.  4 B  shows a front cross-sectional view of the alternative embodiment of the introducer device. 
         FIG.  5 A  shows an alternative embodiment of the introducer device of  FIG.  4 A .  FIG.  5 B  shows an alternative embodiment of the introducer device of  FIG.  5 A . 
         FIGS.  6 A and  6 B  show an alternative embodiment of the introducer device in accordance with the principles of the present invention, where the introducer device is in a delivery state in  FIG.  6 A  and in a deployed state in  FIG.  6 B . 
         FIG.  7    illustrates an exemplary method for using the system of  FIG.  1 A  to measure and monitor intracavitary temperature in accordance with the principles of the present invention. 
         FIGS.  8 A to  8 D  illustrate an exemplary method for manufacturing the expandable structure of  FIG.  1 A . 
     
    
    
     DETAILED DESCRIPTION 
     The systems and methods of the present invention may provide accurate measuring and monitoring of intracavitary tissue temperature by providing an optimal field of view over a large surface area of the intracavitary tissue. In accordance with the principles of the present invention, the systems and methods may be optimized for use in the esophagus to measure and monitor esophageal tissue to effectively prevent esophageal injury and atrio-esophageal fistula. 
     Referring to  FIG.  1 A , an overview of intracavitary probe system  100  in accordance with one embodiment of the present invention is provided. In  FIG.  1 A , components of the system are not depicted to scale on either a relative or absolute basis. Intracavitary probe system  100  comprises introducer device  102  and software-based monitoring system  116 . 
     In the illustrated embodiment, introducer device  102  includes catheter shaft  104 , circuit board  110 , and expandable structure  114 . Catheter shaft  104  has distal end  106  adapted to be inserted in a body lumen, e.g., the esophagus, adjacent to an intracavitary tissue, e.g., wall of body lumen cavity. Catheter shaft  108  also has a lumen extending therethrough for receiving circuit board  110 . Catheter shaft  104  may include opening  108  along a longitudinal axis at distal end  106 , such that opening  108  exposes at least a portion of the lumen of catheter shaft  104 , providing a field of view for circuit board  110  disposed therein. Opening  108  may be formed by cutting out a section of catheter shaft  104  during fabrication of introducer device  102 . Circuit board  110  may be flexible or rigid, and has array of sensors  112  disposed thereon. Preferably, array of sensors  112  are infrared sensors. Expandable structure  114  is formed of transmissive material, e.g., infrared transmissive foil, and shaped and sized to be disposed on distal end  106  of catheter shaft  104  to form a “viewing window” for array of sensors  112 . In one embodiment, array of sensors  112  measures infrared radiation emitted by the intracavitary tissue adjacent to introducer device  102  through opening  108  of catheter shaft  104  and expandable structure  114 . 
     Circuit board  110  may be slidably inserted into a lumen of catheter shaft  104  along rails such that array of sensors  112  is exposed from within catheter shaft  104  creating a field of view through opening  108 . The rails may be rotatable such that circuit board  110  and array of sensors  112  may be rotationally positioned about the longitudinal axis of catheter shaft  104  to face the correct direction, e.g., toward the heart, to achieve the desired field of view. Preferably, circuit board  110  is rotatable such that array of sensors  112  remains exposed in opening  108  in the rotation range permitted by the rails, while providing additional viewing angles. For example, array of sensors  112  may be disposed within opening  108  of catheter shaft  104  to create a field of view having a predetermined angle, e.g., less than 180°, less than 150°, less than 120°, or less than 90°. Accordingly, circuit board  110  housing array of sensors  112  may be rotatable to adjust the angle of the field of view to a second, different predetermined angle, e.g., greater or less than the first predetermined angle. The rails may be rotated manually or may be coupled to a motor such that the rails may be rotated by the motor operated by the clinician. For example, the rails may be rotated by any amount up to 360 degrees. 
