Abstract:
A system and a method for its use are provided to cool a cryotip at the distal end of a probe for a cryosurgical procedure. In particular, the cryotip is cooled by a liquid refrigerant to cryogenic temperatures in order to perform a cryosurgical procedure on biological tissue. For the invention, the system maintains the refrigerant in a liquid state as it transits through the cryotip. In one embodiment, a closed system is disclosed in which liquid refrigerant from the cryotip is recycled and reused. In another disclosed embodiment, liquid refrigerant from the cryotip is evaporated and the resulting vapor is released through a vent.

Description:
[0001]    This application is a continuation-in-part of application Ser. No. 12/425,938, filed Apr. 17, 2009, which is currently pending. Application Ser. No. 12/425,938 claims the benefit of U.S. Provisional Patent Application Ser. No. 61/047,496, filed Apr. 24, 2008. The contents of application Ser. No. 12/425,938 and 61/047,496 are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains generally to systems and methods for performing a cryosurgical procedure. More particularly, the present invention pertains to systems and methods that use a probe having a cryotip for cooling biological tissues to cryogenic temperatures. The present invention is particularly, but not exclusively, useful as an open-loop system wherein a liquid refrigerant remains in a liquid state as it enters and exits the cryotip of a probe. 
       BACKGROUND OF THE INVENTION 
       [0003]    A probe that is to be used for cryosurgery must be designed with an optimally small shape and size to achieve selective cooling of biological tissues. The cryosurgical system must also be designed to provide reliable cooling of the part of the cryoprobe (i.e. the cryotip) that will be in direct thermal contact with the target biological tissue to be treated. 
         [0004]    For many cryogenic treatment applications, temperatures below −90° C. are desirable, and some known cryosurgical systems use liquid refrigerants such as nitrogen, argon, nitrous oxide, carbon dioxide, various hydro/fluorocarbons, and others. Liquid nitrogen has a very desirable low temperature of approximately −200° C., but when it is introduced into the freezing zone of the cryoprobe, where it is in thermal contact with surrounding warm biological tissues, its temperature increases above the boiling temperature (−196° C.). Thus, it evaporates and expands several hundred-fold in volume at atmospheric pressure, and rapidly absorbs heat from the probe tip. This enormous increase in volume results in a “vapor lock” effect when the mini-needle of the cryoprobe gets “clogged” by the gaseous nitrogen. 
         [0005]    Several liquid nitrogen systems have been proposed. For example, improved cryosurgical systems and methods for supplying liquid nitrogen to a probe tip are disclosed in U.S. Pat. No. 5,520,682, and U.S. Pat. No. 7,192,426, both of which issued to Baust et al. Further, a system for the direct and/or indirect delivery of liquid nitrogen to a probe tip is disclosed in U.S. Pat. No. 5,334,181 which issued to Rubinsky et al. For these and other similar type systems, cryosurgical practice shows that current cooling systems and methods that are based on the use of liquid nitrogen as a means to cool a miniature probe tip are not practicably feasible. In large part, this is due to the rapid transition of the liquid nitrogen into the gaseous state followed by an inevitable “vapor lock.” 
         [0006]    Nitrous oxide and carbon dioxide systems typically achieve cooling when pressurized gases are expanded through a Joule-Thomson expansion element such as a small orifice, throttle, or other type of flow construction that is disposed at the end tip of the cryoprobe. For example, a typical nitrous oxide system pressurizes the gas to about 5 to 5.5 MPa to reach a temperature of no lower than about −85 to −65° C. at a pressure of about 0.1 MPa. For carbon dioxide, the temperature of about −76° C. at the same pressure of 0.1 MPa is achieved with an initial pressure of about 5.5 MPa. Nitrous oxide and carbon dioxide cooling systems, however, are not able to achieve the temperature and cooling power provided by liquid nitrogen systems. On the other hand, nitrous oxide and carbon dioxide cooling systems have some advantages because the inlet of high pressurized gas at a room temperature, when it reaches the Joule-Thomson throttling component or other expansion device at the probe tip, excludes the need for thermal insulation of the system. However, because of an insufficiently low operating temperature combined with relatively high initial pressure, cryosurgical applications are strictly limited. Additionally, the Joule-Thomson system typically uses a heat exchanger to cool the incoming high pressure gas with the outgoing expanded gas in order to achieve the necessary drop in temperature by expanding compressed gas. Stated differently, these heat exchanger systems are not compatible with the desired miniature size of probe tips that must be less than at least 3 mm in diameter. 
