Abstract:
Cryosurgical instruments and methods utilizing improved heat transfer characteristics. A cryosurgical device includes: a tubular housing; a cryogen supply passage; a heat exchange enhancing member in the housing, disposed along a longitudinal axis of the housing; an annular cooling passage between the heat exchange enhancing member and the tubular housing; a tip cooling and cryogen flow directing section that transmits a temperature of a cryogen flow to the tip, and an insulation element in the tubular housing.

Description:
BACKGROUND 
     1. Technical Field 
     Embodiments of the present invention relate generally to cryosurgical equipment, and, more particularly, to cryosurgical treatment methods and devices with enhanced heat transfer between an external surface and internal fluid cryogen. 
     2. Description of Related Art 
     Cryoprobes that “boil” a liquid cryogen, when this liquid cryogen is supplied from an external source into the cryoprobe, are known for performing cryosurgical procedures. Generally, a cryogen is delivered into a cryoprobe in the form of two-phase fluid. This is caused by the fact that a certain fraction of the liquid cryogen is evaporated inevitably on the way to the cryoprobe as a result of imperfect thermal insulation of the delivery hose. The cryogen two-phase condition cannot be improved by separating between the liquid and gaseous phases completely in the internal cavity of the cryotip (the distal section of the cryoprobe) without application of special measures. In addition, in particular for the use of nitrogen as a cryogen, the liquid nitrogen interact with solid warmer surface by creating nitrogen gas cushion, known as Liedenfrost effect, thus reduce considerably the ability to absorb heat from the warmer surface. Without such special means, it is impossible to completely use the liquid fraction of the cryogen for effective freezing of a treated tissue, forcing the partial change of phase of the fluid cryogen to take place as close as possible to the targeted surface. 
     Solutions to this problem are known. For example, U.S. Pat. No. 4,726,194 features a conduit with active heating thereof through which liquid nitrogen flows. The conduit terminates in an expansion chamber that is filled with cotton wool, in order to expand the volume available for boiling. 
     Another example is U.S. Pat. No. 4,082,096, which features a deformable mass that receives liquid cryogen, surrounded by a membrane that is impervious to liquid nitrogen. 
     Other examples include U.S. Pat. Nos. 5,520,682, 6,565,556, 4,946,460, 7,189,228 and 5,674,218, each of which features an expansion chamber. 
     BRIEF SUMMARY 
     The background art does not provide a solution that overcomes the problem of causing the boiling to take place close to the warmer surface within a cryosurgical instrument such as a cryoprobe. 
     The Applicants have discovered an advantageous solution to the problems of the background art by considering the nature of boiling nitrogen fluid flow. Their discovery provides solutions that are not encumbered by the drawbacks of the background art. 
     Embodiments of the present invention provide a cryosurgical instrument with a uniquely positioned and arranged heat exchanger. The heat exchanger is in a cryogen supply passage and/or in a cryotip. Such a construction/arrangement facilitates heat exchange with a cryogen. 
     Embodiments of the present invention overcome the above problems of the background art by forcing the fluid to flow through a annular cooling passage, by forcing the fluid under pressure onto the inner surface of the cryosurgical instrument, or by cooling an enhancing element of which at least a portion is in direct contact with the outer surface of the cryosurgical instrument, or a combination thereof. 
     The reduced cross section for the flow close to the inner surface of the cryosurgical instrument, and the expansion of the fluid through partial change of phase process, increases the speed of the flow considerably, and thus increases heat transfer from the inner surface to the fluid. The structure permits the two-phase cryogen flow both into and out of the cryosurgical instrument while controlling temperature transfer at the desired specific locations or elements within that structure. In case of forcing the fluid onto the inner surface of the instrument, the boiling occurs closer to the surface, thus increasing the heat transfer. Bringing the liquid phase of the fluid near the internal surface of the cryotip and directing the obtained liquid phase on the internal surface with following its boiling and evaporation in order to solve the above problem. The element can be made of either metal or ceramic or any other materials that maintain its integrity under the low temperature of the boiling conditions of the cryogenic fluid. 
