Abstract:
A device, system, and method for enhancing cooling uniformity and efficiency of cryogenic fluids and providing a treatment element the shape of which can be adjusted for multiple purposes. The device may include a balloon catheter and fluid dispersion element, the fluid dispersion element directing the flow of coolant from a fluid injection element the interior wall of the balloon. The method of changing the shape of the treatment element may include retracting and extending a shaft to which the distal neck of a balloon is coupled, so that the balloon goes from a first shape to a second shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of patent application Ser. No. 13/360,430, filed Jan. 27, 2012, entitled BALLOON DESIGN TO ENHANCE COOLING UNIFORMITY, the entirety of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    n/a 
       TECHNICAL FIELD 
       [0003]    The present invention relates to a method and system for enhancing cooling uniformity and efficiency of cryogenic fluids and providing a treatment element having a shape that can be adjusted for multiple purposes. 
       BACKGROUND 
       [0004]    Cryoablation therapy is a technique that uses freezing to locally destroy or alter body tissue, such as a tumor, cardiac tissue associated with arrhythmia, or diseased or congenitally abnormal tissue. Surgical cryoprobes and cryoablation catheters are typically used to perform this technique, and may generally include a power source, a coolant source, and one or more treatment elements. Commonly used cryoablation treatment elements include expandable elements (for example, balloons) through which cryogenic fluid, such as a phase-change coolant, circulates. The temperature of phase-change coolants is lowered via the Joule-Thomson effect, which occurs when the coolant expands within the treatment element. 
         [0005]    When the treatment elements of the catheter must chill tissue to below freezing, the coolant itself must attain a substantially lower temperature. Although phase-change coolants can reach sufficient temperatures at expansion, coolant temperature rapidly rises after expansion within the treatment element. For example, a small coolant-filled balloon must overcome the heat of blood flow and surrounding tissue to maintain freezing temperatures. Typically, this problem is solved by injecting coolant into the treatment element at high flow rates and pressures, with rapid removal and replacement with fresh coolant. However, conditions of patient safety must be considered. When high pressures are be required to circulate sufficient coolant through the catheter body to its tip and back, and the overall design of a catheter must be such that fracture of the catheter or leakage of the coolant either does not occur, or if it occurs, is harmless. Further, for an endovascular catheter construction, the presence of the coolant and circulation system should not substantially impair the flexibility or maneuverability of the catheter tip and body. 
         [0006]    Patient safety must also be considered when choosing the shape of the cryoablation treatment element. For example, a balloon catheter should be sized and shaped to adequately occlude an area of the body such as the pulmonary vein. However, ablating tissue with a balloon shape that is optimal for occlusion, such as a teardrop shape, may increase the risk of the balloon getting deep in the vein and leading to pulmonary vein stenosis or other vascular damage. Additionally in order to apply a spherical balloon ‘head-on’ against a flat structure like the posterior wall, the distal “neck” of the balloon will need to be withdrawn sufficiently to allow contact by the rest of the balloon. 
         [0007]    Accordingly, it would be desirable to provide a cryoablation device and system that would more efficiently circulate coolant through the treatment element proximate the target tissue without necessitating potentially dangerous high pressures and flow rates. Additionally, it would be desirable if this cryoablation device and system further included the ability to change the shape of the treatment element to enable a single device to serve multiple purposes. 
       SUMMARY 
       [0008]    The present invention advantageously provides a device, system, and method for not only enhancing cooling uniformity and efficiency of cryogenic fluids, but also changing the shape of a cryoablation treatment element to serve multiple purposes. The device may comprise: a cooling chamber including an interior wall and an exterior wall; a coolant delivery element disposed within the cooling chamber; and a coolant distribution element disposed within the cooling chamber that guides coolant delivered from the coolant delivery element toward the interior wall of the cooling chamber. The cooling chamber may be a balloon. The coolant distribution element may be a membrane disposed within the cooling chamber so as to divide the cooling chamber into a first portion and a second portion, the coolant delivery element being within the first portion and the membrane allowing transit of coolant from the first portion to the second portion. Further, the membrane meters transit of coolant from the first portion to the second portion, and may be at least one of: gas permeable; liquid permeable; and combination thereof. Further, the membrane includes a plurality of apertures. The apertures may be located proximate the interior wall of the cooling chamber. Further, the membrane may includes a first edge and a second edge, the first edge being in contact with a portion of the interior wall of the cooling chamber. The first edge may be affixed to the interior wall of the cooling chamber. 
