Abstract:
A cryosurgical probe that is operative to bring target nerve tissue to a temperature below about −140° C. so as to reduce or eliminate regeneration of the nerve tissue by growing an ice ball. The probe comprises a thermally conductive body, a thermally insulating body and a temperature sensor. The thermally conductive body has a conductive portion adapted to contact the tissue and form an ice ball thereat during use. The thermally insulating body is adjacent to the conductive portion onto which the ice ball forms during use. The temperature sensor is positioned at a predetermined position on the thermally insulating body with respect to the conductive portion. The predetermined position corresponds to a predetermined size of the ice ball grown in the tissue when the sensor reads a predetermined temperature. The insulating body provides sufficient thermal insulation between the conductive body and the surrounding tissue so that the sensor detects freezing of. The surrounding tissue is in contact with the sensor by growth of the ice ball from the conductive portion onto the insulating body. A sleeve for fitting to a probe and a kit comprising at least two sleeves or two probes, each having one sensor but positioned at different locations is also disclosed. Furthermore, a system using a controller for shutting down a cooling of the probe and methods for performing percutaneous thermotherapy by fitting a sleeve on a probe or by shutting down the cooling of the probe are also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of systems for percutaneous thermotherapy. More particularly, the invention relates to an improved cryoprobe used in cryosurgery. 
     BACKGROUND OF THE INVENTION 
     The treatment of back pains still remains a challenge for many reasons. One of such reasons is the difficulty to permanently and exclusively cure the cause of such pains without affecting surrounding tissues in an area of a human body that is a main channel of nerve impulse. 
     Different causes of back pain exist. Of all chronic low back pain problems, about 20% can be attributed to the facet joints. This cause is also known as the chronic lumbar facet joint syndrome. Among patients, 90% are successfully treated through conservative procedures such as active physiotherapy and NSAIDS. For the remaining 10%, further investigation as well as a more aggressive therapeutic approach must be considered. Once the diagnosis of the facet joint syndrome is clinically made, percutaneous thermotherapy procedures may be considered, seeking a minimally invasive treatment with low morbidity and satisfactory clinical efficiency. 
     Discogenic back pain, another cause of back pain, is responsible for close to 60% of chronic low back pain in the general population. Once conservative treatment has been fully used, 5% of the patients remain with back pain that can be considerably invalidating. Usual treatment of this invalidating condition is spinal fusion or disc arthroplasty, both associated with considerable morbidity, off-work time, and social cost. Clinically discogenic pain patients have constant back pain that is amplified in the vertical disc loading positions, with a sitting being even worse or equal to the standing position pain. Disc pain is reproduced by pain provocation procedures such as discograms or discometry. Denervation of a portion of the disc, to relieve some if not most of the pain by a percutaneous procedure, is a known advantageous alternative with a reduction of the cited disadvantages of the more aggressive procedures. 
     Cryotherapy exists as therapy of discogenic back pain or facet joint syndrome since 1961. However, this technique originally used liquid nitrogen as coolant, reaching a treatment temperature of approximately −80 C.°., while the trocar was placed under fluoroscopic guidance. Limited control of the cryoanalgesia process with this combination of technology has resulted in only temporarily pain relief. Studies even showed that there does not exist statistical differences between patients who had such a treatment and patients treated with a placebo pr probe. On the other hand, a study showed that irreversible damage to the nervous structures is obtained only when temperatures reach below −140 C.°. Temperatures above −140 C.° only temporarily affect the nerve tissue. 
     It is therefore possible to divide thermotherapy in two types: moderate and extreme temperature thermotherapy. Moderate temperature thermotherapy only temporarily affects nerve tissues and therefore does not cause permanent damages. Consequently, pain relief is only temporary. Monitoring of such treatments is not as critical as it is with extreme temperature thermotherapy. Should the probe affect tissues that should not have been affected, the effects would only be temporary. Extreme temperature thermotherapy (either extremely high or extremely low temperatures), on the other hand, causes permanent damages to tissues. Destroying tissue with this type of treatment is desirable in order to permanently remove pain generators in a body by destroying the nerves in tissues of any nature, or to treat tumors of any kind in a minimally invasive fashion, such as percutaneously. Because of its permanent effects on the body, careful monitoring of the effects of a probe used for extreme temperature treatment is mandatory. Furthermore, cold, whose propagation is far more predictable in the human body than heat, is more often used for extreme temperature treatment. It follows that careful monitoring of a growth of an ice ball of treated tissues created by a cryoprobe is necessary, especially when treating chronic lumbar facet joint syndrome, where inadequate propagation of the ice ball could affect spinal tissues and permanently paralyze a patient. Up to now, monitoring the size of the ice ball was realized either by imagery or by temperature monitoring. Temperature monitoring is accomplished by positioning a temperature sensor that will detect a variation in a temperature of the surrounding tissues and, consequently, the presence of the ice ball. Doing so requires separately inserting in the patient&#39;s body the cryoprobe and at least one temperature sensor. Then, X-ray, or another imaging method, must be used to verify a position of the temperature sensor with respect to the cryoprobe. 