     In one embodiment, circuit board  110  may be fixed within catheter shaft  104 . For example, stiffening wires made of a biocompatible material, e.g., stainless steel or nitinol, may be inserted through catheter shaft  104  to prevent circuit board  110  from moving from a desired viewing position, e.g., facing toward the heart, as described in further detail below. 
     In one embodiment, circuit board  110  may be reusable whereas catheter shaft  104  is disposable. For example, the more expensive circuit board having array of sensors  112  disposed thereon may be removably inserted into disposable catheter shaft  104  when used by the patient&#39;s clinician for measuring and monitoring purposes. At the end of the measurement and monitoring procedure, the disposable catheter shaft, the portion of introducer device  102  which contacts the patient&#39;s bodily lumen, may be discarded and circuit board  110  may be inserted into a new disposable catheter shaft for use with another patient, or the same patient at a later time. 
     Expandable structure  114  may be made of an infrared transmissive material, e.g., a thin film polymer having a thickness in the range of 5 micron to 1 mm. In addition, the infrared transmissive material may have transparency in the relevant wavelength range between 1 to 30 microns, or 4 to 16 microns, or 10 to 15 microns. For applications not requiring an optimal sensitivity or not needing a rapid detection, materials with less specific infrared transmissivity may be used for, e.g., their more suitable mechanical or physical properties. The space between array of sensors  112  and expandable structure  114  may be at least partially created by cutting out a section of distal end  106  of catheter shaft  104  to create opening  108 . In one embodiment, catheter shaft  104  may include a glue lumen and a plurality of holes extending from the glue lumen to an external wall of catheter shaft  104  such that a glue, e.g., adhesive material, may be inserted within the glue lumen to affix catheter shaft  104  to expandable structure  114 , as described in further detail below. 
     As shown in  FIG.  1 A , expandable structure  114  may be an inflatable bladder formed of infrared transmissive material. In an inflated state, the bladder may have an ovoid shape or an oval cross section to conform to the inside of a body lumen, e.g., esophagus. Preferably, expandable structure  114  is formed of a compliant or semi-compliant material. The bladder may be filled with air or a dry gas, thereby providing space in front of, or surrounding array of sensors  112 , such that array of sensors  112  may see through the air or gas, creating a field of view of the adjacent intracavitary tissue so that array of sensors  112  may measure the tissue temperature directly. Specifically, array of sensors  112  may detect the temperature, e.g., infrared radiation, emitted from the intracavitary tissue through expandable structure  114 , and through the air or gas in the space between array of sensors  112  and expandable structure  114 . For example, the gas may be CO 2 , Ar, He, or any other suitable gas selected based on the required infrared detection specificity and/or sensitivity. Alternatively, when there are no specific clinical requirements, air is preferably used. In addition, upon inflation, the inflatable bladder may provide an optimal viewing distance, e.g., 2 to 8 mm, between array of sensors  112  and the intracavitary tissue to be measured and monitored. As will be understood by a person having ordinary skill in the art, expandable structure  114  may be inflated via, e.g., a syringe pump, coupled to a proximal end of catheter shaft  104 . 
     Software-based monitoring system  116  is installed and runs on a computer, and is used by the patient&#39;s clinician to monitor the measured temperature of the intracavitary tissue and/or to control functioning of introducer device  102 . Preferably, the computer is electrically coupled to circuit board  110  and, thereby, to array of sensors  112 . The computer may be a conventional computer such as a desktop, laptop, tablet, smartphone, mobile device, LCD display, or the like or may be an application specific computer customized for use with introducer device  102 . For example, the computer may include a customized housing having a display for displaying the measured temperature of the intracavitary tissue and a fluid source in fluid communication with expandable structure  114  to expand, e.g., inflate, expandable structure  114 , and may permit the clinician to activate expansion and/or a monitoring session. Introducer device  102  may be coupled, either wirelessly or using a cable, to the computer such that software-based monitoring system  116  may receive data indicative of the temperature of the intracavitary tissue. Software-based monitoring system  116  may be non-transitory computer readable media having instructions stored thereon that, when executed by a processor operatively coupled to circuit board  110 , cause a graphical user interface to display and log internally information indicative of temperature of the intracavitary tissue based on signals received from array of infrared sensors  112 . The instructions stored on software-based monitoring system  116 , when executed by the processor, may also cause the graphical user interface to trigger an alarm if the generated signal indicative of temperature of the intracavitary tissue exceeds a predetermined threshold. Such an alarm allows the patient&#39;s clinician to cease or adjust application of thermal energy, e.g., RF ablation, to a nearby target tissue. 
