Patent Description:
The present invention relates generally to a system for applying energy for the treatment of tissue, and more particularly to a system for mitigating rising impedance via a pump assembly during use of cooled radiofrequency probes.

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 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 an insulated shaft with an exposed conductive 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 a procedure whereby the ability of a neural structure to transmit signals is affected in some way and usually results in the complete inability of a neural structure to transmit signals, thus removing the pain sensations. This procedure may be done in a monopolar mode where a second dispersive electrode with a large surface area is placed on the surface of a patient's body to complete the circuit, or in a bipolar mode where a second radiofrequency electrode is placed at the treatment site. In a bipolar procedure, the current is preferentially concentrated between the two electrodes.

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 power to be applied without causing an unwanted increase in local tissue temperature. The application of a higher power 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.

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. For example, with respect to back pain, which affects millions of individuals every year, high-frequency electrical treatment has been applied to several tissues, including intervertebral discs, facet joints, sacroiliac joints as well as the vertebrae themselves (in a process known as intraosseous denervation). In addition to creating lesions in neural structures, application of radiofrequency energy has also been used to treat tumors throughout the body. Further, with respect to knee pain, which also affects millions of individuals every year, high-frequency electrical treatment has been applied to several tissues, including, for example, the ligaments, muscles, tendons, and menisci.

In certain instances, internally-cooled radiofrequency probes may be susceptible to rising impedance issues, which can prematurely terminate the ablation procedure. More specifically, as the impedance rises, it becomes increasing more difficult to effectively transfer the radiofrequency energy to the tissue and create heat. This can lead to poorly formed lesions, procedural complications, and/or customer dissatisfaction. Such rising impedance issues may be caused due to the inherent higher power demands of internally-cooled radiofrequency probes and/or the difficulty in measuring and controlling to the highest lesion temperature. Rising impedance occurs when excessive heat is generated in the tissue surrounding the active electrode, thereby causing desiccation of the tissue, migration of surrounding conductive ions, and/or accumulation of a carbonized tissue layer around the active tip. Such effects can result in rising impedance by acting as an electrical insulator between the active electrode and the surrounding tissue.

Thus, the art is continuously seeking new and improved systems and methods for treating chronic pain using cooled RF ablation techniques that also consider the aforementioned rising impedance issues.

A prior art medical probe assembly having the features of the preamble of claim <NUM> is disclosed in <CIT>. Further prior art medical probe assemblies are disclosed in <CIT> and <CIT>.

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.

The present invention is directed to a medical probe assembly for delivering energy to a patient's body. The probe assembly includes at least one probe having an elongate member with a distal region and a proximal region. The distal region includes an electrically non-conductive outer circumferential portion. The probe assembly further includes an electrically and thermally-conductive energy delivery device extending distally from the electrically non-conductive outer circumferential portion for delivering one of electrical and radiofrequency energy to the patient's body. The energy delivery device includes a conductive outer circumferential surface and one or more internal lumens configured for circulating a cooling fluid to a distal end of the energy delivery device. The probe assembly also includes an electrically and thermally-conductive protrusion extending from the distal end of the energy delivery device. The electrically and thermally-conductive protrusion is electrically coupled to the energy delivery device. Further, the electrically and thermally-conductive protrusion includes a temperature sensing element. The probe assembly further includes at least one pump assembly for circulating the cooling fluid to and from the electrically and thermally-conductive energy delivery device. In addition, the probe assembly includes one or more sensors for monitoring one or more procedure parameters and a controller communicatively coupled to the sensor(s). The one or more procedure parameters include at least one of a temperature of tissue, an impedance of the tissue, or a power demand of the energy delivery device. The controller further includes a rising impedance detection engine configured to perform one or more operations, including, for example, determining, in real-time, whether a rising impedance event is likely to occur in a predetermined time period based on the one or more procedure parameters. It should also be understood that the probe assembly may further include any of the additional features as described herein.

Reference will now be made in detail to one or more embodiments of the invention, examples of the invention, examples of which are illustrated in the drawings. Each example and embodiment is provided by way of explanation of the invention, and is not meant as a limitation of the invention.

For the purposes of this invention, a lesion refers to the region of tissue that has been irreversibly damaged as a result of the application of thermal energy, 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).

Referring now to the drawings, <FIG> illustrates a schematic diagram of one embodiment of a system <NUM> of the present invention. As shown, the system <NUM> includes a generator <NUM>, a cable <NUM>, first, second, third, and fourth probe assemblies <NUM> (only one probe assembly is shown), one or more cooling devices <NUM>, a pump cable <NUM>, one or more proximal cooling supply tubes <NUM> and one or more proximal cooling return tubes <NUM>. As shown in the illustrated embodiment, the generator <NUM> is a radiofrequency (RF) generator, but may optionally be any power source that may deliver other forms of energy, including but not limited to microwave energy, thermal energy, ultrasound and optical energy. Further, the generator <NUM> may include a display incorporated therein. The display may be operable to display various aspects of a treatment procedure, including but not limited to any parameters that are relevant to a treatment procedure, such as temperature, impedance, etc. and errors or warnings related to a treatment procedure. If no display is incorporated into the generator <NUM>, the generator <NUM> may include means of transmitting a signal to an external display. In one embodiment, the generator <NUM> is operable to communicate with one more devices, for example with one or more of 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 or more 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 or more 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>. Alternatively, the splitter <NUM> may include more than two distal ends. Such a connector is useful in embodiments having more than two devices connected to the generator <NUM>, for example, if more than two probe assemblies are being used.

