Cryoprobe

Abstract

The invention relates to a cryoprobe. An apparatus includes a probe including a probe distal end having an outer surface that contacts tissue of a patient when the distal end is inserted into the body of the patient. A heater and a temperature sensor are located at the distal end, and a gas inlet is coupled to the distal end to provide gas. When the heater is activated, the controller records a first time when the temperature measured by the sensor is equal to or exceeds a preset temperature, and in response to the temperature equal to or exceeding the preset temperature, causes a pulse of gas to pass through the gas inlet so as to cool the distal end of the probe. The controller then records a second time when the temperature measured by the sensor is equal to or exceeds the preset temperature, and estimates a temperature of the outer surface of the distal end of the probe in response to a time difference between the second time and the first time.

Description

Field of the Invention

[0001] The present invention relates generally to probes for freezing material, and particularly to operating the probe while the material is being frozen. Background of the Invention

[0003] Cryoablation is a process that uses extreme low temperatures to destroy tissue. Cryoablation can be performed using a hollow needle (cryoprobe) through which a cryogen is circulated. The cryoprobe can be positioned in contact with the tissue to be destroyed, and then the cryogen is circulated through the probe. Once the tissue has been frozen, the cryoprobe can be retrieved from the tissue. SUMMARY OF THE INVENTION

[0005] An embodiment of the present invention provides a device, the device comprising:

[0006] a probe including a probe distal end having an exterior surface configured to contact tissue of a patient when the probe distal end is inserted into the tissue of the patient;

[0007] a heater located at the distal end of the probe;

[0008] a temperature sensor located at the distal end of the probe;

[0009] a gas inlet coupled to the probe distal end and configured to provide gas to the probe distal end; and

[0010] A controller, when the heater is activated, the controller is configured to:

[0011] registering a first time when the temperature measured by the sensor is equal to or exceeds a preset temperature,

[0012] responsive to the temperature being equal to or exceeding a preset temperature, passing a pulse of gas through the gas inlet to cool the distal end of the probe, recording a second time after the first time when the temperature measured by the sensor is equal to or exceeds the preset temperature, and

[0013] In response to the time difference between the second time and the first time, a temperature of the exterior surface of the distal end of the probe is estimated.

[0014] The apparatus may include a cryogen inlet coupled to the probe distal end and configured to deliver a cryogenic fluid to the probe distal end.

[0015] In a disclosed embodiment, the gas inlet and the refrigerant inlet are a common pipe, and the controller is configured to operate the common pipe as the gas inlet during a first period of time, and to operate the common pipe as the refrigerant inlet during a second period of time different from the first period of time.

[0016] In further disclosed embodiments, the gas is input to the probe as room temperature gas. The room temperature gas may be composed of exhaust gas obtained from a cryogen fluid transported to a remote location.

[0017] In a further embodiment, the temperature sensor includes a thermocouple junction located between the heater and an interior surface of the distal end of the probe.

[0018] In an alternative embodiment, the time difference and the temperature of the outer surface of the distal end of the probe are in a monotonically decreasing functional relationship. The monotonically decreasing function may include a linear function.

[0019] In a further alternative embodiment, a pulse of gas is delivered until the temperature measured by the sensor equals another preset temperature that is lower than the preset temperature.

[0020] According to an embodiment of the present invention, a method is further provided, the method comprising:

[0021] providing a probe including a probe distal end having an exterior surface configured to contact tissue of a patient when the probe distal end is inserted into the tissue of the patient;

[0022] Positioning a heater at the distal end of the probe;

[0023] Positioning a temperature sensor at the distal end of the probe;

[0024] coupling a gas inlet to the distal end of the probe, wherein the gas inlet is configured to provide gas to the distal end of the probe;

[0025] The heater is activated, and, when the heater is activated:

[0026] When the temperature measured by the sensor is equal to or exceeds the preset temperature, the first time is recorded.

[0027] In response to the temperature being equal to or exceeding a preset temperature, pulse a gas through the gas inlet to cool the distal end of the probe, after the first time, recording a second time when the temperature measured by the sensor is equal to or exceeds the preset temperature, and

[0028] In response to the time difference between the second time and the first time, a temperature of the exterior surface of the distal end of the probe is estimated.