     As shown in  FIG.  1 B , the computer, e.g., data acquisition box  115 , may include communication circuitry  117 , e.g., cellular (e.g., 3G, LTE, etc.) chipset, IEEE 802.11 (e.g., WiFi) chipset, Bluetooth chipset, or the like, for wired and/or wireless communication with additional computers, e.g., display  119 . Display  119  may include, for example, a desktop, laptop, tablet, smartphone, mobile device, LCD display, or the like. In this manner, software-based monitoring system  116  may cause data collected at data acquisition box  115  from introducer device  102  to be transmitted remotely to display  119  for, for example, display, analysis, and/or storage. 
     Referring now to  FIG.  2   , a detailed description of circuit board  110  is provided. As described above, circuit board  110  may be flexible or rigid and has array of sensors  112  mounted thereon. A flexible circuit board may be either the full length of catheter shaft  104 , going from a connector at the proximal end of catheter shaft  104  to the distal end of catheter shaft  104 , or the flexible circuit board may be long enough to hold array of sensors  112  such that array of sensors  112  are connected to discrete wires to communicate signals from the flexible circuit board to the connector. In one embodiment, circuit board  110  is slightly longer than opening  108 . The sensors of array of sensors  112  may be spaced apart along circuit board  112  in a manner so as to maximize the field of view of the surface area of the intracavitary tissue desired to be measured and monitored. As will be understood by one of ordinary skill in the art, array of sensors  112  may be selected from infrared sensitive photodiodes, infrared sensitive transistors, infrared sensitive photocells, and infrared sensitive thermopiles. Preferably, array of sensors  112  includes infrared sensitive thermopiles that generate an output voltage proportional to a local temperature difference of the intracavitary tissue. As will also be understood by one of ordinary skill in the art, array of sensors  112  may have more or less than four infrared sensors, e.g., depending on the surface area of the intracavitary tissue desired to be measured and monitored. 
     Each sensor of array of sensors  112  may include integrated circuitry  118 . In one embodiment, array of sensors  112  detects extremely small amounts of energy from the infrared radiation input and filters and amplifies the detected energy into a meaningful and useful value via circuitry  118 . Circuitry  118  may conduct signal processing which varies from a simple filter/amplifier that outputs an analog value, to a more complicated processing system involving circuit temperature compensation and conversion to other formats such as a digital output. For example, circuitry  118  may amplify the signal, filter the signal, perform compensation for local actual temperature of the array of infrared sensors irrespective of the infrared input, and convert the signal to a digital serial stream for convenient use by the clinician&#39;s computer. Circuitry  118  may be electrically coupled to the clinician&#39;s computer such that software-based monitoring system  116  may receive data indicative of the temperature of the intracavitary tissue directly from array of sensors  112 . 
     Circuit board  110  may include orientation markers  120 . For example, orientation markers  120  may be etched into circuit board  110  and viewable under fluoroscopy. As shown in  FIG.  2   , orientation markers  120  may comprise a large circle and two small circles. Alternatively, orientation markers  120  may comprise any pattern of shapers and/or markers easily identifiable under fluoroscopy by the patient&#39;s clinician to ensure proper orientation of circuit board  110 . 
