Abstract:
The invention is directed to a cryosurgical instrument and to an accessory system operating on the base of refrigerant evaporation, wherein the portions of the refrigerant are periodically provided to the distal cryotip of the cryosurgical instrument via a central lumen thereof. The internal surface of the distal cryotip is preferably covered by a porous coating capable of soaking at least one portion of the refrigerant. The vapors obtained as a result of the refrigerant boiling on the porous coating of the cryotip are preferably removed through the central lumen of the cryosurgical instrument into the atmosphere. These features may be combined to construct a cryosurgical instrument with relatively high freezing power and small outer diameter which may be designed as a flexible cryocatheter or alternatively as a rigid cryoprobe.

Description:
CROSS REFERENCE APPLICATION 
     This patent application claims the benefit of the earlier filed Israeli Patent Application Ser. No. 151486 Filed Aug. 26, 2002. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     There is a significant number of patents which describe different constructions of cryosurgical probes and catheters. These patents aims to solve some of the problems, which are common to the cryosurgical probes and catheters of the prior art. 
     One of these problems is the construction of relatively cheap and simple probes or catheters with high reliability and sufficiently effective thermal insulation of their lateral non-operating walls. Moreover, cryosurgical catheters should have high flexibility, especially, when they are used for cardiac procedures. In addition, the closed distal end (cryotip) of such probe or catheter must provide in many cases high specific freezing capacity at sufficiently low-temperatures. 
     Analysis of United States patents related to this field shows, that the structure of the proposed probes and catheters intended for cryosurgery does not satisfy the above-mentioned requirements. 
     For example, U.S. Pat. No. 3,971,383 proposes a cryogenic surgical instrument with a coaxial assembly of flexible tubes, wherein the inner tube is connected to a supply of cryogenic liquid, and the space between the outer wall of the inner tube and the inner wall of an intermediate tube forms a return line for evaporated cryogenic liquid, which is vented to the atmosphere. The space between the outermost coaxial tube and the intermediate tube contains a gas, such as normal butane, for providing thermal insulation of the inner and intermediate lumens. 
     U.S. Pat. No. 5,716,353 describes a probe for cryosurgery which consists of three tubes: an inner tube for supplying a cryogenic refrigerant to a cryotip positioned at the distal end of an outer jacket tube, and an intermediate tube situated concentrically around the inner tube. The channel between the inner and intermediate tubes serves as venting path for venting cryogenic refrigerant from the freezing zone. This construction is simple, but it does not provide sufficient thermal insulation as required in the construction of cryogenic catheters. Consequently, it may cause over-heating of the vented cryogenic refrigerant, as well as over-cooling of tissues adjacent to the intermediate section of the catheter. 
     U.S. Pat. No. 5,573,532 describes a cryosurgical instrument which comprises tubes for cryogenic fluid supply and for the return of cryogenic fluid vapors, wherein these tubes are concentric and the return tube is sealed with a cryotip. Vacuum insulation of the return lumen is also proposed. However, this construction is relatively expensive and has low reliability. In addiiton, the proposed vacuum insulation limits the flexibility of the probe, especially, when it is very long, as in the case of catheter implementations. 
     U.S. Pat. No. 5,674,218 describes a cryosurgical instrument, a system and method of cryosurgery. According to this patent a cryogenic liquid (preferably, liquid nitrogen) is initially sub-cooled below its normal boiling point and in that state supplied into the open proximal end of the internal supply line. The outer lumen of the cryosurgical instrument is provided with active vacuum insulation. 
     Obviously, this construction cannot provide high flexibility and therefore cannot be used as the basis for construction of a catheter for use in cryosurgery. 
     U.S. Pat. No. 5,254,116 describes a cryocatheter with a set of vent holes in the lateral wall of a central feeding lumen, wherein sub-cooled liquid nitrogen is delivered into the central feeding lumen as a cryogenic liquid. This construction, however does not ensure proper thermal insulation of the cryocatheter. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention proposes novel designs for a cryosurgical instrument and for its accessory system. The cryosurgical instrument of the present invention is constructed from two major sub-units: 
     i) a distal cryotip, which is used to contact the target tissue to be treated, wherein the freezing of the cryotip is obtained by evaporation of a cryogenic liquid on its internal surface, said internal surface being covered with a porous coating having open porosity; and
 
ii) an elongated tubular sub-unit for delivering portions of the cryogenic liquid to the distal cryotip and for removing vapors generated in the process of the boiling of the cryogenic liquid in the porous coating of the distal cryotip.
