Cryoprobe

Abstract

To solve the problems of the prior art.SOLUTION: Apparatus is provided, consisting of a probe with a probe distal end having an external surface that contacts tissue when the probe distal end is inserted into a patient. A heater and a temperature sensor are in the distal end, and a gas inlet is coupled to the distal end to provide gas. While the heater is activated, a controller registers a first time when a temperature measured by the temperature sensor equals or exceeds a preset temperature, and, in response to the temperature equaling or exceeding the preset temperature, delivers a gas pulse through the gas inlet so as to cool the probe distal end. The controller then registers a second time when the temperature measured by the temperature sensor equals or exceeds the preset temperature, and, in response to a time difference between the second and first times, estimates a temperature of the external surface of the probe distal end.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to probes used to freeze materials, and more particularly to operating the probe while the material is being frozen. [Background technology]

[0002] Cryoablation is the process of destroying tissue using extreme cold. Cryoablation may be performed using a hollow needle, a cryoprobe, through which cryogen is circulated. The cryoprobe may be positioned in contact with the tissue to be destroyed, and then the cryogen is circulated through the probe. Once the tissue is frozen, the cryoprobe may be withdrawn from the tissue. Summary of the Invention

[0003] One embodiment of the present invention provides an apparatus, the apparatus comprising: a probe including a probe distal end having an outer surface configured to contact tissue of a patient when the probe distal end is inserted into the patient; a heater disposed within the distal end of the probe; a temperature sensor disposed within the distal end of the probe; a gas inlet coupled to the probe distal end and configured to provide gas to the probe distal end; It consists of a controller, The controller will registering a first time that the temperature measured by the temperature sensor is equal to or greater than the preset temperature; in response to the temperature being equal to or greater than the preset temperature, delivering a pulse of gas through the gas inlet to cool the distal end of the probe; registering a second time subsequent to the first time that the temperature measured by the temperature sensor is equal to or greater than the preset temperature; and configured to estimate a temperature of the outer surface of the probe distal end in response to a time difference between the second time and the first time.

[0004] The apparatus may include a cryogen inlet coupled to the probe distal end and configured to transfer a cryogenic fluid to the probe distal end.

[0005] In a disclosed embodiment, the gas inlet and the cryogen inlet are a common tube, and the controller is configured to operate the common tube as the gas inlet during a first time period and to operate the common tube as the cryogen inlet during a second time period different from the first time period.

[0006] In further disclosed embodiments, the gas is input to the probe as room temperature gas, which may consist of exhaust gases displaced from the cryogenic fluid to the distal end.

[0007] In a more particularly disclosed embodiment, the temperature sensor comprises a thermocouple junction disposed between the heater and the inner surface of the distal end of the probe.

[0008] In an alternative embodiment, the time difference and the temperature of the outer surface of the probe distal end are related by a monotonically decreasing function, which may consist of a linear function.

[0009] In a further alternative embodiment, the pulse of gas is delivered until the temperature measured by the temperature sensor is equal to a further preset temperature that is lower than the preset temperature.

[0010] According to one embodiment, there is further provided a method, the method comprising: providing a probe including a probe distal end having an outer surface configured to contact tissue of a patient when the probe distal end is inserted into the patient; disposing a heater within the probe distal end; disposing a temperature sensor within the probe distal end; coupling a gas inlet to the probe distal end configured to provide gas to the probe distal end; activating a heater; While the heater is activated, registering a first time that a temperature measured by the temperature sensor is equal to or greater than a preset temperature; In response to the temperature being equal to or greater than the preset temperature, delivering a pulse of gas through the gas inlet to cool the distal tip of the probe; registering a second time subsequent to the first time during which the temperature measured by the temperature sensor is equal to or greater than the preset temperature; and estimating the temperature of the outer surface of the probe distal end in response to a time difference between the second time and the first time.