         [0007]    Several mixed gas refrigeration systems (e.g. Joule-Thompson systems) have been proposed for performing cryosurgical procedures. In particular, U.S. Pat. No. 5,787,715, U.S. Pat. No. 5,956,958, and U.S. Pat. No. 6,530,234, all of which issued to Dobak, III et al., disclose cryogenic procedures using devices having mixed gas refrigeration systems. Other systems wherein a refrigerant transitions from a liquid to a gas (e.g. a Joule-Thomson effect) include systems disclosed in U.S. Pat. No. 6,074,572 which issued to Li et al. and U.S. Pat. No. 6,981,382 which issued to Lentz et al. 
         [0008]    In review, systems using liquid nitrogen as a means to cool a miniature probe tip are subject to “vapor lock.” On the other hand, systems that use highly pressurized gas mixtures in order to achieve the Joule-Thomson effect cannot provide operating temperatures lower than about −90° C. Thus, they are not desirable for many cryosurgical procedures. 
         [0009]    In light of the above, an object of the present invention is to provide a closed system for performing a cryosurgical procedure with a cryoprobe that maintains a liquid refrigerant in its liquid state as it transits through the cryoprobe. It is yet another object of the present invention to provide a closed system that maintains a liquid refrigerant in its liquid state as it transits through the cryoprobe and recycles refrigerant exiting the cryoprobe and reuses the recycled refrigerant as an input to the cryoprobe. It is another object of the present invention to provide a system that maintains a liquid refrigerant in its liquid state as it transits through a cryoprobe and thereafter evaporates the refrigerant and releases the resulting vapor at a vent provided downstream of the cryoprobe. It is still another object of the present invention to provide a system and method for performing a cryoablation treatment that employs non-evaporative liquid refrigerants at a low pressure (e.g. 0.3 MPa), and at a low temperature (e.g. less than −100° C.). It is another object of the present invention to provide a cryoablation system that can be customized to use any one of several different liquid refrigerants. Still another object of the present invention is to provide a cryoablation system that incorporates a means for removing frozen biological tissue that may adhere to the cryoprobe during a cryosurgical treatment. It is also another object of the present invention to provide a cryoablation system that is easy to use, is relatively simple to manufacture and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0010]    A system and method for performing a procedure for the cryosurgical treatment of biological tissue includes a probe (i.e. a cryoprobe) and a liquid refrigerant for cooling the tip of the probe for the procedure. In one embodiment, the system is closed-loop and, importantly, the liquid refrigerant always remains in a liquid state as it is circulated through the system. As envisioned for the present invention, low temperatures (e.g. less than −100° C.) and low pressures (e.g. as low as 0.3 MPa) are achievable at the tip of the cryoprobe. In another embodiment, the system is closed, but not necessarily closed-loop. Like the closed-loop embodiment, for the closed embodiment, the liquid refrigerant is maintained in its liquid state as it transits through the cryoprobe. However, as detailed further below, for the closed system, liquid refrigerant exiting the probe is removed, recycled and reused by reintroducing the recycled refrigerant into the line which inputs refrigerant into the cryoprobe. In yet another embodiment, the system includes a vent downstream of the cryoprobe. Like the closed-loop and closed system embodiments, for the vented embodiment, the liquid refrigerant is maintained in its liquid state as it transits through the cryoprobe. However, for the vented embodiment, the liquid refrigerant is evaporated downstream of the cryoprobe and the resulting vapor is released at a vent. 