 
     The elongated tubular sub-unit comprises an external shaft comprising a central feeding-venting tube, the lumen of which is used to supply portions of the cryogenic liquid to the porous coating of the distal cryotip and, at the same time, to remove the vapors generated in the process of boiling the cryogenic liquid on the internal surface of the distal cryotip into the atmosphere or into a vacuum pump. 
     In addition, a coaxial tubular piece is positioned in the space between the distal sections of the central feeding-venting lumen and the external shaft, the distal end of said tubular piece being sealed by the external shaft or by the cryotip itself, and its proximal end being sealed by the central feeding-venting tube. Said coaxial tubular piece forms a buffer space between the internal surface of the cryotip&#39;s shaft and the outer surface of the central feeding-venting tube, such that said buffer space facilitates flow of the portion the cryogenic liquid in the central feeding-venting tube toward the cryotip. 
     The proximal section of the external shaft and the proximal end of the central feeding-venting tube are provided with inlet-outlet connections. 
     According to another embodiment of the invention a coaxial intermediate lumen situated between the central feeding-venting lumen and the external shaft replaces the aforementioned coaxial tubular piece, wherein the distal end of this coaxial intermediate lumen is sealed by the external shaft or by the cryotip itself and its proximal end is sealed by the central feeding-venting tube. The proximal end of the external shaft is sealed by the wall of the proximal section of the coaxial intermediate lumen. The proximal section of the coaxial intermediate lumen is provided in this case with an outlet connection. 
     When this proposed device is used as a cryocatheter, the external shaft is made from a polymer material that provides high flexibility. 
     The cryotip of the cryocatheter is made from material with high thermal conductivity (for example, copper, silver, diamond, BeO), and its internal surface is advantageously covered with a porous coating having open porosity (for example, the porous coating that is obtained by sintering copper powder). These features permit high heat transfer coefficients values in the process of boiling the cryogenic liquid. Additionally, the porous coating is adapted to soak completely one portion of the cryogenic liquid provided by an accessory system during the first quarter-period (the first operating state in one operating cycle) of its operation, as will be described hereinafter. 
     The cryocatheter of the invention can be used for inhibiting restenosis of a blood vessel. In this case the cryotip is constructed in a tubular shape, the distal end of the tubular shaped cryotip is sealed with a plug made from a polymer with low thermal conductivity, and its tubular section is fabricated from a thin polymer film of high elasticity. The internal surface of the tubular section is coated with a porous polymer layer having open porosity and high elasticity. 
     The construction of preferable accessory systems for the cryocatheter (or cryoprobe) of the invention will be now described in detail. 
     A first embodiment of the accessory system, which achieves the functioning required for the proposed cryosurgical instrument, comprises: a thermo-insulated tank filled with the cryogenic liquid, wherein the thermo-insulated tank is provided with a relief valve which enables to preset the desired pressure in the thermo-insulated tank; a feed pipe which is situated vertically such that its lower end is positioned in the thermo-insulated tank and near its bottom. An outlet connection of the feed pipe is joined by a flexible thermo-insulated duct with an inlet connection of a multi-way valve. This multi-way valve comprises one additional inlet connection which communicates with a bottle containing pressurized gas (for example, nitrogen), and two outlets communicating with the atmosphere (or a vacuum pump) and with an inlet-outlet connection that communicates with an inlet-outlet connection of the central feeding-venting tube of the cryosurgical instrument. 
     The accessory system comprises four shut-off valves, the first of which is installed on a main duct that communicates between the multi-way valve and the inlet-outlet connection of the central feeding-venting tube of the cryosurgical instrument, the second—on a duct that communicates between the outlet connection of the thermo-insulated tank and the multi-way valve, the third—on the duct that communicates between the bottle comprising the pressurized gas and the multi-way valve, and the fourth—on the thermo-insulated tank; where this fourth shut-off valve is used for filling the thermo-insulted tank with the cryogenic liquid. The fourth shut-off valve is normally opened while filling the thermo-insulated tank with the cryogenic liquid. The second shut-off valve is used for cutting off the supply of the cryogenic liquid to the multi-way valve. The third shut-off valve is used for cutting off the supply of pressurized gas to the multi-way valve and the first shut-off valve for operating the cryosurgical instrument. 
     An electromechanical (or pneumatic) drive is used to perform a periodical changeover of the multi-way valve state at a preset changeover frequency for periodically communicating between the inlet-outlet connection of the central feeding-venting tube and the thermo-insulated tank, the bottle comprising the pressurized gas, and the atmosphere (or the vacuum pump). 