         [0009]    Alternatively, the coolant distribution element may be a second balloon disposed within the cooling chamber. The coolant distribution element may be disposed within the cooling chamber so as to divide the coolant chamber into a first portion within the second balloon and a second portion between the cooling chamber and second balloon, and the second balloon meters transit of coolant from the first portion to the second portion. The coolant delivery element may be disposed within the second balloon, and the second balloon may include a plurality of apertures. Alternatively, the coolant delivery element may be disposed between the balloon and the second balloon, the second balloon being coolant-impermeable. 
         [0010]    The device may further comprise: a first shaft having a proximal end, a distal end, and a first lumen extending therebetween, the proximal neck of the balloon being coupled to the distal end of the first shaft; and a second shaft slidably disposed within the first lumen and having a distal end, the distal neck of the balloon being coupled to the distal end of the second shaft. The second edge of the membrane may be in contact with the second shaft, the second shaft being slidably disposed through the membrane. The second shaft may include the coolant delivery element. Further, the second shaft may be slidably movable with respect to the coolant delivery element. The balloon may have the first shape when the second shaft is in an extended position, and the balloon has the second shape when the second shaft is in a retracted position. The distal neck of the balloon may be oriented outward and away from the expandable element when the balloon is in the first position, and the distal neck of the balloon may be oriented inward and within the first portion of the balloon when the balloon is in the second position. 
         [0011]    Alternatively, the device may comprise: an expandable element including an interior wall, an exterior wall, an adjustable distal neck, and a fixed proximal neck; a fluid distribution membrane disposed within the expandable element so as to divide the expandable element into a first portion and a second portion, the membrane including a plurality of apertures proximate at least a portion of the interior wall that allow the transit of fluid from the first portion to the second portion; and a fluid injection element within the first portion, the expandable element having a first shape when the distal neck is oriented outward and away from the expandable element, and a second shape when the distal neck is oriented inward and within the expandable element. 
         [0012]    The method may comprise: providing an expandable element having an interior wall and an exterior wall, a fluid distribution element disposed within the expandable element so as to divide the expandable element into a first portion and a second portion; injecting coolant through a fluid injection element within the first portion, the fluid distribution element guiding coolant toward the interior wall of the first portion, through the fluid distribution element, and into the second portion. The fluid distribution element may include a plurality of apertures proximate the inner wall of the expandable element, the apertures allowing for the metered transit of the fluid from the first portion to the second portion. The expandable element may have a fixed proximal neck and a distal adjustable neck, the distal neck being coupled to a slidably movable sheath, the expandable element having a first shape when the sheath is in an extended position and having a second shape when the sheath is in a retracted position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0014]      FIG. 1A  shows a system including a first embodiment of a cryoablation treatment element; 
           [0015]      FIG. 1B  shows a cross-sectional view of a first embodiment of a cryoablation treatment element; 
           [0016]      FIG. 2A  shows a cross-sectional view of a second embodiment of a cryoablation treatment element; 
           [0017]      FIG. 2B  shows a further cross-sectional view of a second embodiment of a cryoablation treatment element; 
           [0018]      FIG. 3  shows a cross-sectional view of a third embodiment of a cryoablation treatment element; 
           [0019]      FIG. 4  shows a cross-sectional view of a fourth embodiment of a cryoablation treatment element; 
           [0020]      FIG. 5A  shows a cross-sectional view of a fifth embodiment of a cryoablation treatment element; 
           [0021]      FIG. 5B  shows a further cross-sectional view of a fifth embodiment of a cryoablation treatment element; 
           [0022]      FIG. 6  shows a cross-sectional view of a heart, with exemplary placement of a cryoablation device; 
           [0023]      FIG. 7A  shows a cross sectional view of a first embodiment of a shape-changing cryoablation treatment element having a first shape; 
           [0024]      FIG. 7B  shows a cross-sectional view of a first embodiment of a shape-changing cryoablation treatment element having a second shape; 
           [0025]      FIG. 8A  shows a second embodiment of a shape-changing cryoablation treatment element having a first shape; and 
           [0026]      FIG. 8B  shows a second embodiment of a shape-changing cryoablation element having a second shape. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring now to  FIG. 1A , a system including a first embodiment of a cryoablation treatment element is shown. The system  10  generally includes a device  12  for treating tissue and a console  14  that houses various system controls. The system  10  may be adapted for both radiofrequency ablation (RFA) and cryoablation. The console  14  may include one or more of a coolant reservoir  16 , coolant return reservoir  18 , and RF generator  20 , and may further include various displays, screens, user input controls, keyboards, buttons, valves, conduits, connectors, power sources, and computers for adjusting and monitoring system parameters. 