     One aspect of the present invention provides a cryosurgical instrument that includes: a tubular housing having a longitudinal axis, a proximal end, and a tip at distal end; a cryogen supply passage extending from the proximal end to the distal end along the longitudinal axis, the cryogen supply passage having an upstream portion proximate to the proximal end and a downstream portion proximate to the distal end; a heat exchange enhancing member in the housing, disposed along the longitudinal axis, and surrounding at least some of the downstream portion of the supply passage; an annular cooling passage between the heat exchange enhancing member and the tubular housing, the annular cooling passage in communication with a cryogen exhaust passage, cryogen in the annular cooling passage absorbing heat in the annular cooling passage; a tip cooling and cryogen flow directing section at the distal end and in communication with the cryogen supply passage, the tip cooling and cryogen flow directing section deflecting a flow of cryogen flow to the tip so as to cool the tip, and an insulation element in the tubular housing, disposed along the longitudinal axis, surrounding a portion of the cryogen supply passage, and between the proximal end and the heat exchange enhancing member, the insulation element and the downstream end of the cryogen supply passage defining bounds of a heat exchanging zone. 
     Another aspect of the present invention provides a cryosurgical instrument that includes: a tubular housing having a longitudinal axis, a proximal end, and a tip distal end; a cryogen supply passage extending from the proximal end to the distal end along the longitudinal axis, the supply passage having an upstream portion proximate to the proximal end and a downstream portion proximate to the distal end; a heat exchange enhancing member in the housing, disposed along the longitudinal axis, and surrounding at least some of the downstream portion of the supply passage, the enhancing member having a plurality of return channels circumferentially disposed about the longitudinal axis and extending longitudinally through the enhancing member; a flow deflector between the tip and the supply passage, the flow director adapted and configured to deflect a cryogen flow exiting from the supply passage to the return channels and to absorb heat, thereby cooling the tip, the flow director fixedly and spacedly disposed from the supply passage. The flow of cryogen in the cryogen supply passage urges cryogen that has exited the cryogen supply passage to flow into the return channels. The sum of cross-sectional areas of the plurality of return channels is about equal to a cross-sectional area of the supply passage. 
     Another aspect of the present invention provides a cryoprobe that includes: a tubular housing having a longitudinal axis, a proximal end and a tip at a distal end; a heat exchange enhancing member in the housing, disposed along the longitudinal axis, proximate to the distal end, the enhancing member having a cryogen supply passage extending therethrough along the longitudinal axis and having an radial flow section through which cryogen flows radially through the enhancing member; an peripheral return passage between the enhancing member and the tubular housing, the peripheral return passage in communication with the radial flow section and a cryogen exhaust passage; and a tip cooling and cryogen flow directing section at the distal end and in communication with the cryogen supply passage, the tip cooling and cryogen flow directing section transmitting a temperature of a cryogen flow to the tip. The flow of cryogen in the cryogen supply passage urges cryogen through the radial flow section into the peripheral return passage. 
     Still another aspect of the present invention provides a cryosurgical instrument that includes: a shaft having a central axis, an upstream cryogen supply section, a downstream heat exchanging zone, and a solid tip at an end of the shaft opposite the cryogen supply section; a heat exchange enhancing member in the heat exchanging zone in the shaft and extending along the central axis, the enhancing member having a axial cryogen delivery passage extending therethough along the central axis; a cryogen return passage between the heat exchange enhancing member and the shaft; and a cryogen flow deflector between the tip and the heat exchange enhancing member, the deflector spaced from the enhancing member and adapted and configured to deflect expanded cryogen into the return passage. The cryosurgical instrument does not include a cryogen expansion chamber. 
     Yet another aspect of the presents a cryosurgical instrument that includes: a shaft having a central axis, an upstream cryogen supply section, a downstream heat exchanging zone, and a solid tip at an end of the shaft opposite the cryogen supply section; a heat exchange enhancing member in the heat exchanging zone in the shaft and extending along the central axis, the enhancing member having an axial cryogen delivery passage extending therethough along the central axis and a cryogen return passage; and a cryogen flow deflector between the tip and the heat exchange enhancing member, the deflector spaced from the enhancing member and adapted and configured to deflect cryogen into the return passage. The cryosurgical instrument does not include a cryogen expansion chamber. 
     A further aspect of the present invention provides a method of treatment with a cryosurgical instrument. The method includes: providing a cryosurgical instrument; inserting the cryosurgical instrument into tissue to be treated; delivering cryogen to a supply passage of the cryosurgical instrument; reflecting cryogen from the supply passage, via a reflecting surface that closes off a tip of the cryosurgical device; and forcing cryogen through a heat exchange zone of the cryosurgical instrument, such that partial change of phase occurs at the reflecting surface and at the heat exchange zone. 
     Still another aspect of the present invention provides a method of treatment with a cryosurgical instrument. The method comprises: providing a cryosurgical instrument; inserting the cryosurgical instrument into tissue to be treated; delivering cryogen via a supply passage of the cryosurgical instrument to a hollow tip of the cryosurgical instrument so that the cryogen boils at the tip; and reflecting cryogen from the supply passage, via a reflecting surface that closes off a tip of the cryosurgical device. 