     A control unit used for controlling the changeover frequency of the multi-way valve, or for halting its operation in case of significant deviations from the preset frequency. The control unit also activates the aforementioned second and third shut-off valves. In addition, it is also possible to install pressure and temperature gauges on the main duct of the central feeding-venting tube of the accessory system. Data obtained from these gauges is processed by the control unit and in cases of significant deviations of the measured parameters from the preset values, the control unit cuts off the shut-off valves. 
     Portions of the cryogenic liquid, which remain in the porous coating of the cryotip and in the aforementioned buffer space in the period between communicating between the central feeding-venting tube and the inlet connection of the vacuum pump (or with the atmosphere) and with the feeding pipe of the thermo-insulated tank, generate reasonably high pressure in the central feeding-venting tube which may cause difficulties in introducing another portion of the cryogenic liquid into the central feeding-venting tube. 
     In the aforementioned embodiment, which utilizes a coaxial intermediate lumen with an outlet connection instead of the coaxial tubular piece, there is an auxiliary shut-off valve installed on a duct communicating between the outlet connection of the coaxial intermediate lumen and the atmosphere (or with the vacuum pump), wherein this shut-off valve is mechanically or electro-mechanically coupled to the multi-way valve such that it is opened only at a quarter-period, when the multi-way valve is communicating between the main duct and the bottle comprising the pressurized gas. 
     In addition, the outlet connection of the intermediate lumen can serve as an inlet-outlet connection. In this case, a gas contained in a special bottle is provided into the gap between the coaxial intermediate lumen and the central feeding-venting tube whenever the multi-way valve communicates between the central feeding-venting lumen and the atmosphere (or the vacuum pump). 
     The ducts connecting between the thermo-insulated tank and the multi-way valve, and between the multi-way valve and the inlet-outlet connection of the central feeding-venting tube can be provided with an outer thermal insulation, for example, vacuum insulation. 
     There are various cryogens that can be used as cryogenic liquids, such as liquid nitrogen, liquid argon, liquid R14 and others. 
     In addition, it is possible to utilize two tanks with different cryogenic liquids. For example, the first tank may comprise a cryogenic liquid having low boiling temperature (for example, liquid nitrogen), which is used for cryogenic treatment of a target tissue, and the second tank may comprise a cryogenic liquid having a relatively high boiling temperature (for example, R12B1 that boils at a temperature −3.8° C. at atmospheric pressure), where this second liquid is used for ice-mapping. 
     The second liquid having a normal boiling temperature higher than 0° C. (for example, R11, which has normal boiling temperature 23.65° C.) can be used for fast thawing a tissue, which has been previously frozen by the cryogenic liquid. 
     Application of two liquids with a large difference in their boiling temperatures requires performance of blowing out the central feeding-venting tube, the buffer space, and several ducts, in the period between the procedures of ice-mapping and cryogenic treatment which may follow it. 
     The accessory system comprises in this case two accessory sub-systems, each of which is constructed substantially similar to the accessory system which has been described hereinabove. The accessory sub-systems have a common control unit and a common main duct which splits off into two ducts each communicating with a first and a second multi-way valves. A thermo-insulated tank of the first accessory sub-system contains a cryogenic liquid that is used for freezing the target tissue, and the thermo-insulated tank of the second accessory subunit contains a liquid with relatively high boiling temperature (for example, R12B1) which is used for preliminary ice-mapping. 
     The accessory system also comprises an auxiliary accessory sub-system, which is used for blowing out the cryosurgical instrument and the ducts communicating the first and second accessory sub-systems with the cryosurgical instrument. The auxiliary accessory sub-system consists of an auxiliary bottle with pressurized gas and an auxiliary three-way valve, which is installed on a duct communicating the auxiliary bottle with the main duct. The auxiliary three-way valve is regulated by the common control unit, and it has two outlet connections; the first of which communicates with the main duct and the second with the atmosphere or with a vacuum pump. 
     The blowing out process is performed by closing the shut-off valves that are installed on the ducts communicating between the thermo-insulated tanks and their respective multi-way valves followed by blowing the pressurized gas from the auxiliary bottle into the main duct and the ducts splitting therefrom, and into the central feeding-venting tube and the buffer space by a charging and purging technique. 
     As was previously discussed hereinabove, the gap between the central feeding-venting tube (or the coaxial tubular piece) and the external shaft that is used for thermally insulating the external shaft, especially, its distal section, in order to prevent the possibility of a negative temperature on its outer surface. 