[0029] The present disclosure will be more fully understood based on the following detailed description of embodiments of the present disclosure in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of an apparatus for cryosurgery according to an embodiment of the present invention;

[0031] Figure 2 is a schematic diagram of a probe of an apparatus according to an embodiment of the present invention;

[0032] Figure 3A-3D is a schematic diagram illustrating a distal end of a probe according to an embodiment of the present invention;

[0033] Figure 4 is a schematic block diagram of a device according to an embodiment of the present invention;

[0034] Figure 5 is a flow chart of steps for calibrating a probe according to an embodiment of the present invention;

[0035] Figure 6 is a temperature versus time graph illustrating steps of a flow chart according to an embodiment of the present invention; and

[0036] Figure 7 is a flow chart of actions performed when the device is used in cryosurgery according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] Overview

[0038] The recognized method for treating a patient's tumor is to use a cryoprobe; the doctor places the distal end of the cryoprobe in contact with the tumor, and a cryogen (e.g., liquid nitrogen) is passed through the cryoprobe. The cryogen forms an ice ball around the distal end of the probe and the tumor, and the resulting low temperature freezes and destroys the tumor cells.

[0039] Once the ice ball has formed, the doctor can remove the cryoprobe from the patient. The remaining ice ball and the destroyed tumor cells are naturally absorbed by the patient's body.

[0040] However, when the ice ball is initially formed, it adheres to the outer surface of the holding tube at the distal end of the cryoprobe and thus the probe cannot be easily removed. When the ice ball adheres to the outer surface of the distal retention tube, any attempt to remove the probe will generally cause pain to the patient and may even cause damage to the tissue if a large force is applied.

[0041] Embodiments of the present invention solve this problem by incorporating a heating element and a temperature sensor proximate to the heating element to the distal end of the probe. In addition, the probe includes a gas inlet. To remove the probe after the ice ball is formed, the heating element is activated and the temperature measured by the sensor is recorded. When the recorded temperature increases to a preset value, a first time is recorded and a first gas pulse is delivered to the probe. The gas pulse cools the interior portion of the distal end of the probe (including the portion in contact with the temperature sensor).

[0042] Because the heating element is activated, the temperature rises again to the preset temperature, and a second time when this occurs is recorded. Then, a second gas pulse is delivered to the probe to once again cool the probe distal end. The process of pulsing the probe distal end with cooling gas while the probe is heated can be repeated iteratively. As described above, time is used to provide a measure of the temperature of the external surface of the probe distal end.

[0043] (Because there are large thermal gradients in the distal end, the surface temperature of the distal end's outer surface is very different from the temperature measured at the junction near the heater. The puck has a very low temperature of about -10°C or less, and the heater has a high temperature of about +28°C or more. Due to physical limitations, the temperature sensing junction cannot be located on the outer surface of the distal end.)

[0044] The inventors have found that the time difference between successive occurrences of a preset temperature value provides a good measure of the temperature of the outer surface of the distal end of the probe: the shorter the time difference, the higher the temperature. Typically, during iterations, the time difference decreases as the temperature of the outer surface of the distal end increases.

[0045] In an embodiment of the present invention, the above-described iterative pulses are repeated until a time difference between consecutive times corresponding to a distal outer surface temperature in the range of about 0 to -10° C. is recorded. When such a time difference is recorded, a physician may be notified that the cryoprobe may be removed from the patient.

[0046] Using the above time difference as a measure of the temperature of the distal outer surface applies regardless of the size of the puck. Although different sized pucks may require different heating times before the probe is removed, the time difference measure provides a method for automatically detecting when removal is possible.

[0047] The use of the time difference as a measure of temperature is not limited to "freezing" temperatures and can be used for higher temperatures. Therefore, in an alternative embodiment, the time difference is measured to test whether the temperature of the external surface of the distal end of the probe is approximately 35°C or higher. Such a scenario may occur after the probe has been removed from the patient. If such a higher temperature is recorded, the heating element can be automatically deactivated and / or a notification can be provided to the physician that the heater is still operating.

