Abstract:
A cryosurgical instrument including: a shaft having a closed distal end defining an expansion chamber and an open proximal end adapted and configured to receive an inflow of cryogen and to exhaust a flow of expanded cryogen; and a heat exchanger. The heat exchanger includes: a plurality of cryogen delivery tubes that spiral around a longitudinal axis thereof; and a diffuser having a plurality of branches, each of the branches supplying received cryogen to a respective one of the delivery tubes. The cryogen delivery tubes, where they spiral, are spaced from each other and in fluid tight contact with the inner surface of the shaft so as to form spiraling cryogen exhaust pathways that extend along a portion of a length of the cryosurgical instrument from the distal end of the shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional application of U.S. application Ser. No. 13/232,203, which claims the benefit of U.S. provisional patent application No. 61/484,822, filed May 11, 2011. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Embodiments of the present invention relate generally to cryosurgical instruments such as cryoprobes and, more particularly, to cryosurgical instruments featuring a coiled tube heat exchanger. 
         [0004]    2. Description of related art 
         [0005]    It is known to employ coiled heat exchangers in cryosurgical instruments with cryogen supplied as a pressurized gas. In such heat exchangers, the expansion of the gas causes it to change its temperature. As explained in U.S. Pat. No. 6,706,037, for example, this phenomenon is referred to as the “Joule-Thomson effect”, thermodynamically known as adiabatic expansion. 
         [0006]    It is also known, in coiled heat exchangers, to use gases that cool upon expansion, such as Argon or Nitrogen, for cooling, and gases that heat as a result of the expansion, such as Helium, for heating. In these heat exchangers, the return gases are commonly used to recycle the thermal energy (i.e., the return cooling gas not only cools the outer surface of the cryosurgical instrument but also the inlet pressurized gas). See, for example, U.S. Pat. No. 6,706,037 (at column 15 lines 40-58, and column 16 lines 65-68). Also, as discussed in U.S. Pat. Nos. 3,800,552 and 5,522,870, lowering the inlet temperature may liquefy the expanded gas. 
         [0007]    Still further, approaches to enhancing the cooling and heating regeneration are known. For example, U.S. Pat. No. 5,800,487 discusses enhancing the cooling and heating regeneration by supplying the inlet pressurized gas tube with fins to increase the area of the heat exchanging. 
         [0008]    If the cryogen is supplied as a liquid or a two-phase (gas/liquid) fluid, cooling methods use the energy required for the change of phase of the inlet cryogen. In this case, the temperature of the inlet fluid and the return fluid may be the same or close in value, and would minimize, or annul heat exchange between the inlet and outlet fluids, due to a small differential temperature. The application of coil serves as a separator of the phases in a two-phase flow. This is because the liquid phase has greater specific gravity, which causes the liquid phase to the outer (greater) diameter. The greater diameter of the coil is close to the external surface and, as a result, the boiling or change of phase of the liquid occurs close to the external surface. 
         [0009]    When the cryogens, either in gaseous form or two-phase form, enter in a straight inlet tube, or lumen, flow directing elements (such as those described in U.S. Pat. No. 5,800,487) or baffles (such as those described in U.S. Patent Publication No. 2009/0163902 A1, U.S. Patent Publication No. 2007/0149957 A1, U.S. Patent Publication No. 2007/0149959 A1, and U.S. Patent Publication No. 2009/0182320 A1) have been used. 
       BRIEF SUMMARY 
       [0010]    In one aspect, the innovation disclosed herein yields increased performance of a cryosurgical device by selectively locating the boiling of cryogen in the device. In one implementation, a cryosurgical instrument comprises a coiled tube heat exchanger in which a fluid cryogen flows into a coil that is in energy exchange contact with the outer wall of a portion of a cryosurgical instrument. The heat exchange zone comprises at least the distal/downstream tip of the cryosurgical instrument. 