     Referring now to  FIG.  3 A , an alternative exemplary embodiment of introducer device  100  is provided. Introducer device  102 ′ is constructed similarly to introducer device  102  of  FIG.  1 A , wherein like components are identified by like-primed reference numbers. Thus, for example, catheter shaft  104 ′ in  FIG.  3 A  corresponds to catheter shaft  104  of  FIG.  1 A , circuit board  110 ′ in  FIG.  3 A  corresponds to circuit board  110  of  FIG.  1 A , array of sensors  112 ′ in  FIG.  3 A  corresponds to array of sensors  112  of  FIG.  1 A , etc. As shown in  FIG.  3 A , expandable structure  115  may be an unrestrained pillow shaped inflatable bladder having a flat width with catheter shaft  104 ′ and array of sensors  112 ′ disposed in opening  108 ′ along catheter shaft  104 ′. Specifically, the unrestrained pillow shaped inflatable bladder may completely encapsulate catheter shaft  104 ′ including opening  108 ′ to thereby provide a field of view of the intracavitary tissue to array of sensors  112 ′. In one embodiment, catheter shaft  104 ′ may include a glue lumen and a plurality of holes extending from the glue lumen to an external wall of catheter shaft  104 ′ such that a glue, e.g., adhesive material, may be inserted within the glue lumen to affix catheter shaft  104 ′ to one side of the unrestrained pillow shaped inflatable bladder, e.g., the side adjacent the dorsal side of the esophagus. The unrestrained pillow shaped inflatable bladder may have fixed dimensions upon inflation with an air or gas as described above. Alternatively, the unrestrained pillow shaped inflatable bladder may have dimensions that change upon inflation based on infusion pressure of the air or gas within the bladder. 
     Opening  108 ′ provides array of sensors  112 ′ with field of view FOV by exposing at least a portion of array of sensors  112 ′, such that the field of view depends on the geometry of opening  108 ′. For example, a wider opening provides a wider field of view of a larger surface area of the target intracavitary tissue, and a narrow opening provides a narrower field of view of a smaller surface area of the target intracavitary tissue. As described above, circuit board  110 ′ along with array of sensors  112 ′ may be rotated via rotatable rails within the lumen of catheter shaft  104 ′, thereby changing the field of view. The rotation of array of sensors  112 ′ allows proper orientation in a desired direction toward the target portion of the intracavitary tissue to be measured and monitored. 
     As shown in  FIG.  3 A , the unrestrained pillow shaped inflatable bladder may be inflated such that it has an ovoid shape or an oval cross section to conform to the inside of a body lumen, e.g., esophagus. The unrestrained pillow shaped inflatable bladder may provide an optimal viewing distance, e.g., 2 to 8 mm, between array of sensors  112 ′ and the intracavitary tissue to be measured and monitored. The inflation of the unrestrained bladder may be pressure controlled such that the bladder stops inflating when it conforms to the body lumen or cavity. For application in an esophagus, the bladder&#39;s conformity to the naturally oval shape of the esophagus facilitates the orientation of introducer device  102 ′ and array of sensors  112 ′ with the intracavitary tissue to be measured and monitored. In addition, the oval shape of the inflated bladder may prevent the esophagus from being pushed out of its normal anatomical position in the patient&#39;s body. For example, the esophagus would not be pushed toward the heart during intracavitary temperature measurement and monitoring, thereby avoiding the risk of reducing the tissue-thickness between the esophagus and the heart&#39;s atria which would increase the risk of thermal damage to the esophagus during RF ablation of the atrial tissue. In one embodiment, the unrestrained inflatable bladder may be shaped so that when it is inflated, the bladder may cause the esophagus to pull away from the heart. As will be understood by one of ordinary skill in the art, the unrestrained inflated bladder may have other shapes including a spherical shape, a cylindrical shape, or a dumbbell shape depending on the application. 
     Referring to now to  FIG.  3 B , introducer device  102 ″ is constructed similarly to introducer device  102  of  FIG.  1 A , wherein like components are identified by like-primed reference numbers. Thus, for example, catheter shaft  104 ″ in  FIG.  3 B  corresponds to catheter shaft  104  of  FIG.  1 A , circuit board  110 ″ in  FIG.  3 B  corresponds to circuit board  110  of  FIG.  1 A , array of sensors  112 ″ in  FIG.  3 B  corresponds to array of sensors  112  of  FIG.  1 A , etc. As shown in  FIG.  3 B , expandable structure  117  may be a restrained pillow shaped inflatable bladder. The restrained bladder of  FIG.  3 B  may operate in a similar manner to the unrestrained bladder of  FIG.  3 A . For example, the inflation of the restrained bladder may be pressure controlled, the restrained bladder may be inflated with an air or a dry gas, the restrained bladder may provide an optimal viewing distance, e.g., 2 to 8 mm, between array of sensors  112 ″ and the intracavitary tissue to be measured and monitored, etc. 
