Patent Description:
Lower back injuries and chronic joint pain are major health problems resulting not only in debilitating conditions for the patient, but also in the consumption of a large proportion of funds allocated for health care, social assistance and disability programs. In the lower back, disc abnormalities and pain may result from trauma, repetitive use in the workplace, metabolic disorders, inherited proclivity, and/or aging. The existence of adjacent nerve structures and innervation of the disc are very important issues in respect to patient treatment for back pain. In joints, osteoarthritis is the most common form of arthritis pain and occurs when the protective cartilage on the ends of bones wears down over time.

A minimally invasive technique of delivering high-frequency electrical current has been shown to relieve localized pain in many patients. Generally, the high-frequency current used for such procedures is in the radiofrequency (RF) range, i.e. between <NUM> and <NUM> and more specifically between <NUM>-<NUM>. The treatment of pain using high-frequency electrical current has been applied successfully to various regions of patients' bodies suspected of contributing to chronic pain sensations. In addition to creating lesions in neural structures, application of radiofrequency energy has also been used to treat tumors throughout the body.

The RF electrical current is typically delivered from a generator via connected electrodes that are placed in a patient's body, in a region of tissue that contains a neural structure suspected of transmitting pain signals to the brain. The electrodes generally include one of more probes defining an insulated shaft with an exposed conductive active electrode tip to deliver the radiofrequency electrical current. Tissue resistance to the current causes heating of tissue adjacent resulting in the coagulation of cells (at a temperature of approximately <NUM> for small unmyelinated nerve structures) and the formation of a lesion that effectively denervates the neural structure in question. Denervation refers to affecting a neural structure's ability to transmit signals and usually results in the complete inability of a neural structure to transmit signals, thus removing the pain sensations.

To extend the size of a lesion, radiofrequency treatment may be applied in conjunction with a cooling mechanism, whereby a cooling means is used to reduce the temperature of the tissue near an energy delivery device, allowing a higher voltage to be applied without causing an unwanted increase in local tissue temperature. The application of a higher voltage allows regions of tissue further away from the energy delivery device to reach a temperature at which a lesion can form, thus increasing the size/volume of the lesion compared to conventional (non-cooling) radiofrequency treatments, where the larger size/volume of the lesion can increase the probability of success of ablating a target nerve. Cooled radiofrequency ablation is achieved by delivering, in a closed-loop circulation, cooling fluid (e.g., sterile water) via a peristaltic pump through the probe/active electrode. The cooling fluid continuously transfers heat away from the active electrode, allowing the electrode-tissue interface temperature to be maintained at a level that does not char or significantly dessicate the surrounding tissue, which is the primary limitation of conventional radiofrequency ablation. As a result, more radiofrequency energy can be delivered to the tissue, creating a lesion having a larger volume/size compared to a lesion created by conventional radiofrequency ablation.

Currently, the only way to control the lesion size is by changing the active electrode tip length at a distal end of the probe used to deliver the radiofrequency energy. A user can select active tip lengths in increments of <NUM> millimeters, <NUM> millimeters, <NUM> millimeters, <NUM> millimeters, and <NUM> millimeters depending on the local anatomy, where a longer active electrode tip results in a larger lesion. However, there are several disadvantages to controlling the lesion size based on active electrode tip lengths. For instance, the user must have additional inventory on hand to support multiple active tip lengths, certain anatomies may require multiple lesions of different sizes, which requires the use of multiple active electrode tip length probes, and it may be difficult for users to differentiate the active electrode tip lengths due to their small size.

<CIT> discloses a medical probe assembly and system for treating tissue. The system comprises an energy source, two probe assemblies, and one or more cooling devices to provide cooling to at least one of the probe assemblies. The probe assemblies may be configured in a bipolar mode, whereby current flows preferentially between the probe assemblies. The probe assemblies and system are particularly useful for delivering radio frequency energy to a patient's body.

<CIT> discloses a system for treating a patient having a sympathetically mediated disease associated at least in part with augmented peripheral chemoreflex or heightened sympathetic activation.

<CIT> discloses an ablation electrode for contacting tissue that is coupled to an RF power supply referenced to a second electrode contacting the body. Fluid coolant is circulated to cool the contact surface. Temperature sensing can be used to control the flows of RF heating energy and fluid coolant. Computer capability implements control and provides graphics displays of data, preplans, or controls relative to the ablation.

<CIT> discloses a system for applying energy, particularly radiofrequency (RF) electrical energy, for tissue ablation.

