Cryoablation catheter with internal inflatable member

Abstract

A cryoablation system includes a catheter with a fluid inflow channel and a distal chamber; a fluid source comprising the fluid at a high initial pressure, and arranged to supply the fluid to the catheter via the fluid inflow channel; a primary cooler for cooling the fluid from the fluid source prior to entering the catheter; and a regulator for adjusting the initial pressure to an inflow pressure corresponding to the pressure along the inflow channel. The system further includes a controller programmed and operable to maintain the chamber pressure within a target range based on adjusting the inflow pressure. By monitoring and controlling the chamber pressure, or optionally temperature, the inflow pressure can be substantially lowered during the ablation procedure. In embodiments, the catheter includes an elastic inner balloon which is arranged to contact a rigid outer shell when inflated. Related methods are also described.

Description

CRYOABLATION CATHETER WITH INTERNAL INFLATABLE MEMBERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to application number 63 / 661,401, filed June 18, 2024, and entitled “CRYOABLATION CATHETER WITH INNER INFLATABLE MEMBER”.FIELD AND BACKGROUND OF THE INVENTION

[0002] This is generally directed to surgical systems for applying thermal energy to tissue, and more particularly, to endovascular catheters operable to ablate tissue by cooling the tissue.

[0003] The use of cryoablation in medical procedures is well established. Cryoablation is now used in a wide variety of procedures including, for example, the endovascular catheter treatment of heart disease. Typically, a working fluid such as liquid nitrogen is cooled and circulated through a distal treatment section of the catheter. In order to drive the nitrogen through the catheter, however, the inlet pressure is often required to be high, e.g., greater or equal than 500 psi.

[0004] Maintaining the working fluid at a high pressure can present several challenges in terms of safety and design flexibility. Operating at a high pressure requires more energy to achieve the desired operating conditions, thereby complicating the system. Additionally, the likelihood of leaks is increased at higher pressures, and the potential consequences or damage resulting from any leaks are substantially greater when the cryogen is maintained at a relatively higher pressure.

[0005] Accordingly, a cryoablation system, apparatus and method that can achieve the above- mentioned objectives is desirable.SUMMARY OF THE INVENTION

[0006] In embodiments of the invention, a cryoablation catheter for treating tissue comprises a distal treatment section comprising an inelastic and non-expandable outer shell defining an internal chamber.

[0007] In embodiments, the catheter further comprises a cryoablation element arranged within the internal chamber of the outer shell.

[0008] In embodiments, the cryoablation element is implemented as an elastic and expandable inner shell or balloon.

[0009] At least one fluid inflow channel is arranged in the catheter for transporting high pressurefluid into the inner shell within the internal chamber of the distal treatment section and at least one fluid return channel is arranged in the catheter for transporting low pressure fluid away from the inner shell within the internal chamber of the distal treatment section such that the inner shell makes contact with the outer shell as the fluid circulates through the inner shell, and cooling from the fluid is conducted through the inner shell, through the outer shell and to the tissue to be treated.

[0010] In embodiments, the catheter further comprises an open lumen for receiving a deflection tool, optionally, a pre-shaped, super-elastic metallic stylet.

[0011] In embodiments, the inflow channel is implemented as an inlet tube and extends distally along a majority of the length of the inner shell, and the return channel is implemented as a return tube entering the inner shell and terminating near a proximal end of the inner shell.

[0012] In embodiments, the catheter further comprises a pressure-sensing tube within the inner shell.

[0013] In embodiments, the fluid return channel comprises a larger diameter than the diameter of the fluid inflow channel.

[0014] In embodiments, the inflow channel comprises a plurality of orifices shaped and arranged along its length to optimize the flow of the fluid in the axial direction into the inner shell, ensuring uniform temperature distribution throughout.

[0015] In embodiments, the channels are sealed proximally on their exterior and attached to the inner shell thereby forming the internal chamber.

[0016] In embodiments, the outer shell is defined by a wall constructed from a flexible material.

[0017] In embodiments, the inner shell is spaced from the outer shell by at least 0.1 mm prior to circulating the fluid, and in some embodiments, at least 0.2.

[0018] In embodiments, the catheter further comprises a metallic or plastic braid arranged with the wall, and serving to prevent expansion of the outer shell in the radial direction.