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>. For example, as shown in <FIG>, the cooling devices <NUM> include a pump assembly <NUM> having one or more peristaltic pumps <NUM> operable to circulate a fluid from the cooling devices <NUM> through one or more proximal cooling supply tubes <NUM>, the probe assemblies <NUM>, one or more proximal cooling return tubes <NUM> and back to the one or more cooling devices <NUM>. For example, as shown in the illustrated embodiment of <FIG> and <FIG>, the pump assembly <NUM> includes four peristaltic pumps <NUM> coupled to a power supply <NUM>. In such embodiments, as shown in <FIG>, each of the plurality of pumps <NUM> may be in separate fluid communication with one of the probe assemblies. The fluid may be water or any other suitable fluid. In alternate embodiments, the pump assembly <NUM> may include only one peristaltic pump or greater than four pumps. In addition, as shown in <FIG>, each of the pumps <NUM> may have an independent speed (i.e. RPM) controller <NUM> that is configured to independent adjust the speed of its respective pump.

Still referring to <FIG>, the system <NUM> may include a controller for facilitating communication between the cooling devices <NUM> and the generator <NUM>. In this way, feedback control is established between the cooling devices <NUM> and the generator <NUM>. The feedback control may include the generator <NUM>, the probe assemblies <NUM> and the cooling devices <NUM>, although any feedback between any two devices is within the scope of the present invention. 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 bi-directionally with the probe assemblies <NUM> as well as with the cooling devices <NUM>. In the context of this invention, bi-directional 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. For example, power to each of the probe assemblies <NUM> can be increased when a temperature measurement is low or decreased when a measurement is high. This variation of power may be different for each probe assembly. In some cases, the generator <NUM> may terminate power to one or more probe assemblies <NUM>. Thus, the generator <NUM> may receive a signal (e.g. temperature measurement) from one or both of the first and second probe assemblies <NUM>, determine the appropriate action, and send a signal (e.g. decreased or increased power) back to one or both of the probe assemblies <NUM>. Alternatively, the generator <NUM> may send a signal to the cooling devices <NUM> to either increase or decrease the flow rate or degree of cooling being supplied to one or both of the first and second probe assemblies <NUM>.

More specifically, the pumps 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. In some instances, the peristaltic pumps may respond to the generator <NUM> by changing the flow rate or turning off for a period of time. 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.

In other embodiments, 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. A strip lesion is 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. This occurs because at a given power, the current density is preferentially concentrated between the electrodes and a rise in temperature results from current density.

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 supply tubes <NUM> may include proximal supply tube connectors <NUM> at the distal ends of the one or more proximal cooling supply tubes <NUM>. Additionally, the proximal cooling return tubes <NUM> may include proximal return tube connectors <NUM> at the distal ends of the one or more proximal cooling 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> and <FIG>, the probe assembly <NUM> includes a proximal region <NUM>, a handle <NUM>, a hollow elongate shaft <NUM>, and a distal tip region <NUM> that includes the one or more energy delivery devices <NUM>. Further, as shown, the proximal region <NUM> includes a distal cooling supply tube <NUM>, a distal supply tube connector <NUM>, a distal cooling 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 supply tube <NUM> and distal cooling return tube <NUM> are flexible to allow for greater maneuverability of the probe assemblies <NUM>, but alternate embodiments with rigid tubes are possible.

Further, in several embodiments, 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> may include one or more conductors depending on the specific configuration of the probe assembly <NUM>. For example, in one embodiment, the probe assembly cable <NUM> may include five conductors allowing probe assembly cable <NUM> 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 elements to the generator <NUM> as discussed below.

The energy delivery devices <NUM> may include any means of delivering energy to a region of tissue adjacent to the distal tip region <NUM>. For example, the energy delivery devices <NUM> may include an ultrasonic device, an electrode or any other energy delivery means and the invention is not limited in this regard. Similarly, energy delivered via the energy delivery devices <NUM> may take several forms including but not limited to thermal energy, ultrasonic energy, radiofrequency energy, microwave energy or any other form of energy. 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.

Referring now to <FIG>, the distal cooling supply tube <NUM> and the distal cooling return tube <NUM> may be connected to a shaft supply tube <NUM> and a shaft return tube <NUM>, respectively, within the handle <NUM>, using connecting means <NUM> and <NUM>. The connecting means <NUM>, <NUM> can be any means of connecting two tubes including but not limited to ultraviolet (UV) glue, epoxy or any other adhesive as well as friction or compression fitting. Arrows <NUM> and <NUM> indicate the direction of flow of a cooling fluid supplied by the cooling devices <NUM>. More specifically, in one embodiment, the shaft supply tube <NUM> and the shaft return tube <NUM> may be hypotubes made of a conductive material such as stainless steel that extend from the handle <NUM> through a lumen of the hollow elongate shaft <NUM> to distal tip region <NUM>, as shown in <FIG>, wherein arrow <NUM> indicates the direction of the cooling fluid flow within a lumen <NUM> defined by the energy delivery devices <NUM>. The number of hypotubes used for supplying cooling fluid and the number used for returning cooling fluid and the combination thereof may vary and all such combinations are intended to be within the scope of the present invention.

Referring still to <FIG>, the handle <NUM> may be at least partially filled with a filling agent <NUM> to lend more strength and stability to handle <NUM> as well as to hold the various cables, tubes and wires in place. The filling agent <NUM> may be epoxy or any other suitable material. In addition, the handle <NUM> may be operable to easily and securely couple to an optional introducer tube (discussed below) in one embodiment where an introducer tube would facilitate insertion of the one or more probe assemblies <NUM> into a patient's body. For example, as shown, the handle <NUM> may taper at its distal end to accomplish this function, i.e. to enable it to securely couple to an optional introducer tube.

In one embodiment, the elongate shaft <NUM> may be manufactured out of polyimide sheath and a stainless steel tubular interior, 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>. In one embodiment, the probe assembly <NUM> may also include a marker <NUM> at some point along the handle <NUM> or along the length of the elongate hollow shaft <NUM>. In such embodiments, the marker <NUM> may be a visual depth marker that functions to indicate when the distal tip of the probe assembly <NUM> is located at a distal end of the introducer tube by aligning with a hub of the introducer tube. The marker <NUM> will thus provide a visual indication as to the location of the distal tip of a probe assembly <NUM> relative to an optional introducer tube.