<CIT> discloses an electrosurgical probe with internal cooling for use in systems and methods for lesioning in bone and other tissue is disclosed. The probe includes tubular electrodes configured such that the inner surface of the lesioning electrodes are cooled, directly or indirectly, while keeping the electrodes electrically isolated. One probe has at least two electrically isolated electrical conductors, including an inner electrical conductor and an outer electrical conductor. The inner electrical conductor defines a lumen for the circulation of a cooling fluid therein. An inner electrical insulator is disposed between the electrical conductors to electrically isolate the electrical conductors. The electrical insulator has sufficient thermal conductivity to allow for cooling of the inner and outer electrical conductors when the cooling fluid is circulating within the lumen of the inner electrical conductor.

Thus, a new and improved cooled radiofrequency ablation probe, system and method that addresses the issues noted above would be welcomed in the art.

Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

According to the present invention, there is provided a cooled radiofrequency ablation system according to claim <NUM>.

The first internal cooling fluid tube has a length that is less than a length of the second internal cooling fluid tube. For instance, the length of the first internal cooling fluid tube can be less than about <NUM>% of the length of the second internal cooling fluid tube, such as from about <NUM>% to about <NUM>% of the length of the second internal cooling fluid tube.

In one embodiment, the bidirectional pump assembly can be located upstream from the cooling fluid reservoir in the first direction and downstream from the cooling fluid reservoir in the second direction, or the bidirectional pump assembly can be located downstream from the cooling fluid reservoir in the first direction and upstream from the cooling fluid reservoir in the second direction.

In another embodiment, the radiofrequency generator can include a user input for selecting a lesion size.

In yet another embodiment, the system can include an introducer that has a proximal end having a hub and a cannula extending from the hub that has a distal end. Further, the system can include a stylet that is insertable through the hub and into the cannula of the introducer, wherein the stylet can include a tissue-piercing distal end that extends from the distal end of the cannula when the stylet is inserted into the introducer. In addition, the introducer can electrically insulate the proximal region of the probe assembly when the probe assembly is inserted into the cannula.

Also described herein but not claimed is a method for delivering cooled radiofrequency energy to a target location within tissue via a probe assembly to form a lesion. The method includes positioning a distal tip region of the probe assembly near the target location, wherein the distal tip region includes a conductive portion for delivering energy to the target location, wherein the probe assembly also comprises a proximal region and a hollow elongated shaft defining an internal cavity, wherein a first internal cooling fluid tube and a second internal cooling fluid tube are positioned inside the internal cavity and extend from the proximal region; selecting a lesion size via a user input located on a radiofrequency generator; delivering radiofrequency energy from the radiofrequency generator to the conductive portion of the distal tip region; and delivering cooling fluid to the distal tip region via a cooling device including a cooling fluid reservoir and a bidirectional pump assembly, wherein the bidirectional pump assembly circulates the cooling fluid from the cooling fluid reservoir through the first internal cooling fluid tube, the internal cavity, the second internal cooling fluid tube, and back to the cooling fluid reservoir when the bidirectional pump is operating in a first direction, or from the cooling fluid reservoir through the second internal cooling fluid tube, the internal cavity, the first internal cooling fluid tube, and back to the cooling fluid reservoir when the bidirectional pump is operating in a second direction depending on the lesion size selected.

In one method, a larger lesion can be formed at the target location when the bidirectional pump is operating in the second direction compared to when the bidirectional pump is operating in the first direction.

Before explaining various embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings but by appended claim <NUM>.

For the purposes of this invention, a lesion refers to any effect achieved through the application of energy to a tissue in a patient's body, and the invention is not intended to be limited in this regard. Furthermore, for the purposes of this description, proximal generally indicates that portion of a device or system next to or nearer to a user (when the device is in use), while the term distal generally indicates a portion further away from the user (when the device is in use).

The present invention is directed to a cooled radiofrequency ablation system. The system includes a probe assembly having a proximal region, a distal tip region, and a hollow elongated shaft. The hollow elongated shaft defines an internal cavity, and a first internal cooling fluid tube and a second internal cooling fluid tube are positioned inside the internal cavity and extend from the proximal region. Further, the distal tip region includes a conductive portion for delivering energy to a target location within tissue. The system also includes a radiofrequency generator for delivering energy to the target location within tissue via the conductive portion of the distal tip region of the probe assembly, as well as a cooling device including a cooling fluid reservoir and a bidirectional pump assembly operable to circulate a cooling fluid from the cooling fluid reservoir through the first internal cooling fluid tube, the internal cavity, the second internal cooling fluid tube, and back to the cooling fluid reservoir when the bidirectional pump is operating in a first direction; or from the cooling fluid reservoir through the second internal cooling fluid tube, the internal cavity, the first internal cooling fluid tube, and back to the cooling fluid reservoir when the bidirectional pump is operating in a second direction. The various features of the cooled radiofrequency ablation system will now be discussed in more detail in reference to <FIG>.