     It is of course possible to achieve a higher degree of thermal insulation of the external shaft of the cryosurgical instrument by first of all filling the gap between the external shaft and the coaxial tubular piece with a gas which has, on the one hand, very low thermal conductivity and, on the other hand, a condensation temperature that is lower than the boiling temperature of the cryogenic liquid. For this purpose, the proximal section of the external shaft is provided with an inlet-outlet connection and the accessory system is provided with an additional bottle comprising the aforementioned gas having low thermal conductivity, and with a duct that communicates between the additional bottle and the inlet-outlet connection of the external shaft, wherein said duct is provided with a three-way valve which communicates with the atmosphere or with a vacuum pump. This sub-system allows filling of the gap between the external shaft and the coaxial tubular piece by means of a charging and purging technique. 
     In order to achieve better thermal insulation properties of the distal section of the external shaft (i.e. to prevent its outer surface having a negative temperature) it is possible to apply the heat pipe principle. 
     In this case, the heat pipe principle is realized in the following manner: the outer surfaces of the coaxial tubular piece and a section of the central feeding-venting tube matching this coaxial tubular piece are covered with a porous coating with open porosity, the purpose of this coating being to function as a wick. The gap between the external shaft and the coaxial tubular piece, and its extension to the gap between the central feeding-venting tube and the external shaft is filled with a gas having a condensation temperature that is somewhat higher than the boiling temperature of the cryogenic liquid, wherein the solidification temperature of this gas is somewhat lower than the boiling temperature of the cryogenic liquid. This gas can be introduced into these gaps via the inlet-outlet connection installed on the proximal section of the external shaft. 
     A charging and purging technique can be used to realize the heat pipe principle described hereinabove. This technical solution allows heating the distal section of the external shaft at the expense of the heat provided to the intermediate and proximal sections of the external shaft from the surroundings. 
     It should be noted that the multi-way valve of the accessory system may be replaced by a set of shut-off valves installed on the communicating ducts, wherein the coordinated operation of this set of shut-off valves simulates the operation of the aforementioned multi-way valve. 
     The cryosurgical instrument of the present invention can be provided with a thermocouple positioned in the cryotip for measuring the temperature in the cryotip during of its use in a cryosurgical procedure. 
     In addition, if the cryosurgical instrument of the present invention is used in a cryocatheter implementation, this cryocatheter should be provided with a steering mechanism permitting bending of its distal section. 
     Furthermore, when the cryotip of the present invention is used in a cryocatheter (or cryoprobe) implementation, it may also be provided with an electrode for preliminary detection of electrical signal activity of different sites of the organ to be operated upon. 
     The cyclical operation of the cryosurgical instrument of the invention and its accessory system will be now described in detail. 
     In the first quarter time period, a portion of the cryogenic liquid is introduced via the feed pipe of the thermo-insulated tank into the duct (hereinafter also referred to as main duct) communicating between the multi-way valve and the inlet-outlet connection installed on the proximal end of the central feeding-venting tube. During this first quarter time period the state of the multi-way valve is in a position allowing flow of the cryogenic liquid from the feed pipe into the main duct 
     Thereafter, in the second quarter time period, the state of the multi-way valve is changed in order to cease the flow of the cryogenic liquid from the thermo-insulated tank into the main duct and during the next quarter time period the multi-way valve is set into a position in which it communicates between the bottle comprising the pressurized gas and the main duct, thereby accelerating the velocity of the portion of the cryogenic liquid passing through the main duct and the central feeding-venting tube such that it rapidly reaches the porous coating of the cryotip. 
     In the third quarter time period, the supply of the pressurized gas is shut off by setting the state of the multi-way valve into a state which cuts off the connection between the proximal end of the main duct and the feed pipe. During this time period the cryogenic liquid is boiling in the porous coating of the cryotip which in effect causes elevation of the pressure of the cryogenic liquid vapor in the central feeding-venting tube and in the main duct. 
     In the fourth quarter time period, the multi-way valve is placed into a state that communicates between the main duct and the outlet communicating with the atmosphere or with the vacuum pump. The boiling of the cryogenic liquid in the porous coating of the cryotip may continue during this time period. The aforementioned quarter time periods may of course have different durations. 
     The cryosurgical instrument of the invention may be designed as a cryocatheter intended to treat a blood vessel in order to prevent restenosis. In such cases it may be advantageous to have the cryotip constructed from an elastic polymer. It is therefore important to keep relatively low excessive pressure in the internal chamber of the distal section of this cryocatheter with small deviation from its average value. These conditions are advantageously obtained by the cryocatheter of the invention that is constructed with the coaxial intermediate lumen as was previously described hereinabove. The outlet connection of the coaxial intermediate lumen is provided with a T-shaped manifold, which comprises a crossbar and a main section intersecting perpendicularly with the crossbar. A pressure gauge is installed on one end of the crossbar and an adjusting valve is installed on its other end, wherein this adjusting valve is communicated with the atmosphere or with the vacuum pump. Signals from the pressure gauge are sent to a pressure control unit, which provides corresponding control signals for the operation of the adjusting valve. It should be noted that the pressure control unit may be interconnected with the aforementioned control unit, and by doing so the operations of these control units can be correlated. 