[0019] In embodiments, the outer shell comprises an interior surface, and the inner shell is affixed to the interior surface of the outer shell.

[0020] In embodiments, the catheter further comprises a plurality of metallic electrodes exteriorly disposed on the outer shell.

[0021] In embodiments, the catheter further comprises at least one conductor channel extending through the distal section, the intermediate section and the proximal shaft for housing conducting wires to each of the metallic electrodes.

[0022] In embodiments, the inner shell and outer shell are constructed from a material with enhanced thermal conductivity by incorporating thermal inducers or fillers into a base material of the inner and outer shell.

[0023] In embodiments, the catheter further comprises a first phase during operation, wherein the inner shell is spaced from the outer shell as the inner shell is being filled with the fluid and expands; and a second phase of operation, wherein the inner shell contacts the outer shell, preventing further expansion of the inner shell.

[0024] In embodiments, the proximal shaft, intermediate section and outer shell form a first subassembly and the inner shell, inflow and return channels form a second sub-assembly that is advanced as a whole into the first sub-assembly.

[0025] In embodiments, the first and second sub-assemblies are arranged and operable to define an annular space distal to the inner shell after the inner shell is expanded during operation, and wherein a second pressure sensor is in fluid communication with the annular space to monitor the pressure within the annular space throughout the operation.

[0026] In embodiments, the catheter further comprises a multi-lumen plug upon which a proximal end of the inner shell is hermetically sealed, and through which the channels extend.

[0027] In embodiments, the channels extend through at least a portion of the proximal shaft, through the multi-lumen plug, and into the inner shell, and wherein the channels are enclosed within a vacuum jacket along the proximal shaft.

[0028] In embodiments, the vacuum jacket is hermetically sealed to the multi-lumen plug.

[0029] In embodiments, a cryoablation system for ablating a target tissue comprises a catheter including a distal treatment section comprising an internal chamber, at least one pressure sensor arranged in the internal chamber of the distal treatment section for measuring the chamber pressure within the internal chamber. The system further comprises a fluid source comprising the fluid at a high initial pressure, and arranged to supply the fluid to the catheter via the fluid inflow channel; a primary cooler for cooling the fluid from the fluid source prior to entering the catheter; a regulator for adjusting the initial pressure to an inflow pressure corresponding to the pressurealong the inflow channel; and a controller programmed and operable to maintain the chamber pressure within a target range based on adjusting the inflow pressure.

[0030] In embodiments, the controller is programmed and operable to maintain the chamber pressure within a target range based solely on adjusting the inflow pressure.

[0031] In embodiments, the target range is between 50 and 150 psi, and optionally, between 70 and 80 psi.

[0032] In embodiments, the pressure sensor comprises a tube extending from the internal chamber to an electronic sensor operable to provide an electronic signal to be sent to the controller.

[0033] In embodiments, the inflow channel has a diameter ranging from 0.01-.03”, and the return channel has a diameter ranging from 0.04-0.08”.

[0034] In embodiments, the controller is programmed with a PID algorithm to maintain the chamber pressure within the target range.

[0035] In embodiments, the system further comprises a pre-cooler operable to cool the fluid in the inflow channel using energy from the return channel prior to being cooled by the primary cooler.

[0036] In embodiments, the controller is operable to cool the internal chamber to below -150 degrees C within 10 seconds, and optionally, to below -160 degrees C within 15 seconds.

[0037] In embodiments, the inflow pressure during a first phase is in the range of 100 to 500 psi, and the controller is operable to decrease the inflow pressure to less than 100 psi during a second phase, and optionally, wherein the first phase has a duration of less than 10 seconds.

[0038] In embodiments, the inflow channel comprises a distal orifice or a nozzle where the fluid exits the inflow channel and enters the internal chamber.

[0039] In embodiments, the controller is operable to decrease the temperature to under -150 C within 5 seconds by maintaining the target chamber pressure at 100 psi or less.