         [0028]    Continuing to refer to  FIG. 1A , the device  12  may be an ablation device generally including a handle  22 , an elongate body  24  having a distal end  26  and one or more treatment elements. The handle  22  may include various knobs, levers, user control devices, input ports, outlet ports, connectors, lumens, and wires. The one or more treatment elements may be expandable elements such as balloons  30  (as shown in  FIG. 1A ). Further, the device may include one or more electrodes  32 , such as when thermoelectric cooling and/or RF energy is used in addition to Joule-Thomson cooling. The elongate body  24  may further include one or more lumens, such as a main lumen  34 , a fluid injection lumen  36  in fluid communication with the coolant reservoir  16 , and a fluid return lumen  37  in fluid communication with the coolant return reservoir  18 . In some embodiments, one or more other lumens may be disposed within the main lumen  34 , and/or the main lumen  34  may function as the fluid injection lumen  36  or the fluid return lumen  37 . If the device  12  also includes a thermoelectric cooler or RF electrodes, the elongate body  24  may include a lumen in communication with an RF generator  20  and/or a power source (not shown). Even if not shown in the other figures, the device  12  shown in, for example,  FIGS. 2A ,  3 ,  4 ,  5 A,  7 A, and  7 B may also include these lumens  34 ,  36 ,  37 . 
         [0029]    The elongate body may further include a shaft  38  having a proximal end  38   a  and a distal end  38   b , which may be slidably disposed within the main lumen  34  (as shown and described in  FIGS. 7A and 7B ). Generally, the shaft  38  is any substantially rigid shaft to which at least a portion of the treatment element (such as a balloon  30 , as shown in  FIG. 1A ) may be attached, and may be a guidewire shaft. The coolant return reservoir  18  may be in fluid communication with a vacuum pump  39  that removes expended coolant from the treatment element (such as a balloon  30 , as shown in  FIG. 1A ). The combination of coolant injection and suction from the vacuum pump  39  forces coolant from the treatment element into the fluid return lumen  37 . 
         [0030]    Continuing to refer to  FIG. 1A , the treatment element may be an expandable element, such as the balloon  30  in  FIG. 1A , defining a cooling chamber  40  having an interior wall  42  and an exterior wall  44 . The balloon  30  further includes a proximal neck  30   a  and a distal neck  30   b . The balloon  30  further includes a fluid dispersion element (FDE)  46  that directs the flow of coolant from the fluid injection element  46  to the interior wall  42  of the balloon  30 , and divides the cooing chamber  40  into a first portion  48  and a second portion  50 . A fluid injection element  52  is be disposed within the first portion  48  of the cooling chamber  40 , and may be a discrete element (as shown in  FIG. 1A ) or integrated with the shaft  38  (as shown in  FIG. 2A ). Additionally, the fluid injection element  52  may be associated with the shaft  38  in a way that allows for an adjustment of the direction of fluid delivery corresponding to the direction and degree of shaft  38  movement (as shown in  FIGS. 8A and 8B ). Coolant is at its coldest temperature immediately after expanding once it enters the cooling chamber  40 ; therefore, quickly directing the cold coolant to the area of the cooling chamber closest to target tissue provides a more efficient use of coolant. The FDE  46  shown in  FIG. 1A  is a deformable membrane oriented perpendicular to the primary direction of coolant flow (depicted in the figures by arrows). The membrane  46  includes a plurality of apertures  54 , the apertures  54  being located proximate at least a portion of the interior wall  42 . The membrane  46  has a first edge  56  and a second edge  58 , the first edge  56  being in contact with the interior wall  42  of the balloon  30  and the second edge  58  being in contact with the shaft  38  and/or the fluid injection element  52 . Further, the first edge  56  may be affixed to the interior wall  42  of the balloon  30 . The membrane  46  may be between approximately 0.0001 inch and approximately 0.002 inch thick as measured on the first edge  56 , and the thickness may be substantially constant throughout the membrane  46 , or it may vary. For example, the thickness may be greater near the first edge  56  and lesser near the second edge  58 . 