     It is an object of the present invention to provide a flexible catheter with high flexibility, high specific freezing power and a sufficiently small diameter for cryosurgical procedures in different areas of medicine. 
     It is another object of the present invention to provide a rigid probe with high specific freezing power and a sufficiently small diameter for cryosurgical procedures in different areas of medicine. 
     It is an additional object of the invention to provide a cryosurgical instrument and a suitable accessory system having a high degree of safety and reliability, which are suitable for carrying out cryosurgical procedures. It is a further object of the present invention to provide a cryosurgical instrument capable of ensuring positive temperatures at the distal section of its external shaft, especially, in the vicinity of the cryotip. 
     It is yet another object of the present invention to provide a method for thermal insulation of the distal section of the external shaft a cryosurgical instrument that is based on a heat pipe principle. 
     It is still another object of the present invention to provide a cryocatheter that may be used for inhibiting restenosis of a blood vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Other objectives of this invention will be apparent from the following detail description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a general view of a cryosurgical instrument and a block diagram of a respective accessory system according to one preferred embodiment of the invention. 
         FIG. 2  shows a general view of a cryosurgical instrument and a block diagram of a respective accessory system according to another preferred embodiment of the invention. 
         FIG. 3  shows a general view of a cryosurgical instrument and a block diagram of a respective accessory system according to a further preferred embodiment of the invention in which different liquids are used for preliminary ice-mapping and for carrying out a cryogenic treatment. 
         FIG. 4  shows an axial cross-section view of the cryosurgical instrument of the invention that is implemented with an active thermal insulation based on the heat pipe principle. 
         FIG. 5  shows an axial cross-section view of a cryosurgical instrument of the invention comprising a coaxial tubular piece joined at its distal end with the external shaft of the instrument. 
         FIG. 6  shows an axial cross-section view of a cryosurgical instrument of the invention implemented with a coaxial intermediate lumen instead of the coaxial tubular piece. 
         FIG. 7  shows an axial cross-section view of a cryocatheter of the invention that is suitable for preventing restenosis of blood vessels. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a general view of one preferred embodiment of the invention wherein the cryosurgical instrument comprises: a cryosurgical instrument  100  comprising cryotip  116  and an elongated tubular sub-unit  105 ; and wherein the accessory system comprises: a thermo-insulated tank (or a Dewar flask)  101  for supplying a cryogenic liquid contained therein, said thermo-insulated tank  101  is provided with a relief valve  103  that allows presetting a desired pressure in the thermo-insulated tank, a shut-off valve  102  is used for filling the thermo-insulated tank  101  with the cryogenic liquid, and manometer  104 . 
     The multi-way valve  107  communicates between: a feeding pipe  106  situated in the thermo-insulated tank  101 ; a vacuum pump (or the atmosphere) via duct  121 ; the cryosurgical instrument  100  via a main duct  112 : a first bottle  108  comprising pressurized gas. Sensor  111  is used for controling the preset changeover frequency of the multi-way valve  107 . In addition, there are pressure and temperature gauges  114  and  120  installed on the main duct  112 . Data obtained from these sensor and gauges is processed by a control unit  115 . Whenever a significant deviations of the measured parameters (pressure and/or temperature) from the preset values, the control unit  115  cuts off the shut-off valves  109 ,  110  and  113 . 
     The accessory system further comprises a second bottle  117  for providing a gas having a low thermal conductivity contained therein, for example R14. The second bottle  117  is communicated via duct  119  with the external chamber of the cryosurgical instrument  100  (the gaps shown in  FIGS. 4 and 5  between the internal surface of the external shaft of the cryosurgical instrument  100 , and the outer surface of the coaxial tubular piece and of the proximal section of the central feeding-venting tube). A three-way valve  118  installed on duct  119  and used for filling the external chamber by a charging and purging technique that is typically performed before operating the cryosurgical instrument  100  and carrying out any cryogenic treatment. 
       FIG. 2  shows another preferred embodiment of the invention of a cryosurgical instrument  200  and its respective accessory system wherein there is an oscillating flow in the channel between the central feeding-venting lumen and the coaxial intermediate lumen of the cryosurgical instrument. Cryosurgical instrument  200  comprises two major sub-units: 1) cryotip  217 ; and 2) an elongated tubular sub-unit  218 . 