[0040] In embodiments, a cryoablation system for ablating a target tissue comprises a catheter comprising a distal treatment section, a fluid inflow channel for transporting high pressure fluid to the internal chamber in the distal treatment section, and at least one fluid return channel for transporting low pressure fluid away from the internal chamber of the distal treatment section.The system further comprises a fluid source comprising the fluid at a high initial pressure, and arranged to supply the fluid to the catheter via the fluid inflow channel; a primary cooler for cooling the fluid from the fluid source prior to entering the catheter; a regulator for adjusting the initial pressure to an inflow pressure corresponding to the pressure along the inflow channel; a flowmeter for measuring the fluid delivery flowrate of the fluid entering the catheter; and a controller programmed and operable to maintain the delivery flowrate within a target flowrate range based on adjusting the inflow pressure.[00411 In embodiments, the controller is programmed and operable to maintain the delivery flowrate within a target flowrate range based solely on adjusting the inflow pressure.

[0042] In embodiments, the target flowrate range is between 20 and 90 SLPM.

[0043] In embodiments, the system further comprises a pressure sensor for measuring chamber pressure within the internal chamber, and a pressure safety module programmed and operable to detect for fluid leaks along the flowpath of the fluid during an ablation.

[0044] In embodiments, the controller is programmed with a PID algorithm to maintain the delivery flowrate within the target flowrate range.

[0045] In embodiments, the system further comprises a pre-cooler operable to cool the fluid in the inflow channel using energy from the return channel prior to being cooled by the primary cooler.

[0046] In embodiments, the inflow channel comprises a distal orifice or a nozzle where the fluid exits the inflow channel and enters the internal chamber.

[0047] In embodiments, the fluid for the cryogen is liquid nitrogen, however, other fluids may be used including fluids in supercritical and near critical or other states.BRIEF DESCRIPTION OF DRAWINGS

[0048] FIG. 1 illustrates a schematic drawing of a cryoablation system including a controller operable to control the power based on tip pressure, according to embodiments of the invention;

[0049] FIG. 2 illustrates another schematic drawing of a cryoablation system including a controller operable to control the power based on flowrate, according to embodiments of the invention;

[0050] FIG. 3 illustrates another schematic drawing of a cryoablation system including a console and catheter, according to embodiments of the invention;

[0051] FIG. 4 is a longitudinal cross section of a distal section of a cryoablation catheter, according to embodiments of the invention;

[0052] FIG.5A is an end view of an inlet tube of a cryoablation catheter, according to embodiments of the invention;

[0053] FIG. 5B shows a top view of the inlet tube shown in FIG. 5A, according to embodiments of the invention;

[0054] FIGS. 5C, 5D show views at + / - 60 degrees from the view shown in FIG. 5B, respectively, according to embodiments of the invention;

[0055] FIG. 6 is a longitudinal cross section of an outer sleeve of a distal section of a cryoablation catheter including electrodes, according to embodiments of the invention;

[0056] FIG. 7 is a longitudinal cross section of a distal section of a cryoablation catheter shown with the inner member in an enlarged configuration, according to embodiments of the invention;

[0057] FIG. 8 is a partial perspective longitudinal cross section of the distal section of the cryoablation catheter shown in FIG. 7, according to embodiments of the invention;

[0058] FIG. 9 is a cross sectional view of the cryoablation catheter taken along line 9-9 of FIG. 7, according to embodiments of the invention;

[0059] FIG. 10 is a cross sectional view of a proximal section of a cryoablation catheter, according to embodiments of the invention; and

[0060] FIG. 11 is a chart showing temperature time data for various cryoablation system configurations, according to embodiments of the invention.

[0061] The description, objects and advantages of embodiments of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings.DETAILED DESCRIPTION OF THE INVENTION

[0062] Before the present invention is described in greater detail, it is to be understood that this invention is not limited to particular embodiments described, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges can independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention. Unless defined otherwise, 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 any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are now described. It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims can be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which can be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

[0063] All existing subject matter mentioned herein (e.g., publications, patents, patent applications and hardware) is incorporated by reference herein in its entirety except insofar as the subject matter may conflict with that of the present invention (in which case what is present herein shall prevail).

[0064] Described herein are systems for performing thermal ablation. The systems generally comprise a console and a thermal ablation implement (such as a cryoablation catheter) connected to the console.