Turning first to <FIG>, a schematic diagram of an energy delivery system <NUM> for the delivery of energy, such as RF energy, to a target location within tissue of a patient is provided, and is presented herein for purposes of describing an exemplary operating environment in which the present introducer and assembly may be used. The system <NUM> includes a radiofrequency (RF) generator <NUM>, a cable <NUM>, one or more probe assemblies <NUM> (only one probe assembly is shown), one or more cooling devices <NUM> that include a one or more cooling fluid reservoirs <NUM> and a bidirectional pump assembly <NUM> (see <FIG>), a pump cable <NUM>, one or more proximal cooling fluid supply tubes <NUM>, and one or more proximal cooling fluid return tubes <NUM>. The generator <NUM> may include a display that displays various aspects of a treatment procedure, such as any parameters that are relevant to a treatment procedure, for example temperature, impedance, etc. and errors or warnings related to a treatment procedure. Alternatively, the generator <NUM> may include means of transmitting a signal to an external display. The generator <NUM> is operable to communicate with the first and second probe assemblies <NUM> and the one or more cooling devices <NUM>. Such communication may be unidirectional or bidirectional depending on the devices used and the procedure performed.

In addition, as shown, a distal region <NUM> of the cable <NUM> may include a splitter <NUM> that divides the cable <NUM> into two distal ends <NUM> such that the probe assemblies <NUM> can be connected thereto. A proximal end <NUM> of the cable <NUM> is connected to the generator <NUM>. This connection can be permanent, whereby, for example, the proximal end <NUM> of the cable <NUM> is embedded within the generator <NUM>, or temporary, whereby, for example, the proximal end <NUM> of cable <NUM> is connected to generator <NUM> via an electrical connector. The two distal ends <NUM> of the cable <NUM> terminate in connectors <NUM> operable to couple to the probe assemblies <NUM> and establish an electrical connection between the probe assemblies <NUM> and the generator <NUM>. In alternate embodiments, the system <NUM> may include a separate cable for each probe assembly <NUM> being used to couple the probe assemblies <NUM> to the generator <NUM>.

The cooling device(s) <NUM> may include any means of reducing a temperature of material located at and proximate to one or more of the probe assemblies <NUM>.

The cooling devices <NUM> include a bidirectional pump assembly, operable to circulate a fluid from the cooling devices <NUM> through one or more proximal cooling fluid supply tubes <NUM>, the probe assemblies <NUM> (e.g., through an internal cavity <NUM> of the probe assemblies <NUM> (see <FIG>)), one or more proximal cooling fluid return tubes <NUM>, and back to the one or more cooling devices <NUM>.

The system <NUM> may include a controller for facilitating communication between the cooling devices <NUM> and the generator <NUM> via a feedback control loop. The feedback control may be implemented, for example, in a control module which may be a component of the generator <NUM>. In such embodiments, the generator <NUM> is operable to communicate bidirectionally with the probe assemblies <NUM> as well as with the cooling devices <NUM>, wherein bidirectional communication refers to the capability of a device to both receive a signal from and send a signal to another device.

As an example, the generator <NUM> may receive temperature measurements from one or both of the first and second probe assemblies <NUM>. Based on the temperature measurements, the generator <NUM> may perform some action, such as modulating the power that is sent to the probe assemblies <NUM>. Thus, both probe assemblies <NUM> may be individually controlled based on their respective temperature measurements.

The pumps associated with the cooling devices <NUM> may communicate a fluid flow rate to the generator <NUM> and may receive communications from the generator <NUM> instructing the pumps to modulate this flow rate. With the cooling devices <NUM> turned off, any temperature sensing elements associated with the probe assemblies <NUM> would not be affected by the cooling fluid allowing a more precise determination of the surrounding tissue temperature to be made. In addition, when using more than one probe assembly <NUM>, the average temperature or a maximum temperature in the temperature sensing elements associated with probe assemblies <NUM> may be used to modulate cooling.

The cooling devices <NUM> may reduce the rate of cooling or disengage depending on the distance between the probe assemblies <NUM>. For example, when the distance is small enough such that a sufficient current density exists in the region to achieve a desired temperature, little or no cooling may be required. In such an embodiment, energy is preferentially concentrated between first and second energy delivery devices <NUM> through a region of tissue to be treated, thereby creating a strip lesion characterized by an oblong volume of heated tissue that is formed when an active electrode is in close proximity to a return electrode of similar dimensions.

The cooling devices <NUM> may also communicate with the generator <NUM> to alert the generator <NUM> to one or more possible errors and/or anomalies associated with the cooling devices <NUM>. For example, if cooling flow is impeded or if a lid of one or more of the cooling devices <NUM> is opened. The generator <NUM> may then act on the error signal by at least one of alerting a user, aborting the procedure, and modifying an action.