     In addition, the restrained pillow shaped inflatable bladder may be shaped similar to the unrestrained bladder of  FIG.  3 A  on one side of the restrained bladder, e.g., the side adjacent the ventral side of the esophagus facing the heart, whereas the other side, e.g., the side adjacent the dorsal side of the esophagus, is restrained, thereby creating communication channel  122  running along the longitudinal axis of catheter shaft  104 ″ between the proximal end and the distal end of expandable structure  117 . Communication channel  122  may be formed as a recess between catheter shaft  104 ″ and expandable structure  117 . For example, expandable structure  117  may not completely encapsulate catheter shaft  104 ″, leaving the bottom portion of catheter shaft  104 ″ exposed to engage with the intracavitary tissue, e.g., the dorsal side of the esophagus as shown in  FIG.  3 C . Specifically, expandable structure  117  may be disposed on catheter shaft  104 ″ such that it encapsulates opening  108 ″ to provide a field of view of the intracavitary tissue, but does not encapsulate the bottom portion of catheter shaft  104 ″. As such, expandable structure  117  conforms with the body lumen in front of opening  108 ″ and curves inward toward catheter shaft  104 ″ on opposite sides of catheter shaft  104 ″, thereby creating communication channel  122 . Communication channel  122  may facilitate the displacement of air and liquids on the dorsal side of the body lumen or cavity, e.g., esophagus, while maintaining full continuous temperature measurement on the ventral side of the body lumen or cavity. For example, for applications in esophagus E as shown in  FIG.  3 C , communication channel  122  may be adjacent to the dorsal side of the esophagus, whereas array of sensors  112 ″ have a field of view on the ventral side of the esophagus facing the heart. In addition, as will be understood by one of ordinary skill in the art, the shape of the restrained bladder is not limited to a pillow shape. 
     The restrained bladder may include reinforcement features, e.g., wires, straps, flaps, etc., mounted on or behind the backside of the restrained bladder adjacent to the exposed portion of catheter shaft  104 ″ to improve mechanical stability of introducer device  102 ″, e.g., push-ability, catheter shaft advancement, rotational positioning, etc. The reinforcement features may assist the formation of communication channel  122 . As will be understood by one of ordinary skill in the art, the present invention is not limited to application in the esophagus and may be used for, e.g., measurement of the colon surface during prostate surgery and/or ablation. 
     Referring now to  FIGS.  4 A and  4 B , another embodiment of introducer device  102  is described. Introducer device  102 ′″ is constructed similarly to introducer device  102  of  FIG.  1 A , wherein like components are identified by like-primed reference numbers. Thus, for example, catheter shaft  104 ′″ in  FIGS.  4 A and  4 B  corresponds to catheter shaft  104  of  FIG.  1 A , circuit board  110 ′″ in  FIGS.  4 A and  4 B  corresponds to circuit board  110  of  FIG.  1 A , array of sensors  112 ′″ in  FIGS.  4 A and  4 B  corresponds to array of sensors  112  of  FIG.  1 A , etc. As will be observed by comparing  FIGS.  4 A and  4 B  with previous embodiments, introducer device  102 ′″ may include transmissive material  124 , e.g., infrared transmissive foil, that creates the “viewing window” for array of sensors  112 ′″ by being coupled to catheter shaft  104 ′″ over opening  108 ′″ rather than an expandable structure. Transmissive material  124  encloses the space between array of sensors  112 ′″ and transmissive material  124  and may be made of an infrared transmissive material, e.g., a thin film polymer having a thickness in the range of 5 micron to 1 mm. In addition, infrared transmissive material  124  may have transparency in the relevant wavelength range between 1 to 30 microns, 4 to 16 microns, or 10 to 15 microns. As described above, for applications not requiring an optimal sensitivity or not needing a rapid detection, materials with less specific infrared transmissivity may be used for, e.g., their more suitable mechanical or physical properties. The space between array of sensors  112 ′″ and transmissive material  124  may be at least partially created by cutting out a section of distal end  106 ′″ of catheter shaft  104 ′″ to create opening  108 ′″, and covering opening  108 ′″ by sealing or gluing transmissive material  124  to the edges of opening  108 ′″. 