[0065] FIG.l illustrates a cryoablation system 100 in accordance with an embodiment of theinvention. The cryoablation system 100 is shown including a catheter comprising an insulated shaft 101, ablation element 102, and a plurality internal tubes 104, 105, and 106 that are insulated by an evacuated space 103.

[0066] The length of the distal cryoablation element 102 can vary. An exemplary length ranges from 10 mm to 150 mm.

[0067] The outer diameter of the cryoablation element 102 can vary. An exemplary OD is between 1 mm and 5 mm, and preferably 1 to 3 mm.

[0068] The flexibility of the cryoablation element 102 may also vary. In embodiments, it is flexible. However, in some embodiments it is rigid.

[0069] The internal channels 104, 105, and 106 serve various functions. In embodiments, channel 104 is for high pressure cryogen delivery, channel 105 is a low-pressure cryogen return line 105, and channel 106 is a pressure tube for pressure measurement that is connected to an external pressure sensor 107. External pressure sensor 107 is operable to provide an electrical signal output, discussed further herein.

[0070] FIG. 1 also shows a cryocooler 108. In operation, a cryogen in its liquid or near-critical phase (such as liquid nitrogen, for example) is generated by the cryocooler 108. An exemplary cryocooler is a liquid nitrogen-based cooler, mechanical cooler (such as Stirling Free Piston cooler, GM cooler, pulse tube cooler), as well as any type of a near-critical fluid generator. As shown, the cryogen is injected into the input line 104 of the catheter 101 at an elevated pressure (100-500 psi) and delivered to the cryoablation element 102 of the catheter. In embodiments, the input line 104 comprises a small orifice or a single nozzle or a plurality of nozzles at its distal end where the fluid is ejected.

[0071] Without intending to be bound to theory, the small orifice or nozzles serve to prevent pressure drop along the inlet line 104. Additionally, in embodiments, the inlet line 104 is well thermally insulated (e.g., by vacuum) such that there is no phase change in the fluid along the inlet line.

[0072] The tip 102 may have a blunt end such as a gently curved rounded end as shown in FIG. 1. Tip 102 also comprises a chamber or cavity 152 in which the fluid from the inlet line 104 is delivered. The hydraulic resistance of the chamber 152 of the ablation element 102 is lower than that of the inlet line 104, therefore the cryogen is expected to flow at the reduced pressure. Thisexpansion provides an additional cooling effect due to enthalpy change.

[0073] The fluid is evacuated by the return line 105. In embodiments, the diameter of the return line 105 is larger than that of the inlet line 104 so the hydraulic resistance is lower, and no significant pressure build-up will occur as the fluid transitions from the inlet line, through the chamber 152, and into the return line 105.

[0074] Exemplary inner diameters range from 0.01-.03” for the inlet line and 0.04-0.08” for the return line.

[0075] Additionally, the cross-sectional shape of the lines 104, 105, 106 may vary. Exemplary shapes include, without limitation, circular, oval, triangular, square, and rectangular. The tubes may be arranged side by side as well as coaxial or concentric. Preferably, however, the return line is shaped and sized to provide a lower hydraulic resistance than the inlet line.

[0076] Optionally, system 100 includes a counterflow heat-exchanger 109 to initially pre-cool the cryogen with the return flow of cryogen from the return line 105.

[0077] In embodiments, the system 100 includes an electronic pressure / flow regulator 110. The electronic pressure regulator 110 is operable to condition pressure from an external fluid source 111 based on the feedback from the pressure sensor 107 that is measuring the internal pressure (Ptip) of the cryoablation element 102. An electronic controller 113 is programmed and operable to maintain pressure inside the cryoablation element 102 at some predetermined relatively low- pressure value (e.g., between 50 and 100 psi) at all times during the duration of the ablation phase.

[0078] In an embodiment, a method for ablating tissue comprises several phases or cycles. Initially, or at the beginning of the procedure, when the temperature of the entire catheter including its ablation element 102 is relatively high (e.g., about body temperature), a considerably higher pressure at the inlet (Pi) of the catheter is required to sustain the cryogen flow through the catheter. A high inlet pressure during this first phase is desired to achieve the fastest possible cooling rate.