[0011] The present disclosure will be more fully understood from the following detailed description of the embodiments thereof when considered in conjunction with the drawings in which: [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an apparatus being used in a cryogenic procedure, according to one embodiment of the present invention. [Figure 2] 2 is a schematic diagram of a probe of the apparatus, according to one embodiment of the present invention. [Figure 3A] FIG. 2 is a schematic diagram illustrating the distal end of a probe, according to one embodiment of the present invention. [Figure 3B] FIG. 2 is a schematic diagram illustrating the distal end of a probe, according to one embodiment of the present invention. [Figure 3C] FIG. 2 is a schematic diagram illustrating the distal end of a probe, according to one embodiment of the present invention. [Figure 3D] FIG. 2 is a schematic diagram illustrating the distal end of a probe, according to one embodiment of the present invention. [Figure 4] 1 is a schematic block diagram of an apparatus according to one embodiment of the present invention; [Figure 5] 1 is a flowchart of steps for calibrating a probe according to one embodiment of the present invention. [Figure 6] 1 is a temperature versus time graph illustrating the steps of a flowchart according to one embodiment of the present invention. [Figure 7] 1 is a flowchart of operations performed when the device is used in a cryogenic procedure, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] An accepted method for treating tumors in a patient is to use a cryoprobe: the physician positions the distal tip of the cryoprobe in contact with the tumor, and a cryogen, such as liquid nitrogen, is advanced through the cryoprobe. The cryogen forms an ice ball around the distal tip of the probe and the tumor, and the resulting low temperature freezes and destroys the tumor's cells.

[0014] Once the ice balls have formed, the physician withdraws the cryoprobe from the patient, and the remaining ice balls, as well as any destroyed tumor cells, are naturally absorbed by the patient's body.

[0015] However, when the ice ball first forms, it sticks to the outer surface of the holding tube at the distal end of the cryoprobe, making it impossible to easily withdraw the probe. Any attempt to withdraw the probe while the ice ball is attached to the outer surface of the distal holding tube typically causes pain to the patient and, if too much force is applied, may even cause tissue damage.

[0016] An embodiment of the present invention overcomes this problem by incorporating a heating element and a temperature sensor proximate to the heating element into the distal end of the probe. In addition, the probe includes a gas inlet. To withdraw the probe after the ice ball has formed, the heating element is activated and the temperature measured by the sensor is registered. When the registered temperature rises to a preset value, a first time is recorded and a first pulse of gas is delivered to the probe. The gas pulse cools an interior portion of the distal end of the probe, including the portion in contact with the temperature sensor.

[0017] As the heating element is activated, the temperature rises again to the preset value, and the second time that this occurs is recorded. A second pulse of gas is then delivered to the probe to cool the probe distal tip again. The process of pulsing the probe distal tip with cooling gas while the probe distal tip is heated may be repeated iteratively. As described below, time is used to provide a metric for the distal tip outer surface temperature.

[0018] (The surface temperature of the outer surface of the distal tip is very different from the temperature measured near the junctions close to the heater due to the large thermal gradient at the distal tip. There are extremely low ice ball temperatures below about -10°C and high heater temperatures above about +28°C. Due to physical constraints, the temperature-sensing junctions cannot be located on the outer surface of the distal tip.)

[0019] The inventors have found that the time difference between successive times at which preset temperature values ​​occur provides a good metric for the temperature of the probe distal tip exterior surface. The shorter the time difference, the higher the temperature. Typically, during an iteration, the time difference decreases as the distal tip exterior surface temperature increases.

[0020] In one embodiment of the present invention, the above-described repetitive pulses are repeated until a time difference between successive times corresponding to a distal tip outer surface temperature within the approximate range of 0° C. to −10° C. is registered. When such a time difference is registered, a notice may be provided to the physician that the cryoprobe may be withdrawn from the patient.

[0021] Using the time difference described above as the distal tip surface temperature metric applies regardless of the size of the ice ball. Different size ice balls may require different heating times before the probe can be removed, but the time difference metric provides a way to automatically detect when removal is possible.

[0022] The use of time difference as a metric of temperature is not limited to "ice" temperature, but may be used for higher temperatures. Thus, in an alternative embodiment, the time difference is measured to test whether the probe distal tip outer surface temperature is above about 35°C. Such a scenario may occur after the probe has been removed from the patient. If such a higher temperature is registered, the heating element may be automatically deactivated and / or a notification may be provided to the physician that the heater is still active.

[0023] (Detailed explanation) In the following description, like elements in the figures are identified by like numerals and, where necessary, distinguished by adding a letter to the numeral.

[0024] Reference is now made to Figure 1, which is a schematic illustration of an apparatus 20 used for a cryogenic procedure, according to one embodiment of the present invention. By way of example, the procedure envisioned in the following description relates to breast tumors, although it will be understood that the apparatus 20 may be used for other treatments, such as prostate or kidney tumors, and all such treatments are considered to fall within the scope of the present invention.