     Referring now to  FIG.  5 A , another embodiment of introducer device  102  is described. Introducer device  502  is constructed similarly to introducer device  102 ′″ of  FIG.  4 A . For example, circuit board  510  in  FIG.  5 A  corresponds to circuit board  110 ′″ in  FIG.  4 A , array of sensors  512  in  FIG.  5 A  corresponds to array of sensors  112 ′″ in  FIG.  4 A , transmissive material  524  in  FIG.  5 A  corresponds to transmissive material  124  in  FIG.  4 A , etc. As will be observed by comparing  FIG.  5 A  with previous embodiments, catheter shaft  504  may include wire lumen  506  and glue lumen  516 . A stiffening wire(s) made of, e.g., stainless steel or nitinol, may be inserted through lumen  506  of  FIG.  5 A  to prevent circuit board  510  from moving after circuit board  510  has been positioned in its desired location, e.g., facing the ventral side of the esophagus. The stiffening wire(s) may also keep the orientation of circuit board  510  planar within catheter shaft  504 . Alternatively or additionally, the stiffening wire(s) may be inserted within cavity  514  of catheter shaft  504 . 
     Catheter shaft  504  may be encapsulated by an unrestrained pillow shaped inflatable bladder. Accordingly, glue lumen  516  of  FIG.  5 A  may have holes  518  extending therefrom to the external wall of catheter shaft  504  along the longitudinal axis of catheter shaft  504 , thereby connecting glue lumen  516  with the external wall of catheter shaft  504 . Holes  518  may include a plurality of holes spaces apart along the longitudinal axis of catheter shaft  504  or may be one single elongated hole. As such, a glue, e.g., adhesive material, may be inserted within glue lumen  516  of  FIG.  5 A , and exit via holes  518 , such that catheter shaft  504  may be affixed to one side of the unrestrained pillow shaped inflatable bladder, e.g., the side adjacent the dorsal side of the esophagus. 
     Referring now to  FIG.  5 B , another embodiment of introducer device  502  is described. Introducer device  502 ′ is constructed similarly to introducer device  502  of  FIG.  5 A , wherein like components are identified by like-primed reference numbers. Thus, for example, wire lumen  506 ′ in  FIG.  5 B  corresponds to wire lumen  506  in  FIG.  5 A , circuit board  510 ′ in  FIG.  5 B  corresponds to circuit board  510  in  FIG.  5 A , array of sensors  512 ′ in  FIG.  5 B  corresponds to array of sensors  512  in  FIG.  5 A , glue lumen  516 ′ in  FIG.  5 B  corresponds to glue lumen  516  in  FIG.  5 A , holes  518 ′ in  FIG.  5 B  corresponds to holes  518  in  FIG.  5 A , transmissive material  524 ′ in  FIG.  5 B  corresponds to transmissive material  524  in  FIG.  5 A , etc. Accordingly, catheter shaft  504 ′ may be encapsulated by an unrestrained pillow shaped inflatable bladder such that a glue may be inserted within glue lumen  516 ′ of  FIG.  5 B , and exit via holes  518 ′, such that catheter shaft  504 ′ may be affixed to one side of the unrestrained pillow shaped inflatable bladder, e.g., the side adjacent the dorsal side of the esophagus. 