     These, additional, and/or other aspects and/or advantages of the present invention are: set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more readily understood from the detailed description of embodiments thereof made in conjunction with the accompanying drawings of which: 
         FIG. 1   a  is a longitudinal cross-sectional view of a cryoprobe consistent with an embodiment of the present invention, with an annular cooling passage provided for return flow and a closed tip; 
         FIG. 1   b  shows a portion of the cryoprobe of  FIG. 1   a  in more detail; 
         FIG. 1   c  is a cross-sectional view of the cryoprobe of  FIG. 1   a  along line I of  FIG. 1   a;    
         FIG. 2  is a longitudinal cross-sectional view of a cryoprobe consistent with an embodiment of the present invention, with an annular cooling passage provided for return flow for an open cryotip; 
         FIG. 3   a  is a longitudinal cross-sectional view of a cryoprobe consistent with an embodiment of the present invention, with a plurality of grooves provided for return cryogen flow for a closed cryotip and for improved temperature transfer; 
         FIG. 3   b  is a cross-sectional view of the cryoprobe of  FIG. 3   a  taken along line II of  FIG. 3   a;    
         FIG. 4   a  is a longitudinal cross-sectional view of a cryoprobe consistent with an embodiment of the present invention, with a plurality of grooves provided for return cryogen flow for a closed cryotip; 
         FIG. 4   b  is a cross-sectional view of the cryoprobe of  FIG. 4   a  along line III of  FIG. 4   a;    
         FIG. 5   a  is a longitudinal cross-sectional view of a cryoprobe consistent with an embodiment of the present invention, with an annular cooling passage provided for return flow for an open cryotip; 
         FIG. 5   b  is a cross-sectional view of the cryoprobe of  FIG. 5   a  along line IV of  FIG. 5   a;    
         FIG. 6   a  is a longitudinal cross-sectional view of a cryoprobe consistent with an embodiment of the present invention, with an annular cooling passage provided for return flow for a closed, optionally solid, cryotip; 
         FIG. 6   b  is a cross-sectional view of the cryoprobe of  FIG. 6   a  along line V of  FIG. 6   a ; and 
         FIGS. 7 and 8  are flowcharts, illustrating respective exemplary methods of treatment each of which is consistent with embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The term “cryosurgical instrument” refers herein to any type of cryo instrument, including but not limited to cryoprobes and cryocatheters. Although the description centers around cryoprobes, this is for the purpose of illustration only and is without any intention of being limiting. 
     Referring to  FIGS. 1   a - 1   c , cryoprobe  100  comprises a tubular housing  108 , having a longitudinal axis, a proximal end and a tip  105  (cryotip) at the distal end. Preferably tip  105  is a closed, optionally solid, tip, closed at its proximal end by a reflecting surface  110 , which acts as a cryogen direction section, to reverse the flow of cryogen. Reflecting surface  110  also transmits the temperature of the cryogen flow to tip  105 , and also separates tip  105  from a cryogen supply passage  102 . Cryogen supply passage  102  extends from the proximal end to the distal end along the longitudinal axis, cryogen supply passage  102  has an upstream portion proximate to the proximal end and a downstream portion proximate to the distal end. Cryogen supply passage  102  receives cryogen from a cryogen inlet  109  and supplies the cryogen to the reflecting surface  110 . Reflecting surface  110  is shown as flat perpendicular surface with respect to the flow direction, however other shapes and orientations of reflecting surfaces can be employed to change the direction of the incoming flow towards the return cooling passage. Optionally and preferably as shown, cryoprobe  100  lacks an expansion chamber. 
     The return cryogen enters an annular cooling passage  107  between the heat exchange enhancing element  101  and the inner surface of the tubular housing  104 , increasing the velocity of the cryogen and enhancing heat transfer between the cryoprobe  100  and the cryogen. The heat exchange zone  111  is indicated with arrows; heat is absorbed from the external environment at heat exchange zone  111 . The cryogen then leaves the cryoprobe through a cryogen exhaust passage  103 . 
     Thermal insulation  104  preferably terminates the heat transfer from the cryoprobe  100  and the cryogen flow in the cryogen exhaust passage  103 , thereby determining the boundaries of the heat exchange zone  111 . 
