Abstract:
An invention relates to the area of cryosurgical equipment. It proposes a cryosurgical system, which incorporates measuring and computing means for estimation of a real time ice ball diameter and operation temperature of a cryotip (the distal section of a cryosurgical probe). The cryosurgical probe of the cryosurgical system operates by blowing in a gaseous medium at cryogenic temperature.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0001]    Not applicable. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to the field of cryosurgical equipment and, particularly, to cryosurgical systems intended to perform internal cryogenic treatments. 
       BACKGROUND OF THE INVENTION 
       [0003]    Common cryosurgical instruments can be divided into two categories: 
         [0000]    a) Cryosurgical devices operating with application of a liquid refrigerant (or refrigerant in the form of liquid-gaseous mixture) such as liquid nitrogen or liquid argon;
 
b) Cryosurgical devices operating on the base of expansion of highly pressurized gas (Joule-Thomson effect).
 
         [0004]    Each of these categories of cryosurgical equipment has its advantages and drawbacks. However, none of this cryosurgical equipment allows to estimate the right now temperature of a cryotip (the distal section of a cryosurgical probe) and the real time ice ball diameter formed around the cryotip. Application of a thermocouple, which is in a good thermal contact with the internal surface of the cryotip, for measuring the temperature of the cryotip presents a complicated technical problem. Ultrasound imaging devices, which are commonly used to estimate the diameter of an ice ball formed around the cryotip, require adequate skill and ability of a surgeon executing a cryosurgical procedure. 
         [0005]    Application of gaseous medium at cryogenic temperatures as means for performance of cryosurgical procedures is mentioned in U.S. Pat. No. 5,254,116. The authors of this patent hold that “for miniature cryoprobes cold nitrogen gas or helium gas is often used instead of liquid nitrogen. This compromise has proven unsatisfactory because the heat transfer efficiency between the gas and the probe tip in contact with the tissue is very low and consequently, the ice ball created at the tip is not large enough and the temperature is not low enough for typical clinical applications. Moreover, the pressure used for such probes is often in excess of 500 or 600 psi, which requires special safeguards to prevent potential hazards”. 
         [0006]    However, calculated values of heat transfer coefficient for gaseous helium at cryogenic temperatures, demonstrate that for sufficiently small hydraulic diameter of the cryotip, it is possible to achieve heat transfer coefficient of 1000 W/m 2 ° C. or more (see: S. G. Kandlikar et al. HEAT TRANSFER AND FLUID FLOW IN MINICHANNELS AND MICROCHANNELS, ELSEVIER 2006, Chapter I and Chapter III). 
         [0007]    Additional increase of heat transfer coefficient for gaseous medium can be achieved by enhancing the internal surface of the cryotip. 
         [0008]    On the other hand, application of the gaseous medium at cryogenic temperature as means for performance of cryosurgical procedures, provides some advantages in controlling and measuring of an ice ball formation; these advantages cannot be obtained with the other cryosurgical systems mentioned above. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    A proposed cryosurgical system with a built-in control unit for estimation of some parameters related to ice-ball formation around a cryotip consists of following means for calculation of the cryotip temperature and the ice-ball diameter: a mass flow rate measuring sub-unit, means for measuring temperature of the gaseous medium before its introduction into cryosurgical probe and temperature of the gaseous medium immediately after its escape from the cryosurgical probe. It gives possibility to calculate amount of heat transferred from the surrounding tissue into cryotip and according to this value to estimate the diameter of an ice ball formed around the cryotip. Moreover, mass flow rate value is presented indirectly in dimensionless Reynolds number. 
         [0010]    Therefore, heat transfer coefficient of the internal surface of the cryotip for the flow of a specific gaseous medium can be estimated as a function of the mass flow rate. 
         [0011]    Heat rate, which is transferred through the internal wall of the cryotip, can be calculated in two ways: 
         [0000]        Q=M ·( T   out   −T   in   −ΔT   shaft )· C   (1)
 
         [0000]    where Q—heat rate, M—mass flow rate, C—specific heat of gaseous medium, T out —temperature of escaped gaseous medium, T in —temperature of supplied gaseous medium, ΔT shaft —systematic temperature error caused by heat transfer through the cryoprobe shaft. 
         [0000]        Q=K·S·[T   w −( T   out   +T   in   −ΔT   shaft )/2]  (2),
 
         [0000]    where: K—heat transfer coefficient, S—the internal surface area of the cryotip. Instead of T w −(T out +T in −ΔT shaft )/2 the log mean temperature difference can be calculated. 