Referring in detail to <FIG>, a perspective cut-away view of one embodiment of the distal tip region <NUM> of the probe assembly <NUM> is illustrated. As shown, the distal tip region <NUM> includes one or more temperature sensing elements <NUM> which are operable to measure the temperature at and proximate to the one or more energy delivery devices <NUM>. The temperature sensing elements <NUM> may include one or more thermocouples, thermometers, thermistors, optical fluorescent sensors or any other means of sensing temperature. In one embodiment, the temperature sensing elements <NUM> are connected to the generator <NUM> via probe assembly cable <NUM> and cable <NUM> although any means of communication between the temperature sensing elements <NUM> and the generator <NUM>, including wireless protocols, are included within the scope of the present invention. More specifically, as shown, the temperature sensing element(s) <NUM> may include a thermocouple junction made by joining a stainless steel hypotube <NUM> to a constantan wire <NUM>, wherein the constantan wire <NUM> is insulated by insulation <NUM>. In this embodiment, the junction of hypotube <NUM> and the constantan wire <NUM> is made by laser welding, although any other means of joining two metals may be used. Furthermore, in this embodiment, the hypotube <NUM> and the constantan wire <NUM> extend through a lumen of the elongate shaft <NUM> and connect to the probe assembly cable <NUM> within the handle <NUM>.

Further, as shown particularly in <FIG>, the temperature sensing element <NUM> of each probe <NUM> protrudes beyond the energy delivery device <NUM>. More specifically, as shown, the temperature sensing element <NUM> may have a length <NUM> of less than about <NUM> millimeter (mm) that extends from a distal end <NUM> of the energy delivery device <NUM>. In addition, as shown particularly in <FIG>, the length <NUM> of the temperature sensing element <NUM> element may be chosen to assist in creating lesions of different sizes. For example, in such embodiments, a user may select one or more probes from a plurality of probes having different lengths <NUM> based on, e.g. a desired lesion size and/or a desired rate of power delivery based on a treatment procedure type of the tissue. In particular embodiments, the different lengths of the temperature sensing elements <NUM> may range from about <NUM> to about <NUM>. In additional embodiments, each of the temperature sensing elements <NUM> may also have a different shape or volume. Thus, since an actual lesion size will vary with the different lengths <NUM> of the temperature sensing elements <NUM>, temperature sensing elements <NUM> having longer lengths (e.g. probes (C) and (D)) are configured to generate lesions of smaller sizes, whereas temperature sensing elements <NUM> having shorter lengths (e.g. probes (A) and (B)) are configured to generate lesions of larger sizes.

Accordingly, the different lengths of the temperature sensing elements <NUM> are configured to control and optimize the size of the lesion for different anatomical locations, for instance creating smaller lesions in regions adjacent to critical structures such as arteries and motor nerves. Thus, the different lengths of the temperature sensing elements <NUM> of the present disclosure provide several advantages including for example, the ability to create custom lesion volumes for different procedures (i.e. the control of the lesion volume is intrinsic to the mechanical design of the probe, which is independent of the generator <NUM> and algorithms). As such, existing equipment and settings can be used. In addition, the protrusion distance can be optimized to provide maximum energy output while minimizing rising impedance and power roll-off conditions. Moreover, the different lengths of the temperature sensing elements <NUM> creates a mechanical safety mechanism to prevent over-ablation in sensitive anatomical regions.

In addition, the length <NUM> of the temperature sensing element <NUM> is configured to increase (or decrease) a power demand of the energy delivery device <NUM>. Further, as shown, whereby the temperature sensing element <NUM> includes a stainless steel hypotube <NUM>, the hypotube <NUM> may be electrically conductive and may be electrically coupled to the energy delivery device <NUM>. Thus, in such an embodiment, whereby energy may be conducted to the protrusion and delivered from the protrusion to surrounding tissue, the protrusion may be understood to be a component of both temperature sensing element <NUM> as well as the one or more energy delivery devices <NUM>. Placing the temperature sensing elements <NUM> at this location, rather than within a lumen <NUM> defined by the energy delivery device <NUM>, is beneficial because it allows the temperature sensing element <NUM> to provide a more accurate indication of the temperature of tissue proximate to the energy delivery device <NUM>. This is due to the fact that, when extended beyond the energy delivery device <NUM>, the temperature sensing element <NUM> will not be as affected by the cooling fluid flowing within the lumen <NUM> as it would be were it located within lumen <NUM>. Thus, in such embodiments, the probe assembly <NUM> includes a protrusion protruding from the distal region of the probe assembly, whereby the protrusion is a component of the temperature sensing element <NUM>.

Referring still to <FIG>, the probe assembly <NUM> may further include one or more secondary temperature sensing elements <NUM> located within the elongate shaft <NUM> at some distance away from the energy delivery device <NUM>, and positioned adjacent a wall of the elongate shaft <NUM>. The secondary temperature sensing elements <NUM> may similarly include one or more thermocouples, thermometers, thermistors, optical fluorescent sensors or any other means of sensing temperature. For example, as shown, the secondary temperature sensing element <NUM> is a thermocouple made by joining copper and constantan thermocouple wires, designated as <NUM> and <NUM> respectively. Further, in certain embodiments, the copper and constantan wires <NUM> and <NUM> may extend through a lumen of the elongate shaft <NUM> and may connect to the probe assembly cable <NUM> within the handle <NUM>.

In addition, the probe assembly <NUM> may further include a thermal insulator <NUM> located proximate to any of the temperature sensing elements <NUM>, <NUM>. As such, the thermal insulator <NUM> may be made from any thermally insulating material, for example silicone, and may be used to insulate any temperature sensing element from other components of the probe assembly <NUM>, so that the temperature sensing element will be able to more accurately measure the temperature of the surrounding tissue. More specifically, as shown, the thermal insulator <NUM> is used to insulate the temperature sensing element <NUM> from cooling fluid passing through the shaft supply tube <NUM> and the shaft return tube <NUM>.