         [0031]    Continuing to refer to  FIG. 1A , the apertures  54  may be any shape that preserves the integrity of the membrane  46 , including circular, angular, flap-like (creating a flap of membrane material that is only partially attached to the membrane  46 ), or slit-like (an elongated aperture not having a flap of membrane material). Further, the apertures  54  may be located around the entire circumference of the membrane  46  proximate the first edge  56 , or only a portion thereof. Further, the apertures  54  may be arranged in a single row, multiple rows, or any other configuration that meters coolant flow from the first portion  48  to the second portion  50  of the balloon  30 . The membrane may be composed of a material such as polyester, nylon, Pebax®, polyurethane or silicone, for example. Further, the membrane  46  may be composed of a material that is gas permeable, liquid permeable, or both, or may be permeable to the coolant by virtue of the apertures  54  alone. 
         [0032]    Referring now to  FIG. 1B , a cross-sectional view of a first embodiment of a cryoablation treatment element is shown.  FIG. 1B  shows the first portion  48  of the cooling chamber  40  as taken along axis B-B in  FIG. 1A . As shown and described in  FIG. 1A , the balloon  30  defines a cooling chamber  40  (the first portion  48  of the cooling chamber  40  is shown in  FIG. 1B ) and includes an FDE  46  that is a membrane having a plurality of apertures  54 . Coolant is injected into the first portion  48  of the cooling chamber  40  and directed through the apertures  54  of the membrane  46  and into the second portion  50  (not shown in  FIG. 1B ). The flow of coolant is depicted with arrows. 
         [0033]    Referring now to  FIGS. 2A and 2B , cross-sectional views of a second embodiment of a cryoablation treatment element are shown.  FIG. 2B  shows the first portion  48  of the cooling chamber  40  as taken along axis B-B in  FIG. 1A . Like  FIGS. 1A and 1B , the treatment element of  FIGS. 2A and 2B  is a balloon  30  defining a cooling chamber  40  having a first portion  48  and a second portion  50 . The balloon  30  further includes an FDE  46  that is a membrane having a plurality of apertures  54 . In  FIGS. 2A and 2B , the fluid injection element  52  is integrated with the shaft  38 , rather than being a separate element disposed about the shaft  38 , as shown in  FIGS. 1A and 1B . In this embodiment, the fluid injection lumen  36  is within the shaft  38  and the shaft  38  includes a plurality of apertures or outlet ports in fluid communication with the fluid injection lumen  36 . Expanded coolant flows from the second portion  50  into the fluid return lumen  37 . The cross section shown in  FIG. 2B  is along the B-B axis shown in  FIG. 2A . The flow of coolant is depicted with arrows. 
         [0034]    Referring now to  FIG. 3 , a cross-sectional view of a third embodiment of a cryoablation treatment element is shown. Like  FIG. 1A , the treatment element of  FIG. 3  is a balloon  30  defining a cooling chamber  40  and having an interior wall  42  and an exterior wall  44 . The balloon  30  further includes an FDE  46  disposed within the cooling chamber  40 , dividing the cooling chamber  40  into a first portion  48  and a second portion  50 . Unlike the membrane  46  of  FIG. 1A , the FDE  46  of  FIG. 3  is not in contact with the interior wall  42  of the balloon  30 . Rather, the FDE  46  in  FIG. 3  is a second balloon  62  of smaller size than the balloon  30  (“first balloon  30 ”). The second balloon  62  includes a plurality of apertures  64 , and the fluid injection element  52  is located within the second balloon  62 . The fluid injection element of  FIG. 3  is shown as being integrated with the shaft  38  (as shown in  FIG. 2A ), but could also be disposed about or adjacent to the shaft  38  (as shown in  FIG. 1A ). The apertures  64  of the second balloon  62  direct and meter flow of coolant from the first portion  48  within the second balloon  62  to the second portion  50  between the first balloon  30  and second balloon  62 . Expanded coolant flows from the second portion  50  into the fluid return lumen  37  (as shown in  FIGS. 1A and 2A ). The flow of coolant is depicted with arrows. 