[0025] The procedure is performed by physician 24 on patient 28, and the physician can observe the results of the procedure on a display 32 included in device 20. The physician can interact with elements of device 20 via a keypad or pointing device 34. (Typically, a procedure for a breast tumor involves performing a scan, such as an ultrasound, CT (computed tomography), or MRI (magnetic resonance imaging) scan, of patient 28's breast and presenting the results of the scan on display 32. The scan is usually performed by a professional other than physician 24; details of the scan are not relevant to this disclosure, and for simplicity, the professional is not shown in FIG. 1 .)

[0026] The device 20 includes a console 42 within which the elements of the device are housed, as described in more detail below. The device 20 is controlled by a controller 36 coupled to a memory 40 within which software 44 for the device's operation is stored. The controller 36 and memory 40 are typically mounted within the console 42, as shown. The software 44 in the memory 40 may be downloaded to the controller in electronic form, for example, over a network. Alternatively or additionally, the software may be provided on a non-transitory, tangible medium, such as an optical, magnetic, or electronic storage medium.

[0027] To perform the procedure, in a first, insertion phase of the procedure, the physician 24 inserts the distal end 48 of a cryogenic probe 58 into the patient 28. The cryogenic probe 58 is connected to a cryogen pump 56 in the console 42 by flexible tubing 152. The cryogenic probe 58, also referred to herein as a cryoprobes 58 or probes 58, and its distal end 48 are described in more detail below with respect to Figures 2 and 3A-3D.

[0028] Once inserted, physician 24 controls device 20 to pump cryogenic fluid from cryogenic pump 56 in console 42 through tubing 152 to distal tip 48. The cryogenic fluid creates an ice sphere that surrounds the distal tip, and the physician controls the flow of cryogenic fluid to the distal tip until an ice sphere of the physician's desired size is formed. Formation of the desired size ice sphere concludes the insertion phase of the procedure.

[0029] FIG. 2 is a schematic diagram of a probe 58, according to one embodiment of the present invention. As shown in FIG. 2, the probe 58 includes a handle 104 attached to a probe shaft 108 at its proximal end. The shaft 108 terminates in a pointed distal end 48, and as shown in section 116, the shaft 108 includes three concentric tubes, typically formed from thin-walled stainless steel, with the tubes having a common axis of symmetry 50. A first, inner tube 76 surrounds a central lumen 124, and the inner tube is surrounded by a second tube 120. The first and second tubes are separated by an intermediate space 132. A third, outer, retaining tube 60 surrounds the second tube 120, and the second and third tubes are separated by a space 140.

[0030] Flexible tubing 152 has an internal structure generally similar to that of shaft 108 and is coupled to the shaft via handle 104. Lumens within tubing 152 are configured to carry cryogenic fluid from pump 56 to central lumen 124 and to transfer returning cryogenic fluid from intermediate space 132 to the pump.

[0031] 3A-3D are schematic diagrams illustrating the distal tip 48 of a probe 58, according to one embodiment of the present invention. Figures 3A and 3B are perspective views of the distal tip 48. Figure 3C is a cross-sectional view of the distal tip 48 taken along an axis of symmetry 50 of the probe 58, and Figure 3D is a cross-sectional view of the distal tip taken along a plane 54 perpendicular to the axis of symmetry and centered approximately on a heat exchanger 88, described below.

[0032] As mentioned above, probe 58 includes an outer retention tube 60 having an outer surface 64 and an inner surface 68 in the region of distal end 48. Fixedly connected to retention tube 60 is distal tip 72 of the distal end. For clarity, retention tube 60 is shown as transparent in FIG. 3A and is not shown in FIG. 3B. In FIG. 3B, heat exchanger 88 is shown as transparent.

[0033] The central inner tube 76 has a terminal end 80 adjacent the distal tip 72, and during operation of the device 20, the cryogenic pump 56 pumps cryogenic fluid through the inner tube 76, where the fluid is discharged from the terminal end 80 into the distal tip 72. It will be understood that the terminal end 80 acts as a cryogenic fluid inlet for the distal end 48, and as explained further below, the terminal end 80 also acts as a gas inlet for the distal end.