[0079] As the internal components of the catheter, as well as the tissue that is in contact with the ablation element 102 gets colder, the cryogen flows more easily due to increase in its density. Less inlet pressure (Pi) is required to maintain the required pressure (Ptip) inside the cryoablation element. As a result, the inlet pressure will be highest at the very beginning of the cooling cyclebut will be progressively reduced until reaching a stable final value.

[0080] In embodiments, the value of the internal cryoablation element pressure (Ptip) is maintained constant at all times using a controlling algorithm (such as PID or fuzzy logic algorithms, for example).

[0081] Without intending to be bound to theory, the cooling associated with embodiments described herein results at least in pail by an enthalpy change arising from the change in fluid’s density or phase / state, and not a large expansion or pressure change as results from other cooling schemes such as a Joule Thomson effect.

[0082] FIG. 2 illustrates another embodiment of a cryoablation system 200 in accordance with an embodiment of the invention. The cryoablation system 200 shown in FIG. 2 is similar to that described above in FIG. 1 except that instead of controlling the internal pressure of the tip 202 / 252 based on measuring the pressure at the tip, the control loop uses a mass flowrate of the cryogen through the catheter.

[0083] In some embodiments, a mass flowmeter 214 is positioned along the cryogen inlet flowpath 204. The electronic output from the flowmeter 214 is used by a controller 213 to regulate a pressure regulator 210, optionally incorporating external input from a system computer 215. Examples of such external inputs from the computer include, but are not limited to, PID control to maintain consistent flow throughout the entire cryoablation cycle, and control based on calculations of the total cryoablation energy. The flowrate value from flowmeter 214 is maintained at a constant rate by conditioning the pressure at the inlet (Pi). As such, the initial inlet pressure (Pi) is expected to be relatively high during the first phase while the temperature of the tissue in contact with the tip 202 and the internal catheter components is relatively high. Then, during a second phase, the inlet pressure is anticipated to be substantially lower since the temperature of the tissue in contact with the tip and the internal catheter components is decreased.

[0084] Optionally, as shown in FIG. 2, a pressure tube 206 fluidly connects the tip 202 to an electronic sensor 207. In embodiments, the signal from the electronic sensor 207 is used for purposes unrelated to controlling the pressure at the tip 202. An example of an unrelated purpose is to monitor for leaks in the flowlines 204, 205. For example, a sharp change in pressure can indicate a leak has occurred along the cryogen flowpath. The physician can halt ablation. In other embodiments, the pressure can be delivered to the controller and the controller is programmed and operable to halt the ablation upon receipt of a pressure signature indicative of a

[0085] Preferably, the channels 204, 205 are vacuum insulated with space 203 defined by outer shaft 201.

[0086] Optionally, the system 200 includes a counterflow heat-exchanger 209 to precool the cryogen prior to cryocoolcr 208.

[0087] An exemplary fluid for the cryogen is liquid nitrogen, however, other fluids may be used including fluids in supercritical and near critical or other states.

[0088] With reference to FIG. 3, another system is shown including a console 550 and a cryoablation catheter 500. The cryoablation catheter 500 includes a distal treatment section 510, a handle 520, and an umbilical cord 530. The catheter supply and exhaust lines are arranged within the umbilical cord. The proximal end of the umbilical cord 530 terminates in connector 540, which is inserted into receptacle port 560 on console 550.

[0089] One or more ancillary connector lines 570 arc shown extending proximally from the handle 520. The tubular lines 570 may serve to provide various functionality including without limitation (a) flushing; (b) vacuum; (c) thermally conductive fluid supply; (d) articulation, and / or (e) temperature and pressure sensor conductors.

[0090] The catheter 500 is also shown having electrical connector 580 extending proximally from the handle 520. Electrical connector 580 may be coupled to an EP recording system for analyzing electrical information detected in the distal treatment section 510, discussed further herein. Examples of systems for analyzing the electrical activity include, without limitation, the GE Healthcare CardioLab II EP Recording System, manufactured by GE Healthcare, USA and the LabSystcm PRO EP Recording System manufactured by Boston Scientific Inc.(Marlborough, MA). The recorded electrical activity may also be used to evaluate or verify the continuous contact with the target tissue as described in U.S. Patent No. 11,051,867, entitled “TISSUE CONTACT VERIFICATION SYSTEM”, filed June 13, 2018 by Babkin, et al., the entire contents of which are incorporated herein by reference for all purposes.