In further embodiments, the probe assembly <NUM> may also include a radiopaque marker <NUM> incorporated somewhere along the elongate shaft <NUM>. For example, as shown, in <FIG>, an optimal location for a radiopaque marker may be at or proximate to the distal tip region <NUM>, adjacent the energy delivery device <NUM>. The radiopaque markers are visible on fluoroscopic x-ray images and can be used as visual aids when attempting to place devices accurately within a patient's body. These markers can be made of many different materials, as long as they possess sufficient radiopacity. Suitable materials include, but are not limited to silver, gold, platinum and other high-density metals as well as radiopaque polymeric compounds. Various methods for incorporating radiopaque markers into or onto medical devices may be used, and the present invention is not limited in this regard.

Referring now to <FIG>, cross-sectional views of portions of the distal tip region <NUM>, as indicated in <FIG>, are illustrated. Referring first to <FIG>, three hypotubes <NUM>, <NUM>, and <NUM> are positioned within the lumen <NUM> defined by the elongate shaft <NUM> and the energy delivery device <NUM>. The shaft supply tube <NUM> and the shaft return tube <NUM> carry cooling fluid to and from the distal end of distal tip region <NUM>, respectively. In this embodiment, hypotube <NUM> is made of a conductive material such as stainless steel and is operable to transmit energy from the probe assembly cable <NUM> to the energy delivery device <NUM>. In addition, the hypotube <NUM> defines a lumen within which a means of connecting the one or more temperature sensing elements <NUM> to the probe assembly cable <NUM> may be located. For example, if the one or more temperature sensing elements <NUM> includes a thermocouple, then a constantan wire <NUM> may extend from probe assembly cable <NUM> to the thermocouple junction through hypotube <NUM> as is shown in <FIG>. Alternatively, more than one wire may be passed through the lumen of hypotube <NUM> or the lumen of hypotube <NUM> may be utilized for another purpose.

Further, as shown, the elongate shaft <NUM> and the electrode <NUM> overlap to secure the electrode in place. In this embodiment, the lumen defined by the elongate shaft <NUM> and the electrode <NUM> at this portion of the distal tip region <NUM> contains a radiopaque marker <NUM> made of silver solder, which fills the lumen such that any cooling fluid supplied to the probe assembly <NUM>, that is not located within one of the cooling tubes described earlier, is confined to the distal tip region <NUM> of probe assembly <NUM>. Thus, in such an embodiment, the silver solder may be referred to as a flow impeding structure since it functions to restrict the circulation of fluid to a specific portion (in this case, at least a portion of distal region <NUM>) of the probe assembly <NUM>. In other words, cooling fluid may flow from the cooling devices <NUM>, through the cooling supply tubes to the distal tip region <NUM> of the probe assembly <NUM>. The cooling fluid may then circulate within the lumen <NUM> defined by the electrode <NUM> to provide cooling thereto. As such, the internally-cooled probe as described herein is defined as a probe having such a configuration, whereby a cooling medium does not exit probe assembly <NUM> from a distal region of probe assembly <NUM>. The cooling fluid may not circulate further down the elongate shaft <NUM> due to the presence of the silver solder, and flows through the cooling return tubes back to the cooling devices <NUM>. In alternate embodiments, other materials may be used instead of silver solder, and the invention is not limited in this regard. As described above, providing cooling to the probe assemblies <NUM> allows heat delivered through the energy delivery devices <NUM> to be translated further into the tissue without raising the temperature of the tissue immediately adjacent the energy delivery device <NUM>.

Referring now to <FIG>, a cross-section of a portion of the distal tip region <NUM>, proximal from the cross-section of <FIG> as illustrated in <FIG>, is illustrated. As shown, the secondary temperature sensing element <NUM> is located proximate to an inner wall of the elongate shaft <NUM>. This proximity allows the secondary temperature sensing element <NUM> to provide a more accurate indication of the temperature of surrounding tissue. In other words, the secondary temperature sensing element <NUM> may be operable to measure the temperature of the inner wall of the elongate shaft <NUM> at the location of the secondary temperature sensing element <NUM>. This temperature is indicative of the temperature of tissue located proximate to the outer wall of the elongate shaft <NUM>. Thus, it is beneficial to have the secondary temperature sensing element <NUM> located proximate to an inner wall of the elongate shaft <NUM>, rather than further away from the inner wall.

<FIG> also illustrate the relative positions of the three hypotubes used in a first embodiment of the present invention. In this embodiment, the three hypotubes are held together in some fashion to increase the strength of probe assembly <NUM>. For example, the three hypotubes may be bound together temporarily or may be more permanently connected using solder, welding or any suitable adhesive means. Various means of binding and connecting hypotubes are well known in the art and the present invention is not intended to be limited in this regard.

As mentioned above, the system <NUM> of the present invention may further include one or more introducer tubes. Generally, introducer tubes may include a proximal end, a distal end, and a longitudinal bore extending therebetween. Thus, the introducer tubes (when used) are operable to easily and securely couple with the probe assembly <NUM>. For example, the proximal end of the introducer tubes may be fitted with a connector able to mate reversibly with handle <NUM> of probe assembly <NUM>. An introducer tube may be used to gain access to a treatment site within a patient's body and a hollow elongate shaft <NUM> of a probe assembly <NUM> may be introduced to said treatment site through the longitudinal bore of said introducer tube. Introducer tubes may further include one or more depth markers to enable a user to determine the depth of the distal end of the introducer tube within a patient's body. Additionally, introducer tubes may include one or more radiopaque markers to ensure the correct placement of the introducers when using fluoroscopic guidance.

The introducer tubes may be made of various materials, as is known in the art and, if said material is electrically conductive, the introducer tubes may be electrically insulated along all or part of their length, to prevent energy from being conducted to undesirable locations within a patient's body. In some embodiments, the elongate shaft <NUM> may be electrically conductive, and an introducer may function to insulate the shaft leaving the energy delivery device <NUM> exposed for treatment. Further, the introducer tubes may be operable to connect to a power source and may therefore form part of an electrical current impedance monitor (wherein at least a portion of the introducer tube is not electrically insulated). Different tissues may have different electrical impedance characteristics and it is therefore possible to determine tissue type based on impedance measurements, as has been described. Thus, it would be beneficial to have a means of measuring impedance to determine the tissue within which a device is located. In addition, the gauge of the introducer tubes may vary depending on the procedure being performed and/or the tissue being treated. In some embodiments, the introducer tubes should be sufficiently sized in the radial dimension so as to accept at least one probe assembly <NUM>. In alternative embodiments, the elongate shaft <NUM> may be insulated so as not to conduct energy to portions of a patient's body that are not being treated.