       FIG. 1   b  shows heat exchange enhancing element  101 , tip  105 , annular cooling passage  107  and tubular housing  108  in more detail. In addition, the direction of cryogen flow is shown with arrows  106 , as the cryogen reaches reflecting surface  110 , and then returns through annular cooling passage  107 . The dimensions of annular cooling passage  107  are preferably adjusted so as to provide the above described increased cryogen velocity, such that preferably a cross-sectional area of the annular cooling passage  107  is of the same order as the cross-sectional area of the supply passage  102  and wherein a velocity of a flow of cryogen in the return passage  107  is greater than a velocity of a flow of cryogen in the supply passage  102 ; for a typical cryoprobe, such dimensions of the annular cooling passage  107  would optionally and preferably be up to 1-2 mm but more preferably are 0.1 mm to 0.3 mm. Also reflecting surface  110  is preferably constructed of any suitable material for transmitting cold to tip  105 , which is itself constructed of a suitable material for becoming cold; non-limiting illustrative examples of materials for both components include but are not limited to metals, whether pure, alloys or composites, that are thermally conductive. 
     In the operation of cryoprobe  100 , cryogen enters through cryogen inlet  109  to cryogen supply passage  102 , and travels down cryogen supply passage  102  until it reaches reflecting surface  110 . The cryogen then cools tip  105  and then returns through annular cooling passage  107  and is exhausted through annular exhaust passage  103 . 
     Referring to  FIG. 2 , cryoprobe  200  is similar in construction to cryoprobe  100 , except that cryoprobe  200  features a hollow tip  205 . An expansion chamber  210  is located within tip  105  (in place of the above described reflecting surface of cryoprobe  100  of  FIGS. 1   a  and  1   b ). 
     In the operation of cryoprobe  200 , cryogen enters through cryogen inlet  209  to cryogen supply passage  202 , and travels down cryogen supply passage  202  until it enters expansion chamber  210 . The cryogen then expands and cools tip  205  directly within expansion chamber  210 . The partially phase changed cryogen then returns through annular cooling passage  207  and is exhausted through cryogen exhaust passage  203 . 
     The expansion chamber  210  is in communication with the downstream portion of the supply passage  202  and arranged (i) to permit cryogen exiting from the supply passage  202  to expand and to cool the tip  205 , and (ii) to direct expanded cryogen that has exited the cryogen supply passage  202  to flow into the annular cooling passage  207 . Due to heat absorption from the surrounding in contact with  205 , the heat exchanging zone  211  increases to include the tip  205 . 
     Referring to  FIGS. 3 and 3   b , cryoprobe  300  features a closed, optionally solid, tip  305  and a reflecting surface  310  preferably located at tip  305 . Like cryoprobe  100 , cryoprobe  300  preferably lacks an expansion chamber, as shown. Unlike cryoprobe  100 , cryoprobe  300  features a plurality of grooves  307 , which are preferably straight grooves and which function as a plurality of return channels for receiving the expanded return cryogen; grooves  307  are preferably in communication with a cryogen exhaust passage  303  for then exhausting the cryogen out of cryoprobe  300 . Grooves  307  surround at least a portion of the downstream portion of the supply passage  302  and are preferably circumferentially disposed about the longitudinal axis and extending longitudinally. 
     The above construction increases the speed of the return flow. By increasing the speed of the return flow and causing a partial change of phase of the cryogen to take place in the grooves  307 , the heat is absorbed from the cryoprobe  300  directly through the boiling at the grooves  307 , and indirectly by conducting the heat through the contact surface of  301  with  308 . Thermal insulation  304  terminates the heat transfer from the cryoprobe  300 . The heat exchange zone  311  is indicated with arrows; heat is absorbed from the external environment at heat exchange zone  311 . 
     As shown in  FIG. 3   b , cryogen travels through cryogen supply passage  302  and returns through straight grooves  307 , which are located at the edge of tubular housing  308 . 
     In the operation of cryoprobe  300 , cryogen enters through cryogen inlet  309  to cryogen supply passage  302 , and travels down cryogen supply passage  302  until it reaches reflecting surface  310 . The cryogen then cools tip  305  by cooling reflecting surface  310  and also by cooling grooves  307 . The expanded cryogen then returns through grooves  307  and is exhausted through cryogen exhaust passage  303 . 
     Preferably a sum of cross-sectional areas of the plurality of grooves  307  is about equal to a cross-sectional area of the supply passage  302 , and a velocity of a flow of cryogen in the grooves  307  is greater than a velocity of a flow of cryogen in the supply passage  302 , due to the partial change of phase. 