         [0012]    Heat transfer coefficient K is a function of (T out +T in −ΔT shaft )/2, which can be found by testing or theoretically calculated, and its values are recorded in the control unit memory. The change of heat transfer coefficient K with changing average temperature of the gaseous medium is caused by variation of viscosity and thermal conductivity of the gaseous medium with the temperature varying. 
         [0013]    It should be noted that ΔT shaft  is a function of (T out +T in )/2; however, as a first approximation for vacuum thermal insulation of the cryoprobe shaft, this systematic temperature error can be assumed to be constant and measured experimentally by a preliminary testing procedure. 
         [0014]    It allows calculating the temperature of the internal surface of the cryotip as: 
         [0000]        T   w   =[M· ( T   out   −T   in   −ΔT   shaft )· C+K·S· ( T   out   +T   in   −ΔT   shaft )/2 ]/K·S   (3)
 
         [0015]    This calculated value of the cryotip temperature allows to estimate final diameter of the formed ice ball; the estimation may be done analytically or by empirical data in form of diagrams or nomograms and recorded in the control unit memory (such data is presented, for example, in the book V. G. Vedenkov et al. CRYOGENIC MEDICAL TECHNIQUE, METHODICAL RECOMMENDATIONS, Moscow 1991, in Russian). 
         [0016]    Moreover, changing T w  over a cryosurgical operation period, allows to indicate stagnation in changing T w  and to cease the cryosurgical operation or to do alternation to a thawing mode (if the cryosurgical operation should be performed by two or more cycles freezing-thawing). 
         [0017]    In addition, this method of a cryotip temperature measuring can be applied for thawing control, when the gaseous medium at temperature above 0° C. serves for thawing an ice ball formed around the cryotip. In this case, calculated temperature of the cryotip indicates the absence or presence of adhesion between the cryotip and the ice ball. 
         [0018]    In such a way, the proposed cryosurgical system (without the cryoprobe itself) consists of some basic units: a source of pressurized gaseous medium, preferably, helium at cryogenic temperature; a flexible thermo-insulated hose (preferably with vacuum thermo-insulation); at least two temperature sensors, which are measuring T out —temperature of escaped gaseous medium and T in —temperature of supplied gaseous medium; a mass flowmeter for measuring mass flow rate of the gaseous medium (preferably helium); a control unit with recorded data regarding estimated final diameters of the formed ice balls as a function of final temperature of the cryotip and thermo-physical properties of the tissue to be destroyed by cryosurgical operation. 
         [0019]    There are five main designs of the source of pressurized gaseous medium at cryogenic temperature: 
         [0020]    1. Combination of a bottle with pressurized gaseous medium and a Dewar flask with an embedded heat exchanger; the pressurized gaseous medium is supplied from the bottle into the embedded heat exchanger via a supply line, which is provided with an installed mass flow rate gauge. The pressurized gaseous medium at cryogenic temperature exits the heat exchanger and enters the proximal section of a central feeding conduit, which is situated in the internal space of the Dewar flask. The distal external end of the central feeding conduit should be coupled with a flexible thermo-insulated hose. 
         [0021]    2. Combination of a bottle with pressurized gaseous medium and a Dewar flask with an external heat exchanger of recuperative type; the pressurized gaseous medium is supplied from the bottle into the external heat exchanger via a supply line, which is provided with an installed mass flow rate gauge. 
         [0022]    At the same time, liquid-gaseous mixture of cryogen is supplied into the external heat exchanger. The pressurized gaseous medium at cryogenic temperature exits the heat exchanger and enters the proximal section of a central feeding line of the flexible thermo-insulated hose. The external heat exchanger is provided with an external thermo-insulation (preferably—with a vacuum thermo-insulation). In another preferable embodiment the flexible hose and the external heat exchanger have a common vacuum thermo-insulation. Evaporated cryogen is cleared out of the heat exchanger into the atmosphere or into an additional heat exchanger of recuperative type for precooling the pressurized gaseous medium. 
         [0023]    3. Evaporation of liquid cryogen in the Dewar flask under a certain pressure provides the pressurized gaseous medium at cryogenic temperature; the pressurized gaseous medium is entering into the open proximal end of the central feeding conduit. 