[0048] Detailed Description

[0049] In the following description, like elements in the drawings are identified by like numerals and are distinguished by appending letters to the numerals as necessary.

[0050] Reference Figure 1 , Figure 1 Schematic diagram of a device 20 for cryosurgery according to an embodiment of the present invention. By way of example, the surgery presented in the following description is performed on a breast tumor, but it should be understood that the device 20 can be used for other surgeries, such as prostate tumors or kidney tumors, and all of these surgeries are considered to be included within the scope of the present invention.

[0051] The surgery is performed by a doctor 24 on a patient 28, and the doctor is able to observe the results of the surgery on a display 32 included in the device 20. The doctor is also able to interact with the elements of the device 20 via a keyboard or pointing device 34. (Typically, surgery on a breast tumor includes scanning the breast of the patient 28, such as an ultrasound, CT (computed tomography) or MRI (magnetic resonance imaging) scan, and presenting the scan results on the display 32. The scan is usually performed by a professional other than the doctor 24. The details of the scan are not relevant to the present disclosure, and for simplicity, the professional is not described in detail. Figure 1 . )

[0052] The device 20 includes a console 42 in which the elements of the device are contained, as will be described in more detail below. The device 20 is controlled by a controller 36 coupled to a memory 40 in which software 44 for operating the device is stored. The controller 36 and memory 40 are typically installed in the console 42, as shown. For example, the software 44 in the memory 40 may be downloaded to the controller in electronic form over a network. Alternatively or additionally, the software may be provided on a non-transitory tangible medium (e.g., an optical, magnetic, or electronic storage medium).

[0053] To perform the procedure, in the first (insertion) phase of the procedure, the physician 24 inserts the distal end 48 of the cryogenic probe 58 into the patient 28. The cryogenic probe 58 is connected to the cryogen pump 56 in the console 42 by a flexible tube 152. The cryogenic probe 58 (also referred to herein as the cryoprobe 58 or the probe 58) and its distal end 48 will be described below with reference to Figure 2 and Figure 3A-3D Describe in more detail.

[0054] Once inserted, the doctor 24 controls the device 20 to deliver cryogenic fluid from the cryogen pump 56 in the console 42 through the tube 152 to the distal end 48. The cryogenic fluid creates an ice ball around the distal end, and the doctor controls the flow of the cryogenic fluid to the distal end until an ice ball of the size desired by the doctor is formed. The formation of an ice ball of the desired size ends the insertion phase of the procedure.

[0055] Figure 2 Schematic diagram of a probe 58 according to an embodiment of the present invention. Figure 2 , the probe 58 includes a handle 104 attached to a shaft 108 of the probe at the proximal end of the shaft. The shaft 108 terminates at a pointed distal end 48 and, as shown in section 116, comprises three concentric tubes, typically made of thin-walled stainless steel, having a common axis of symmetry 50. The first inner tube 76 surrounds a central lumen 124, and the inner tube is then surrounded by a second tube 120. The first and second tubes are separated by an intermediate space 132. The third outer retaining tube 60 surrounds the second tube 120, and the second and third tubes are separated by a space 140.

[0056] Flexible tube 152 has an internal structure generally similar to that of shaft 108 and is coupled to the shaft via handle 104. The lumen within tube 152 is configured to convey cryogenic fluid from pump 56 to central lumen 124 and to convey return cryogenic fluid from intermediate space 132 to the pump.

[0057] Figure 3A-3D is a schematic diagram illustrating distal end 48 of probe 58 in accordance with an embodiment of the present invention. Figure 3A and Figure 3B is a perspective view of distal end 48 . Figure 3C is a cross-sectional view of distal end 48 taken along axis of symmetry 50 of probe 58, and Figure 3D is a cross-sectional view of the distal end taken orthogonal to the axis of symmetry and along plane 54 approximately centered on heat exchanger 88, as described below.

[0058] As described above, the probe 58 includes an outer retaining tube 60, and the tube 60 has an outer surface 64 and an inner surface 68 in the region of the distal end 48. The distal tip 72 of the distal end is fixedly coupled to the retaining tube 60. For clarity, the Figure 3A In FIG. 6 , the holding tube 60 is shown as transparent and in FIG. Figure 3B Not shown. Figure 3B The middle heat exchanger 88 is shown as transparent.