         [0011]    Structurally, the cryoablation system of the present invention includes a container for holding a liquid refrigerant. Depending on the particular liquid refrigerant being used, the liquid refrigerant is held in the container, as a liquid, at a base pressure “P B ” and at a temperature “T R ”. Specifically, T R  is substantially the same or slightly cooler than the environmental temperature where the container is located. For purposes of the present invention the liquid refrigerant is preferably selected from a group of refrigerants including R124, R218, R290, R1270 and R600A. 
         [0012]    In addition to the liquid refrigerant container, the system also includes a cryoprobe. In detail, this cryoprobe includes a hollow, substantially tubular-shaped vacuum shell having a proximal end and a distal end. A cryotip that is formed with a liquid-tight chamber is attached to the distal end of the vacuum shell. And, a cold inlet line extends through the vacuum shell from its proximal end to its distal end to establish fluid communication with the chamber of the cryotip. Similarly, a return line extends proximally from the chamber of the cryotip, and back through the vacuum shell, to establish fluid communication between the chamber of the cryotip and the proximal end of the cryoprobe. Preferably, the outside diameters of the cryotip and of the vacuum shell are less than approximately 3 mm. As intended for the present invention, the vacuum shell is provided to thermally isolate the cold inlet line and the return line from contact with surrounding tissue while the cryoprobe is positioned for a procedure. Further, a turbulator can be positioned in the chamber of the cryotip to assist in the movement of liquid refrigerant through the cryoprobe. 
         [0013]    A pump is positioned along the cold inlet line, between the liquid refrigerant container and the cryoprobe. For the present invention, the liquid pump is used to initially move liquid refrigerant from the container and subsequently through the system at an elevated operational pressure P opn . For the closed-loop embodiment, a refrigerator is positioned along the cold inlet line, between the pump and the cryoprobe to receive liquid refrigerant from the pump at the operational pressure P opn , and to then cool it to a temperature T min . For the closed system embodiment, an external refrigerator can be used in place of the in-line refrigerator to cool the refrigerant. A secondary container of cooled refrigerant from the external refrigerator is then attached to the inlet line (replacing the initial container) where it can be pumped through the inlet line to the cryoprobe. For the vent embodiment, an in-line refrigerator (described above for the closed-loop embodiment) or an external refrigerator (described above for the closed system embodiment) may be used. Exemplary values for T min  and P opn  are, respectively, a temperature less than about −100° C., and a pressure in a range between approximately 0.3 MPa and approximately 5.0 MPa. Thus, the liquid refrigerant enters the cold inlet line for transfer to the chamber of the cryotip at the temperature T min  and the pressure P opn . 
         [0014]    In a preferred embodiment of the present invention, the system provides a means for separating the cryotip from target tissue when there is an adhesion. For this purpose, the cold inlet line may also include a heater for receiving a portion of the liquid refrigerant from the pump, and for heating the portion of liquid refrigerant. The heated, or warmed, liquid refrigerant is then directly transferred to the cryoprobe for the purpose of removing any adhesion of biological tissue that may have occurred during the cryosurgical treatment. In this operation, the temperature of the heated liquid refrigerant can be controlled. More specifically, the system includes a first slide valve that is used for controlling the flow of liquid refrigerant from the pump to the refrigerator. There is also a second slide valve for controlling the flow of liquid refrigerant from the pump to the heater. The operation of the first and second slide valves can then be coordinated to mix liquid refrigerant from the heater with liquid refrigerant from the refrigerator to establish a predetermined temperature T P  for liquid refrigerant in the cryoprobe that will remove the adhesion. To do this, of course, T P  needs to be greater than T R . 