         [0024]    4. There are two bottles with pressurized gases; the first one serves as a source of the pressurized gaseous medium, which cools the cryotip to cryogenic temperature; and the second one serves as a source of highly pressurized gas being expanded via an orifice tube in a heat exchanger; the expansion causes the cooling of the gas on account of Joule-Thomson effect with following cooling of the pressurized gaseous medium in the counter-flow heat exchanging unit arranged in the heat exchanger. 
         [0025]    5. There is a combination of two cooling sources for lowering the temperature of the pressurized gaseous medium to a cryogenic temperature. The first source is a liquid cryogen, which is contained in a Dewar flask and serves for preliminary cooling of a highly pressurized gas below its inversion temperature (when the Joule-Thomson (Kelvin) coefficient μ JT  is negative). This cooled highly pressurized gas serves for further lowering its temperature by its expansion via an orifice tube with Joule-Thomson effect and following cooling of the pressurized gaseous medium in the heat exchanger as it is described in the version four. 
         [0026]    In the second version mentioned above, the lower internal section of the Dewar flask is provided with an electrical heater; a wattmeter is measuring the rate of heating the liquid cryogen. It allows to transform a value measured by the wattmeter into the mass flow rate of the pressurized gaseous medium. 
         [0027]    In a preferable design of the flexible thermo-insulated hose with a vacuum thermo-insulation, the distal section of the central feeding conduit is provided with a vacuum thermo-insulation, which is common with the vacuum thermo-insulation of the central conduit of the flexible thermo-insulated hose. It allows minimizing heat transfer from the surroundings to this central conduit. 
         [0028]    The central feeding conduit is in fluid communication with the central conduit of the flexible thermo-insulated hose. 
         [0029]    The upper edge of the neck of the Dewar flask is sealed with a plug, which provided with a safety valve and a manometer, and serves at the same time for installation of the distal section of the central feeding conduit and the inlet section of the embedded heat exchanger (in the case of application of the bottle with pressurized gaseous medium). 
         [0030]    In the other case, when the Dewar flask itself serves as a source of the gaseous medium, feeding cables of the electrical heater pass via the plug. 
         [0031]    The distal end of the flexible thermo-insulated hose is provided with an outlet connection, which, in turn, is joined with a coupling unit intended for coupling with an associated proximal coupling unit of the cryoprobe. 
         [0032]    The associated proximal coupling unit of the cryoprobe is preferably joined with a central feeding lumen, which supplies the gaseous medium into the internal space of the cryotip. The external shaft of the cryoprobe is preferably provided with a vacuum thermo-insulation. The exhausted gaseous medium is removed from the internal space of the cryotip through an annular channel formed between the vacuum thermo-insulation and the central feeding lumen and cleared out via an outlet connection in the coupling unit of the flexible hose. 
         [0033]    The outlet connection of the flexible thermo-insulated hose and the outlet connection of its coupling unit are provided with two temperature sensors measuring the temperature of the supplied and cleared out gaseous medium. 
         [0034]    Signals from these temperature sensors are directed to the control unit, which processes all data obtained from the temperature sensors and the mass flow rate gauge, and in accordance with the data recorded in the control unit shows on its display the calculated temperature of the cryotip and the estimated ice ball diameter, as a function of the cryosurgical procedure period and the cryotip temperature. In addition, the control unit can summarize the cold introduced into treated tissue during cryosurgical procedure and estimate on this basis the ice ball diameter. 
         [0035]    In the case, when the pressurized gaseous medium is used as well as a thawing gaseous medium, there is a by-pass line providing immediate fluid communication of the bottle with the pressurized gaseous medium and the outlet connection of the flexible thermo-insulated hose. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0036]      FIG. 1   a  demonstrates a cryosurgical system comprising a combination of a bottle with pressurized gaseous medium, an axial cross-sectional view of a Dewar flask with an embedded heat exchanger and a flexible thermo-insulated hose, which is coupled with a cryoprobe. 
           [0037]      FIG. 1   b  demonstrates the cryosurgical system comprising combination of the bottle with pressurized gaseous medium, the axial cross-sectional view of the Dewar flask with the embedded heat exchanger, the flexible thermo-insulated hose, which is coupled with the cryoprobe and a by-pass line intended for thawing of a cryotip. 
           [0038]      FIG. 1   c  demonstrates an axial cross-section of the Dewar flask with the embedded heat exchanger. 
           [0039]      FIG. 1   d  demonstrates an enlarged axial cross-section of the cryoprobe, which is coupled with a distal section of the flexible thermo-insulated hose. 