[0059] The central inner tube 76 has a terminal end 80 proximate the distal tip 72, and in operation of the apparatus 20, the cryogen pump 56 pumps a cryogenic fluid through the inner tube 76, and the fluid is discharged from the terminal end 80 into the distal tip 72. It should be understood that the terminal end 80 functions as a cryogen fluid inlet for the distal end 48; as further explained below, the terminal end 80 also functions as a gas inlet for the distal end.

[0060] At the distal end 48, a heater 84 formed of a resistive wire is wound around the inner tube 76. (For simplicity, the wiring connections of the heater 84 are not shown in the figure.) The heat exchanger 88 is tubular and has a cylindrical inner surface 90 surrounding the heater 84. The heat exchanger 88 has an outer ribbed surface 92; the surface 92 contains a plurality of straight, substantially similar channels 96, which are parallel to the symmetry axis 50 of the probe 58 and are symmetrically arranged about the axis. In the embodiment shown in the figure, there are six channels 96, but other embodiments may have more or less than six straight channels. Each channel 96 is located between a pair of substantially similar ribs 100 of the heat exchanger, and the heat exchanger is sized so that the outer surface 104 of the rib contacts the inner surface 68 of the tube.

[0061] One of the ribs 100 (rib 100A) is foreshortened in both length and depth and has a thermocouple 114 at a junction 112 located at the foreshortened portion. Junction 112 functions as a temperature sensor and is also referred to herein as sensor 112. Foreshortened rib 100A has a terminal end 134, which in one embodiment is approximately located on plane 54, and sensor 112 is located at terminal end 134. It should be understood that sensor 112 records the temperature of the outer ribbed surface 92 of heat exchanger 88, and this temperature is approximately the temperature of tube inner surface 68.

[0062] As described above, the probe 58 includes a second inner tube 120 that is coaxial with the inner tube 76 and larger than the inner tube 76. During the first stage of the operation, the refrigerant fluid discharged from the distal tip 72 is returned to the pump 56 through the passage 96 and the space 132 between the first tube 76 and the second tube 120. As described above, the passage 96 is configured to be straight, because the inventors have observed that if the passages for returning the discharged refrigerant fluid (which typically include refrigerant gas and refrigerant liquid in different proportions) are not straight, for example, if they contain spirals, vibrations will occur. If the passage 96 is straight, as described in the embodiments described herein, vibrations will not occur during the operation.

[0063] Figure 4 is a schematic block diagram of an apparatus 20 according to an embodiment of the present invention. As described above, the apparatus 20 includes a console 42 and a probe 58, and Figure 4, the elements of the console 42 are shown as being surrounded by dashed lines. As shown in the figure, the cryogen pump 56 includes a Dewar 74, which contains a liquid cryogen 52 during the operation performed by the doctor 24. The cryogen 52 is typically liquid nitrogen, but in other embodiments, the cryogen may include other liquids, such as liquid argon.

[0064] Pump 56 includes a motor 70 that drives a piston or bellows of the pump. For simplicity, the piston or bellows are not shown in the figure. A description of a pump similar to pump 56 is provided in U.S. Patent No. 11,633,224, which has been assigned to the assignee of the current disclosure and is incorporated herein by reference. When motor 70 is started, fluid cryogen (usually nearly 100% liquid) leaves the lower space 82 of the Dewar flask via the one-way valve 78 and the outlet pipe 94 to reach the probe 58 and the distal end 48. The fluid cryogen (usually a gas-liquid mixture) returns through the return pipe 106 and the liquid / gas separator 110, which separates the returning liquid into the lower space 82 of the Dewar flask and separates the returning gas into the upper space 86.

[0065] During the insertion phase of the above-described procedure (i.e., formation of an ice ball of a desired size), at least some of the gas returned to the upper space 86 (also referred to herein as exhaust) is exhausted from the Dewar via exhaust tube 98. A gas compressor 102 connected to tube 98 compresses the exhaust into a gas container 128. A pulse of stored compressed gas from container 128 can be injected from the container into outlet tube 94 via container tube 122, a solenoid switch 126 in the container tube operated by controller 36, and a T-junction 130 that connects the container tube to the outlet tube. The pulse of gas is intended for use in the second (removal) phase of the procedure, as described below.