Still referring to <FIG>, the proximal cooling fluid supply tubes <NUM> may include proximal supply tube connectors <NUM> at the distal ends of the one or more proximal cooling fluid supply tubes <NUM>. Additionally, the proximal cooling fluid return tubes <NUM> may include proximal return tube connectors <NUM> at the distal ends of the one or more proximal cooling fluid return tubes <NUM>. In one embodiment, the proximal supply tube connectors <NUM> are female luer-lock type connectors and the proximal return tube connectors <NUM> are male luer-lock type connectors although other connector types are intended to be within the scope of the present invention.

In addition, as shown in <FIG>, the probe assembly <NUM> includes a proximal region <NUM>, a handle <NUM>, a hollow elongate shaft <NUM>, which can also be referred to as an electrocap, and a distal tip region <NUM> that includes the one or more energy delivery devices <NUM> and that can also be referred to as the active tip. The elongate shaft <NUM> may be manufactured out of polyimide, which provides exceptional electrical insulation while maintaining sufficient flexibility and compactness. In alternate embodiments, the elongate shaft <NUM> may be any other material imparting similar qualities. In still other embodiments, the elongate shaft <NUM> may be manufactured from an electrically conductive material and may be covered by an insulating material so that delivered energy remains concentrated at the energy delivery device <NUM> of the distal tip region <NUM>. The proximal region <NUM> includes a distal cooling fluid supply tube <NUM>, a distal supply tube connector <NUM>, a distal cooling fluid return tube <NUM>, a distal return tube connector <NUM>, a probe assembly cable <NUM>, and a probe cable connector <NUM>. In such embodiments, the distal cooling fluid supply tube <NUM> and distal cooling fluid return tube <NUM> are flexible to allow for greater maneuverability of the probe assemblies <NUM>, but alternate embodiments with rigid tubes are possible.

The distal supply tube connector <NUM> may be a male luer-lock type connector and the distal return tube connector <NUM> may be a female luer-lock type connector. Thus, the proximal supply tube connector <NUM> may be operable to interlock with the distal supply tube connector <NUM> and the proximal return tube connector <NUM> may be operable to interlock with the distal return tube connector <NUM>.

The probe cable connector <NUM> may be located at a proximal end of the probe assembly cable <NUM> and may be operable to reversibly couple to one of the connectors <NUM>, thus establishing an electrical connection between the generator <NUM> and the probe assembly <NUM>. The probe assembly cable <NUM> includes one or more conductors to transmit RF current from the generator <NUM> to the one or more energy delivery devices <NUM>, as well as to connect multiple temperature sensing devices to the generator <NUM> as discussed below.

The energy delivery devices <NUM> may include any means of delivering radiofrequency energy to a region of tissue adjacent to the distal tip region <NUM>. For example, the energy delivery devices <NUM> may include an electrode or any other energy delivery means For example, in one embodiment, the energy delivery devices <NUM> may include an electrode. The active region of the electrode may be <NUM> to <NUM> millimeters (mm) in length and energy delivered by the electrode is electrical energy in the form of current in the RF range. The size of the active region of the electrode can be optimized for placement within an intervertebral disc, however, different sizes of active regions, all of which are within the scope of the present invention, may be used depending on the specific procedure being performed. In some embodiments, feedback from the generator <NUM> may automatically adjust the exposed area of the energy delivery device <NUM> in response to a given measurement such as impedance or temperature. For example, in one embodiment, the energy delivery devices <NUM> may maximize energy delivered to the tissue by implementing at least one additional feedback control, such as a rising impedance value.

<FIG> also depicts an introducer <NUM> and a stylet <NUM>, wherein the combination of the RF probe assembly <NUM>, the introducer <NUM>, and the stylet <NUM> define an RF ablation probe system <NUM> in accordance with aspects of the present invention.

Referring to <FIG>, generally, the introducer <NUM> has a proximal end <NUM> configured with a hub <NUM> and a cannula <NUM> (defining an internal lumen) having a distal end <NUM>. As understood in the art, the introducer <NUM> is operable to easily and securely couple with the RF probe assembly <NUM>. For example, the proximal hub <NUM> is configured with a connector, such as a luer-lock connector, able to mate with the handle <NUM> of the RF probe assembly <NUM>. The introducer cannula <NUM> is used to gain access to a tissue treatment site within a patient's body, wherein the elongate shaft <NUM> of the RF probe assembly <NUM> may be introduced to the treatment site through the longitudinal lumen of the introducer cannula <NUM>.