The system may also include one or more stylets. A stylet may have a beveled tip to facilitate insertion of the one or more introducer tubes into a patient's body. Various forms of stylets are well known in the art and the present invention is not limited to include only one specific form. Further, as described above with respect to the introducer tubes, the stylets may be operable to connect to a power source and may therefore form part of an electrical current impedance monitor. In other embodiments, one or more of the probe assemblies <NUM> may form part of an electrical current impedance monitor. Thus, the generator <NUM> may receive impedance measurements from one or more of the stylets, the introducer tubes, and/or the probe assemblies <NUM> and may perform an action, such as alerting a user to an incorrect placement of an energy delivery device <NUM>, based on the impedance measurements.

In one embodiment, the first and second probe assemblies <NUM> may be operated in a bipolar mode. For example, <FIG> illustrates one embodiment of two probe assemblies <NUM>, wherein the distal tip regions <NUM> thereof are located within an intervertebral disc <NUM>. In such embodiments, electrical energy is delivered to the first and second probe assemblies <NUM> and this energy is preferentially concentrated therebetween through a region of tissue to be treated (i.e. an area of the intervertebral disc <NUM>). The region of tissue to be treated is thus heated by the energy concentrated between first and second probe assemblies <NUM>. In other embodiments, the first and second probe assemblies <NUM> may be operated in a monopolar mode, in which case an additional grounding pad is required on the surface of a body of a patient, as is known in the art. Any combination of bipolar and monopolar procedures may also be used. It should also be understood that the system may include more than two probe assemblies. For example, in some embodiments, three probe assemblies may be used and the probe assemblies may be operated in a triphasic mode, whereby the phase of the current being supplied differs for each probe assembly.

In further embodiments, the system may also be configured to control one or more of the flow of current between electrically conductive components and the current density around a particular component. For example, a system of the present invention may include three electrically conductive components, including two of similar or identical dimensions and a third of a larger dimension, sufficient to act as a dispersive electrode. Each of the electrically conductive components should beneficially be operable to transmit energy between a patient's body and a power source. Thus, two of the electrically conductive components may be probe assemblies while the third electrically conductive component may function as a grounding pad or dispersive/return electrode. In one embodiment, the dispersive electrode and a first probe assembly are connected to a same electric pole while a second probe assembly is connected to the opposite electric pole. In such a configuration, electrical current may flow between the two probe assemblies or between the second probe assembly and the dispersive electrode. To control the current to flow preferentially to either the first probe assembly or the dispersive electrode, a resistance or impedance between one or more of these conductive components (i.e. the first probe assembly and the dispersive electrode) and a current sink (e.g. circuit 'ground') may be varied. In other words, if it would be desirable to have current flow preferentially between the second probe assembly and the dispersive electrode (as in a monopolar configuration), then the resistance or impedance between the first probe assembly and the circuit 'ground' may be increased so that the current will prefer to flow through the dispersive electrode to 'ground' rather than through the first probe assembly (since electrical current preferentially follows a path of least resistance). This may be useful in situations where it would be desirable to increase the current density around the second probe assembly and/or decrease the current density around the first probe assembly. Similarly, if it would be desirable to have current flow preferentially between the second probe assembly and the first probe assembly (as in a bipolar configuration), then the resistance or impedance between the dispersive electrode and 'ground' may be increased so that the current will prefer to flow through the first probe assembly to 'ground' rather than through the dispersive electrode. This would be desirable when a standard bipolar lesion should be formed. Alternatively, it may desirable to have a certain amount of current flow between the second probe assembly and the first probe assembly with the remainder of current flowing from the second probe assembly to the dispersive electrode (a quasi-bipolar configuration). This may be accomplished by varying the impedance between at least one of the first probe assembly and the dispersive electrode, and 'ground', so that more or less current will flow along a desired path. This would allow a user to achieve a specific, desired current density around a probe assembly. Thus, this feature of the present invention may allow a system to be alternated between monopolar configurations, bipolar configurations or quasi-bipolar configurations during a treatment procedure.

Referring now to <FIG>, a flow diagram of one example of a method <NUM>, not covered by the claims, for treating tissue of a patient's body, such as an intervertebral disc <NUM>, using the probe assemblies described herein is illustrated. As shown at <NUM>, the method may first include preparing the cooled radiofrequency probe assembly <NUM> for use to treat tissue of a patient's body. For example, as shown at <NUM>, preparing the cooled radiofrequency probe assembly <NUM> to treat the tissue may include determining a desired lesion size (or volume) and/or a rate of power delivery required to treat the tissue. Further, as shown at <NUM>, a user may select one or more probes <NUM> from a plurality of probes based on the length <NUM> of the temperature sensing element <NUM> thereof that achieves the desired lesion size or the desired rate of power delivery.

Once the appropriate probe assembly(ies) <NUM> have been selected having the temperature sensing element(s) <NUM> of a determined length, as shown at <NUM>, the method <NUM> includes positioning the probe assembly(ies) <NUM> into the patient's body. More specifically, the method <NUM> may generally include inserting the energy delivery device(s) <NUM> into the patient's body and routing the energy delivery device(s) <NUM> to the tissue of the patient's body. For example, in one embodiment, with a patient lying on a radiolucent table, fluoroscopic guidance may be used to percutaneously insert an introducer with a stylet to access the posterior of an intervertebral disc. In addition to fluoroscopy, other aids, including but not limited to impedance monitoring and tactile feedback, may be used to assist a user to position the introducer or probe assembly(ies) <NUM> within the patient's body. The use of impedance monitoring has been described herein, whereby a user may distinguish between tissues by monitoring impedance as a device is inserted into the patient's body. With respect to tactile feedback, different tissues may offer different amounts of physical resistance to an insertional force. This allows a user to distinguish between different tissues by feeling the force required to insert a device through a given tissue. One method of accessing the disc is the extrapedicular approach in which the introducer passes just lateral to the pedicle, but other approaches may be used. A second introducer with a stylet may then be placed contralateral to the first introducer in the same manner, and the stylets are removed. Thus, the probe assemblies <NUM> can be inserted into each of the two introducers placing the electrodes <NUM> in the tissue at suitable distances, such as from about <NUM> to about <NUM>.