     As will be observed by comparing  FIG.  5 B  with  FIG.  5 A , wire lumen  506 ′ may be positioned below a center line of catheter  502 ′, e.g., toward the dorsal side of the esophagus. Accordingly, array of electrodes  512 ′ may be spaced farther apart from transmissive material  524 ′ when compared with array of electrodes  512  and transmissive material  524  of  FIG.  5 A , such that opening  508 ′ may be larger than opening  508 . 
     Referring now to  FIGS.  6 A and  6 B , an alternative embodiment of introducer device  602  is described. Introducer device  602  is constructed similarly to introducer device  102  of  FIG.  1 A , wherein like components are identified by like-primed reference numbers. Thus, for example, catheter shaft  604  in  FIGS.  6 A and  6 B  corresponds to catheter shaft  104  of  FIG.  1 A , opening  608  in  FIGS.  6 A and  6 B  corresponds to opening  108  of  FIG.  1 A , circuit board  610  in  FIGS.  6 A and  6 B  corresponds to circuit board  110  of  FIG.  1 A , etc. As shown in  FIGS.  6 A and  6 B , introducer device  602  may have support members  624 . Each support member  624  has end portions  626  and  630 , and middle portion  628 . End portions  626  and  630  of support members  624  are coupled to the ends of catheter shaft  604  adjacent to the proximal and distal ends of opening  608  such that middle portion  628  is parallel to the longitudinal axis of catheter shaft  604  in a delivery state as shown in  FIG.  6 A , and curved outwardly away from catheter shaft  604  to engage the intracavitary tissue in a deployed state as shown in  FIG.  6 B . As middle portion  628  of support members  624  curves outwardly away from catheter shaft  604  as introducer device  602  transitions from the delivery state to the deployed state, end portion  630  causes the portion of catheter shaft  604  coupled to end portion  630  to move over circuit board  610  toward end portion  626 . In this embodiment, a transmissive material covering opening  608  may create a field of view for the array of sensors. As will be understood by one of ordinary skill in the art, introducer device  602  may have more or less than two support members  624 . For example, introducer device  602  may have three or more support members  624 . 
     Referring now to  FIG.  7   , exemplary method  700  for using the system of  FIG.  1 A  to measure and monitor intracavitary temperature in accordance with the principles of the present invention is provided. At  702 , the clinician positions introducer device  102  adjacent to an intracavitary tissue to be measured and monitored, e.g., esophageal tissue, such that opening  108  of catheter shaft  104  is oriented toward the intracavitary tissue. As described above, circuit board  110  may be slidably inserted into the lumen of catheter shaft  104  along rotatable rails. As such, circuit board  110  may be slidably inserted into the lumen of catheter shaft  104  after introducer device  102  has been positioned adjacent to the intracavitary tissue. Alternatively, circuit board  110  may be slidably inserted and fixed within catheter shaft  104  prior to the positioning of introducer device  102  adjacent to the intracavitary tissue. 
     At  704 , the clinician inflates expandable structure  114 , e.g., unrestrained or restrained pillow shaped inflatable bladder described above, to provide array of sensors  112  a field of view of the portion of the intracavitary tissue to be measured and monitored through opening  108 , transmissive expandable structure  114 , and the air or gas used to inflate expandable structure  114  therebetween. In addition, inflating expandable structure  114  provides an optimal viewing distance between array of sensors  112  and the intracavitary tissue. 
     At  706 , the clinician optionally rotates circuit board  110  within the lumen of catheter shaft  104  to achieve a desired field of view of the portion of the intracavitary tissue to be measured an monitored. The clinician may rotate circuit board  110  within a range of 360 degrees about the longitudinal axis of catheter shaft  104  in either direction, e.g., clockwise or counter-clockwise. The physician may rotate circuit board  110  manually or via a motor coupled to the rails. In addition, the clinician may adjust circuit board  110  along the longitudinal axis of catheter shaft  104  by sliding circuit board  110  along the rails to assist in achieving the desired field of view of the intracavitary tissue. In an embodiment where the catheter shaft includes one or more wire lumens, a stiffening wire may be inserted within the one or more wire lumens to prevent the circuit board from moving after being positioned in the desired location. 