Function of the stylet <NUM> is understood in the art. Generally, the stylet <NUM> includes a proximal hub <NUM> fixed to an elongate needle <NUM> having a beveled tip at the distal end <NUM> thereof. The elongate needle slides through the introducer <NUM> such that the stylet hub <NUM> connects to the introducer hub <NUM>, for example via a luer-lock connection between the hubs <NUM> and <NUM>, as depicted in <FIG>. The distal end <NUM> of the stylet needle <NUM> extends past the distal end <NUM> of the introducer cannula <NUM> to facilitate insertion of the introducer cannula <NUM> into the patient's body at the treatment target site. Various forms of stylets <NUM> are well known in the art and the present invention is not limited to include only one specific form. Further, the stylet <NUM> may be operable to connect to a power source and may therefore form part of an electrical current impedance monitor.

Referring to <FIG>, the introducer <NUM> may include a fluid introduction port <NUM> in the proximal hub <NUM> that is in fluid communication with the proximal end <NUM> of the cannula <NUM>. This port <NUM> may be defined at a ninety-degree angle relative to a longitudinal axis of the introducer <NUM>, as depicted particularly in <FIG>. A flexible or rigid fluid delivery tube <NUM> can be connected to the port <NUM>, and a fitting <NUM> may be connected to the opposite end of the tube <NUM>, wherein fluids such as saline or a local anesthesia can be injected into the target tissue via the fitting <NUM> and port <NUM> while the RF probe assembly <NUM> remains inserted in the introducer <NUM>. The tube <NUM> may be fixed to the port <NUM> and the fitting <NUM> with a suitable medical grade adhesive. The fitting <NUM> may include a check valve that allows fluid to be injected into the fluid delivery port <NUM> through the fitting <NUM>, for example with a syringe, while preventing backflow of fluid when the syringe is removed.

As discussed, the present invention encompasses a system for the application of RF energy <NUM> that includes an RF ablation probe system <NUM> (<FIG>) for use in locating an RF probe assembly <NUM> at a target location within tissue to treat or manage pain in a patient. The system <NUM> includes the RF probe assembly <NUM>, the introducer <NUM> discussed above, as well as the stylet <NUM> that is insertable through the proximal hub <NUM> and into the cannula <NUM>. The characteristics and features of the introducer <NUM> and stylet <NUM> discussed above with respect to <FIG> are applicable to the introducer <NUM> and stylet <NUM> that can be used in conjunction with the RF ablation probe system <NUM> discussed in more detail with respect to <FIG>.

Referring to <FIG>, the RF ablation probe system <NUM> of the present invention is shown in a first configuration (<FIG>) and a second configuration (<FIG>). Regardless of the particular configuration that is selected during a particular procedure or during a particular part of a procedure as the case may be, the RF ablation probe system <NUM> includes a probe assembly <NUM> having a proximal region or end <NUM> including a handle <NUM> and a distal tip region <NUM> that can also be referred to as an active tip that includes an energy delivery device or conductive portion <NUM> for delivering energy to a target location within a patient's tissue located at or near the distal region. The distal tip region <NUM> can also include a thermocouple junction <NUM> for sensing the temperature of the active tip during an RF ablation procedure. Further, the probe assembly cable <NUM>, the distal cooling fluid supply tube <NUM>, and the distal cooling fluid return tube <NUM> discussed above with respect to <FIG> can be connected to the probe assembly <NUM> via the handle <NUM> at the proximal region or end <NUM> of the probe assembly <NUM>.

Further, a single piece hollow elongate shaft or electrocap <NUM> extends from the handle <NUM> to the distal tip region <NUM> of the probe assembly <NUM> to define an internal cavity <NUM>. A hypodermic tube <NUM>, such as a <NUM>-gauge metal hypodermic tube, can extend concentrically through the center of internal cavity <NUM> of the hollow elongate shaft <NUM> and can penetrate the tip of the hollow elongate shaft <NUM> at the distal tip region <NUM> of the probe assembly. The hypodermic tube <NUM> can be circumferentially welded to the hollow elongate shaft <NUM> near the handle <NUM> of the probe assembly <NUM> forming a water tight and structurally strong bond at location <NUM>. A wire <NUM>, such as a constantan wire containing a copper/nickel alloy, can extend concentrically through the center of the hypodermic tube <NUM>. In some embodiments, the wire <NUM> can be a <NUM>-gauge solid core constantan wire. The wire <NUM> can be electrically insulated along its entire length expect at the distal tip region <NUM> of the probe assembly <NUM> where it is welded to the hypodermic tube <NUM> forming a dome-shaped thermocouple junction <NUM>. Further, as shown, during an RF ablation procedure, the hollow elongate shaft <NUM> can be placed concentrically inside the introducer <NUM> that is electrically insulated along its entire length. The length of the introducer <NUM> is shorter than the length of the hollow elongate shaft <NUM>, resulting in a section of the hollow elongate shaft <NUM> being electrically exposed, where the length of this section is known as the active tip length L3.