     Imagery monitoring typically uses technologies such as MRI, CT scanning, or ultrasound. However, simultaneously using such imagery systems while operating adds to the complexity of the operation. 
     Different types of cryoprobes have been suggested. For example, U.S. Pat. No. 6,551,309 describes a cryoprobe comprising, at its tip, several sensors used to monitor that the tip is cooled. However, these sensors are laid out on a thermally and electrically conductive surface and are therefore only adapted to measure the temperature of the tip of the cryoprobe but not that of the surrounding tissues. Consequently, this cryosurgery system requires the use of an MRI imaging system. 
     US patent application No. 20040024391 describes an apparatus and a method to protect certain tissues during a cryosurgery. This document describes a probe provided with a temperature sensor laid out on a portion remote from its tip. The temperature sensor is used to follow a change of the induced temperature to treated tissues. However, this document does not disclose placing the temperature sensor at a specific distance from the tip such as to monitor the growth of an ice ball and control the cooling by the probe accordingly. Consequently, the apparatus and method described in this document still requires the use of an imagery method such as X rays, ultrasounds, CT or MRI. 
     There is therefore a need for an improved system for percutaneous thermotherapy that does not require constant visual monitoring of the surgery so that such treatment may be conducted without resorting to imagery systems, which may not be available in all health facilities, and that does not require the use of an additional external temperature sensor. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a system for percutaneous thermotherapy that overcomes the above drawbacks. 
     It is another object of the present invention to provide a system for percutaneous thermotherapy that does not necessarily require special imagery systems. 
     It is another object of the present invention to provide a system for percutaneous thermotherapy that automatically stops the cooling of a conductive portion of the probe when an ice ball of treated tissues has reached a predetermined size. 
     It is another object of an aspect of the present invention to provide an insulated portion having one or more sensors that is capable of being accurately positioned on an existing probe for thermotherapy. 
     According to one aspect of the invention, there is provided a cryosurgical probe that is operative to bring target nerve tissue to a temperature below about −140° C. so as to reduce or eliminate regeneration of the nerve tissue by growing an ice ball. The probe comprises a thermally conductive body, a thermally insulating body and a temperature sensor. The thermally conductive body has a conductive portion adapted to contact the tissue and form an ice ball thereat during use. The thermally insulating body is adjacent to the conductive portion onto which the ice ball forms during use. The temperature sensor is positioned at a predetermined position on the thermally insulating body with respect to the conductive portion. The predetermined position corresponds to a predetermined size of the ice ball grown in the tissue when the sensor reads a predetermined temperature. The insulating body provides sufficient thermal insulation between the conductive body and the surrounding tissue so that the sensor detects freezing of the surrounding tissue in contact with the sensor by growth of the ice ball from the conductive portion onto the insulating body. 
     In a variation of this aspect of the invention, the conductive body is located at a distal tip of the probe opposed to a grabbing end. Such a probe may be used for treating lumbar discs pain. 
     In another variation of this aspect of the invention, the insulating body is located at the distal tip of the probe opposed to the grabbing end. Such a probe may be used for treating spinal facet joint syndrome. 
     In another aspect of the invention, there is provided a method of manufacturing a cryosurgical probe as defined here above. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue. 