           [0040]      FIG. 2   a  demonstrates a cryosurgical system comprising combination of a bottle with pressurized gaseous medium, an axial cross-sectional view of a Dewar flask with an external heat exchanger of recuperative type and a flexible thermo-insulated hose, which is coupled with a cryoprobe. 
           [0041]      FIG. 2   b  demonstrates the external heat exchanger of  FIG. 2   a.    
           [0042]      FIG. 3   a  demonstrates a cryosurgical system operating by evaporation of liquid cryogen in the Dewar flask under a certain pressure; the obtained vapors of the cryogen are supplied as the pressurized gaseous medium at cryogenic temperature into a flexible thermo-insulated hose, which is coupled with a cryoprobe. 
           [0043]      FIG. 3   b  demonstrates the Dewar flask and its siphon according to  FIG. 3   a.    
           [0044]      FIG. 4   a  demonstrates a cryosurgical system comprising combination of a first bottle with pressurized gaseous medium and a second bottles with highly pressurized gas; the first one serves as a source of the pressurized gaseous medium, which cools the cryotip to cryogenic temperature; and the second one serves as a source of highly pressurized gas being expanded via a orifice tube in a heat exchanger; this figure demonstrates in addition a flexible thermo-insulated hose, which is coupled with a cryoprobe. 
           [0045]      FIG. 4   b  shows an axial cross-section of the heat exchanger of  FIG. 4   a.    
           [0046]      FIG. 5   a  demonstrates a cryosurgical system comprising: a bottle with pressurized gaseous medium and a combination of two cooling sources for lowering the temperature of the pressurized gaseous medium to a cryogenic temperature; a flexible thermo-insulated hose, which coupled is with a cryoprobe. 
           [0047]      FIG. 5   b  shows an axial cross-section of the heat exchanger of  FIG. 5   a.    
           [0048]      FIG. 5   c  shows an axial cross-section of the heat exchanging chamber of  FIG. 5   a.    
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0049]      FIG. 1   a  shows an axial cross-sectional view of an exemplary Dewar flask  101  with a recuperative heat exchanger  150  installed in its neck according to preferred embodiments of the present invention, an axial cross-section view of a flexible hose  120  and an axial cross-sectional view of cryoprobe  130 . The recuperative heat exchanger  150  and its auxiliary parts comprise a coil-type heat exchanger  151  itself with its inlet conduit  152  and an outlet conduit  153 , which is provided with vacuum thermal insulation  154 . The upper sections of the inlet conduit  152  and the vacuum thermal insulation  154  of the outlet conduit  153  are installed in bushing  155 . Jacket  104  surrounds bushing  155  with gap  115  formed between them. The upper edge of jacket  104  is sealed with bushing  155  as shown. 
         [0050]    There is also a seal for sealing jacket  104  to the Dewar flask  101 , this seal is designed as is an annular rubber ring  105  installed on jacket  104  and inserted partially into neck  102  for holding bushing  155  in neck  102 . Safety and relief valves  109  and  110  are installed on ports of the outer section of jacket  104 . Jacket  104  also preferably features a pressure gauge  114 , which is installed on its outer section for measuring internal pressure in the Dewar flask  101 . 
         [0051]    The lower section of the internal surface of jacket  104  is provided with an internal threading  117  with an internal diameter, which fits the outer diameter of bushing  155 . 
         [0052]    The distal external ends of the vacuum thermal insulation  154  of the outlet conduit  153  are joined with a vacuum thermal insulation  121  and a central lumen  122  of a flexible hose  120 ; in doing so the outlet conduit  153  and the flexible hose  120  have a common vacuum thermal insulation. The distal end of the central lumen  122  is provided with a coupling unit  123 . 
         [0053]    The coupling unit  123  is provided with an inlet connection  124  and an outlet connection  125 . 
         [0054]    Thermocouples  126  and  127  are installed in these inlet and outlet connections  124  and  125 . 
         [0055]    The coupling unit  123  is coupled with an associated coupling unit  135  of cryoprobe  130 . Cryoprobe  130  comprises as well cryotip  131 , central feeding lumen  132 , an external shaft  133  and a vacuum thermal insulation  134 . 
         [0056]    Pressurized gaseous medium is provided into the inlet conduit  153  of the coil-type heat exchanger  151  from bottle  140  via a control valve  141 , a mass flow rate gauge  142  and a coupling unit  143 , which serves for coupling a supply line  144  with the inlet conduit  152 . 