[0034] At the distal end 48, a heater 84 formed of resistive wiring is wound around the inner tube 76. (For simplicity, the heater 84's connections to the wiring are not shown in the figures.) The heat exchanger 88 is tubular and has a cylindrical inner surface 90 that surrounds the heater 84. The heat exchanger 88 has an external ribbed surface 92 that is parallel to the axis of symmetry 50 of the probe 58 and includes a plurality of linear, substantially similar channels 96 arranged symmetrically about the axis. In the illustrated embodiment, there are six channels 96, although other embodiments may have more or fewer linear channels. Each channel 96 is located between a pair of substantially similar ribs 100 of the heat exchanger, which is dimensioned so that the outer surfaces 104 of the ribs contact the inner tube surface 68.

[0035] One of the ribs 100, i.e., rib 100A, is reduced in both its length and its depth, and a thermocouple 114 having a junction 112 is positioned in the reduced section. The junction 112 acts as a temperature sensor and is also referred to herein as sensor 112. The reduced rib 100A has a terminus 134 that, in one embodiment, lies approximately on plane 54, and the sensor 112 is positioned at terminus 134. It will be understood that the sensor 112 registers the temperature of the outer ribbed surface 92 of the heat exchanger 88, which approximates the temperature of the inner tube surfaces 68.

[0036] As mentioned above, the probe 58 includes a second inner tube 120 that is coaxial with and larger than the inner tube 76. During a first stage of treatment, the discharged cryogenic fluid from the distal end 72 returns to the pump 56 via the channel 96 and the space 132 between the first tube 76 and the second tube 120. As mentioned above, the channel 96 is configured to be straight because the inventors have observed that vibrations occur if the channels that return the discharged cryogenic fluid, which typically contain different fractions of cryogen and liquid, are not straight, for example, if they include a spiral. If the channel 96 is straight, as illustrated in the embodiments described herein, vibrations do not occur during treatment.

[0037] Figure 4 is a schematic block diagram of apparatus 20, according to one embodiment of the present invention. As mentioned above, apparatus 20 includes console 42 and probe 58, with elements of console 42 included within dashed lines in Figure 4. As shown, cryogen pump 56 includes dewar 74, which holds liquid cryogen 52 during a procedure performed by physician 24. Cryogen 52 is typically liquid nitrogen, although in other embodiments, the cryogen may include other liquids, such as liquid argon.

[0038] Pump 56 includes a motor 70 that drives a pump piston or bellows. For simplicity, the piston or bellows is not shown. A description of a pump similar to pump 56 is provided in U.S. Pat. No. 11,633,224, which is assigned to the assignee of the present disclosure and incorporated herein by reference. After activation of motor 70, the fluid cryogen, typically about 100% liquid, exits the dewar's lower volume 82 through one-way valve 78 and outlet tube 94 to probe 58 and distal tip 48. The fluid cryogen, typically a gas-liquid mixture, returns through return tube 106 and liquid / gas separator 110, which separates the returning liquid into the dewar's lower volume 82 and the returning gas into the dewar's upper volume 86.

[0039] During the insertion phase of the process described above, i.e., the formation of ice balls of the desired size, at least a portion of the gas returning to the headspace 86, also referred to herein as exhaust gas, is removed from the dewar via exhaust tube 98. A gas compressor 102 connected to tube 98 compresses the exhaust gas into a gas reservoir 128. A pulse of stored compressed gas from reservoir 128 may be injected into outlet tube 94 via reservoir tube 122 from the reservoir, a solenoid switch 126 in the reservoir tube actuated by controller 36, and a T-junction 130 connecting the reservoir tube to the outlet tube. The pulse of gas is used in the second, removal phase of the process, as described below.

[0040] At the end of the insertion phase, the controller 36 deactivates the pump motor 70 so that the valve 78 is closed and no cryogen is expelled into the tubing 94. The removal phase of the procedure may then begin. During the removal phase, the distal tip 48 of the probe 58 is removed from the patient, while the ice ball generated during the insertion phase remains. However, because the ice ball is attached to the distal tip 48 at the end of the insertion phase, attempts to remove the distal tip typically cause trauma to the patient. As described below, embodiments of the present invention provide a method for safely unsticking the distal tip 48 from the ice ball during the removal phase to allow for easy removal of the distal tip.

[0041] At the start of the removal phase, controller 36 activates heater 84 to begin warming distal tip 48 by closing heating switch 118. While heater 84 is activated, controller 36 monitors the temperature of heat exchanger 88 as registered by thermocouple junction 112.