         [0035]    Referring now to  FIG. 4 , a cross-sectional view of a fourth embodiment of a cryoablation treatment element is shown. Like the treatment element of  FIG. 3 , the treatment element of  FIG. 4  is a balloon  30  defining a cooling chamber  40  and having an interior wall  42  and an exterior wall  44 . The balloon  30  further includes an FDE  46  disposed within the cooling chamber  40 . Like the FDE  46  of  FIG. 3 , the FDE  46  in  FIG. 4  is a second balloon  62  of a smaller size than the balloon  30  (“first balloon  30 ”). The fluid injection element  52  is located between the first balloon  30  and the second balloon  62 . Further, the second balloon  62  does not meter the flow of coolant from a first portion to a second portion, but does direct the flow of coolant from the fluid injection element  52  to the interior wall  42  of the cooling chamber  40 , from where the expanded coolant flows into the fluid return lumen  37  (as shown in  FIGS. 1A and 2A ). The fluid injection element  52  may be a separate element (as shown in  FIG. 4 ) or may be integrated with the shaft  38  (as shown in  FIGS. 2A and 3 ). Further, the second balloon  62  may include a second fluid injection element  66  for inflating the second balloon  62 . The flow of coolant is depicted with arrows. 
         [0036]    Referring now to  FIGS. 5A and 5B , cross-sectional views of a fifth embodiment of a cryoablation treatment element are shown.  FIG. 5B  shows the first portion  48  of the cooling chamber  40 , as taken along axis B-B in  FIG. 1A . Like the treatment element of  FIG. 4 , the treatment element of  FIGS. 5A and 5B  is a balloon  30  defining a cooling chamber  40  and having an interior wall  42  and an exterior wall  44 . The balloon  30  further includes an FDE  46  disposed within the cooling chamber  40 . Like the second balloon  62  of  FIG. 4 , the FDE  46  of  FIGS. 5A and 5B  does not meter the flow of coolant from a first portion to a second portion, but does direct the flow of coolant from the fluid injection element  52  to the interior wall  42  of the cooling chamber  40 , from where the expanded coolant flows into the fluid return lumen  37  (as shown in  FIGS. 1A and 2A ). The center portion  68  (general area depicted in dashed lines) of the cooling chamber  40  is substantially bypassed; that is, coolant may flow directly from the fluid injection element  52 , to the interior wall  42 , to the fluid return lumen  37  without flowing into the center portion  68 . Unlike the FDE  46  of  FIGS. 1-4 , however, the FDE  46  of  FIGS. 5A and 5B  is also the fluid injection element  52 . The FDE  46  may be a collapsible or deformable cage, basket, or mesh being in fluid communication with the fluid injection lumen  36  and having a plurality of outlet ports  72 . The outlet ports  72  may be directed toward the interior wall  42  of the cooling chamber  40  (as shown in  FIG. 5B ), and may be located along the splines  74  of the cage-type FDE  46 . Further, the FDE  46 /fluid injection element  52  may (as shown in  FIGS. 1A ,  2 A,  3 , and  4 ) or may not (as shown in  FIG. 4 ) be associated with a shaft  38 . Expanded coolant flows from the second portion  50  into the fluid return lumen  37  (as shown in  FIGS. 1A and 2A ). The flow of coolant is depicted with arrows. 
         [0037]    It will be understood that a device contemplated herein may include any combination of the features of the embodiments of  FIGS. 1-5 . Further, the balloon  30  may have any shape or form, and may further be double layered (as in double-balloon catheters) for enhanced safety. Further, the balloon  30  and a second balloon  52  may have the same or different shapes, and may be made of the same or different materials. The figures may not be drawn to scale. 
         [0038]    Referring now to  FIG. 6 , a cross-sectional view of a heart, with exemplary placement of a cryoablation device is shown. A mammalian heart includes pulmonary veins that lead blood from the lungs into the left atrium, and pulmonary vein (PV) ablation is a common treatment for cardiac arrhythmias. In a typical procedure, an ablation device  12  such as a balloon catheter (as shown in  FIGS. 1-7 ) is inserted into the left atrium and positioned at the opening of a PV. Before ablating tissue, a visualization medium (such as a dye or contrast medium) may first be injected into the PV to ensure that the PV is completely occluded by the device  12 . Once the occlusion is achieved, ablation may begin. Even though a single balloon catheter having a static shape may provide both occlusion and ablation functionality, it has been found that ablating PV tissue with certain balloon shapes, such as the teardrop or ovate shape in  FIG. 7A , may increase the risk of PV stenosis associated with ablation therapy. As shown and described in  FIGS. 7A and 7B , the balloons  30  of  FIGS. 1-5  may be adjustable from a first shape (“occlusion mode”) to a second shape (“ablation mode”). 