         [0015]    Further, in the preferred embodiment of the present invention, the refrigerator will include a pressure vessel for holding a liquid cryogen. A portion of the cold inlet line that connects the container in fluid communication with the cryoprobe will then be coiled and submerged in the liquid cryogen. For the present invention, the liquid cryogen is preferably liquid nitrogen having a temperature in a range between −180° C. and −150° C. at a pressure in a range between 0.5 and 3.0 MPa, that will cool the liquid refrigerant to T min . 
         [0016]    In the return line of the closed-loop embodiment, a heat exchanger and a check valve are positioned between the cryoprobe and the container. Functionally, this heat exchanger is positioned in the return line to heat the liquid refrigerant to T R . And, the check valve is positioned in the return line to reduce pressure on the liquid refrigerant to P B . Thus, the liquid refrigerant is returned to the container substantially at the temperature T R , at the pressure P B . 
         [0017]    In the closed embodiment, the return line can include a check valve that is positioned between the cryoprobe and a secondary container. The secondary container receives refrigerant from the cryoprobe for recycling. Once the secondary container is full, or at the end of a procedure, the secondary container can be detached from the return line and placed within an external refrigerator. Once the refrigerant is at the proper temperature, the secondary container can be removed from the external refrigerator and attached to the inlet line (replacing the initial container) allowing the refrigerant from the return line to be reused. 
         [0018]    In the vented embodiment, the return line can include a check valve that is positioned between the cryoprobe and an evaporator/vent unit. Refrigerant reaching the evaporator/vent unit is evaporated and the resulting vapor is allowed to pass through a vent. 
         [0019]    In an operation of the closed-loop system of the present invention, a liquid refrigerant is initially held in a container, as a liquid, at a predetermined temperature and pressure (T R  and P B ). The liquid pump then pressurizes the liquid refrigerant to an operational pressure (P opn ) while the liquid refrigerant remains substantially at the temperature (T R ). Next, the refrigerator lowers the temperature of the liquid refrigerant from (T R ) to (T min ). The chilled and pressurized liquid refrigerant is then transferred through the vacuum shell to the cryotip where it is used for a cryosurgical procedure (T min  and P opn ). 
         [0020]    Once the liquid refrigerant has passed through the cryotip, it is warmed by a heat exchanger to the predetermined temperature (T R ). Additionally, a check valve reduces pressure on the liquid refrigerant to (P B ). The purpose here is twofold. For one, it insures that the refrigerant remains in its liquid phase through the cryotip and, thus, the system. For another, the liquid refrigerant can then be returned to the container at the initial temperature and pressure (T R  and P B ) for recycling. 
         [0021]    In an alternate embodiment of the cryoprobe, as noted above, the liquid refrigerant can be heated at the conclusion of a cryosurgical procedure to remove the cryotip of the probe from any adhesion it may have established with biological tissue. More specifically, this intermediate heating will take the liquid refrigerant up to a temperature (T P ) in the cryotip for removal of the adhesion therefrom. Additionally, if the refrigerant&#39;s temperature in this procedure is maintained above 60° C. it can be used to produce local tissue coagulation that eliminates bleeding. In detail, this heating will be caused by liquid refrigerant that is heated as it bypasses the refrigerator, but before it is introduced into the cryotip. The liquid refrigerant can then be subsequently cooled to T R  as disclosed above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0023]      FIG. 1  is a schematic drawing of a cryoprobe system in accordance with the present invention; 
           [0024]      FIG. 2  is an alternate embodiment of a refrigerator for use with the cryoprobe system; 
           [0025]      FIG. 3  is yet another alternate embodiment of a refrigerator for use with the cryoprobe system shown in combination with a heater for use in releasing the cryotip of the cryoprobe system from biological tissue after completion of a cryosurgical procedure; 
           [0026]      FIG. 4  is a phase diagram for an exemplary liquid refrigerant showing pressure and temperature changes of the liquid refrigerant during an operational cycle of the cryoprobe system using R124 refrigerant; 