As shown at <NUM>, the method <NUM> includes coupling a power source (e.g. the generator <NUM>) to the probe assembly(ies) <NUM>. Once in place, a stimulating electrical signal may be emitted from either of the electrodes <NUM> to a dispersive electrode or to the other electrode <NUM>. This signal may be used to stimulate sensory nerves where replication of symptomatic pain would verify that the disc is pain-causing. In addition, as shown at <NUM>, since the probe assembly(ies) <NUM> are connected to the RF generator <NUM> as well as to peristaltic pumps <NUM>, the method <NUM> includes simultaneously circulating the cooling fluid through the internal lumens <NUM>, <NUM> via the peristaltic pumps <NUM> and delivering energy from the RF generator <NUM> to the tissue through the energy delivery devices <NUM>. In other words, radiofrequency energy is delivered to the electrodes <NUM> and the power is altered according to the temperature measured by temperature sensing element <NUM> in the tip of the electrodes <NUM> such that a desired temperature is reached between the distal tip regions <NUM> of the two probe assemblies <NUM>.

During the procedure, a treatment protocol such as the cooling supplied to the probe assemblies <NUM> and/or the power transmitted to the probe assemblies <NUM> may be adjusted and/or controlled to maintain a desirable treatment area shape, size and uniformity. More specifically, as shown at <NUM>, the method <NUM> includes actively controlling energy delivered to the tissue by controlling both an amount of energy delivered through the energy delivery devices <NUM> and individually controlling the flow rate of the peristaltic pumps <NUM>. In further embodiments, the generator <NUM> may control the energy delivered to the tissue based on the measured temperature measured by the temperature sensing element(s) <NUM> and/or impedance sensors.

More specifically, as shown in <FIG>, a block diagram of one example of a treatment procedure, not covered by the claims, for actively controlling the energy delivered to the tissue by controlling both the amount of energy delivered through the energy delivery devices <NUM> and the flow rate of the peristaltic pumps <NUM> is illustrated. As shown at <NUM>, ablation is initialized. As shown at <NUM>, the energy dosage may be calculated using simple numerical integration techniques. As shown at <NUM>, the calculated energy dosage may then be compared against a preset energy dosage threshold. If the dosage is not satisfied as shown at <NUM>, the procedure continues to <NUM> to mitigate rising impedance of the internally-cooled probe assemblies <NUM> during the treatment procedure. More specifically, as shown, one or more procedure parameters are monitored while delivering the energy from the generator <NUM> to the tissue through the energy delivery devices <NUM>. The procedure parameter(s) described herein include at least one of a temperature of the tissue, an impedance of the tissue, a power demand of the energy delivery device <NUM>, or combinations thereof. Further, as shown, the procedure parameter(s) <NUM> may be fed into a rising impedance detection engine <NUM>. As shown at <NUM>, the rising impedance detection engine <NUM> is configured to determine, e.g. in real-time, whether a rising impedance event is likely to occur in a predetermined time period (i.e. whether the rising impedance event is imminent) based on the received procedure parameter(s) <NUM>. The rising impedance detection engine <NUM> can then determine a command for the pump assembly <NUM> based on whether the rising impedance event is likely to occur in the predetermined time period.

If not imminent, as shown at <NUM>, the cooling rate can be increased, e.g. by increasing the pump speed (e.g. via the RPM controllers <NUM>) of the peristaltic pumps <NUM> as shown at <NUM>. After the cooling rate is increased, the ablation <NUM> continues. If a rising impedance event is imminent, as shown at <NUM>, the cooling rate can be reduced, e.g. by decreasing the pump speed (e.g. via the RPM controllers <NUM>) of the peristaltic pumps <NUM> as shown at <NUM>. In other words, in several embodiments, the peristaltic pumps <NUM> may be independently controlled via their respective RPM controllers <NUM> to alter the rate of cooling to each electrode <NUM> of the probe assemblies <NUM>. In such embodiments, the power supply <NUM> of the pump assembly <NUM> may be decoupled, at least in part, from the generator <NUM>. Further, as shown, the system <NUM> operates using closed-loop feedback control <NUM>, <NUM>. As used herein, closed loop feedback control refers to control whereby the generator <NUM> controls the flow rate to the probes via the peristaltic pumps <NUM> in order to modulate the power to a set point independent of temperature. Alternatively, closed loop feedback may also refer to control whereby the generator <NUM> controls the flow rate to the probes via the peristaltic pumps <NUM> in order to modulate the power to achieve desired total delivered energy into the tissue.

Once the energy dosage threshold is satisfied, as shown at <NUM>, the treatment procedure is configured to check if the thermal dosage threshold has been satisfied as shown at <NUM>. If the thermal dosage has not been satisfied, as shown at <NUM>, the treatment procedure proceeds through the independent temperature-power feedback control loop as shown at <NUM>. More specifically, in certain embodiments, the amount of energy delivered through the energy delivery device <NUM> may be controlled by defining a predetermined threshold temperature for treating the tissue, ramping up the temperature of the tissue via the generator <NUM> through the energy delivery device <NUM> to the predetermined threshold temperature, and maintaining the temperature of the tissue at the predetermined threshold temperature to create a lesion in the tissue. In such embodiments, the temperature of the tissue may be maintained at the predetermined threshold temperature as a function of at least one of a power ramp rate, an impedance level, an impedance ramp rate, and/or a ratio of impedance to power.