         [0039]    Referring now to  FIGS. 7A and 7B , a first embodiment of a shape-changing cryoablation treatment element having a first and second shape is shown. In  FIGS. 7A and 7B , the cryoablation treatment element is a balloon  30 , which defines a cooling chamber  40  and includes an interior wall  42 , an exterior wall  44 , a proximal neck  30   a , and a distal neck  30   b  (the balloon  30  may have the general characteristics of any of the balloons  30  of  FIGS. 1-5 ). The proximal neck  30   a  of the balloon is coupled to the distal end  26  of the elongate body  24 , and the distal neck  30   b  is coupled to the distal end  38   b  of the shaft  38 . Movement of the shaft causes the balloon to assume a first shape (“occlusion mode”) or a second shape (“ablation mode”), and all intermediate shapes between the first shape and second shape. When in occlusion mode, the flow rate of the coolant may be lower than that required for ablation. For example, the flow of coolant may be sufficient to inflate the balloon  30 , but not enough to reach ablation temperatures. 
         [0040]    Referring now to  FIG. 7A , a cross sectional view of the balloon  30  having a first shape is shown. In the first shape, the cooling chamber  40  may have an elongated shape, such as a teardrop or ovate shape as shown in  FIG. 7A . If the FDE  46  is a membrane oriented perpendicular to coolant flow (as in  FIGS. 1-2 ) as the fluid travels from the first portion  48  to the second portion  50  and into the fluid return lumen  37 , the first portion  48  of the cooling chamber  40  may be extended to accommodate the shape change as shown and described in  FIG. 7B . The distal neck  30   b  may be coupled to the distal end  38   b  of the shaft  38  such that the distal neck  30   b  is directed outward (as shown in  FIGS. 7A and 7B ). That is, the interior wall  42  of the distal neck  30   b  is coupled to the distal end  38   b  of the shaft  38 . However, the distal neck  30   b  may alternatively be directed inward, with the exterior wall  44  of the balloon  30  coupled to the distal end  38   b  of the shaft  38  (as shown in  FIGS. 8A and 8B ). Further, the shaft  38  may be slidably movable within the main lumen  34  of the elongate body  24  (depicted with a double-headed arrow). 
         [0041]    Continuing to refer to  FIG. 7A , the balloon  30  may further include one or more sensors  70 . The sensors  70  may be used to detect pressure, temperature, or other detectable parameters within the system  10 , device  12 , or patient&#39;s body. The sensors  70  may be located anywhere within or on the surface of the balloon  30 , but at least one sensor  70  may be located such that movement of the shaft  38  will also effectively reposition the sensors  70 . For example, the sensors  70  may be located a distance away from the distal end  38   b  of the shaft  38  when the balloon  30  is in the first position (as seen in  FIG. 7A ). As the balloon  30  transitions from the first position to the second position (and the distal end  38   b  of the shaft  38  is moved closer to the elongate body  24 ), the sensors  70  will be brought closer to the distal face  72  of the balloon  30  (as shown in  FIG. 7B ). The distal face  72  is shown as the bracketed area in  FIG. 7B . 
         [0042]    Referring now to  FIG. 7B , a cross-sectional view of a shape-changing cryoablation treatment element having a second shape is shown. The balloon of  FIG. 7B  is in the second shape, or ablation mode. When in ablation mode, the flow rate of the coolant may be increased so that the balloon  30  reaches a temperature sufficient to ablation tissue. To change the balloon  30  to the second shape, the shaft is retracted a distance (“D”) within the main lumen  34 . Moving the shaft  38  also moves the position of the distal neck  30   b  of the balloon  30 , which may cause the distal neck  30   b  to be refracted inward and the distal end of the balloon  30  to fold over on itself. The distal neck  30   b  may be coupled to the distal end  38   b  of the shaft  38  in other ways, such as folded under (with the exterior wall  44  of the balloon  30  coupled to the distal end  38  of the shaft); however, the method of affixing the balloon  30  to the shaft  38  should not hinder the shape-changing functionality of the device  12 . 