           [0027]      FIG. 5  is a schematic drawing of another embodiment in accordance with the present invention in which a closed system for cryoablation includes an external refrigerator; 
           [0028]      FIG. 6  is a schematic drawing of another embodiment in accordance with the present invention having an evaporator/vent unit on the return line; and 
           [0029]      FIG. 7  is a schematic drawing of yet another embodiment in accordance with the present invention in which a closed system for cryoablation includes an external refrigerator. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Referring initially to  FIG. 1 , a system for performing a cryosurgical procedure in accordance with the present invention is shown and is generally designated  10 . As shown, the system  10  essentially includes a liquid container  12  and a cryoprobe  14 . In detail, the cryoprobe  14  includes a substantially tubular shaped vacuum shell  16  having a distal end  18  and a proximal end  20 . For purposes to be disclosed in greater detail below, the proximal end  20  may be bifurcated into separate proximal ends  20   a  and  20   b . In any event, the cryoprobe  14  will also include a cryotip  22  that is affixed to a plug  24  at the distal end  18  of the vacuum shell  16 . Structurally, the cryotip  22  is formed with a liquid-tight chamber  26 , and a turbulator  28  may be positioned inside the liquid-tight chamber  26 . As indicated in  FIG. 1 , the outside diameter  30  of the cryoprobe  14  is substantially the same for both the vacuum shell  16  and the cryotip  22  and is, preferably, less than 3 mm. 
         [0031]      FIG. 1  also shows that the system  10  includes a cold inlet line  32  that extends from the liquid container  12  for fluid communication with the liquid-tight chamber  26  of the cryotip  22 . Integrated into the cold inlet line  32  between the container  12  and the proximal end  20   a  of the cryoprobe  14  are a liquid pump  34  and a refrigerator  36 . Further,  FIG. 1  shows that the system  10  includes a return line  38  that extends from the fluid-tight chamber  26  of the cryotip  22  through the proximal end  20   b  of the vacuum shell  16  for fluid communication with the container  12 . Importantly, as emphasized by the exaggerated bifurcation of proximal ends  20   a  and  20   b  of the vacuum shell  16  shown in  FIG. 1 , the cold inlet line  32  and the return line  38  need to be thermally isolated from each other. The plug  24  mentioned above is provided to help accomplish this. Specifically, the plug  24  is located between the liquid-tight chamber  26  and the vacuum shell  16  to contain the liquid refrigerant  44  inside the liquid-tight chamber  26 . Thus, the interior of vacuum shell  16  is separated from the cryotip  22  to thereby thermally insolate the cold inlet line  32  and the return line  38  from the liquid-tight chamber  26 . Further, the vacuum in the vacuum shell  16  thermally isolates the cold inlet line  32  from the return line  38  inside the vacuum shell  16 . 
         [0032]    As intended for the system  10  of the present invention, a liquid refrigerant  44  remains in its liquid state at all times during an operational cycle. Further, it is important that the liquid refrigerant  44  be capable of attaining a temperature below approximately −100° C., at a relatively low pressure (e.g. in a range between about 0.3 MPa and 1.5 MPa, as it applies to R124 refrigerant). Several commercially available liquid refrigerants  44  have this capability and the preferred refrigerants  44  for use with the present invention are set forth in the TABLE below. 
         [0000]                                                          TABLE                       Molecular   Normal   Normal           Chemical   mass   freezing   boiling       Refrigerant   formula   (kg/mol)   point (° C.)   point (° C.)                                R124   C 2 HClF 4     136.5   −199   −12.1       R218   C 3 F 8     188.02   −150   −36.7       R290   C 3 H 8     44.1   −183   −88.6       R1270   C 3 H 6     42.08   −185   −47.7       R600A   i-C 4 H 10     58.12   −159.5   −11.8                    
Importantly, the various liquid refrigerants  44  set forth in the above TABLE can be used selectively. Specifically, depending on the viscosity and temperature/pressure parameters of a liquid refrigerant  44  selected from the above TABLE, the system  10  can be effectively customized for a particular cryosurgical procedure.