[0066] At the end of the insertion phase, the controller 36 stops the pump motor 70 so that the valve 78 is closed and no refrigerant is discharged into the tube 94. The extraction phase of the operation can then begin. In the extraction phase, the distal end 48 of the probe 58 is removed from the patient's body, while the ice ball created during the insertion phase remains. However, at the end of the insertion phase, the ice ball adheres to the distal end 48, so that an attempted removal of the distal end may generally cause damage to the patient. As described below, embodiments of the present invention provide methods for safely disengaging the distal end 48 from the ice ball during the extraction phase to allow easy removal of the distal end.

[0067] At the beginning of the withdrawal phase, the controller 36 activates the heater 84 by closing the heating switch 118 to begin warming the distal end 48. While the heater 84 is activated, the controller 36 monitors the temperature of the heat exchanger 88, as recorded by the thermocouple junction 112.

[0068] When the temperature registered by the connector 112 reaches a preset temperature value, the controller 36 activates the electromagnetic switch 126 to open briefly to deliver a pulse of gas from the container 128 to the outlet tube 94 via the T-connector 130. The controller 36 also records the time at which the preset temperature value is reached. In the exemplary embodiment, the preset temperature is set to approximately 40° C., and when the temperature registered by the connector 112 drops to another preset value (approximately 35° C. in the exemplary embodiment), the electromagnetic switch 126 closes. Typically, the electromagnetic switch 126 remains open for a period of approximately 1-3 seconds, which corresponds to the time that the gas pulse is delivered.

[0069] The gas pulse delivered from container 128 to outlet tube 94 includes gas at approximately room temperature. The gas pulse passes through outlet tube 94 toward distal end 48 (because valve 78 is closed, gas cannot move toward pump 56). Within distal end 48, some of the thermal energy of the gas pulse is transferred to heat the puck contacting exterior surface 64, and the gas pulse is thereby cooled. Although heat exchanger 88 transfers thermal energy from heater 84, and is therefore heated, the cooled gas pulse reduces the temperature of the heat exchanger, and thus reduces the temperature recorded by junction 112.

[0070] Once the gas pulse passes through and leaves the distal end 48, the temperature recorded by the connector 112 begins to rise until the preset temperature value is reached again because the heater 84 is still activated. At this time, a pulse of gas is delivered again.

[0071] Embodiments of the present invention use a repeated, iterative process of transporting gas to estimate the temperature of the external surface 64. For a calibrated probe (e.g., probe 58), the estimate is based on measuring the time difference between a series of pulses for a given preset temperature. The calibration process and how the calibrated probe is used will be described below.

[0072] Figure 5 is a flowchart 200 of steps for calibrating probe 58 according to an embodiment of the present invention, and Figure 6 is a graph illustrating the temperature versus time for these steps.

[0073] In the setup step 204, the device 20 is configured as follows Figure 4 The distal end 48 of the probe 58 is inserted into a material having properties similar to those of human tissue, and a temperature sensor (herein assumed to comprise a thermocouple junction) is placed in contact with the outer surface 64 of the distal end.

[0074] Also in step 204, the value of the preset temperature (also referred to as the threshold temperature in this article) is set to th ) is stored in software 44 in memory 40. In one embodiment, as described above, the threshold temperature T th is set to about 40°C, but other embodiments may have a threshold temperature T less than or greater than 40°C. th .

[0075] In the freezing step 208, which simulates the first (insertion) stage of the procedure mentioned above, the pump 56 is activated so that the cryogen is delivered to the distal end 48 so as to begin to form an ice ball around the distal end. Activation continues until an ice ball having a diameter in the range of about 40 mm to about 50 mm is formed, at which time the activation of the pump 56 is stopped so that no more cryogen is transported to the distal end.