     In yet another aspect of the invention, there is provided a sleeve for fitting to a cryosurgical probe having a conductive portion. The sleeve is operative to bring target nerve tissue to a temperature below about −140° C. so as to reduce or eliminate regeneration of the nerve tissue by growing an ice ball. The sleeve comprises a thermally insulating body and a temperature sensor. The temperature sensor is positioned on the thermally insulating body so that when the sleeve is installed on the cryosurgical probe, the temperature sensor is at a predetermined position with respect to the conductive portion of the cryosurgical probe. The predetermined position corresponds to a predetermined size of the ice ball grown in the tissue when the sensor reads a predetermined temperature. The insulating body provides sufficient thermal insulation between the conductive body and surrounding tissue that the sensor detects freezing of the surrounding tissue being in contact with the sensor by growth of the ice ball from the conductive portion onto the insulating body. 
     In a variation of this aspect of the invention, the sleeve has a closed ended tip and the conducting body is located at the tip. This type of sleeve may be used for treating lumbar discs pain. 
     In another variation of this aspect of the invention, the sleeve has a closed ended tip and the insulating body is located at the tip. This type of sleeve may be used for treating spinal facet joint syndrome. 
     In yet another aspect of the invention, there is provided a method of manufacturing a sleeve as defined here above. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue. 
     In a further aspect of the invention, there is provided a system for percutaneous thermotherapy for use with a cryosurgical probe having a conductive portion. The system comprises a controller and a sleeve as defined here above. The sleeve is adapted to be placed on the probe so that the sensor is at a predetermined longitudinal position from the conductive portion. The sensor is operative to send a signal to the controller. The controller is operative to control a cooling of the conductive portion based on the signal sent by the sensor. 
     In another aspect of the invention, there is provided a method of manufacturing such a system for percutaneous thermotherapy. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue. 
     In yet a further aspect of the invention, there is provided a system for percutaneous thermotherapy comprising a controller and a probe as defined here above. The sensor of the probe is operative to send a signal to the controller. The controller is operative to control a cooling of the conductive portion based on the signal sent by the sensor. 
     In another aspect of the invention, there is provided a method of manufacturing such a system for percutaneous thermotherapy. The method comprises the step of determining the predetermined position as a function of a desired ice ball size and thermal characteristics of the surrounding tissue. 
     In yet another aspect of the invention, there is provided a method for performing percutaneous cryotherapy using a cryosurgical probe. The method comprises the step of selecting an insulating body having a temperature sensor adapted to be placed at a predetermined distance from a conductive portion of the probe, based on a desired size of an ice ball of tissues surrounding the conductive portion. 
     In yet another aspect of the invention, there is provided a method for performing percutaneous cryotherapy that comprises the step of automatically shutting down by a controller an imposed thermal variation of a conductive portion of a cryoprobe inserted in a patient&#39;s body once a signal from a single temperature sensor placed on a thermally insulating portion of the cryoprobe for sensing a size of an ice ball in surrounding tissues has reached a threshold value. 
     In still another aspect of the invention, there is provided a kit comprising at least two cryosurgical probes as defined here above. Each one of the probes has its temperature sensor located at a different longitudinally distance from the conductive portion. 
     In yet another aspect of the invention, there is provided a kit comprising at least two sleeves as defined here above. Each one of the sleeves has its temperature sensor located at a different longitudinally position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the invention will become more readily apparent from the following description in which reference is made to the appended drawings wherein: 
         FIG. 1  is a cross-sectional view of a probe according to an embodiment of the invention. 
         FIG. 2  is schematic view of a system for percutaneous thermotherapy according to another embodiment of the invention. 
         FIG. 3  is a schematic view of a system for percutaneous thermotherapy according to another embodiment of the invention. 
         FIG. 4  is a cross-sectional view of a sleeve for a standard probe for use in disc surgery according to an embodiment of the invention. 
         FIG. 5  is a cross-sectional view of a spine where two probes of  FIG. 4  are placed for disc surgery. 
         FIG. 6  is a cross-sectional view of a probe for facet surgery according to another embodiment of the invention. 
         FIG. 7  is a cross-sectional view of a sleeve for a standard probe for use in facet surgery according to another embodiment of the invention. 
         FIG. 8  is a cross-sectional view of a spine where two probes of  FIG. 7  are placed for facet surgery. 
         FIG. 9  is a cross-sectional view of a probe according to another embodiment of the invention. 
         FIG. 10   a  is a perspective view of a kit of sleeves for standard probes for use in disc surgery according to an embodiment of the invention 
         FIG. 10   b  is a perspective view of a kit of sleeves for a standard probes for use in facet surgery according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention may be used for thermotherapy, either by submitting a patient to heat or to cold. Because transmission of cold in a human body is more predictable than transmission of heat, cryotherapy is more often used. Hence, the present invention will now be described with respect to a cryoprobe used for cryosurgery. 