     Referring to  FIGS. 4   a - 4   c , cryoprobe  400  is similar in construction to cryoprobe  300 , except that straight grooves  407  are located internally, close to but external to cryogen supply passage  402 , and are sealingly capped by an inner surface of tubular housing  408 . The heat exchange zone  411  is indicated with arrows; heat is absorbed from the external environment at heat exchange zone  411 . Cryogen absorbs heat from heat exchange enhancing element  401 , which in turn absorbs heat from tubular housing  408  in the heat exchange zone  411  through thermal conductivity. Only cools  401  through cryogen supply passage  402  and straight grooves  407 . 
     In both cryoprobes  300  and  400 , a two-phase flow of cryogen (liquid and gas) preferably enters to the tip  305  or  405 . The two-phase flow is then exposed to the heat absorption surface portion of the tip  305  or  405 , and again is exhausted as a two-phase flow. The ratio of gas to liquid is higher in the exhausted two phase flow, however, the opening cross section is similar in size to the cross section of the cryogen exhaust passage  303  or  403 , such that the speed of the exhausted two-phase flow is greater. 
     Referring to  FIGS. 5   a  and  5   b , cryoprobe  500  features a hollow tip  505  that receives cryogen, and hence cooling, directly from a cryogen supply passage  502 . The cryogen returns through a plurality of radial through holes  510  to an annular cooling passage  507 . Preferably, the cryogen is forced through holes  510 , on the surface of hollow tip  505  and of annular cooling passage  507 , under pressure. Holes  510  therefore preferably extend into hollow tip  505 , which acts as an expansion chamber. Annular cooling passage  507  operates as previously described. 
     In the operation of cryoprobe  500 , cryogen enters through cryogen inlet  509  to cryogen supply passage  502 , and travels down cryogen supply passage  502  until it reaches hollow tip  505 . The cryogen then expands and cools tip  505 . As shown, tip  505  optionally features an additional solid tip  530  over hollow tip  505 , which is cooled as hollow tip  505  is cooled. The expanded cryogen then returns through holes  510  to annular cooling passage  507 , thereby providing additional cooling of hollow tip  505 , and is exhausted through cryogen exhaust passage  303 . The direction of cryogen flow is shown with arrows  506 . 
     Preferably a cross-sectional area of the return passage  507  is about equal to a cross-sectional area of the supply passage  502 , and also preferably a flow of cryogen in the cryogen supply passage  502  urges cryogen through the radial flow section into the peripheral return passage  507 . 
     Referring to  FIGS. 6   a  and  6   b , cryoprobe  600  is similar in some aspects to cryoprobe  100 , in that a reflecting surface  610  closes off tip  605 , which may optionally be solid. Reflecting surface  610  preferably acts as a flow deflector between tip  605  and supply passage  602 , and is fixedly and spacedly disposed from supply passage  602 . Cryogen and is forced through annular cooling passage  607 , which preferably features a plurality of radial throughholes  631  in the radial flow section. Such radial throughholes  631  increase the space for boiling of the cryogen, such that the cryogen cools tip  605  through cooling reflecting surface  610  and radial throughholes  631  in return passage  607 . 
       FIG. 7  is a flowchart illustrating a method of treatment with a cryosurgical instrument consistent with an embodiment of the present invention. The cryosurgical instrument may be, by way of non-limiting examples, any of the cryoprobes  100 ,  300 ,  400 , and  600 . 
     In operation  10 , a cryosurgical instrument is provided. In operation  20 , the cryosurgical instrument is inserted to the tissue to be treated. In operation  30 , cryogen enters the cryogen supply passage. In operation  40 , the cryogen is reflected by a reflecting surface, which closes off the tip, which may optionally be solid. In operation  50 , the cryogen is forced through a heat exchange zone of the cryosurgical instrument, such that partial change of phase occurs at the reflecting surface and at the heat exchange zone. In operation  60 , the boiling cryogen causes an ice ball to form at the cryotip and the surrounding tissue to freeze. 
       FIG. 8  is a flowchart illustrating a method of treatment with a cryosurgical instrument consistent with an embodiment of the present invention. The cryosurgical instrument may be, by way of non-limiting examples, cryoprobe  200  or  500 . 
     In operation  10 , a cryosurgical instrument is provided. In operation  20 , the cryosurgical instrument is inserted to the tissue to be treated. In operation  30 , cryogen enters the cryogen supply passage. In operation  40 , the cryogen travels to the cryotip, which is hollow. In operation  50 , the cryogen is forced against the surface of the cryotip, such that boiling occurs at the cryotip (and optionally also in a heat exchange zone of the cryosurgical device. In operation  60 , the partially phase changed cryogen causes an ice ball to form at the cryotip and the surrounding tissue to freeze. 
     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. 
     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. 
     Also 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.