         [0057]    A control unit  160  receives data from a mass flow rate gauge  142  and thermocouples  126 ,  127 ; it allows calculating temperature of cryotip  131  as it has been described in the summary of the invention. 
         [0058]      FIG. 1   b  demonstrates the cryosurgical system with components, which correspond to similar components described with regard to  FIG. 1   a.    
         [0059]    In addition,  FIG. 1   b  comprises a by-pass line  146 , which provides fluid communication via a control valve  147  between the supply line  144  and the inlet connection  124  of the coupling unit  123 . 
         [0060]      FIG. 1   c  demonstrates an axial cross-section of the Dewar flask with the embedded heat exchanger  150  and components, which correspond to similar components described with regard to  FIG. 1   a.    
         [0061]      FIG. 1   d  demonstrates an enlarged axial cross-section of the cryoprobe  130  coupled with a distal section of the flexible thermo-insulated hose  120 . 
         [0062]    The distal section of the vacuum thermal insulation  121  and a central lumen  122  of the flexible hose  120  are provided with a coupling unit  123 . 
         [0063]    The coupling unit  123  is provided with an inlet connection  124  and an outlet connection  125 . 
         [0064]    Thermocouples  126  and  127  are installed in these inlet and outlet connections  124  and  125 . 
         [0065]    The coupling unit  123  is coupled with an associated coupling unit  135  of cryoprobe  130 . Cryoprobe  130  comprises as well: cryotip  131 ; central feeding lumen  132 ; an external shaft  133  and a vacuum thermal insulation  134 . 
         [0066]      FIG. 2   a  shows: an axial cross-sectional view of an exemplary Dewar flask  101  with a recuperative heat exchanger  250  installed outside; an axial cross-section view of a flexible hose  120  and an axial cross-sectional view of cryoprobe  130 . 
         [0067]    The Dewar flask  101  comprises siphon  261  installed in its neck  102  according to preferred embodiments of the present invention, which is intended to be filled with a liquid cryogen. Siphon  261  comprises a feeding conduit  262  with a vacuum thermal insulation  263  of its middle and upper sections. There is jacket  264  surrounding the feeding conduit  262  and the vacuum thermal insulation  263  with gap  265  formed between them. The upper edge of jacket  264  is sealed with the vacuum thermal insulation  263  as shown. There is also a seal for sealing jacket  264  to the Dewar flask, and there is an annular rubber ring  266  installed on jacket  264  and inserted partially into neck  102  for holding siphon  261  in Dewar flask  101 . 
         [0068]    Also, preferably, a shut-off valve  268  is installed on the outer section of the feeding conduit  262 . The shut-off valve  268  ensures supply control of the liquid cryogen. 
         [0069]    In the preferred embodiment, safety and relief valves  269  and  270  are installed on ports of the outer section of jacket  264  for this purpose. Jacket  164  also preferably features a pressure gauge  280  for measuring internal pressure in the Dewar flask  101 . 
         [0070]    The lower section of the internal surface of jacket  264  is provided with an internal threading  217  with an internal diameter, which fits the outer diameter of the vacuum thermal insulation  263 . An electrical heater  271  is placed on the lower section of the feeding conduit  262 ; this allows achieving operation pressure in the internal space of the Dewar flask  101 . 
         [0071]    An electrical cable  212  is supplying current to this electrical heater  271 . 
         [0000]    Gaseous-liquid mixture of cryogen is supplied by siphon  261  into a recuperative heat exchanger  250 , which comprising a housing  281 , a vacuum thermal insulation  282 , a coil-type heat exchanging element  283  that is arranged in housing  281  and has inlet and outlet connections  284  and  285 , and inlet and outlet connections  289  and  287 , which serve for supplying the liquid-gaseous cryogen mixture from the dewar flask  101  and removal of evaporated cryogen from the internal space of the recuperative heat exchanger  250 . The outlet connection  285  is provided with a thermal vacuum insulation  288 , which is common with the vacuum thereto-insulation  121  of the flexible thermo-insulated hose  123 . 
         [0072]    A sub-system of gaseous medium supplying unit, a control unit  160 , a flexible hose  120  and cryoprobe  130  are designed as the same units in  FIG. 1   a.    
         [0073]      FIG. 2   b  demonstrates an axial enlarged cross-section the recuperative heat exchanger  250  of  FIG. 2   a.    