       FIG. 1  generally represents a cryoprobe  10 . The cryoprobe  10  is fitted with a conductive portion  12 , a body  14  that comprises a grabbing portion  16  for holding by a surgeon, and an insulating portion  18 . The cryoprobe  10  is typically equipped with a Joule-Thomson cooler  20  for providing a high-pressure gas to a cooling chamber  22  inside the conductive portion  12 . When a high-pressure cooling gas such as argon expands in cooling chamber  22 , so as to form a cryogenic pool, it effectively cools the surface of conductive portion  12 . The conductive portion  12  is made of a thermally conductive material such as stainless steel. The function of the conductive portion  12  is to induce a zone of thermo-surgical temperature in surrounding tissues of a patient. In the case of cryotherapy, this zone of thermo-surgical temperature corresponds to a treated tissue zone having the shape of an ice ball of treated tissues  24 , created around the conductive portion  12 . Thermo surgical temperatures are temperatures that induce irreversible damages to treated tissues. 
     Alternatively, a high-pressure heating gas such as helium may be used for operating conductive portion  12  in a heating mode via a reverse Joule-Thomson process, so as to enable treatment by cycles of cooling-heating, and further for shortening the treatment time by thawing the ice ball of treated tissues  24  and preventing it to stick to the cryoprobe  10  when extracting the cryoprobe  10  from the patient&#39;s body. 
     The insulating portion  18  of the body  14  is made of an insulating material such as Teflon. Alternatively, the whole body  14  could be made of the insulating material. This allows for preventing surrounding tissues that need not be desensitized by cryotherapy from being affected by the cold. The insulating portion  18  is fitted with a temperature sensor  26 . The temperature sensor  26  senses the temperature of surrounding tissues and in use, the temperature of the ice ball of treated tissues  24 . 
     Turning now to  FIG. 2 , a gas distribution module  28  controls the flow of pressurized gas, such as argon, into the cryoprobe  10  thorough delivery tube  30 . The gas, upon expanding into the cooling chamber  22 , cools the conductive portion  12 . The gas then returns to the gas distribution module  28  through return tube  32 . As the conductive portion  12  gets cooled, the tissues surrounding the conductive portion become frozen and the ice ball of treated tissues  24  starts forming around the conductive portion  12 . As the process continues, the ice ball grows in size. The temperature sensor  26  records a decrease in body temperature and sends a signal  34  to a controller  36 . The controller  36  compares the temperature signal  34  sent by the temperature sensor  26  with a threshold temperature. Although it may be otherwise, the water freezing temperature (0° C.) is often used as the threshold temperature. Hence, the temperature sensor  26  is used to monitor the progression of a forming front of the ice ball of treated tissues  24 . In order to correlate the temperature at the temperature sensor  26  with a size of the ice ball of treated tissues  24 , the temperature sensor  26  is placed at a predetermined position with respect to the conductive portion  12 . It is possible to correlate different temperatures than 0° C. with the size of ice ball of treated tissues  24  by modeling the response of the tissues to temperature changes as a function of time. However, it has been found that monitoring the forming front of the ice ball of treated tissues  24  is more convenient and gives a direct indication of the ice ball size. As the ice ball of treated tissues  24  continues to grow in size, the temperature further decreases at temperature sensor  26  until the signal  34  sent to the controller  36  reaches the threshold temperature. At that point, the controller  36  automatically shuts down the gas distribution module  28 , thereby stopping the growth of the ice ball of treated tissues  24 . Alternatively, the controller  36  may be set-up such that it shuts down the gas distribution module  28  only after a predetermined amount of time has elapsed after the temperature sensor  26  has read the threshold temperature or only when the temperature sensor  26  has read a predetermined shut down temperature that is different from the threshold temperature. It will be understood that when the controller  36  shuts down the gas distribution module  28  when the temperature sensor  26  reads the threshold temperature, it is because the shut don temperature is set up to be the same as the threshold temperature. Typically, the temperature sensor  26  is located on the insulating portion  18  approximately 10 mm from the conductive portion. A user may adjust the controller such as to vary the size of the ice ball of treated tissues  24 . Another way of adjusting the size of the ice ball of treated tissues  24  is to locate the temperature sensor  26  at different longitudinal positions from the conductive portion  12 . This may be either accomplished by having different models of cryoprobe  10  where the temperature sensor  26  is located at different distances from the conductive portion  12 , or by providing the cryoprobe with many temperature sensors  26  that are located at different longitudinal positions along the insulated portion  24  of the cryoprobe  10 . Then, the controller decides which temperature sensor  26  to monitor. This information may also be provided manually to the controller  36  by a user. 