         [0043]    Continuing to refer to  FIG. 7B , the one or more sensors  70  are on the distal face  72  of the balloon  30  when the balloon  30  is in the second position. On the distal face  72 , the sensors  70  may be in an optimal position to contact surfaces within the patient&#39;s body and/or to measure parameters detectable by the sensors. 
         [0044]    Referring now to  FIGS. 8A and 8B , a second embodiment of a shape-changing cryoablation element having a first and second position is shown. Like  FIGS. 7A and 7B , the cryoablation treatment element is a balloon  30  (“first balloon”), which defines a cooling chamber  40  and includes an interior wall  42 , an exterior wall  44 , a proximal neck  30   a , and a distal neck  30   b  (the first balloon  30  may have the general characteristics of any of the balloons  30  of  FIGS. 1-5 ). The proximal neck  30   a  of the first balloon  30  is coupled to the distal end  26  of the elongate body  24 , and the distal neck  30   b  is coupled to the shaft  38  either at or proximate the distal end  38   b ). Unlike the distal neck  30   b  of the balloon  30  shown in  FIGS. 7A and 7B , the distal neck  30   b  of the first balloon  30  in  FIGS. 8A and 8B  may be oriented inward, with the exterior wall  44  of the balloon being coupled to the distal end  38   b  of the shaft  38 . Movement of the shaft causes the balloon to assume a first shape (“occlusion mode”) or a second shape (“ablation mode”), and all intermediate shapes between the first shape and second shape. 
         [0045]    Referring now to  FIG. 8A , a cross sectional view of the balloon  30  having a first shape is shown. The first balloon  30  may include an FDE  46  that is a second balloon  62  (as shown in  FIG. 4 ) having a proximal neck  62   a  and distal neck  62   b , in which the fluid injection element  52  is located. The second balloon  62  may direct coolant in any of a variety of directions, depending on the movement of the shaft  38 . The second balloon  62  may include a plurality of apertures  64  through which coolant is injected into the cooling chamber  40 . As shown in  FIGS. 8A and 8B  (and in contrast to  FIGS. 3 and 4 ), the proximal neck  62   a  of the second balloon  62  may be coupled to the distal end  26  of the elongate body  24 , like the proximal neck  30   a  of the first balloon  30 . The proximal neck  30   a  of the balloon may be in contact with and coupled to the proximal neck  62   a  of the second balloon  62 , the distal end  26  of the elongate body  24 , or both. Further, the distal neck  62   b  of the second balloon  62  may be coupled to the shaft  38 , like the distal neck  30   b  of the first balloon  30 . Thus, movement of the shaft  38  may not only affect the shape of the first balloon  30 , but also of the second balloon  62 . As shown in  FIG. 8A , when the first balloon  30  is in the first position, the coolant may be directed through the second balloon  62  in directions substantially perpendicular to the shaft  38  (that is, toward areas the interior wall  42  of the first balloon  30  that are not at the distal face  72  of the balloon  30 ). 
         [0046]    Referring now to  FIG. 8B , a cross sectional view of the balloon  30  having a second shape is shown. To change the balloon  30  to the second shape, the shaft is retracted a distance (“D”) within the main lumen  34  (as shown in  FIG. 7B ). Moving the shaft  38  also moves the position of the distal neck  30   b  of the balloon  30 , which may cause the distal neck  30   b  to be retracted inward. Because the distal neck  30   b  of the balloon  30  is directed inward, the distal neck  30   b  may not fold over on itself as shown in  FIG. 7B , where the distal neck  30   b  is directed outward. As the shaft  38  is retracted within the main lumen  34  of the device  12 , both the first balloon  30  and second balloon  62  are changed to a second shape. When the balloon  30  is in the second position, the distal neck  62   b  of the second balloon  62  is also drawn toward the distal end  26  of the elongate body  24  (as shown in  FIG. 8B ). Thus, the apertures of the fluid injection element  52  are oriented toward the distal face  72  of the balloon  30  (similar to the way the sensors  70  are moved in  FIGS. 7A and 7B ). This orientation of the second balloon  62  may ensure more efficient cooling of the distal face  72 , which may be in contact with a surface within a patient&#39;s body. The second balloon  62  may be any distance from the interior wall  42  of the first balloon  30  that provides sufficient cooling to the distal face  72  of the first balloon  30  in the second position. 
         [0047]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.