     In this preferred embodiment the accessory system comprises a thermo-insulated tank (or a Dewar flask)  201  for supplying a cryogenic liquid contained therein. The thermo-insulated tank  201  is provided with a relief valve  203  which is used to preset a desired pressure in the thermo-insulated tank  201 , with valve  202  which is used for filling the thermo-insulated tank  201  with the cryogenic liquid, and with manometer  204 . 
     A multi-way valve  208  comprised in the accessory system communicates between: a feeding pipe  205  situated in the thermo-insulated tank  201 ; a vacuum pump or the atmosphere; the cryosurgical instrument  200  (via main duct  215 ); a first bottle  210  which supplies a pressurized gas contained therein.; the accessory system further comprise a three-way valve  211 , which is coupled mechanically via coupling  212  to the multi-way valve  208 . The three-way valve  211  is used to communicate the coaxial intermediate lumen (exemplified in FIGS.  4 – 7 )—via duct  222 , or the central feeding-venting tube of the cryosurgical instrument  200  via the multi-way valve  208 , to the atmosphere (or vacuum pump) or to the first bottle  210  that is used for supplying a pressurized gas contained therein. A shut-off valve  213 , is installed on the duct which communicates between the first bottle  210  and the three-way valve  211 . Coupling  212  is designed to set the state of the three-way valve  211  into a state that communicates between duct  222  and the first bottle  210  whenever the multi-way valve  208  communicates between the main duct  215  and the atmosphere (or vacuum pump), and vice versa, namely—to set the state of the three-way valve  211  into a state that communicates between ducts  222  and the atmosphere (or vacuum pump) whenever the multi-way valve  208  communicates between the main duct  215  and the first bottle  210 . 
     Sensor  209  is provided in the multi-way valve  208  and used for controlling its preset changeover frequency. Data obtained from this sensor is processed by a control unit  223 . Whenever there are significant deviations of the measured parameters from the preset values, the control unit  223  closes the shut-off valve  207  that is installed on duct  206  and communicates between the feeding pipe  205  and the multi-way valve  208 , a shut-off valve  214  installed on a duct communicating between the first bottle  210  and the multi-way valve  208 , a shut-off valve  216  installed on the main duct  215 , and a shut-off valve  213  installed on a duct communicating between first bottle  210  and the three-way valve  211 . 
     The accessory system further comprise a second bottle  219  used for supplying a gas with low thermal conductivity contained therein, for example, R14. The second bottle  219  communicates via duct  220  with the external chamber (exemplified in  FIGS. 4–7 ) of the cryosurgical instrument  200  (the gap between the external shaft of the cryosurgical instrument  200  and its coaxial intermediate lumen). A three-way valve  221  installed on duct  220  is used for filling the external chamber of the cryosurgical instrument  200  with a gas having low thermal conductivity by a charging and purging technique, which is typically performed before operating the cryosurgical instrument  200  and carrying out any cryogenic treatment. 
       FIG. 3  shows a further preferred embodiment of the invention which comprises a cryosurgical instrument and a respective accessory system that is adapted to supply two different liquids which are used for carrying out preliminary ice-mapping and a cryogenic treatment. 
       FIG. 3  shows a cryosurgical instrument  300  with its cryotip  332  and an elongated tubular sub-unit  333 , and a respective accessory system which comprises a first tank  301  used for supplying a first liquid contained therein which has cryogenic boiling temperature (for example, liquid nitrogen). The first tank  301  is provided with a relief valve  302  used for presetting the desired pressure in said first tank  301 , valve  304  which is used for filling the first tank  301  with said first liquid, and with manometer  303 . 
     The accessory system also comprise a multi-way valve  310  which communicates via duct  306  between: a feeding pipe  305  situated in the first tank  301 ; a vacuum pump or the atmosphere; the cryosurgical instrument  300  via a main duct  322 , wherein the main duct splits into two ducts  313  and  337 ; and a first bottle  308  used for supplying a first pressurized gas contained therein. A shut-off valve  307  is installed on duct  306 , a shut-off valve  338  is installed on duct  313 , and a shut-off valve  309  is installed on a duct that communicates between the first bottle  308  and the multi-way valve  310 . Sensor  312  is placed in the multi-way valve  310  for controlling its preset changeover frequency. Data obtained from this sensor is processed by a control unit  331 , and whenever there are significant deviations of the measured parameter from a preset value, the control unit  331  closes the shut-off valves  307 ,  338  and  329 . 
     The accessory system also comprises a second tank  314  used for supplying a second liquid contained therein and which has relatively high boiling temperature. The second tank  314  is provided with: a relief valve  315  that is used for presetting the desired pressure in the second tank  314 ; valve  317  used for filling the second tank  314  with the second liquid; and manometer  316 . 