 
         [0033]    A preferred embodiment of the refrigerator  36  is shown in  FIG. 2 . There it will be seen that the cold inlet line  32  is formed with a coil  46  that is immersed in a liquid cryogen  48 , such as liquid nitrogen. In this case, the liquid cryogen  48  is held in the refrigerator  36  at a temperature in a range between −180° C. and −150° C. at a pressure in a range between 0.5 and 3.0 MPa. Further, for this preferred embodiment of the refrigerator  36 , a relief valve  50  is provided to help control the conditions for holding the liquid cryogen  48  as it may boil in the refrigerator  36 . As will be appreciated by cross-referencing  FIG. 2  with  FIG. 1 , the refrigerator  36  shown in  FIG. 2  is incorporated into the system  10  by connections with the cold inlet line  32  at respective points  52  and  54 . 
         [0034]    An alternate embodiment of the cold inlet return line  32  is shown in  FIG. 3 . There, in addition to the refrigerator  36 , it is seen that the cold inlet line  32  of the system  10  may incorporate a heat exchanger  56 . In this embodiment, a slide valve  58  can be used to divert liquid refrigerant  44  flowing from the container  12  around the refrigerator  36  via a by-pass line  60 . At the same time, a slide valve  62  can be manipulated to control the flow of liquid refrigerant  44  to the refrigerator  36 . Thus, in essence, the refrigerator  36  can be completely, or partially, by-passed. The purpose here is to warm the refrigerant  44  for removal (detachment) of the cryotip  22  from any adhesion with biological tissue it may have established. This is accomplished by a concerted and coordinated use of the slide valves  58  and  62 . Similar to the connections disclosed above for refrigerator  36  in  FIG. 2 , the embodiment of refrigerator  36  shown in  FIG. 3  is incorporated into the system  10  by connections with the cold inlet line  32  at respective points  52  and  54 . 
       Operation 
       [0035]    An operation of the system  10  of the present invention will be best appreciated by referring to  FIG. 4 , with cross-reference back to  FIG. 1 . For purposes of cross-referencing  FIG. 4  with  FIG. 1 , a capital letter on the phase diagram ( FIG. 4 ) corresponds to temperature and pressure conditions for liquid refrigerant  44  at the point indicated by the same capital letter shown on the system  10  ( FIG. 1 ). For example, the capital letter “A” shown on the phase diagram in  FIG. 4  indicates a temperature and pressure for the liquid refrigerant  44  that will be manifested at the location “A” shown on the system  10  in  FIG. 1 . In overview, the operation of system  10  involves a closed-loop manipulation of the liquid refrigerant  44  wherein it is continuously recycled through the system  10 . Importantly, the liquid refrigerant  44  remains in its liquid state throughout each entire cycle. 
         [0036]    To begin, a liquid refrigerant  44  is selected (see TABLE), and is held in a container  12  at a temperature T R  (i.e. an environmental temperature of the system  10 ) and a pressure P B . This corresponds to the point A shown in  FIG. 4  where liquid refrigerant  44  is in its liquid state as it is introduced into the cold inlet line  32  (see  FIG. 1 ). After the liquid refrigerant  44  leaves the container  12 , the liquid pump  34  increases pressure on the liquid refrigerant  44 . This pressure increase is accomplished at a substantially constant temperature T R , from P B  to P opn  (i.e. from point A to point B in the diagram  FIG. 4 ). Next, the temperature of the liquid refrigerant  44  is decreased in the cold inlet line  32  by the refrigerator  36 , while pressure on the liquid refrigerant  44  is maintained substantially constant at P opn . This decrease is from the essentially environmental temperature T R  to the operational cryoablation temperature T min . In  FIGS. 4 and 1 , this is represented as a change from point B (T R , P opn ) to point C (T min , P opn ). With liquid refrigerant  44  under the conditions of point C (T min , P opn ), it passes through the cryotip  22  for the purpose of performing a cryosurgical procedure. 