         [0000]    It comprises: a housing  281 ; a vacuum thermal insulation  282 ; a coil-type heat exchanging element  283  that is arranged in housing  281  and has inlet and outlet connections  284  and  285 ; and inlet and outlet connections  289  and  287 . 
         [0074]      FIG. 3   a  demonstrates an axial cross-sectional view of an exemplary Dewar flask  101  with evaporation of liquid cryogen in this Dewar flask  101  under a certain pressure; in such a way the Dewar flask  101  with its siphon  361  provides the pressurized gaseous medium at cryogenic temperature. In addition,  FIG. 3  shows: the axial cross-sectional view of the Dewar flask  101 ; an axial cross-section view of a flexible hose  120 ; an axial cross-sectional view of cryoprobe  130  and a control unit  303 . 
         [0075]    The Dewar flask  101  comprises siphon  361  installed in its neck  102  according to preferred embodiments of the present invention. Siphon  361  comprises a feeding conduit  362  with a vacuum thermal insulation  363  of its middle and upper sections. There is jacket  364  surrounding the feeding conduit  362  and the vacuum thermal insulation  363  with gap  365  formed between them. The upper edge of jacket  364  is sealed with the vacuum thermal insulation  363  as shown. There is also a seal for sealing jacket  364  to the Dewar flask, an there is an annular rubber ring  366  installed on jacket  364  and inserted partially into neck  102 , for holding siphon  361  in Dewar flask  101 . 
         [0076]    Also, preferably a shut-off valve  368  is installed on the outer section of the feeding conduit  162 . Safety and relief valves  369  and  370  are installed on ports of the outer section of jacket  364  for this purpose. Jacket  364  also preferably features a pressure gauge  114  for measuring internal pressure in the Dewar flask  101 . 
         [0077]    The lower section of the internal surface of jacket  364  is provided with an internal threading  317  with an internal diameter, which fits the outer diameter of the vacuum thermal insulation  363 . An electrical heater  371  is placed on the lower section of the feeding conduit  362 ; this electrical heater is thermo-insulated on the outside by a thermal insulation  301 . This allows achieving operation pressure in the internal space of the Dewar flask  101  and to evaporate cryogen at required rate. 
         [0078]    The upper section of the feeding conduit  362  is provided with a demister  302 , which separates droplets from gaseous-liquid mixture of cryogen with returning the droplets into the lower section of the feeding conduit  362 . 
         [0079]    The control unit  303  comprises a wattmeter measuring the heating power of the electrical heater  371  and allowing to calculate mass flow rate of gaseous medium without application of a mass flow rate gauge. 
         [0080]    As in the case of  FIG. 1   a  and  FIG. 2   a  the control unit  303  receives data from thermocouples  126 ,  127 ; it allows calculating temperature of cryotip  131  as it has been described in the summary of the invention. 
         [0081]      FIG. 3   b  demonstrates an axial cross-sectional view of the Dewar flask  101  with evaporation of liquid cryogen in this Dewar flask  101  under a certain pressure; in such a way the Dewar flask  101  with its siphon  361  provides the pressurized gaseous medium at cryogenic temperature. Siphon  361  comprises a feeding conduit  362  with a vacuum thermal insulation  363  of its middle and upper sections. There is jacket  364  surrounding the feeding conduit  362  and the vacuum thermal insulation  363  with gap  365  formed between them. The upper edge of jacket  364  is sealed with the vacuum thermal insulation  363  as shown. There is also a seal for sealing jacket  364  to the Dewar flask, and there is an annular rubber ring  366  installed on jacket  364  and inserted partially into neck  102  for holding siphon  361  in Dewar flask  101 . 
         [0082]    Also, preferably a shut-off valve  368  is installed on the outer section of the feeding conduit  162 . Safety and relief valves  369  and  370  are installed on ports of the outer section of jacket  364  for this purpose. Jacket  364  also preferably features a pressure gauge  114  for measuring internal pressure in the Dewar flask  101 . 
         [0083]    The lower section of the internal surface of jacket  364  is provided with an internal threading  317  with an internal diameter, which fits the outer diameter of the vacuum thermal insulation  363 . An electrical heater  371  is placed on the lower section of the feeding conduit  362 ; this electrical heater is thermo-insulated on the outside by a thermal insulation  301 . This allows achieving operation pressure in the internal space of the Dewar flask  101  and to evaporate cryogen at required rate. 