     A multi-way valve  321  is used for communicating between: a feeding pipe  318  that is situated in the second tank  314  (via duct  319 ) the atmosphere; the cryosurgical instrument  300  via the main duct  322  and duct  337 ; and a second bottle  323  with a second pressurized gas. A shut-off valve  320  is installed on duct  321 , shut-off valve  325  is installed on duct  324  for communicating between the second bottle  323  and the multi-way valve  321 , and a shut-off valve  326  is installed on duct  337 . Sensor  330  is provided in the multi-way valve  321  and used for controlling its preset changeover frequency. Data obtained from sensor  330  is processed by the control unit  331 , and whenever there are significant deviations of the measured parameter from a preset value, the control unit  331  closes the shut-off valves  320 ,  325  and  326 . 
     A third bottle  328  is provided for supplying a third pressurized gas contained therein and which is communicated to the cryosurgical instrument  300  via ducts  327 ,  337  and  322 . A three-way valve  329  is installed on duct  327  for communicating it with the atmosphere, according to control signal received from the control unit  331  which controls its state of operation. The three-way valve  329  is used for blowing out the ducts and the cryosurgical instrument  300  after carrying out an ice-mapping process in order to remove the second liquid and its vapors. Charging and purging technique is used to carry out the blowing out process. 
     A fourth bottle  334  is provided for supplying a gas with low thermal conductivity contained therein, for example, R14. The fourth bottle  334  is communicated via duct  335  with the external chamber (illustrated in  FIGS. 4–7 ) of the cryosurgical instrument  300  (the gap between the external shaft of the cryosurgical instrument  300 , and its coaxial tubular piece and the proximal section of the central feeding-venting tube). A three-way valve  336  installed on duct  335  is used for communicating it with the atmosphere and for filling the external chamber of the cryosurgical instrument  300  by charging and purging technique, which is typically performed previously to operating the cryosurgical instrument  300  and carrying out any cryogenic treatment. 
       FIG. 4  shows an axial cross-section of a cryosurgical instrument  400  comprising an active thermal insulation based on a heat pipe principle. 
     A cryosurgical instrument  400  is constructed from two major sub-units: a distal cryotip  402  adapted for immediate contact with a target tissue, wherein the freezing action performed by this cryotip is obtained by evaporation of cryogenic liquid on its internal porous coating  403  which is formed from a porous metal with open porosity; and an elongated tubular sub-unit used for delivering portions of the cryogenic liquid on the internal porous coating  403  and for the removal of vapors generated in the boiling process of the cryogenic liquid in the internal porous coating  403 . 
     The elongated tubular sub-unit comprises: an external shaft  404 ; a central feeding-venting tube  401  which is used for supplying portions of the cryogenic liquid to the internal porous coating  403  of the distal cryotip  402  and also for removal of vapors, which are generated in the process of boiling of the cryogenic liquid in the internal coating  403 , into the atmosphere. 
     The elongated tubular sub-unit further comprises a coaxial tubular piece  405  positioned in the gap between the distal sections of the central feeding-venting tube and the external shaft  404 ; the distal end of the coaxial tubular piece  405  is sealed by cryotip  402 , and its proximal end is sealed by the central feeding-venting tube  401 . 
     The outer surfaces of the coaxial tubular piece  405  and a section of the central feeding-venting tube  401  mating this coaxial tubular piece are covered with a porous coating  406  with open porosity that is functioning as a wick when the gap between the external shaft  404 , the coaxial tubular piece  405  and the mating section of the central feeding-venting tube  401  is filled with vapors of a gas that its condensation temperature is higher than the boiling temperature of the applied cryogenic liquid. 
     The proximal end of the feeding-venting central tube is provided with an inlet-outlet connection  407 , and the proximal section of the external shaft  404  is provided with an inlet-outlet connection  408 . 
       FIG. 5  is an axial cross-section of a cryosurgical instrument  500  comprising a coaxial tubular piece  505  that is joined at its distal end with the external shaft  504  of the cryosurgical instrument  500 . 
     Cryocatheter  500  (or cryoprobe) is constructed from two major sub units: a distal cryotip  502 , which is used for contacting a target tissue, wherein the freezing action of cryotip  502  is obtained by evaporation of a cryogenic liquid in its internal porous coating  503 , which is formed from porous metal with open porosity; an elongated tubular sub-unit used for delivering portions of the cryogenic liquid to the internal porous coating  503  and for removal of vapors generated in the process of the boiling the cryogenic liquid in the internal porous coating  503 . 