         [0011]    One aspect of the present application provides a cryosurgical instrument including: a shaft having a closed distal end defining an expansion chamber and an open proximal end adapted and configured to receive an inflow of cryogen and to exhaust a flow of expanded cryogen; and a heat exchanger. The heat exchanger includes: a plurality of cryogen delivery tubes that spiral around a longitudinal axis thereof; and a diffuser having a plurality of branches, each of the branches supplying received cryogen to a respective one of the delivery tubes. The cryogen delivery tubes, where they spiral, are spaced from each other and in fluid tight contact with the inner surface of the shaft so as to form spiraling cryogen exhaust pathways that extend along a portion of a length of the cryosurgical instrument from the distal end of the shaft. 
         [0012]    Another aspect of the present invention provides a cryosurgical instrument including: a shaft having a closed distal end defining an expansion chamber and an open proximal end adapted and configured to receive an inflow of cryogen and to exhaust a flow of expanded cryogen; and a heat exchanger. The heat exchanger includes: a solid core element extending along a longitudinal axis of the heat exchanger; and a cryogen delivery tube that spirals around and contacts the solid core element. The spirals of the cryogen delivery tube are spaced from each other and in fluid tight contact with the solid core and an inner surface of the shaft so as to form a spiraling cryogen exhaust pathway from the distal end of the shaft to the proximal end of the shaft. 
         [0013]    Still another aspect of the present invention provides a cryosurgical instrument including: a shaft having a closed distal end defining an expansion chamber and an open proximal end adapted and configured to receive an inflow of cryogen and to exhaust a flow of expanded cryogen; and a heat exchanger. The heat exchanger includes: a solid core element extending along a longitudinal axis of the heat exchanger; and first and second cryogen delivery tubes, the first cryogen delivery tube including an uncoiled portion extending along the longitudinal axis and a coiled portion that spirals around and contacts the solid core element, the second cryogen delivery tube having a coiled portion that spirals around and contacts the uncoiled portion of the first cryogen delivery tube. The coiled portions are spaced apart. The spirals of the cryogen delivery tubes are spaced from each other and in fluid tight contact with an inner surface of the shaft so as to form a spiraling cryogen exhaust pathway from the distal end of the shaft to the proximal end of the shaft. 
         [0014]    Yet another aspect of the present invention provides a cryosurgical instrument including: a shaft having a closed distal end defining a tip and an open proximal end adapted and configured to receive an inflow of cryogen and to exhaust a flow of expanded cryogen; a cryogen flow path from a cryogen supply to the distal end and comprising a cryogen inlet tube in fluid communication with a diffuser that is in fluid communication with a plurality of cryogen delivery tubes that spiral around a longitudinal axis thereof, the diffuser having a plurality of branches, each of the branches supplying received cryogen to a respective one of the delivery tubes; an expansion chamber that receives cryogen from the delivery tubes and permits the received cryogen to expand and cool; and a cryogen exhaust path from the distal end to a cryogen exhaust outlet at the proximal end and comprising spaces between the spirals of the delivery tubes, a return plenum, and a return tube between the cryogen inlet tube and an inner surface of the shaft. The cryogen delivery tubes, where they spiral, are spaced from each other and in fluid tight contact with the inner surface of the shaft so as to form spiraling cryogen exhaust pathways that extend along a portion of a length of the cryosurgical instrument from the distal end of the shaft. 
         [0015]    The aforementioned and/or other features, aspects, details, utilities, and advantages of the present invention are: set forth in the detailed description which follows and/or illustrated in the accompanying drawings; possibly inferable from the detailed description and/or illustrated in the accompanying drawings; and/or learnable by practice of the present invention. 
         [0016]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is neither intended to identify key features or essential features of the claimed subject matter, nor should it be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantage noted in any part of this application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will be more readily understood from the detailed description of embodiments thereof made in conjunction with the accompanying drawings of which: 
           [0018]      FIGS. 1A and 1B  illustrate a non-limiting example of a cryosurgical instrument consistent with an exemplary embodiment of the present invention; 
           [0019]      FIG. 2  is a view of a non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention; 
           [0020]      FIG. 3  is a view of a non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention; 
           [0021]      FIGS. 4A and 4B  are views of non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention; and 
           [0022]      FIGS. 5 and 6  are views of non-limiting examples of heat exchangers consistent with exemplary embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
         [0024]    Although the following text sets forth a detailed description of at least one embodiment or implementation, it is to be understood that the legal scope of protection of this application is defined by the words of the claims set forth at the end of this disclosure. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments and/or implementations are both contemplated and possible, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims 
         [0025]    It is to be understood that, unless a term is expressly defined in this application using the sentence “As used herein, the term ” is hereby defined to mean . . . ” or a similar sentence, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to in this patent in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term by limited, by implication or otherwise, to that single meaning. Finally, unless a claim element is defined by reciting the word “means” and a function without the recital of any structure, it is not intended that the scope of any claim element be interpreted based on the application of 35 U.S.C. §112, sixth paragraph. 