Referring still to <FIG>, two lengths of internal cooling fluid tubing are positioned inside the internal cavity <NUM> of the hollow elongate shaft <NUM> from the handle <NUM> towards the distal tip region <NUM>. As shown, the first internal cooling fluid tube <NUM> has a length L1 that is shorter than a length L2 of the second internal cooling fluid tube <NUM>. Further, the present inventor has found that by specifically controlling the ratio of the length L1 to the length L2 to fall within a certain percentage, the width, height, and surface area of a resulting lesion can be precisely controlled without having to adjust the active tip length L3 of the probe assembly <NUM>, which results in a more efficient and more accurately controlled RF ablation procedure. In one particular embodiment, the length L1 of the first (shorter) internal cooling fluid tube <NUM> should have a length that is less than about <NUM>% of the length L2 of the second (longer) internal cooling fluid tube <NUM>. For instance, the length L1 should be from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>% of the length L2.

More specifically, in a first flow direction configuration (e.g., configuration <NUM> as shown in <FIG>), the shorter first internal cooling fluid tube <NUM> can serve as the inlet for the cooling fluid by virtue of being connected to the distal cooling fluid supply tube <NUM>, and the longer second internal cooling fluid tube <NUM> can serve as the outlet for the cooling fluid by virtue of being connected to the distal cooling fluid return tube <NUM>. Meanwhile, in a second flow direction configuration (e.g., configuration <NUM> as shown in <FIG>, the longer second internal cooling fluid tube <NUM> can serve as the inlet for the cooling fluid by virtue of being connected to the distal cooling fluid supply tube <NUM>, and the shorter first internal cooling fluid tube <NUM> can serve as the outlet for the cooling fluid by virtue of being connected to the distal cooling fluid return tube <NUM>. In either configuration, a water tight barrier at location <NUM> can be formed at the proximal end <NUM> of the hollow elongate shaft <NUM> at the handle <NUM>, thus allowing the cooling fluid to circulate within the internal cavity <NUM> prior to flowing out through the distal cooling fluid return tube <NUM>. The overall length of the longer second internal cooling fluid tube <NUM> scales with the overall length of the hollow elongate shaft <NUM>, regardless of the overall length, and the longer tubing is inserted almost completely into the hollow elongate shaft <NUM>.

Referring now to <FIG>, the ability to control the size of a lesion formed in a target location within tissue during a radiofrequency ablation procedure using the probe assembly with multiple configurations as described in <FIG> is discussed in more detail. Specifically, the system <NUM> of the present invention contemplates the use of an RF generator <NUM> in conjunction with a cooling device <NUM> that utilizes a cooling fluid reservoir <NUM> in conjunction with a bidirectional pump assembly <NUM> located either upstream (<FIG>) or downstream (<FIG>) of the cooling fluid reservoir <NUM> that is capable of delivering cooling fluid to the probe assembly in a first direction and an opposite second direction to control lesion size.

As shown in <FIG> and depending on instructions transmitted via a controller to the bidirectional pump assembly <NUM> via a signal <NUM> from, for instance, a user input such as a graphical user interface present on the RF generator <NUM>, the bidirectional pump <NUM> is capable of pumping cooling fluid into the internal cavity <NUM> of the hollow elongate shaft <NUM> of the probe assembly <NUM> in a first direction <NUM> so that the cooling fluid enters the shorter first internal cooling fluid tube <NUM> and then travels toward the distal tip region <NUM> and into the longer second internal cooling fluid tube <NUM> to exit the probe assembly <NUM>. In some embodiments and based upon the specific location of the pump assembly <NUM> in relation to the shorter first internal cooling fluid tube <NUM> and the longer second internal cooling fluid tube <NUM>, the pump assembly <NUM> operates in a counterclockwise direction, although it is to be understood that depending on the particular arrangement of the system <NUM> components, the pump assembly <NUM> may operate in a clockwise direction in order to deliver cooling fluid to the shorter first internal cooling fluid tube <NUM>, where the cooling fluid exits the probe assembly <NUM> via the longer second internal cooling fluid tube <NUM>.