Only when the thermal dosage threshold has been satisfied, as shown at <NUM>, the procedure terminates as shown at <NUM>. Thus, the system and method of the present disclosure provides the unique features of probe(s) with inherently high-power demand (i.e. short thermocouple protrusion), a pump-modulated power algorithm, a preset energy dosage or total average power threshold, and/or a rising impedance detection engine <NUM>.

Referring now to <FIG>, graphs of power (y-axis) versus time (x-axis) and temperature (y-axis) versus time (x-axis) for the same test procedure are depicted to illustrate advantages of modulating power based on the rate of cooling. More specifically, as shown, the ablation is started with the pump assembly <NUM> set to its nominal speed. At time T<NUM> into the test procedure, the cooling rate supplied to the energy delivery device <NUM> is decreased step-wise as shown at <NUM>. This results in a decrease of the power demand as shown at <NUM>, while the temperature remains the same as shown at <NUM>. As such, the control for the cooling rate operates as an independent feedback control loop from the primary temperature-power feedback control loop (as shown at <NUM>), the latter being responsible for ramping and maintaining the temperature set-point of the tissue. Thus, the temperature set-point does not change with changes to the cooling rate since the power required to heat the tissue is decoupled from the power required to offset the effects of the cooling.

Referring now to <FIG> and <FIG>, example graphs are depicted to illustrate various advantages of mitigating rising impedance during an internally-cooled probe treatment procedure according to the present disclosure. More specifically, <FIG> illustrates graphs of impedance (y-axis) versus time (x-axis), temperature (y-axis) versus time (x-axis), and power (y-axis) versus time (x-axis), respectively, for three treatment procedures that each utilize an internally-cooled probe with inherently high power demand and manual feedback control, when no impedance mitigation is implemented. As shown at <NUM>, the test procedure results in high impedance errors. This results in insufficient thermal dosage and incomplete procedures as shown via the temperature <NUM>. Further, the power demand <NUM> exceeds the predetermined threshold <NUM>.

In contrast, <FIG> illustrates graphs of impedance (y-axis) versus time (x-axis), temperature (y-axis) versus time (x-axis), and power (y-axis) versus time (x-axis), respectively, for three treatment procedures that utilize an internally-cooled probe with pump-modulated power control. Thus, as shown, the test procedure can be fully completed with no high impedance errors. Further, as shown, the temperature achieves the set point. Moreover, as shown in the graph of power (y-axis) versus time (x-axis), the pump speed was slowly ramped from the lowest setting starting at the beginning of the procedure and maintained below a predetermined threshold. It should be understood that the predetermined threshold may be determined using historical testing data, or may be dynamic. In addition to controlling to a power threshold(s), other embodiments may control based on power ramp rate(s) (dP/dt), impedance level(s) (Z), impedance ramp rate(s) (dZ/dt), and/or a ratio of impedance to power. Regardless of the feedback mechanism, all embodiments are configured to determine the likelihood of a rising impedance event and adjust the power demand accordingly by controlling the rate of cooling to the energy delivery devices <NUM>. For example, in several embodiments, the power demand of the energy delivery device may be compared to a predetermined threshold. If the power demand is greater than the predetermined threshold, the rising impedance engine <NUM> may decrease a speed of the pump assembly <NUM>. If the power demand is less than the predetermined threshold, the rising impedance engine <NUM> may increase the speed of the pump assembly <NUM>.

Following treatment, energy delivery and cooling may be stopped and the probe assemblies <NUM> are removed from the introducers, where used. A fluid such as an antibiotic or contrast agent may be injected through the introducers, followed by removal of the introducers. Alternatively, the distal tips of the probe assemblies <NUM> may be sharp and sufficiently strong to pierce tissue so that introducers may not be required. As mentioned above, positioning the probe assemblies <NUM>, and more specifically the energy delivery devices <NUM>, within the patient's body, may be assisted by various means, including but not limited to fluoroscopic imaging, impedance monitoring and tactile feedback. Additionally, some examples of this method may include one or more steps of inserting or removing material into a patient's body. For example, as has been described, a fluid may be inserted through an introducer tube during a treatment procedure. Alternatively, a substance may be inserted through the probe assembly <NUM>, in embodiments where probe assembly <NUM> includes an aperture in fluid communication with a patient's body. Furthermore, material may be removed from the patient's body during the treatment procedure. Such material may include, for example, damaged tissue, nuclear tissue and bodily fluids. Possible treatment effects include, but are not limited to, coagulation of nerve structures (nociceptors or nerve fibers), ablation of collagen, biochemical alteration, upregulation of heat shock proteins, alteration of enzymes, and alteration of nutrient supply.

Referring now to <FIG>, a graph <NUM> of energy (y-axis) versus lesion area (x-axis) is provided to illustrate further advantages of the present disclosure. More specifically, as shown, the graph <NUM> provides energy versus lesion area for three different treatment procedures. Assuming a perfectly spherical lesion volume, a predetermined desired diameter lesion is represented by the vertical dashed line <NUM>. A first test procedure <NUM> created a lesion using a conventional thermal dosage approach. A second test procedure <NUM> created a lesion with a shorter ablation time but without pump-modulated power control. A third test procedure <NUM> created a lesion with a shorter ablation time and pump-modulated power control. As shown via data <NUM>, by running the ablation for a shorter time, a lesion of sufficient size cannot be created. However, if pump-modulated power control is also implemented (as illustrated by results <NUM>), lesions can be created on the order of using the conventional thermal dosage approach as represented by data <NUM>. Thus, by controlling the temperature and the energy delivery rate (i.e. by modulating the pumps <NUM>), the energy delivery rate can be maximized, thereby result in a much faster ablation time. In certain instances, the ablation time can be reduced by as much as half when compared to conventional ablation techniques.