[0076] In the start heater step 212 at the beginning of the second (removal) phase of the simulated surgery, the controller 36 activates the heater 84 using the switch 118. The controller begins recording the temperature provided by the connector 112 and the temperature of the external surface 64 of the distal end, and stores the recorded temperatures. In the following description, the temperature provided by the connector 112 is also referred to as the internal distal end temperature, T int , and the temperature of the distal outer surface 64 is also referred to as the external distal temperature, T ext The controller also records the time when the temperature was recorded.

[0077] In decision step 216, for each recorded internal remote temperature, the controller checks whether the recorded internal remote temperature is greater than or equal to a threshold temperature T th If the determination returns in the affirmative, the controller proceeds to the pulse step 220, where the controller 36 activates the solenoid switch 126 to inject a pulse of gas into the probe 58, and records the time of injection. If the determination returns in the negative, the controller returns to the determination step.

[0078] During the pulse step 220 , the electromagnetic switch 126 may be activated as described in the exemplary embodiment above.

[0079] As indicated by arrow 224 in the graph, decision step 216 and pulse step 220 are repeated, typically until the external remote temperature approaches 0°C.

[0080] Figure 6 250 shows the temperature versus time generated during the repetitive process. int Curve 254 shows the external remote temperature T extCurve 250 shows six iterations at times t1, t2, ... t6, at each time point, a gas pulse is injected, causing T int The value dropped sharply.

[0081] Once the iterations of steps 216 and 220 are complete, the flow chart continues to an analysis step 228 .

[0082] In analysis step 228, controller 36 performs the following calculations:

[0083] Recall the time at which the gas pulse was injected; in curve 250 there are six times t1, t2, ... t6.

[0084] Calculate the time intervals between successive pulses; there are five time intervals Δt in curve 250 12 , Δt 23 , Δt 34 , Δt 45 , Δt 56 .

[0085] Determine the external remote temperature T at each time interval ext In one embodiment, the last temperature of each time interval is identified; in curve 254, there are five such temperatures, referred to herein as T ext2 , T ext3 , T ext4 , T ext5 , T ext6 .

[0086] A correspondence is developed and stored that relates the time intervals to the identified external remote temperatures. In an embodiment, the correspondence comprises a lookup table; alternatively or additionally, the correspondence comprises an algebraic relationship such as illustrated in equation (1).

[0087] T ext =F(Δt) (1)

[0088] Where T ext is the external remote temperature,

[0089] Δt is the time interval between successive injection times, and

[0090] F() is a function related to temperature and time interval.

[0091] In some embodiments, the function F() is a monotonically decreasing function, that is, as the temperature T ext As the value increases, the time interval Δt decreases.

[0092] In the disclosed embodiment, the function F() is a linear monotonically decreasing function, that is, equation (1) can be written as equation (2):

[0093] T ext =-m·Δt+c (2)

[0094] Where T ext , Δt is the same as defined in equation (1) above, and m and c are possible Figure 5 A positive number generated during the calibration process.

[0095] Once the probe 58 has been calibrated, the resulting correspondence can be used to implement Figure 1 The surgical algorithm is shown in . Figure 7 The described algorithm measures the time interval between consecutive pulses and uses the measured time interval to estimate the external remote temperature.

[0096] Figure 7 300 is a flow chart of actions performed when using device 20 in cryogenic surgery according to an embodiment of the present invention. The flow chart describes an algorithm that illustrates how physician 24 may be notified that the external distal temperature of distal end 48 (i.e., the temperature of external surface 64) has reached a certain value, referred to herein as a target temperature value, T tar , at which temperature the probe 58 is suitable for removal. In an embodiment, the temperature T tar It is set to approximately -5°C, but other embodiments may have a target temperature value higher or lower than -5°C.

[0097] In the initial step 304, for a selected critical temperature T th , the calibration correspondence of the probe 58 developed as described in the flowchart 200 is stored in the software 44 of the memory 40. For clarity, the correspondence is assumed to be in the form of equation (2) in the following description, and a person skilled in the art will be able to make necessary modifications to the description for other forms of the correspondence. For example, if the correspondence is in the form of a lookup table, the controller 36 may use interpolation and / or extrapolation to derive values ​​that are not in the table.