Meanwhile, as shown in <FIG> and also depending on instructions transmitted to the bidirectional pump assembly <NUM> via a signal <NUM> from, for instance, a graphical user interface present on the RF generator <NUM>, the bidirectional pump <NUM> is capable of pumping cooling fluid into the internal cavity <NUM> of the hollow elongate shaft <NUM> of the probe assembly <NUM> in a second, opposite direction <NUM> so that the cooling fluid enters the longer second internal cooling fluid tube <NUM> first and then travels toward the proximal region <NUM> and into the shorter first internal cooling fluid tube <NUM> to exit the probe assembly <NUM>. In some embodiments and based upon the specific location of the pump assembly <NUM> in relation to the shorter first internal cooling fluid tube <NUM> and the longer second internal cooling fluid tube <NUM>, the pump assembly <NUM> operates in a clockwise direction, although it is to be understood that depending on the particular arrangement of the system <NUM> components, the pump assembly <NUM> may operate in a counterclockwise direction in order to initially deliver cooling fluid to the longer second internal cooling fluid tube <NUM>, where the cooling fluid exits the probe assembly <NUM> via the shorter first internal cooling fluid tube <NUM>.

Thus, the system <NUM> of the present invention contemplates creation of a lesion having a predetermined size at a target location within tissue via the delivery of cooling fluid in a particular direction via the bidirectional pump assembly <NUM>. Further, although the configuration of <FIG> where the bidirectional pump assembly <NUM> is located upstream from the cooling fluid reservoir <NUM> results in the formation of smaller lesion since the cooling fluid enters the shorter first internal cooling fluid tube <NUM> before the longer second internal cooling fluid tube <NUM>, and the configuration of <FIG> where the bidirectional pump assembly <NUM> is located downstream from the cooling fluid reservoir <NUM> results in the formation of a larger lesion since the cooling fluid inters the longer second internal cooling fluid tube <NUM> before the shorter first internal cooling fluid tube <NUM>, it is to be understood that the location of the bidirectional pump assembly <NUM> in relation to the cooling fluid reservoir <NUM> can be reversed in some embodiments. For instance, in <FIG>, the bidirectional pump assembly <NUM> could be located downstream of the cooling fluid reservoir <NUM> to create a smaller lesion, while in <FIG>, the bidirectional pump assembly <NUM> could be located upstream of the cooling fluid reservoir so long as the cooling fluid enters the appropriate internal cooling fluid tube <NUM> or <NUM> first based on whether a smaller lesion or a larger lesion, respectively, is desired.

Referring to <FIG>, a method <NUM> for delivery of cooled radiofrequency energy to a target location of tissue can include a user responding to prompts on a graphical user interface (not shown) of an RF generator <NUM>, where, in step <NUM>, the user is asked if the user wants to activate a smaller lesion function. If the answer is yes, then in step <NUM>, the pump assembly <NUM> is instructed to operate in a first direction, after which a small thermal lesion is created in step <NUM>. Meanwhile, if the answer is no in step <NUM>, then the user is asked if the user wants to activate a larger lesion function in step <NUM>. If the answer is yes, then in step <NUM>, the pump assembly <NUM> is instructed to operate in a second direction that is opposite from the first direction, after which a large thermal lesion is created in step <NUM>. Further, although the method <NUM> described above describes inquiring about the activation of a smaller lesion function first, the method <NUM> also contemplates asking the user if the user wants to activate a larger lesion function first, or the user can be asked which lesion size should be formed, and the user can select the smaller lesion function or the larger lesion function. In one particular method, the user can either activate the smaller lesion function or the larger lesion function. If the smaller lesion function is activated, the RF generator <NUM> instructs the pump assembly <NUM> to rotate in the counter-clockwise direction, pumping cooling fluid from the reservoir through the shorter first internal cooling fluid tube <NUM> as the inlet, where the fluid is returned to the reservoir of the cooling device <NUM> through the longer second internal cooling fluid tube <NUM> (flow configuration <NUM>) resulting in a small thermal lesion. Conversely, if the larger lesion function is activated, the RF generator <NUM> instructs the pump assembly <NUM> to rotate in the clockwise direction, pumping cooling fluid from the reservoir of the cooling device <NUM> through the longer second cooling fluid tube <NUM> as the inlet, where the fluid is returned to the reservoir of the cooling device <NUM> through the shorter first internal cooling fluid tube <NUM> (flow configuration <NUM>), resulting in a large thermal.

The present invention may be better understood by reference to the following example.