     At  708 , clinician instructs array of sensors  112  to detect the infrared radiation emitting from the intracavitary tissue. At  710 , integrated circuitry  118  of each infrared sensor of array of sensors  112  processes the detected infrared radiation to generate a signal indicative of temperature of the intracavitary tissue. Processing the detected infrared radiation may include amplifying the signal, filtering the signal, performing compensation for local actual temperature of the one or more infrared sensors, and converting the signal to a digital serial stream for convenient use by the clinician&#39;s computer. The generate signal is then received by the clinician&#39;s computer either wirelessly or by a cable coupled to both circuit board  110  and the clinician&#39;s computer. 
     At  712 , the information indicative of temperature of the intracavitary tissue based on the generated signal may be displayed on a graphical user interface. In addition, at  714 , an alarm may be triggered on the graphical user interface to alert the clinician or the patient if the generated signal indicative of temperature of the intracavitary tissue exceeds a predetermined threshold. As a result, the clinician may adjust operations, e.g., reduce RF ablation of atrial tissue so as to avoid injuring the intracavitary tissue, thereby preventing, for example, esophageal injury and/or atrio-esophageal fistula. 
     Referring now to  FIGS.  8 A-D , an exemplary method for manufacturing an expandable structure, e.g., a bladder, is described. As shown in  FIG.  8 A , tube  800  may be provided for manufacturing the expandable structure. Tube  800  may be formed of a thin, flexible, infrared-transmissive material, e.g., high-density polyethylene (HDPE) or other materials having similar properties, such that tube  800  may be expanded and contracted. Preferably, tube  800  is formed of a compliant or semi-compliant material. Tube  800  is shaped and sized to at least partially encapsulate an introducer device as described above, and may have a lumen extending therethrough having, e.g., a circular cross-sectional area. 
     As shown in  FIG.  8 B , the expandable structure is stamped out of tube  800  by sealing tube  800  via a sealing machine. For example, sealing of tube  800  may be achieved by applying a heating plate on portion  802  of tube  800 . As will be understood by a person having ordinary skill in the art, any commercially available sealing machine may be used to seal tube  800 . The heating plate will apply heat to portion  802  to form mid-portion  808 , conical portion  804 , and straight end portion  806  of the expandable structure, such that the lumen of tube  800  extends continuously through mid-portion  808 , conical portion  804 , and end portion  806 . As shown in  FIG.  8 B , heat may be applied by a heating plate to an upper portion and a lower portion of portion  802  of tube  800 , or heat may be applied circumferentially around portion  802 . As heat is applied to portion  802 , the cross-sectional area of tube  800  at mid-portion  808 , changes from a first cross-sectional shape, e.g., a circular cross-sectional shape, to a second cross-sectional shape, e.g., an oval cross-sectional shape. Advantageously, heat applied to conical portion  804  and end portion  806  causes mid-portion  808  to change cross-sectional shape from the first shape to the second shape without the need to apply the heating plate to mid-portion  808 . The cross-sectional shape of end portion  806  may be circular or oval in shape, and is preferably sized and shaped to receive a catheter shaft of the introducer device described herein. Sealed tube  800  having mid-portion  808 , conical portion  804 , and end portion  806  is illustrated in  FIG.  8 C . 
     As shown in  FIG.  8 D , the excess materials are cut off end portion  806  of sealed tube  800  to form one end of the expandable structure having mid-portion  808 , conical portion  804 , and remaining end portion  806 . The above described method steps may be applied to another portion of tube  800  simultaneously or at a different time, a predetermined distance from end portion  806  such that mid-portion  808  has a desirable length for the applications described herein, thereby forming the other end of the expandable structure to form a complete expandable structure.  FIG.  8 D  shows forming conical portion  804  and end portion  806  of two separate expandable members. The expandable members may have a shape such as that shown in  FIG.  3 A . 
     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 therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true scope of the invention.