[0098] In addition, the target temperature value T tar is stored in the software 44, and the controller 36 calculates the temperature corresponding to the target temperature T from the stored correspondence. tar Target time interval Δt tar In one embodiment, Δt tar About 12 seconds.

[0099] 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 the cryogen is transported to the distal end 48 so as to begin to form an ice ball around the distal end 48. The priming is typically performed discontinuously, i.e., pumping, then stopping, then pumping again. The priming continues until an ice ball of the desired size is formed, at which point the physician stops priming the pump 56 so that no more cryogen is transported to the distal end.

[0100] Once the act of the freezing step has been performed, such that the first phase of the procedure has been performed, physician 24 is able to perform the second (retrieval) phase of the procedure.

[0101] In the first step 312 of the removal phase, the physician 24 activates the heater 84 by allowing the controller 36 to close the heating switch 118 to begin warming the distal end 48. When the heater is activated, the controller 36 begins monitoring the internal distal end temperature, T, recorded by the thermocouple junction 112. int .

[0102] In a first decision step 316, the controller 36 checks the expression T int ≥T th Is it valid. If the expression is invalid, that is, the expression returns negative, the check continues. If the expression is valid, and therefore returns positive, the flowchart continues to the first pulse step 320.

[0103] In the pulse step 320, the controller 36 activates the electromagnetic switch 126 to inject a gas pulse into the probe 58. The activation can be in accordance with the exemplary embodiment described above. The controller also records when the decision step 316 returns to the affirmative, that is, when the internal distal temperature T int Equal to or exceeding the critical temperature T th The time of time,.

[0104] The flowchart continues to the second decision step 324, which is substantially the same as the first decision step 316, that is, the controller 36 checks the expression T int ≥T th Is it valid. If the expression is invalid, the check continues. If the expression is valid, the flowchart continues to the second pulse step 328.

[0105] The pulse step 328 is substantially the same as the first pulse step 320. That is, the controller 36 activates the solenoid switch 126 to inject a pulse of gas into the probe 58. The controller also records the time when the decision step 324 returns affirmative.

[0106] The flowchart continues to the third decision step 332, where the controller 36 checks whether the time interval Δt between the previous consecutive gas pulse times is less than or equal to the target time interval Δt calculated in step 304. tar .

[0107] If the decision step 332 returns negative, then, in the repetition step 336, the expression T is checked. int ≥T th The process of determining whether the gas pulse is effective and, if effective, repeats. The repetition continues until decision step 332 returns positive, i.e., until the time interval between successive gas pulses is less than or equal to the target time interval Δt tar .

[0108] When the decision step 332 returns positive, the expression Δt≤Δt tar Valid, the flowchart continues to the final step 340 .

[0109] In step 340 , the controller 36 records the external distal temperature T of the distal end 48 . ext The target temperature T has been reached tar , and the controller can notify the doctor 24 that the target temperature has been reached and the probe 58 is in a state suitable for removal. The notification can be any convenient way known in the art, such as presenting a notification on the display 32.

[0110] The above description illustrates how embodiments of the present invention may be used to measure the temperature of exterior surface 64 of distal end 48 when the measured temperature is "freezing" temperature, i.e., a temperature of approximately 0° C. However, it should be understood that embodiments of the present invention may be used to measure temperatures outside of this range.

[0111] For example, the target temperature T of the external surface 64 tar can be set to 40°C, and the controller 36 can calculate Δt tar The steps of flowchart 300 may then be followed, and in a final step 340, appropriate notification may be provided to physician 24, e.g., heater 84 is still enabled. Alternatively or additionally, in a final step 340, controller 36 may be configured to automatically deactivate the heater.

[0112] As used herein, the term "about" or "approximately" for any numerical value or range indicates a suitable dimensional tolerance that allows a part or component set to be used for the intended purpose as described herein. More specifically, "about" or "approximately" may refer to a range of ±20% of the value, i.e., "approximately 80%" may refer to a range of values ​​from 64% to 96%.