     For better reliability, it is possible to equip the insulating portion  18  with more than one temperature sensor  26  at the same distance from the conductive portion  12 . The controller  36  then processes the information gathered by the temperature sensors  26  and takes a decision to shut down or to continue cooling accordingly. 
     The details of the structure of the cooling system used in the probe are well known in the art and as such will not be described in further details in the present description. 
       FIG. 3  schematically shows the detail of the controller  36 , which may be a computer. The controller  36  comprises a thermal model storage medium  38 , a size determinator  40 , a comparator  42  and a thermal application module  46 . The thermal model storage medium  38  stores all thermal models. The thermal models are mathematical models of heat transfer in a body based on parameters such as the type of surgery, type of tissue, type of gas used for cooling, probe model, etc. For instance, tissue types vary whether they are intradiscal or interdiscal tissues, flesh surrounding prostate gland, etc. The thermal model includes the size of the ice ball of treated tissues  24 . The thermal model storage medium  38  feeds a desired size signal  48  to the comparator  42 . From a user interface  50 , the surgeon may select a thermal model desired  52 . Optionally, the surgeon may bypass the thermal model storage medium  38  and impose the size of the ice ball of treated tissues  24  with the desired size signal  48  of his own. Optionally, the surgeon may bypass all parameters. The surgeon sends a start command  54 , through the user interface  50 , to the comparator  42 . The size determinator  40  determines the actual size of the ice ball of treated tissues  24  based on the signal  34  received from the temperature sensor or sensors  26 . The comparator  42  compares an actual size signal  56  received from the size determinator  40  with desired size signal  48  received from the thermal model  52 . Whenever the actual size signal  56  indicates a smaller size than the desired size signal  48 , the comparator  42  sends an “ON” signal  58  to the thermal application module  46 . In turns, the thermal application module  46  sends a thermal application command signal  60  to the gas distribution module  28  to send cooling gas to the probe  10 . Preferably, the size determinator  40  is hooked to a display  62  to show the surgeon the actual size of the ice ball of treated tissues  24 . 
       FIG. 4  shows another embodiment of the invention. In this case, a sleeve  64  having an insulating portion  18  is fitted over a standard cryoprobe  66  which has its body  14  ended by the conductive portion  12 . In the present description, the term “sleeve” is used to describe a device that covers a probe and that may be either open at both its extremities, or closed at one extremity. In the present embodiment, the sleeve  64  is open at both extremities. The sleeve  64  is specially designed to fit over a given model of standard cryoprobe  66 . The sleeve  64  is equipped with the temperature sensor  26 . The sleeve  64  is positioned over the body  14  such that the conductive portion  12  extends from the sleeve  64 . Similarly to the previous embodiment, in use, the ice ball of treated tissues  24  forms at the conductive portion  12  and grows until it reaches the temperature sensor  26 , which continuously sends a signal to the controller  36  (not shown in the Figure). The position of the temperature sensor  26  on the sleeve  64  is adjusted so that the longitudinal position of the temperature sensor  26  with respect to the conductive portion  12  corresponds to the desired size of ice ball of treated tissues  24 . The position of the temperature sensor  26  with respect to the conductive portion  12  may be set by way of locating means  68 . Here, the locating means  68  are depicted as a stopper against which the standard cryoprobe  66  abuts. However, the locating means could be a mark on the standard cryoprobe  66  or simply an edge of the sleeve  64  used to locate the sleeve  64 , and therefore the temperature sensor  26 , with respect to the conductive portion  12 . Optionally, the sleeve  64  may comprise an air chamber  70 , which also thermally insulates the temperature sensor  26  from the standard cryoprobe  66 . For example, the standard cryoprobe  66  may be 4 mm in diameter, the air chamber  70  may be 1 mm thick and the sleeve  64  may be 2 mm thick, including the air chamber  70 . Preferably, Teflon is used as the insulating material of the sleeve  64 . As shown in  FIG. 5 , now concurrently referred to, this type of cryoprobe is particularly well adapted for cryosurgery of discs of a spine. 