         [0026]    Referring to  FIGS. 1A and 1B , there is shown a non-limiting example of a cryosurgical instrument comprising a heat exchanger that features multiple helical coils, which is consistent with an exemplary embodiment of the present invention.  FIG. 1A  is cross-sectional view of the cryosurgical instrument  100  with the heat exchanger  101 .  FIG. 1B  shows the heat exchanger  101  without the cryosurgical instrument  100 . 
         [0027]    As shown, the cryosurgical instrument  100  includes a shaft  103  surrounding an inlet  102 , a diffuser  112  connected to a core  116 , a helical (i.e. coiled) heat exchanger  101 , and a tip  109 . The portion of the cryosurgical instrument from the tip  109  to just past the diffuser  112  defines a cooling zone  105 . Freezing of tissue occurs around the cooling zone  105 . 
         [0028]    The inlet  102  receives cryogen and delivers the received cryogen into the shaft  103 . The shaft  103  features insulation  104  that surrounds the shaft  103  and is mounted to the inner surface of the shaft  103 . The insulation  104  is disposed outside of the cooling (heat exchange) zone  105 . The presence of the insulation  104  ensures that freezing occurs only where treatment is desired, which is around the cooling zone  105 . 
         [0029]    In operation, cryogen enters through the inlet  102 , as indicated by inlet flow arrows  114 , to the diffuser  112 . The flow then enters the diffuser  112 , which divides the flow into a plurality of branches  155 , of which two are shown for the purpose of illustration only. From the branches  155  of the diffuser  112 , the flow enters the heat exchanger  101  through an entrance  150  thereof. 
         [0030]    The diffuser  112  preferably comprises four branches  155  as shown in  FIG. 1B . However, it is to be understood that other numbers of branches are both contemplated and possible. When formed with four branches, the heat exchanger may comprise four coiled tubes  154 , as illustrated in  FIG. 1B . 
         [0031]    The heat exchanger  101  spirals around the core  116  and between the core and the inner surface of the shaft  103 . The flow of cryogen through the coiled tubes  154  of the heat exchanger  101  is subjected to centrifugal forces as previously described, such that cryogen is forced against the outer surface of the heat exchanger  101 , which is closest to the inner surface of shaft  103 , within the cooling zone  105 . 
         [0032]    As used herein, the term centrifugal force refers to the tendency of a flow following a curved path to be urged away from the center of curvature due to inertia. Centrifugal force is referred to as a force for convenience and ease of explanation. This centrifugal force urges the liquid phase of two-phase flow following a curved path to be urged away from the center of curvature due to greater specific gravity than the gaseous phase. 
         [0033]    As cryogen exits the heat exchanger  101  as indicated by arrows  156 , it is reflected against a reflective surface  108  of the tip  109 . In this embodiment, the tip  109  is hollow, and the reflective surface  108  is optionally placed close to the inner surface of tip  109  as shown. It is to be understood, however, that the tip  109  need not be hollow and/or the reflective surface  108  may be placed distal to the inner surface of the tip  109  (not shown). Boiling of cryogen occurs within the heat exchanger  101 , at reflective surface  108 , and in a return flow gap  152  between the coiled tubes  154  of the heat exchanger  101 , the core  116 , and the inner surface of the outer shaft  103 . 
         [0034]    After being reflected by the reflective surface  108 , the exhausted cryogen flows through the gap  152  between the heat exchanger  101  and the shaft  103 , as shown. The curved gap  152  enhances the continued boiling of the liquid phase close to the external wall, as described before. The direction of this return flow is shown by return flow arrows  115 . The cryosurgical instrument  100  may optionally include a solid core  116  at the innermost part of the shaft  103  and in cooling zone  105 , such that neither the heat exchanger  101  nor the gap  152  are present within the core  116 . Instead, both the heat exchanger  101  and the gap  152  are preferably arranged around the core  116  as shown. However, as previously described, heat exchange between the inlet and the outlet flow is negligible in this arrangement, due to the negligible temperature difference between the respective flows. 