Referring now to <FIG>, a graph <NUM> depicting the high correlation <NUM> between delivered energy (y-axis) and lesion size (x-axis) is illustrated. More specifically, as shown, the lesion width <NUM> is illustrated by solid dots and the lesion length <NUM> is represented by hollow dots. <FIG> illustrates a graph <NUM> depicting the inverse correlation between thermocouple protrusion lengths (x-axis) and the total delivered energy (y-axis). In addition, <FIG> illustrates a graph <NUM> depicting the correlation between lesion size (y-axis) and thermocouple protrusion distance (x-axis). Taken together, <FIG> demonstrate the effects that the thermocouple protrusion length or distance can have on the generated lesion size through controlling the amount of delivered energy into the tissue. More specifically, thermocouple protrusion length and lesion size are inversely correlated. As such, this characteristic can be exploited to generate various lesion sizes targeting different anatomical locations.

A system of the present invention may be used in various medical procedures where usage of an energy delivery device may prove beneficial. Specifically, the system of the present invention is particularly useful for procedures involving treatment of back pain, including but not limited to treatments of tumors, intervertebral discs, facet joint denervation, sacroiliac joint lesioning or intraosseous (within the bone) treatment procedures. Moreover, the system is particularly useful to strengthen the annulus fibrosus, shrink annular fissures and impede them from progressing, cauterize granulation tissue in annular fissures, and denature pain-causing enzymes in nucleus pulposus tissue that has migrated to annular fissures. Additionally, the system may be operated to treat a herniated or internally disrupted disc with a minimally invasive technique that delivers sufficient energy to the annulus fibrosus to breakdown or cause a change in function of selective nerve structures in the intervertebral disc, modify collagen fibrils with predictable accuracy, treat endplates of a disc, and accurately reduce the volume of intervertebral disc tissue. The system is also useful to coagulate blood vessels and increase the production of heat shock proteins.

Using liquid-cooled probe assemblies <NUM> with an appropriate feedback control system as described herein also contributes to the uniformity of the treatment. The cooling distal tip regions <NUM> of the probe assemblies <NUM> helps to prevent excessively high temperatures in these regions which may lead to tissue adhering to the probe assemblies <NUM> as well as an increase in the impedance of tissue surrounding the distal tip regions <NUM> of the probe assemblies <NUM>. Thus, by cooling the distal tip regions <NUM> of the probe assemblies <NUM>, higher power can be delivered to tissue with a minimal risk of tissue charring at or immediately surrounding the distal tip regions <NUM>. Delivering higher power to energy delivery devices <NUM> allows tissue further away from the energy delivery devices <NUM> to reach a temperature high enough to create a lesion and thus the lesion will not be limited to a region of tissue immediately surrounding the energy delivery devices <NUM> but will rather extend preferentially from a distal tip region <NUM> of one probe assembly <NUM> to the other.

As has been mentioned, a system of the present invention may be used to produce a relatively uniform lesion substantially between two probe assemblies <NUM> when operated in a bipolar mode. Oftentimes, uniform lesions may be contraindicated, such as in a case where a tissue to be treated is located closer to one energy delivery device <NUM> than to the other. In cases where a uniform lesion may be undesirable, using two or more cooled probe assemblies <NUM> in combination with a suitable feedback and control system may allow for the creation of lesions of varying size and shape. For example, preset temperature and/or power profiles that the procedure should follow may be programmed into the generator <NUM> prior to commencement of a treatment procedure. These profiles may define parameters (these parameters would depend on certain tissue parameters, such as heat capacity, etc.) that should be used to create a lesion of a specific size and shape. These parameters may include, but are not limited to, maximum allowable temperature, ramp rate (i.e. how quickly the temperature is raised) and the rate of cooling flow, for each individual probe. Based on temperature or impedance measurements performed during the procedure, various parameters, such as power or cooling, may be modulated, to comply with the preset profiles, resulting in a lesion with the desired dimensions.

Similarly, it is to be understood that a uniform lesion can be created, using a system of the present invention, using many different pre-set temperature and/or power profiles which allow the thermal dose across the tissue to be as uniform as possible, and that the present invention is not limited in this regard.

It should be noted that the term radiopaque marker as used herein denotes any addition or reduction of material that increases or reduces the radiopacity of the device. Furthermore, the terms probe assembly, introducer, stylet etc. are not intended to be limiting and denote any medical and surgical tools that can be used to perform similar functions to those described. In addition, the invention is not limited to be used in the clinical applications disclosed herein, and other medical and surgical procedures wherein a device of the present invention would be useful are included within the scope of the present invention.

Claim 1:
A medical probe assembly (<NUM>) for delivering energy to a patient's body, the probe assembly (<NUM>) comprising:
at least one probe having an elongate member (<NUM>) with a distal region (<NUM>) and a proximal region (<NUM>), said distal region (<NUM>) comprising an electrically non-conductive outer circumferential portion;
an electrically and thermally-conductive energy delivery device (<NUM>) extending distally from said electrically non-conductive outer circumferential portion for delivering one of electrical and radiofrequency energy to the patient's body, said energy delivery device (<NUM>) comprising a conductive outer circumferential surface and one or more internal lumens (<NUM>) configured for circulating a cooling fluid to a distal end (<NUM>) of said energy delivery device (<NUM>);
an electrically and thermally-conductive protrusion extending from said distal end (<NUM>) of said energy delivery device (<NUM>), said electrically and thermally-conductive protrusion being electrically coupled to said energy delivery device (<NUM>), said electrically and thermally-conductive protrusion comprising a temperature sensing element (<NUM>);
at least one pump assembly (<NUM>) for circulating the cooling fluid to and from the electrically and thermally-conductive energy delivery device (<NUM>);
one or more sensors (<NUM>) for monitoring one or more procedure parameters, the one or more procedure parameters comprising at least one of a temperature of tissue, an impedance of the tissue, or a power demand of the energy delivery device (<NUM>); and
a controller communicatively coupled to the one or more sensors (<NUM>), the controller comprises a rising impedance detection engine (<NUM>) configured to perform one or more operations,
characterized in that:
the one or more operations comprise determining, in real-time, whether a rising impedance event is likely to occur in a predetermined time period based on the one or more procedure parameters.