[0042] When the temperature registered by contacts 112 reaches a preset temperature, controller 36 activates solenoid switch 126 to briefly open in order to deliver a pulse of gas from container 128 into outlet tube 94 via T-contact 130. Controller 36 also records the time at which the preset temperature value is reached. In an exemplary embodiment, the preset temperature is set to approximately 40°C, and solenoid switch 126 closes when the temperature registered by contacts 112 drops to another preset value, which in the exemplary embodiment is approximately 35°C. Typically, solenoid switch 126 remains open for a period of time of approximately 1-3 seconds, which corresponds to the time the gas pulse is delivered.

[0043] The pulse of gas delivered from reservoir 128 into outlet tube 94 contains gas at approximately room temperature. The pulse of gas traverses outlet tube 94 toward distal end 48 (the gas cannot proceed toward pump 56 because valve 78 is closed). Within distal end 48, some of the thermal energy of the gas pulse is transferred to heat the ice ball in contact with exterior surface 64, and the gas pulse then cools. Heat exchanger 88 is transferring heat from heater 84 and is therefore heated, but the cooled gas pulse reduces the temperature of the heat exchanger and therefore the temperature registered at junction 112.

[0044] Once the gas pulse has traversed and exited distal tip 48, with heater 84 still activated, the temperature registered by junction 112 will begin to rise until it again reaches the preset temperature value, at which point a pulse of gas is again delivered.

[0045] An embodiment of the present invention uses a repeated iterative process of delivering gas pulses to estimate the temperature of the exterior surface 64. For a probe such as calibrated probe 58, the estimation is based on measuring the time difference between a series of pulses over a given preset temperature. The calibration process, and how a calibrated probe is used, is described below.

[0046] FIG. 5 is a flowchart 200 of steps for calibrating probe 58, and FIG. 6 is a temperature versus time graph illustrating the steps, according to one embodiment of the present invention.

[0047] In a setup step 204, the device 20 is configured as shown in Figure 4. The distal end 48 of the probe 58 is inserted into a material having properties similar to those of certain human tissue, and a temperature sensor, herein considered to include a thermocouple junction, is placed in contact with the outer surface 64 of the distal end.

[0048] Also in step 204, a preset temperature value, also referred to as threshold temperature Tth, is stored in software 44 in memory 40. In one embodiment, the threshold temperature T this set to about 40° C., as described above, although other embodiments may use a threshold temperature T th It may have.

[0049] In a freezing step 208, which simulates the first insertion phase of the procedure described above, pump 56 is activated to transfer cryogen to distal tip 48 to initiate the formation of an ice sphere around the distal tip. Activation continues until an ice sphere having a diameter within the range of about 40 mm to about 50 mm is formed, at which point activation of pump 56 is stopped so that no further cryogen is delivered to the distal tip.

[0050] In an activate heater step 212, which simulates the start of the second, removal phase of the procedure, the controller 36 activates the heater 84 using the switch 118. The controller begins recording the temperature provided by the contacts 112 and the temperature of the outer surface 64 of the distal tip, and stores the recorded temperatures. In the following description, the temperature provided by the contacts 112 is referred to as the inner distal tip temperature T int The temperature of the outer surface 64 of the distal tip is referred to as the external distal tip temperature T ext The controller also registers the time at which the temperature is recorded.

[0051] In decision step 216, for each recorded internal distal tip temperature, the controller checks whether the recorded internal distal tip temperature is greater than or equal to the threshold temperature Tth. If the decision returns positive, control proceeds to pulse step 220, where the controller 36 activates the solenoid 126 to inject a pulse of gas into the probe 58 and records the injection time. If the decision returns negative, control returns to the decision step.

[0052] In a pulse step 220, the solenoid 126 may be activated according to the description of the exemplary embodiment above.

[0053] As indicated in the chart by arrow 224, the determining step 216 and pulsing step 220 are typically repeated until the external distal tip temperature approaches 0°C.

[0054] 6 shows a graph of temperature versus time generated during the iterative process. Graph 250 shows the internal distal tip temperature T int and graph 254 shows the external distal tip temperature T ext Graph 250 shows six repetitions at times t1, t2, ... t6, at each of which a gas pulse is injected to generate T int The value of decreases sharply.