         [0037]    During a cryosurgical procedure, the cryotip  22  is positioned against the tissue (not shown) that is to be cryoablated. As a consequence of heat transfer from the tissue, the cryosurgical procedure will cause the liquid refrigerant  44  to warm inside the cryotip  22 . Despite this warming, it can happen that the cryotip  22  will adhere (i.e. freeze) to the tissue. When this happens, in order to overcome any adhesion that may have been established between the cryotip  22  and tissue, the system  10  may provide for additional warming of the cryotip  22  after the cryosurgical procedure has been completed. Specifically, this additional warming is provided by a heat exchanger  56  that is integrated into the cold inlet line  32  of the system  10 , substantially as shown in  FIG. 3 . 
         [0038]    Functionally, the amount of additional warming of the liquid refrigerant  44  provided by the heat exchanger  56  can be controlled by a concerted operation of the respective slide valves  58  and  62 . For example, at the operational extremes, a cryosurgical procedure would likely be accomplished with slide valve  58  open, and slide valve  62  closed. On the other hand, the refrigerator  36  can be completely by-passed when the slide valve  58  is closed and the slide valve  62  is open. As will be appreciated by the skilled artisan, selective operation of the valves  58  and  62  will provide a warmer liquid refrigerant  44  for the cryotip  22 , as desired. In any event,  FIG. 4  indicates that the liquid refrigerant  44  is warmed to a nominal temperature T P  while passing through the cryotip  22  (i.e. liquid refrigerant  44  moves from point C to point D in  FIG. 4 ). Subsequently, after the liquid refrigerant  44  leaves the cryotip  22  it passes through a heat exchanger  40  where it is warmed to the environmental temperature T R  (i.e. point E in  FIG. 4 ). A check valve  42  then returns the pressure on the liquid refrigerant  44  to the pressure P B  for its return to the container  12  (see point F in  FIG. 4 ). The liquid refrigerant  44  can then be recycled as desired. 
         [0039]    Referring now to  FIG. 5 , another embodiment of a system for performing a cryosurgical procedure in accordance with the present invention is shown and is generally designated  10 ′. As shown, the system  10 ′ includes a liquid container  12 ′ and a cryoprobe  14 ′. In detail, the cryoprobe  14 ′ includes a substantially tubular shaped vacuum shell  16 ′ having a distal end  18 ′ and bifurcated proximal ends  20   a ′,  20   b ′. Also shown, the cryoprobe  14 ′ includes a cryotip  22 ′ that is affixed to the distal end  18 ′ of the vacuum shell  16 ′. Structurally, the internal configuration of the cryotip  22 ′ and the interface between the cryotip  22 ′ and vacuum shell  16 ′ is the same as the embodiment of the cryoprobe  14  shown in  FIG. 1 . 
         [0040]      FIG. 5  also shows that the system  10 ′ includes a cold inlet line  32 ′ that extends from the liquid container  12 ′ to the cryotip  22 ′. Integrated into the cold inlet line  32 ′ between the container  12 ′ and the proximal end  20   a ′ of the cryoprobe  14 ′ is a liquid pump  34 ′. Further,  FIG. 5  shows that the system  10 ′ includes a return line  38 ′ that extends from the cryotip  22 ′ through the proximal end  20   b ′ of the vacuum shell  16 ′, through check valve  42 ′ and establishes fluid communication with a secondary container  64 . Like the closed-loop embodiment shown in  FIG. 1  and described above, for the closed system embodiment shown in  FIG. 5 , the liquid refrigerant  44  is maintained in its liquid state as it transits through the cryoprobe  14 ′. However, as shown in  FIG. 5 , for the closed system, liquid refrigerant  44  exiting the cryoprobe  14 ′ is removed, recycled and reused by reintroducing the recycled refrigerant into the inlet line  32 ′. More specifically, secondary container  64  can be attached to return line  38 ′ using detachable fittings to allow the secondary container  64  to be detached from the return line  38 ′. Once the secondary container  64  is full, or at the end of a procedure, the secondary container  64  can be detached from the return line  38 ′ and engaged with an external refrigerator  66 , as illustrated by arrow  68 . After sufficient cooling of the refrigerant in secondary container  64 , the secondary container  64  can be attached to the inlet line  32 ′, replacing the container  12 ′ (illustrated by arrow  70 ). 