       FIG. 6  shows yet another embodiment of the present invention. This design of cryoprobe  10  is adapted for the cryotherapy of facets, as shown in  FIG. 7  and now concurrently referred to. In this embodiment, the conductive portion  12  is not located at a tip  72  of the cryoprobe  10 , but rather at a mid-portion of the cryoprobe  10 . The tip  72  is made of the insulating material so as to become the insulating portion  18 . As can be seen, in the case of facet cryotherapy, the insulating portion  18  is placed at the tip  72  to prevent nerve roots in this spine area from being damaged by the cold. The temperature sensor  26  may be placed on either the insulated tip  72  or the body  14  as long as it is on a thermally insulated portion of the cryoprobe  10  and as long as it is at the predetermined distance from the conductive portion  12  such as to detect a condition of the surrounding tissues. However, it might be advantageous to place the temperature sensor  26  on the insulated tip  72  such as to monitor the ice ball growth closer to the freeze sensitive region where major nerve roots are located. The insulating portion  18  may also be used to position the cryoprobe  10 . When the insulating portion  18  abuts a bone or a disc, for example, the conductive portion  12  is in contact with surrounding tissues, such as sensitive nerve cells, where cellular destruction is desired. Positioning the temperature sensor  26  at the insulated tip  72  of the insulating portion  18  enables constant thermal monitoring of the surrounding tissues. Once the temperature sensor  26  detects the front of the ice ball of treated tissues  24 , that is when the temperature sensor  26  reads temperatures close to the freezing point, cryotherapy may be automatically stopped if the threshold temperature corresponds with the shut down temperature. 
       FIG. 7  depicts a variant of the present embodiment where a sleeve  64 , closed at its distal extremity, is fitted to a standard cryoprobe  66 . The sleeve  64  comprises the insulated tip  72 , the conductive portion  12  and the grabbing portion  16 . Optionally, the grabbing portion  16  may be made of metal. However, in this case, gap is required between the standard cryoprobe  66  and the sleeve  64  in the grabbing portion  16 . As shown in  FIG. 8 , now concurrently referred to, this type of cryoprobe is particularly well adapted for cryosurgery of facets joints. 
     In a particular example, the insulated tip  72  may be 6 mm in diameter and made of an insulating material such as Teflon. An interior air chamber  70  may be provided for added insulation. The temperature sensor  26  is positioned on the insulated tip  72 , approximately 6 mm or more from the distal end of the insulated tip  72 . The conductive portion  12  is made of a conductive metal and is in contact with the standard cryoprobe  66  inside the sleeve  64 . The conductive portion  12  is also 6 mm in outside diameter. The length of the conductive portion  12  depends on the size of the desired treated tissue zone. The standard cryoprobe  66  may be 2 mm in diameter, and the insulated tip  72  may be 1 mm thick, which leaves 1 mm thickness for the air chamber  70 . 
       FIG. 9  shows yet another embodiment of the present invention. A thermally conductive tip cover  76  is screwed to the insulating portion  18 . The tip cover  76  closely matches the external surface of a probe tip  78  such that heat transfer occurs between the probe tip  78  and the tip cover  76 . The temperature sensor  26  is precisely positioned with respect to the probe tip  78  due to the fact that the probe tip  78  bottoms out in the tip cover  76 . 
     Now turning to  FIGS. 10   a  and  10   b , there is depicted yet another embodiment of the present invention where kits  80  are provided that comprise a plurality of sleeves  64  for fitting to a standard cryoprobe. In  FIG. 10   a , the kit comprises sleeves  64  having the insulating portions  24 . The sleeves  64  are provided with two opposed openings so that the standard cryoprobe protrudes through each sleeve  64 , such as described previously and shown in  FIG. 4 . The only difference between each sleeve  64  of the kit is that the temperature sensor  26  is placed at different longitudinal locations on the insulating portion  18 . Hence, a surgeon may select, prior to cryotherapy, the required sleeve  64  depending on the particular needs of the surgery, or depending on the patient. Similarly, in  FIG. 10   b , the kit  80  also comprises sleeves  64 . This time, the sleeves  64  are of a close-ended model where the insulating portion  18  corresponds to the insulating tip  72 . The sleeves  64  are adapted to fit a standard cryoprobe  66  (not shown in this Figure), such as described previously and shown in  FIG. 7 . The insulated tips  74  are differentiated from each other by the fact that the temperature sensors  26  are placed at different longitudinal locations from the conductive portion  12 , for the particular needs of a given cryosurgery. For convenience, the kit  80 , or the sleeves  64  themselves may carry an identification of an ice ball size for each sleeve  64 . The ice ball size may be a function of a predetermined body part tissue as the ice ball may grow differently depending on the body part tissue. 