[0091] Console 550 is also shown including a housing 512 supported by rollers 514 (e.g., castors or wheels). The housing 512 can enclose the functional components described above in connection with FIGS. 1-2.

[0092] A computer 555 can be arranged within the housing. In embodiments, the computer 555is programmed and operable to control the components as described above. The console is shown having a built-in dashboard 557 which can include buttons and lights to control and indicate power on / off, mode, time, time elapsed, temperature, etc. The console is also shown including a keyboard 558 and display 562. Optionally, the console includes a communication module and one or more ports to connect directly to external devices including laptops, computers, landlines, and local area networks. Optionally, the console includes a wireless communication module to communicate with portable computer devices including tablets, smart phones and customized devices, catheters, and instruments having wireless capability.

[0093] FIG. 4 is a longitudinal cross-sectional illustration of a distal section of a cryoablation catheter 400, in accordance with various embodiments of the invention.

[0094] As shown, the catheter 400 includes a tubular proximal section 401, a distal outer shell 410, and an inner cryoablation element 414.

[0095] Both the inner and outer shells are constructed from a thermally conductive material, preferably a material with enhanced thermal conductivity, facilitating heat transfer.

[0096] Additionally, the distal outer shell 410 is preferably non-elastic, and optionally flexible. The non-elastic outer shell 410 is preferably constructed from a flexible material and optionally, incorporates a metallic or plastic braid within its walls. When present, the braid serves to prevent expansion in the radial direction.

[0097] In some embodiments, the inner cryoablation element 414 is elastic and has a cylindrical shape. In other embodiments, the inner cryoablation element is an inflatable balloon. A nonlimiting exemplary material for the inner shell 414 is Pebax or another elastic material that is thermally enhanced with certain thermally conductive inclusions or fillers. Exemplary filler materials include, and are not limited to, aluminum, copper, silver and gold. In some embodiments, the filler can be a ceramic material that has good thermal conductivity and preferably is electrically insulating in order to isolate any electrodes that are included on the catheters ablation portion as discussed herein. Exemplary ceramic filler materials include, and are not limited to, BN (boron nitride), AIN (aluminum nitride), Si3N4 (silicon nitride), SiC (silicon carbide), A12O3 (aluminum oxide) and ZnO (zinc oxide). Still other materials having a high thermal conductivity, preferably electrically non-conductive, and which are combinable or integratable with the base material, can be used as the filler material.

[0098] In embodiments, the inner shell 414 houses inlet tubing 404, return tubing 405, pressure tube 406, and stylet tube 420. In embodiments, the inner shell and tubing are sealed at the proximal end of the inner shell 414. An exemplary seal 430 is a multi-lumen plug hermetically sealed to each of the individual tubes. Then, as described further herein, the inner shell is bonded to the plug, and the outer shell is affixed to the plug such that the outer shell encloses and optionally, compresses the proximal end of the inner shell to the plug, thereby creating an improved hermetic seal between the inner shell and the plug. In an embodiment, the plug, tubes, and inner shell are heat fused together.

[0099] In the embodiment shown in FIG. 4, the inlet tubing 404 is shown extending distally along the full length of the inner shell 414 whereas the return tubing 405 is substantially shorter and terminates near the proximal end of the inner shell 414.

[0100] The pressure-sensing tube 406 is also shown terminating near the proximal end of the inner shell 414. As described above, the pressure tube is fluidly coupled to an external electronic sensor which can convert the pressure force to a digital output.

[0101] The stylet channel 420 is shown extending through the center of the inner shell. The stylet or central channel is shaped and adapted to receive a deflection tool, such as a preshaped, super-elastic metallic stylet, for example. Consequently, the catheter 400 may take a wide variety of shapes according to the one or more stylets. Exemplary stylet shapes are shown in US Patent No. 11,564,725 to Babkin et al. The inner diameter of the stylet channel 420 may vary and in embodiments, ranges from 0.3 to 1 mm.

[0102] The channels also extend proximally from the inner shell 414 along shaft 401. The channels are enclosed within a vacuum jacket formed by the shaft 401 , which provides the thermal insulation. This vacuum jacket 401 is also connected to a proximal side of seal 430 of the inner shell 414.