         [0041]    Referring now to  FIG. 6 , another embodiment of a system for performing a cryosurgical procedure in accordance with the present invention is shown and is generally designated  10 ″. As shown, the system  10 ″ includes a liquid container  12 ″ and a cryoprobe  14 ″. In detail, the cryoprobe  14 ″ includes a substantially tubular shaped vacuum shell  16 ″ having a distal end  18 ″ and bifurcated proximal ends  20   a ″,  20   b ″. Also shown, the cryoprobe  14 ″ includes a cryotip  22 ″ that is affixed to the distal end  18 ″ of the vacuum shell  16 ″. Structurally, the internal configuration of the cryotip  22 ″ and the interface between the cryotip  22 ″ and vacuum shell  16 ″ is the same as the embodiment of the cryoprobe  14  shown in  FIG. 1 . 
         [0042]      FIG. 6  also shows that the system  10 ″ includes a cold inlet line  32 ″ that extends from the liquid container  12 ″ to the cryotip  22 ″.  FIG. 6  illustrates the container  12 ″ can be coupled with external refrigerator  66 ′ and then moved from external refrigerator  66 ′ (to the position labelled  12 ″) and attached to inlet line  32 ″. A liquid pump  34 ″ is integrated into the cold inlet line  32 ″ between the container  12 ″ and the proximal end  20   a ″ of the cryoprobe  14 ″. Further,  FIG. 6  shows that the system  10 ″ includes a return line  38 ″ that extends from the cryotip  22 ″ through the proximal end  20   b ″ of the vacuum shell  16 ″, through check valve  42 ″ and establishes fluid communication with an evaporator/vent unit  72 . Refrigerant reaching the evaporator/vent unit  72  is evaporated and the resulting vapor is allowed to pass through a vent. Although  FIG. 6  shows the use of external refrigerator  66 ′, it is to be appreciated that external refrigerator  66 ′ can be replaced with the in-line refrigerator  36  show in  FIG. 2 , for the  FIG. 6  embodiment. 
         [0043]    Referring now to  FIG. 7 , a portion of an embodiment of a closed system for performing a cryosurgical procedure in accordance with the present invention is shown and is generally designated  10 ′″. As shown, the system  10 ′″ includes a liquid container  12 ′″ and a cold inlet line  32 ′″ that extends from the liquid container  12 ′″ (e.g. to a cryotip  22  shown in  FIG. 1 ). Integrated into the cold inlet line  32 ′″ is a liquid pump  34 ′″. Further,  FIG. 7  shows that the system  10 ′″ includes a return line  38 ′″ (i.e. that extends from a cryotip such as the cryotip  22  shown in  FIG. 1 ) that includes check valve  42 ′″ and establishes fluid communication with container  64 ′″. Like the embodiment shown in  FIG. 5 , for the closed system  10 ′″, liquid refrigerant from the return line  38 ′″ is removed, recycled and reused by reintroducing the recycled refrigerant into the input line  32 ′″. More specifically, refrigerant in secondary container  64 ′″ can be selectively transported to container  74  that is coupled with external refrigerator  66 ′″ via conduit  76 . As shown, a control unit  78  having a valve and/or pump can be used to selectively transport refrigerant from the container  64 ′″ to the container  74 . It can also be seen that refrigerant in container  74  can be selectively transported to container  12 ′″ via conduit  80 . As shown, a control unit  82  having a valve and/or pump can be used to selectively transport refrigerant from the container  74  to the container  12 ′″. 
         [0044]    While the particular All-Liquid Cryoablation Catheter as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.