[0055] Once the iterations of steps 216 and 220 are complete, the flowchart continues with an analysis step 228 .

[0056] In the analysis step 228, the controller 36 performs the following calculations: ● Evoke the time at which the gas pulse is injected. In graph 250, there are six times t1, t2, ... t6. Calculate the time periods between successive pulses. In graph 250, five time periods Δt 12 , Δt 23 , Δt 34 , Δt 45 , Δt 56 There is. Identify the outer distal tip temperature Text for each of the time periods. In one embodiment, the temperature at the end of each time period is identified. In the graph 254, T ext2 , T ext3 , T ext4 , T ext5 , T ext6 There are five such temperatures, called Formulate and store a correspondence relating time periods and determined external distal tip temperatures. In one embodiment, the correspondence comprises a look-up table; alternatively or additionally, the correspondence comprises an algebraic relationship such as that illustrated in equation (1).

number

[0057] In some embodiments, the function F() is a monotonically decreasing function, i.e., as the temperature Text increases, the time period Δt decreases.

[0058] In the disclosed embodiment, the function F() is a linear monotonically decreasing function (a first-order monotonically decreasing function), i.e., equation (1) may be written as equation (2).

number

[0059] Once the probe 58 is calibrated, the generated correspondence may be used in implementing an algorithm for treatment such as that shown in Figure 1. The algorithm described below with respect to Figure 7 measures the time period between successive pulses and uses the measured time period to estimate the external distal tip temperature.

[0060] 7 is a flowchart 300 of operations performed when apparatus 20 is used in cryogenic operation, according to one embodiment of the present invention. The flowchart illustrates the operation of determining whether the distal tip temperature of distal tip 48, i.e., the temperature of outer surface 64, reaches a target temperature value T tar The present invention describes an algorithm that indicates how the physician 24 may be notified that a temperature called T tar is set to approximately -5°C, although other embodiments may have target temperature values ​​higher or lower than -5°C.

[0061] In an initial step 304, a calibration correspondence for the probe 58 formulated as described in flowchart 200 is calculated for a selected threshold temperature T th The correspondence is stored in software 44 in memory 40 for calculation. For clarity, in the following description, the correspondence is assumed to be in the form of equation (2), but one skilled in the art can apply the description mutatis mutandis to other forms of correspondence. For example, if the correspondence is in the form of a look-up table, controller 36 may use interpolation and / or extrapolation to derive values ​​not in the table.

[0062] In addition, the target temperature T tar The value of is stored in the software 44 and from the stored correspondence, the controller 36 calculates the target temperature T tar The corresponding target time Δt tar In one embodiment, Δt tar is about 12 seconds.

[0063] In the freezing step 308, the physician 24 inserts the distal end 48 of the probe 58 into the patient 28. The physician then activates the pump 56 so that cryogen is transferred to the distal end 48 to initiate the formation of an ice sphere around the distal end 48. Activation is typically performed discontinuously: pump, then pause, then pump again. Activation continues until an ice sphere of the desired size is formed, at which point the physician stops activating the pump 56 so that no further cryogen is transferred to the distal end.

[0064] Once the freezing process operation has been performed so that the first stage of the procedure is performed, the physician 24 can then perform the second, removal stage of the procedure.

[0065] In the first step 312 of the removal phase, the physician 25 activates the heater 84 to begin warming the distal tip 48 by having the controller 36 close the heating switch 118. After activation of the heater, the controller 36 detects the internal distal tip temperature T int Start monitoring.

[0066] In a first decision step 316, the controller 36 determines the equation T int ≧T th is valid. If the expression is not valid, i.e., if the expression returns a negative, the check continues. If the expression is valid and the return is positive, the flowchart continues to the first pulse step 320.

[0067] In a pulse step 320, the controller 36 activates the solenoid switch 126 to inject a pulse of gas into the probe 58. The activation may be in accordance with the exemplary embodiment described above. The controller also determines when the decision step 316 returns a positive result, i.e., when the internal distal tip temperature T int is the threshold temperature T th Record when it is equal to or greater than this.

[0068] The flowchart continues with a second decision step 324 that is substantially the same as the first decision step 316. That is, the controller 36 determines whether the equation T int ≧T th is valid. If the formula is not valid, the check continues. If the formula is valid, the flowchart continues to the second pulse step 328.