[0113] It should be appreciated that the embodiments described above are listed by way of example, and the present invention is not limited to those that have been particularly shown and described above. On the contrary, the scope of the present invention includes the combination and sub-combination of the various features described above, as well as variations and modifications thereof that will occur to those skilled in the art upon reading the foregoing description and that are not disclosed in the prior art.

Claims

1. A device comprising: a probe comprising a probe distal end having an exterior surface configured to contact tissue of a patient when the probe distal end is inserted into the tissue of the patient; a heater, the heater being located at the distal end of the probe; a temperature sensor, the temperature sensor being located at 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; as well as A controller, when the heater is activated, the controller is configured to: Recording a first time when the temperature measured by the sensor equals or exceeds a preset temperature, responsive to said temperature being equal to or exceeding said predetermined temperature, delivering a pulse of gas through said gas inlet to cool said probe distal end, After the first time, recording a second time when the temperature measured by the sensor equals or exceeds the preset temperature, and In response to the time difference between the second time and the first time, a temperature of the exterior surface of the probe distal end is estimated. 2 . The apparatus of claim 1 , comprising a cryogen inlet coupled to the probe distal end and configured to deliver a cryogenic fluid to the probe distal end.

3. The device according to claim 2, wherein: The gas inlet and the refrigerant inlet include a common pipe, and wherein the controller is configured to operate the common pipe as the gas inlet during a first period of time, and to operate the common pipe as the refrigerant inlet during a second period of time different from the first period of time.

4. The device according to claim 1, wherein: The gas is input into the probe as room temperature gas.

5. The device according to claim 4, wherein: The room temperature gas includes exhaust gas resulting from cryogen fluid delivered to the remote end.

6. The apparatus according to claim 1, 2 or 4, wherein: The temperature sensor includes a thermocouple junction located between the heater and an interior surface of the distal end of the probe.

7. The apparatus of claim 1, 2 or 4, wherein: The time difference is in a monotonically decreasing functional relationship with the temperature of the outer surface at the distal end of the probe.

8. The device according to claim 7, wherein: The monotonically decreasing function includes a linear function.

9. The apparatus of claim 1, 2 or 4, wherein: The gas pulse is delivered until the temperature measured by the sensor is equal to another preset temperature that is lower than the preset temperature.

10. A method comprising: providing a probe including a probe distal end having an exterior surface configured to contact tissue of a patient when the probe distal end is inserted into the tissue of the patient; positioning a heater at the distal end of the probe; positioning a temperature sensor at the distal end of the probe; coupling a gas inlet to the probe distal end, wherein the gas inlet is configured to provide gas to the probe distal end; The heater is activated, and when the heater is activated: Recording a first time when the temperature measured by the sensor equals or exceeds a preset temperature, in response to the temperature being equal to or exceeding the predetermined temperature, passing a pulse of gas through the gas inlet to cool the probe distal end, After the first time, a second time is recorded when the temperature measured by the sensor is equal to or exceeds the preset temperature, and In response to the time difference between the second time and the first time, a temperature of the exterior surface of the probe distal end is estimated.

11. The method of claim 10, comprising coupling a cryogen inlet to the probe distal end, and configuring the cryogen inlet to deliver a cryogenic fluid to the probe distal end.

12. The method according to claim 11, wherein: The gas inlet and the refrigerant inlet include a common pipe, and the method includes operating the common pipe as the gas inlet during a first period of time, and operating the common pipe as the refrigerant inlet during a second period of time different from the first period of time.

13. The method according to claim 10, wherein: The gas is input to the probe as room temperature gas.

14. The method according to claim 13, wherein: The room temperature gas includes exhaust gas resulting from cryogen fluid delivered to the remote end.

15. The method according to claim 10, 11 or 13, wherein: The temperature sensor includes a thermocouple junction located between the heater and an interior surface of the distal end of the probe.

16. The method according to claim 10, 11 or 13, wherein: The time difference is in a monotonically decreasing functional relationship with the temperature of the outer surface at the distal end of the probe.

17. The method according to claim 16, wherein: The monotonically decreasing function includes a linear function.

18. The method according to claim 10, 11 or 13, wherein: The gas pulse is delivered until the temperature measured by the sensor is equal to another preset temperature that is lower than the preset temperature.

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