         [0084]    The upper section of the feeding conduit  362  is provided with a demister  302 , which separates droplets from gaseous-liquid mixture of cryogen with returning the droplets into the lower section of the feeding conduit  362 . 
         [0085]      FIG. 4   a  demonstrates a cryosurgical system comprising a combination of a first bottle with pressurized gaseous medium and a second bottle with pressurized gas; the first one serves as a source of the pressurized gaseous medium, which cools the cryotip to cryogenic temperature; and the second one serves as a source of highly pressurized gas being expanded via an orifice tube in a heat exchanger serving for cooling the pressurized gaseous medium. 
         [0086]    This heat exchanger  401  comprises an internal chamber  402  with a proximal coil-type heat exchanging unit  403 , its inlet connection  404  and a middle lumen  405 , which is terminated at its distal end with an orifice tube  406 . The inlet connection  404  is in fluid communication with a second bottle  420  with pressurized gas via a coupling unit  422 , line  423  and a control valve  421 . An outlet connection  408  in the proximal section of the internal chamber  402  serves for clearing out the expended gas from its internal space. 
         [0087]    In addition, there is a second distal coil-type heat exchanging unit  407 , which is arranged in the internal chamber  402 , with an inlet connection  410  and an outlet connection  409 , this inlet connection is in fluid communication with the supply line  144 . A coupling unit  143  serves for coupling the inlet connection  410  with the supply line  144  and the control valve  141 . 
         [0088]    The internal chamber  402  is provided with an outer vacuum thermal insulation  414 . 
         [0089]    In addition, the outlet connection  409  is provided with a vacuum thermal insulation  412 . 
         [0090]    A coupling unit  413  serves for coupling this outlet connection  409  with the flexible hose  120 . 
         [0091]    The flexible hose  120 , cryoprobe  130  and a control unit  160  are designed in the same manner as these units in  FIG. 1   a.    
         [0092]      FIG. 4   b  shows an enlarged axial cross-section of the heat exchanger  401  of  FIG. 4   a.    
         [0093]    It comprises an internal chamber  402  with a proximal coil-type heat exchanging unit  403 , its inlet connection  404  and a middle lumen  405 , which is terminated at its distal end with an orifice tube  406 . The inlet connection  404  is in fluid communication with the second bottle with pressurized gas via a coupling unit  422  and line  423 . An outlet connection  408  in the proximal section of the internal chamber  402  serves for clearing out the expended gas from its internal space. 
         [0094]    In addition, there is a second distal coil-type heat exchanging unit  407 , which is arranged in the internal chamber  402 , with an inlet connection  410  and an outlet connection  409 ; this inlet connection  410  is in fluid communication with the supply line  144 . A coupling unit  143  serves for coupling the inlet connection  410  with the supply line  144  and the control valve  141 . The internal chamber  402  is provided with an outer vacuum thermal insulation  414 . 
         [0095]    In addition, the outlet connection  409  is provided with a vacuum thermal insulation  412 . 
         [0096]    A coupling unit  413  serves for coupling this outlet connection  409  with the flexible hose. 
         [0097]      FIG. 5   a  demonstrates a cryosurgical system, which comprises: a bottle with pressurized gaseous medium and a combination of two cooling sources for lowering the temperature of the pressurized gaseous medium to a cryogenic temperature; an axial cross-section view of a flexible hose and an axial cross-sectional view of a cryoprobe. 
         [0098]    The Dewar flask  101  serves for preliminary cooling the pressurized gas, which is circulating in a compression-expansion circuit; this Dewar flask  101  comprises siphon  261  installed in its neck  102  according to preferred embodiments of the present invention, which is intended to be filled with a liquid cryogen. Siphon  261  comprises a feeding conduit  262  with a vacuum thermal insulation  263  on its middle and upper sections. There is jacket  264  surrounding the feeding conduit  262  and the vacuum thermal insulation  263  with gap  265  formed between them. The upper edge of jacket  264  is sealed with the vacuum thermal insulation  263  as shown. 
         [0099]    There is also a seal for sealing jacket  264  to the Dewar flask, an there is an annular rubber ring  266  installed on jacket  264  and inserted partially into neck  102 , for holding siphon  261  in Dewar flask  101 . 
         [0100]    Also, preferably a shut-off valve  268  is installed on the outer section of the feeding conduit  262 . The shut-off valve  268  ensures the control of the supply of the liquid cryogen. 