[0069] Pulse step 328 is substantially the same as first pulse step 320, i.e., controller 36 activates solenoid switch 126 to inject a pulse of gas into probe 58. The controller also notes when decision step 324 returns a positive answer.

[0070] The flowchart continues with a third decision step 332 in which the controller 36 determines whether the time period Δt between the previous series of gas pulses is equal to the target time period Δt calculated in step 304. tar Check if it is the following:

[0071] If decision step 332 returns negative, then in iteration step 336, the formula T int ≧T th is valid, and if so, repeat pulsing with gas until decision step 332 returns a positive result, i.e., the time period between successive gas pulses is equal to or exceeds the target time period Δt tar Continue until:

[0072] Formula Δt≧Δt tar When decision step 332 returns a positive answer, such that is valid, the flowchart continues to final step 340 .

[0073] In step 340, controller 36 calculates the external distal tip temperature T ext is the target temperature value T tar , and the controller may notify the physician 26 that the target temperature has been reached and that the probe 58 is ready for removal. Notification may be by any convenient means known in the art, such as by presenting a notification on the display 32.

[0074] The above description illustrates how embodiments of the present invention may be used to measure the temperature of the outer surface 64 of the distal end 48 when the measured temperature is at "ice" temperature, i.e., a temperature of approximately 0° C. However, it will be understood that embodiments of the present invention may be used to measure temperatures outside of this range.

[0075] For example, the target temperature T for the outer surface 64 tar may be set to 40°C, and the controller 36 controls the arThe steps of flowchart 300 may then be followed, and in final step 340, appropriate notification may be provided to physician 26 that heater 84 is still activated, for example. Alternatively or additionally, in final step 340, controller 36 may be configured to automatically deactivate the heater.

[0076] As used herein, the terms "about" or "approximately" in reference to any numerical value or range indicate appropriate dimensional tolerances that enable a portion or collection of components to function for its intended purpose as described herein. More specifically, "about" or "approximately" may refer to a range of ±20% of the recited value; for example, "about 80%" may refer to a range of 64% to 96% of the value.

[0077] The above-described embodiments have been cited by way of example, and it will be understood that the present invention is not limited to what has been particularly shown and described above. Rather, the scope of the present invention includes both combinations and subcombinations of the various configurations described above, as well as variations and modifications thereof which would occur to one skilled in the art after reading the foregoing description and which are not disclosed in the prior art.

Claims

1. a probe including a probe distal end having an outer surface configured to contact tissue of a patient when the probe distal end is inserted into the patient; a heater disposed within the probe distal end; a temperature sensor disposed within the distal end of the probe; a gas inlet coupled to the probe distal end and configured to provide a gas to the probe distal end; a controller; The controller, while the heater is activated, registering a first time period during which the temperature measured by the temperature sensor is equal to or greater than a preset temperature; in response to the temperature being equal to or greater than the preset temperature, delivering a pulse of gas through the gas inlet to cool the probe distal tip; registering a second time subsequent to the first time during which the temperature measured by the temperature sensor is equal to or greater than the preset temperature; estimating a temperature of the exterior surface of the probe distal end in response to a time difference between the second time and the first time; It is configured as follows: Device.

2. The apparatus of claim 1 , comprising a cryogen inlet coupled to the probe distal end and configured to transfer a cryogenic fluid to the probe distal end.

3. 3. The apparatus of claim 2, wherein the gas inlet and the cryogen inlet include a common tube, and the controller is configured to operate the common tube as the gas inlet for a first time period and to operate the common tube as the cryogen inlet for a second time period different from the first time period.

4. The apparatus of claim 1 , wherein the gas is input to the probe as a room temperature gas.

5. The apparatus of claim 4 , wherein the room temperature gas comprises exhaust gas obtained from a cryogenic fluid transferred to the distal end of the probe.

6. 5. The apparatus of claim 1, 2 or 4, wherein the temperature sensor comprises a thermocouple junction disposed between the heater and an inner surface of the probe distal end.

7. 5. The apparatus of claim 1, 2 or 4, wherein the time difference and the temperature of the outer surface of the probe distal end are related by a monotonically decreasing function.

8. The apparatus of claim 7 , wherein the monotonically decreasing function comprises a linear function.

9. 5. The apparatus of claim 1, 2 or 4, wherein the pulse of gas is delivered until the temperature measured by the temperature sensor equals a further preset temperature that is lower than the preset temperature.

Images