         [0035]    The return flow of exhausted cryogen leaves the cooling zone  105  and then continues as the return flow  113 , as shown, through a return plenum  111  and into a return curved gap  107 . The exhausted cryogen then exits through a cryogen exhaust outlet  153  at an end of the cryosurgical instrument  100  distal from the tip  109 . 
         [0036]      FIG. 1B  shows the heat exchanger  101  of  FIG. 1A  in more detail. As shown in  FIG. 1A , the heat exchanger  101  and the diffuser  112  are both disposed in the cooling zone  105 . The illustrated heat exchanger  101  includes four coiled tubes  154  arranged around and spiraling (wrapping) around a solid core  116 . Each of the four branches  155  of the diffuser  112  feeds into a respective one of the coiled tubes of heat exchanger  101  (i.e., in a 1:1 relationship). The coiled tubes  154  have a spiral shape (and may be said to spiral) and are coiled as shown. This configuration advantageously induces the cryogen flowing through the tubes  154  to undergo centrifugal forces as previously described. 
         [0037]    It is to be appreciated that the number of coiled tubes and branches need not be four and that other numbers are both possible and contemplated. It is also to be appreciated that the coiled tubes  154  may spiral at varied spiral pitches. 
         [0038]    The return flow is preferably permitted only between the inlet tube of the heat exchanger  101  and the inner surface of the shaft  103  at the cooling zone  105 , by providing a core  116  that prevents the return flow from returning through the inner gap of the cryosurgical instrument  100  (i.e., the inlet and the return flow are centrifugal). Flow in the center of the helical coil (defined by coiled tubes  154 ) would have been straight. 
         [0039]      FIG. 2  shows another non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention. The illustrated heat exchanger  201  includes four coiled tubes  254  arranged around and spiraling around a central, longitudinal axis (not shown) in a cooling zone  205  of a cryosurgical device. In contrast to heat exchanger  101  of  FIGS. 1A and 1B , heat exchanger  201  does not spiral (i.e., wrap) around a core. 
         [0040]    Each of the four branches of the diffuser  212  feeds into a respective one of the coiled tubes of heat exchanger  201  (i.e., in a 1:1 relationship). The coiled tubes  254  spiral and are coiled as shown. This configuration advantageously induces the cryogen flowing through the tubes  254  to undergo centrifugal forces as previously described. 
         [0041]    It is to be appreciated that the number of coiled tubes  254  and branches need not be four and that other numbers are both possible and contemplated. It is also to be appreciated that the coiled tubes  254  may spiral at varied spiral pitches. 
         [0042]      FIG. 3  shows another non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention. As shown, the heat exchanger  301  has a single tube  354  that spirals (i.e., wraps) around a core  316 . The single tube  354  preferably wraps around the core  316  with a consistent spiral pitch and does so in the cooling zone  305  of a cryosurgical device. The heat exchanger  301  does not include any type of diffuser. Instead, cryogen enters via an inlet flow  314  that is directed to the tube  354 . 
         [0043]    It is to be appreciated that the coiled tubes  354  may spiral at varied spiral pitches. 
         [0044]      FIG. 4A  shows a non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention. The illustrated heat exchanger  401  is similar to the heat exchanger  201  of  FIG. 2  in some respects and is usable with the cryosurgical instrument  100  of  FIG. 1A . As shown, the heat exchanger  401  comprises a plurality of tubes  454  that spiral in the cooling zone  405  of a cryosurgical instrument. The heat exchanger  401  differs from the heat exchanger  201  of  FIG. 2  in that at least one tube  454  is longer than at least one other tube  454 . For the purpose of illustration, a longer tube  454  is designated by  454 A. The distal end  460  of this longer tube  454 A is disposed more closely to a tip of a cryosurgical instrument (not shown) such as tip  109  of  FIG. 1 , such that discharge of cryogen from distal end  460  occurs more closely to tip  109 , as compared to discharge from the remaining tubes  454 . 