The ability to control lesion size based on directional cooling flow as contemplated by the present invention was demonstrated on a sample of tissue <NUM>, as represented by raw chicken breast in this Example. In configuration <NUM>, the inlet cooling fluid flow was through a section of shorter internal cooling fluid tubing having a length of <NUM> millimeters inside a probe having a length of <NUM> millimeters, while the outlet cooling fluid flow was through longer internal cooling fluid tubing having a length of <NUM> millimeters, where the shorter fluid tubing was <NUM>% of the length of the longer fluid tubing. In configuration <NUM>, the inlet cooling fluid flow was through the longer internal cooling fluid tubing having a length of <NUM> millimeters, while the outlet cooling fluid flow was through the shorter internal cooling fluid tubing having a length of <NUM> millimeters. As shown in Table <NUM> below, the lesion height and width were increased for configuration <NUM> compared to configuration <NUM>, demonstrating that using the longer internal cooling fluid tubing for the inlet tubing and the shorter internal cooling tubing for the outlet tubing results in a larger lesion having an increased length/height and width. In addition, <FIG> shows that lesions formed in configuration <NUM>, as represented by reference numeral <NUM>, were generally smaller in overall surface area compared to lesions formed in configuration <NUM>, as represented by reference numeral <NUM>. In other words, the lesions <NUM> formed by configuration <NUM> were generally larger in overall surface area compared to lesions <NUM> formed in configuration <NUM>.

Referencing the bar graphs of <FIG>, ex-vivo thermal lesions were created in chicken breast using the same probe with a configuration <NUM> flow direction and a configuration <NUM> flow direction. The bar graph in <FIG> compares the difference in lesion width between configuration <NUM> and configuration <NUM>. This graph indicates that configuration <NUM> creates a larger on average lesion width than configuration <NUM>, the difference in width being statistically significant. The bar graph in <FIG> compares the difference in lesion height between configuration <NUM> and configuration <NUM>. This graph indicates that configuration <NUM> creates a larger on average lesion height than configuration <NUM>, the difference in height also being statistically significant. This data suggests that with the same probe, configuration <NUM> flow direction (e.g., where the inlet cooling fluid flows through the longer length of internal cooling fluid tubing inside the probe) creates a larger overall lesion than configuration <NUM> flow direction (e.g., where the inlet cooling fluid flows through the shorter internal cooling fluid tubing inside the probe).

The underlying mechanism of this effect is likely due to differences in heat transfer efficiencies. In configuration <NUM>, the cooling fluid inlet through the shorter fluid tubing allows the fluid to exit into the hollow elongate shaft/electrocap internal cavity closer its proximal end. When the fluid exits, it transitions into a much larger cross-sectional area, resulting in a significant reduction in flow velocity and increase in transient time, which, in turn, allows for increased heat transfer from the warmer surrounding to the cooler cooling fluid. By the time the cooling fluid reaches the active tip, sufficient cooling efficiency is lost to result in a reduced cooling effect on the thermocouple and in response a decreased application of RF energy from the generator. Meanwhile, in configuration <NUM>, the cooling fluid inlet through the longer fluid tubing can maintain high flow velocity until it reaches the distal tip, thus preserving the cooling efficiency and allowing the generator to apply greater amounts of RF energy.

Claim 1:
A cooled radiofrequency ablation system (<NUM>) comprising:
a probe assembly (<NUM>) comprising a hollow elongated shaft (<NUM>) extending from a handle (<NUM>) at a proximal end (<NUM>) of the probe assembly to a distal tip region (<NUM>) of the probe assembly, the hollow elongated shaft defining an internal cavity (<NUM>) having a first internal cooling fluid tube (<NUM>) and a second internal cooling fluid tube (<NUM>) positioned therein, the first internal cooling fluid tube extending a first distance from the handle and the second internal cooling fluid tube extending a second distance from the handle, the second distance being greater than the first distance, and the distal tip region (<NUM>) comprising a conductive portion (<NUM>) for delivering energy to a target location within tissue;
a radiofrequency generator (<NUM>) for delivering energy to the target location via the conductive portion of the distal tip region of the probe assembly;
a cooling device (<NUM>) including a cooling fluid reservoir (<NUM>) and a bidirectional pump assembly (<NUM>) operable to circulate a cooling fluid through the probe assembly; and
a controller configured to operate the bidirectional pump assembly (<NUM>) in a first operating mode and a second operating mode based on a user selection, wherein:
in the first operating mode, the bidirectional pump assembly (<NUM>) rotates in a first direction to transfer the cooling fluid from the cooling fluid reservoir (<NUM>) through the first internal cooling fluid tube (<NUM>), the internal cavity (<NUM>), the second internal cooling fluid tube (<NUM>), and back to the cooling fluid reservoir,
in the second operating mode, the bidirectional pump assembly rotates in a second direction to transfer the cooling fluid from the cooling fluid reservoir (<NUM>) through the second internal cooling fluid tube (<NUM>), the internal cavity (<NUM>), the first internal cooling fluid tube (<NUM>), and back to the cooling fluid reservoir, and
the first operating mode produces a first size of lesion and the second operating mode produces a second size of lesion that is larger than the first size of lesion by allowing the generator to apply greater amounts of RF energy without causing unwanted increase in local tissue temperature in the second operating mode.