         [0101]    In the preferred embodiment, preferably safety and relief valves  269  and  270  are installed on ports of the outer section of jacket  264  for this purpose. Jacket  264  also preferably features a pressure gauge  280  for measuring internal pressure in the Dewar flask  101 . 
         [0102]    The lower section of the internal surface of jacket  264  is provided with an internal threading  217  with an internal diameter, which fits the outer diameter of the vacuum thermal insulation  263 . An electrical heater  271  is placed on the lower section of the feeding conduit  262 ; this allows achieving operation pressure in the internal space of the Dewar flask  101 . An electrical cable  212  is supplying current to this electrical heater  271   
         [0103]    Gaseous-liquid mixture of cryogen is supplied by siphon  261  into a recuperative heat exchanger  510 , which comprising housing  511 , a vacuum thermal insulation  512 , a first coil-type heat exchanging unit  513 , which is arranged in housing  511  and has inlet and outlet connections  514  and  515 , and an outlet connection  516 , which serves for removal of evaporated cryogen from the internal space of the recuperative heat exchanger  510 . The outlet connection  515  is provided with a thermal vacuum insulation  518 . 
         [0104]    The compression-expansion circuit, which has been mentioned above comprises following units: 
         [0105]    bottle  520 , which serves for charging the compression-expansion circuit with a working gaseous medium, preferably, neon; 
         [0106]    a vacuum pump  521  serving for preliminary purging the compression-expansion circuit from other gases; 
         [0107]    a shut-off valve  522  which is installed in line  523  and provides fluid communication between the compression-expansion circuit and shut-off valve  522 ; 
         [0108]    the first coil-type heat exchanging unit  513 , which is arranged in the internal space of a heat exchanger  510  and serves for preliminary cooling the working gaseous medium (preferably—neon) to temperature below its inversion temperature; a coupling unit  519  serves for coupling the inlet connection  514  with a line providing fluid communication with compressor  534 ; 
         [0109]    a second coil-type heat exchanging unit  524 , which is arranged in a heat exchanging chamber  530  with a vacuum thermal insulation  531  and has an inlet connection  543  and a middle lumen  544 , which is terminated at its distal end with an orifice tube  532 ; the expanded working gaseous medium is cleared out from the heat exchanging chamber  530  through an outlet connection  533 , which is disposed in the proximal section of the heat exchanging chamber  530 , and is directed into compressor  534  by line  535 ; 
         [0110]    a third coil-type heat exchanging unit  536  is arranged in the distal section of the heat exchanging chamber  530  and serves for cooling the pressurized gaseous medium which is supplied into this third coil type heat exchanging unit  535  via an inlet connection  537  and is removed from the coil type heat exchanging unit  536  via an outlet connection  538 , which is provided with a vacuum thermal insulation  539 . 
         [0111]    The pressurized gaseous medium is provided into the third coil type heat exchanging unit  536  from bottle  140  via a control valve  141 , a mass flow rate gauge  142  and a coupling unit  541 , which serves for coupling a supply line  144  with the inlet connection  537  of the third coil type heat exchanging unit  536 . 
         [0112]    A coupling unit  540  serves for coupling the outlet connection  538  with the flexible hose  120 . 
         [0113]    The flexible hose  120 , the control unit  160  with its associated measuring means and cryoprobe  130  are designed in the same manner as these units in  FIG. 1   a.    
         [0114]      FIG. 5   b  shows an axial cross-section of the heat exchanger  510  with the same units as in  FIG. 5   a.    
         [0115]    It comprises: the first coil-type heat exchanging unit  513 , which is arranged in the internal space of the heat exchanger  510  and serves for preliminary cooling the working gaseous medium (preferably—neon) to temperature below its inversion temperature; the inlet connection  514  is in fluid communication with the compressor. 
         [0116]      FIG. 5   c  shows an axial cross-section of the heat exchanging chamber  530  with the same units as in  FIG. 5   a.    
         [0117]    It comprises: the second coil-type heat exchanging unit  524 , which is arranged in the heat exchanging chamber  530  with the vacuum thermal insulation  531  and has the inlet connection  543 ; the middle lumen  544 , which is terminated at its distal end with the orifice tube  532 ; the expanded working gaseous medium is cleared out from the heat exchanging chamber  530  through the outlet connection  533 , which is disposed in the proximal section of the heat exchanging chamber  530  and is in fluid communication with line  535 .