         [0045]      FIG. 4B  shows a non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention. The illustrated heat exchanger  401 ′ is similar to the heat exchanger  401  of  FIG. 4A  in some respects. As shown, a heat exchanger  401 ′ comprises a plurality of tubes  454 ′. However, in heat exchanger  401 ′, each tube  454 ′ is of a different length, such that discharge of cryogen from tubes  454 ′ occurs at different points, spread along the ablation zone  405 ′. 
         [0046]    It is to be appreciated that the number of coiled tubes and branches need not be four and that other numbers are both possible and contemplated. It is also to be appreciated that the coiled tubes  454  and  454 ′ may spiral at varied spiral pitches. 
         [0047]      FIG. 5  shows a non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention. The illustrated heat exchanger  501  is similar to the heat exchanger  301  of  FIG. 3  in some respects. As shown, the heat exchanger  501  has a single tube  554  that spirals (wraps) around a core  516  in the cooling zone  505  of a cryosurgical instrument. Unlike the heat exchanger  301 , the single tube  554  spirals around the core  516  with a varied spiral pitch. Varying the pitch of the single tube  554  alters the centrifugal forces on the cryogen at a plurality of different points along the single tube  554 . 
         [0048]    Heat exchanger  501  does not include any type of diffuser. Instead, cryogen enters via an inlet flow  514  that is directed to tube  554 . 
         [0049]      FIG. 6  shows a non-limiting example of a heat exchanger consistent with an exemplary embodiment of the present invention. The illustrated heat exchanger  601  comprises two tubes  654 A and  654 B. Both tubes spiral around a longitudinal axis of and in the ablation zone  605  of the heat exchanger  601 . Tube  654 B includes a straight (uncoiled) portion that is upstream and a spiral portion downstream that spirals (wraps) around a solid core  616  in the cooling zone  605  of a cryosurgical instrument. Tube  654 A spirals (wraps around) the straight portion of tube  654 B. Tubes  654 A and  654 B have different spiral pitches. Tubes  654 A and  654 B have different inlet flows of cryogen, indicated with arrows. 
         [0050]    Heat exchanger  601  does not include any type of diffuser; instead, cryogen enters via inlet flows that are respectively directed to tubes  654 A and  654 B. 
         [0051]    By way of non-limiting examples, among the many advantages of this arrangement, the inlet flow of a cryogen (whether as a liquid or as two phase (gas/liquid) flow) is subjected to a centrifugal force of rotation. Such force causes the cryogenic liquid to boil close to the outer surface of the coiled tube (for example, tubes  654 A and  654 B of  FIG. 6 ), which in turn is the portion of the coiled tube that is located proximal to the inner wall of the ablation (heat exchange) zone  601 . Thus, boiling occurs within the cryosurgical instrument  600  at a location that provides the most efficient heat transfer to the heat exchange zone  601 , which is the desired portion of the cryosurgical instrument  600  to receive such heat transfer. 
         [0052]    Such advantages are more apparent in case of two-phase flow since the conduction coefficient of the liquid phase to the outer surface is by far greater than the conduction coefficient of the gaseous phase, and the centrifugal forces, due to the difference in mass density. This approach is optionally and preferably used twice, in the inlet flow as well as the outlet flow, such that two coiled tubes  654 A and  654 B are entwined but preferably do not come into contact. Heat exchange between the inlet and the outlet flow is negligible in this arrangement, due to the small or non-existence of dT (temperature differential) to permit it. 
         [0053]    Examples of various features/aspects/components/operations have been provided to facilitate understanding of the disclosed embodiments of the present invention. In addition, various preferences have been discussed to facilitate understanding of the disclosed embodiments of the present invention. It is to be understood that all examples and preferences disclosed herein are intended to be non-limiting. 
         [0054]    Although selected embodiments of the present invention have been shown and described individually, it is to be understood that at least aspects of the described embodiments may be combined. 
         [0055]    Although selected embodiments of the present invention have been shown and described, it is to be understood the present invention is not limited to the described embodiments. Instead, it is to be appreciated that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and the equivalents thereof.