     Surgery 
     When operating, the surgeon has to precisely monitor both the placement of the cryoprobe  10  into the patient&#39;s body and the growth of the ice ball of treated tissues  24  such as to avoid damaging fragile tissues. With the cryoprobes of prior art, MRI was often used as an imaging system. Advantageously, with the present invention, such costly techniques are not absolutely required since the controller  36  automatically shuts down the gas distribution module  28 , thereby not requiring continuous visual monitoring of the growth of the ice ball of treated tissues  24  by the surgeon. With the thermotherapy system of the present invention, less costly and more readily available imaging techniques such as fluoroscopy, diagnostic ultrasound, etc, can be used. Moreover, when using techniques other than MRI, the composition of the cryoprobe  10  is not restricted to non-ferromagnetic materials, which lowers its cost. 
     Facet Cryosurgery 
     Reference is now made to  FIG. 8 . For facet cryosurgery, the cryoprobe  10  is inserted under local anaesthesia using a preliminary trocar through a 6 mm incision. For facet cryotherapy, the cryoprobe  10  is positioned on a posterior-inferior portion of foramina close to the nerve root for protection and the conductive portion  12  is placed alongside a lateral facet joint for joint denervation. Position is verified on both antero-posterior and lateral fluoroscopy. 
     The freezing process is then started: A first step of freezing takes place at −180° C. (temperatures colder than −140° C. are preferred) while monitoring the growth of the ice ball of treated tissues  24  with the temperature sensors  26 . The controller  36  shuts down the gas distribution module  28  when the first temperature threshold is reached, which normally takes approximately 7 minutes. The controller  36  maintains the gas distribution module  28  shut down for 2 minutes for passive thawing to occur. The controller  36  then turns on the gas distribution module  28  once again for a second step of freezing at −180° C. until a second temperature threshold is reached, which takes approximately another 7 minutes. The first and second threshold temperatures may be the same or different, depending on the desired results. To remove the cryoprobes  10 , heating the cryoprobes  10  for a few seconds is sometimes required. Stitches are then applied to the patient. The patient is encouraged to resume his normal activities rapidly and weak to moderate analgesia is necessary for the first week. Cryoprobe tract pain normally disappears after one to two weeks. 
     Discs Cryosurgery 
     Reference is now made to  FIG. 5 . For discs cryosurgery, 6 mm pointed trocars are inserted through a 6 mm skin puncture. The trocar is inserted bilaterally to postero-lateral corners of the targeted disc  82  at a 45 degrees angle from the skin at 10 cm from a midline under local anaesthesia with AP and lateral fluoroscopy. Through this trocar is inserted a 2 mm drill to perforate the annulus. The drill is then replaced by the cryoprobe  10  which conductive portion  12  penetrates 1-1.5 cm deep into the disc  82 . The insertion into the disc  82  is bottomed by a conic end of the insulating portion  18 . Typically, two cryoprobes  10  are used for disc cryosurgery, one on each side of the disc  82 . Both cryoprobes  10  should nearly meet in the middle of the disc  82 . The freezing process, similar to the one used for facets cryosurgery, is then started while monitoring treated tissues temperatures with the temperature sensors  26  is performed. To remove the cryoprobes  10  and the trocar, heating the cryoprobes  10  for a few seconds is sometimes required. A stitch is then applied to the skin once the cryoprobes  10  are removed and normal activities may be resumed shortly. Mild to moderate analgesia is prescribed for the first week. 
     While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art. For example, the assembly of some parts of the probe were depicted as a threaded assembly. However, the person skilled in the art would readily understand that this assembly could also be a snap-fit or other adequate assembly method, for example. Accordingly, the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.