     The elongated tubular sub-unit comprises an external shaft  504  and a central feeding-venting tube  501 , which is used for supplying portions of the cryogenic liquid to the internal porous coating  503  of the distal cryotip  502  and for removal of vapors, generated in the process of boiling of the cryogenic liquid on the internal porous coating  503 , into the atmosphere. 
     The elongated tubular sub-unit further comprises a coaxial tubular piece  505  positioned in the gap between the distal sections of the central feeding-venting tube  501  and the external shaft  504 , wherein the distal end of the coaxial tubular piece  505  is sealed with the external shaft  504  and its proximal end is sealed by the central feeding-venting tube  501 . The proximal end of the feeding-venting central tube  501  is provided with an inlet-outlet connection  506 , and the proximal section of the external shaft  504  is provided with an inlet-outlet connection  507 . 
       FIG. 6  shows an axial cross-section of a cryosurgical instrument  600  comprising a coaxial intermediate lumen instead of the coaxial tubular piece that was used in the previously described cryosurgical instrument. 
     A cryosurgical instrument  600  is constructed from two major sub-units: a distal cryotip  602 , which is used for contacting a target tissue, wherein the freezing action of cryotip  602  is obtained by evaporation of a cryogenic liquid on its internal porous coating  603  formed from porous metal with open porosity; and an elongated tubular sub-unit used for delivering portions of the cryogenic liquid to the porous coating and for removal of vapors generated in the boiling process of the cryogenic liquid in the internal porous coating  603 . 
     The elongated tubular sub-unit comprises an external shaft  604  and a central feeding-venting tube  601 , which is used for supplying portions of cryogenic liquid to the internal porous coating  603  of the distal cryotip  602  and for removal of the vapors, generated in the boiling process of the cryogenic liquid in the internal coating  603 , into the atmosphere. 
     The elongated tubular sub-unit further comprises a coaxial intermediate lumen  605  positioned in the gap between the central feeding-venting tube  601  and the external shaft  604 ; the distal end of the coaxial intermediate lumen  605  is sealed by the external shaft  604  and its proximal end is sealed by the central feeding-venting tube  601 . In addition, the proximal end of the external shaft  604  is sealed by the proximal section of the coaxial intermediate lumen  605 . The proximal end of the feeding-venting central tube  601  is provided with an inlet-outlet connection  607 , the proximal section of the external shaft  604  is provided with an inlet-outlet connection  609 , and the proximal section of the coaxial intermediate lumen  605  is provided with an inlet-outlet connection  608 . The outer surface of the coaxial intermediate lumen  605  is covered with a porous coating  606  starting at its distal end and ending near its proximal end. The porous coating  606  is used as a wick when a heat pipe principle is used for heating the distal section of the external shaft. 
       FIG. 7  shows an axial cross-section of a cryocatheter  700  adapted for preventing restenosis of blood vessels. 
     Cryocatheter  700  is constructed from two major sub-units: a distal cryotip, which is used for contacting a target tissue, wherein the freezing action of the cryotip is obtained by evaporation of a cryogenic liquid in an internal porous coating  704  formed from porous elastic polymer with open porosity which is provided on the internal surface of an external tubular piece  703  made from an elastic polymer. 
     The distal end of the external tubular piece  703  is sealed by plug  702  manufactured from a polymer material having low thermal conductivity. 
     An elongated tubular sub-unit is used for delivering portions of the cryogenic liquid to the internal porous coating  704  and for removal of vapors generated in the boiling process of the cryogenic liquid in the internal porous coating  704 . 
     The elongated tubular sub-unit comprises an external shaft  706 , and a central feeding-venting tube  701 , which is used for supplying portions of the cryogenic liquid to the internal porous coating  704  and for removal of the vapors, generated in the boiling process of the cryogenic liquid in the internal porous coating  704 , into the atmosphere. 
     Orifice  705  provided at the distal end of the central feeding-venting tube  701  is used for reducing the pressure in the internal chamber of the cryotip formed by plug  702  and in the external tubular piece  703  with the internal porous coating  704 . 
     In addition, there is a coaxial intermediate lumen  707  positioned in the gap between the central feeding-venting tube  701  and the external shaft  706 , wherein the distal end of this intermediate lumen  707  is sealed by the external shaft  706  and its proximal end is sealed by the central feeding-venting tube  701 . The proximal end of the external shaft  706  is sealed by the proximal section of the coaxial intermediate lumen  707 . The proximal end of the feeding-venting central tube  701  is provided with an inlet-outlet connection  708 , the proximal section of the external shaft  706  is provided with an inlet-outlet connection  710 , and the proximal section of the coaxial intermediate lumen  707  is provided with an inlet-outlet connection  709 .