[0103] In the embodiment shown in FIG. 4, a plurality of orifices 407 are arranged along the length of the inlet tube 404. These orifices are designed to optimize the flow of the cryogen in the axial direction (A), ensuring uniform temperature distribution throughout the inner shell 414. In embodiments the orifices are equally spaced along the length of the inlet channel in the inner shell 414.

[0104] However, and with reference to FIGS. 5A-5D, the arrangement of the orifices orholes (462a, 462b, 462c, 462d; 464a, 464b, 464c, 464d; and 466a, 466b, 466c, 466d) along the inlet tube 450 may be unequally spaced. As shown in FIGS. 5B-5D, the density of the holes increases closer to the distal end of the inlet tube where the change in spacing roughly decreases by a factor of two as the orifices get closer to the distal end.

[0105] Additionally, adjacent holes shown in FIGS, 5A-5D are radially offset from each other by an angle (alpha a). In FIGS. 5B-5D, alpha is 60 degrees. However, alpha is not intended to be so limited. Alpha may vary. An exemplary range for alpha is 30 to 90 degrees, and more preferably 45-60 degrees.

[0106] The diameter (DIA) of the orifices may vary. A nonlimiting exemplary range for the characteristic diameter of the orifices is 0.001 to 0.2 in.

[0107] The total number of orifices in the wall of the inlet tube 450 may vary. An exemplary number of orifices ranges from 5- 30, and in some embodiments, 9-21.

[0108] Additionally, the shape of the orifices may vary. The shape of the orifices may be circular, an elongate slot or slit, or another geometric shape.

[0109] The table below shows exemplary orifice configurations along the inlet tube having a total length (Liotai of 105 mm or about 4 in), an inner diameter (I.D. of about 0.4-0.5 in), and an outer diameter (O.D. of about 0.7-0.8 in) according to embodiments of the invention:

[0110] Indeed, the shape and arrangement of the orifices may vary. Inventors have found adding numerous orifices, radially offset by an angle, and increasing in density serve to increasethe flow in the axial direction of the cryogen through inner shell, thereby increasing uniformity of the flow and cooling power.

[0111] In embodiments, during the first phase before or as the inner member is being inflated, there is minimal or no thermal contact between the inner flexible shell (indicated by the dotted line contour 414) and the outer shell 410. Then, once the inner member 414 reaches its working pressure as described above, the elastic shell expands (as shown by the solid line contour) and forms a firm thermal contact with the radially rigid external shell 410.Consequently, the combined cooling element is created, and the ablative temperatures are confined to the region where the two shells make a firm thermal connection.

[0112] In embodiments, during the first phase, the space or gap between the elastic inner member and the radially rigid outer member ranges from 0.001 to 0.004”.

[0113] In embodiments, in an area distal to the inflated inner shell 410, an annular space is formed between the sub-assemblies (namely, the inner elastic member 414 and components therein and the outer shell 410). In embodiments, the pressure within this annular space is continuously monitored throughout the clinical procedure. This monitoring serves to detect in real-time any leaks in the inner subassembly. Additionally, in combination with the sealed outer subassembly, this design provides a double-layer of protection against potential internal cryogen leaks.

[0114] FIG. 6 shows an outer subassembly 300 of another catheter design in accordance with embodiments of the invention. The catheter assembly 300 includes a proximal shaft 310, distal treatment section 330, and an elbow region 320 between the proximal and distal regions which may be articulated as described herein.

[0115] In embodiments, the proximal main shaft 310 is longer and stiffer than the shorter, more flexible distal elbow section 320. In embodiments, the length of the stiffer main shaft section 310 ranges from 20 to 100 inches, and in some embodiments, 30- 50 inches. In embodiments, the length of the elbow or articulation section 320 can range from the 1 to 10 inches, and in some embodiments 2 to 4 inches. In embodiments, the length of the distal region 330 is as described herein, or between 10 mm and 150 mm.

[0116] As described above, when the inner subassembly is arranged within the distal treatment section, and the inner elastic member (not shown) is expanded, only the distal treatmentsection where firm contact is made between the inner member and outer member 332 is active to freeze tissue. Consequently, in embodiments, the elbow 320 is a non-freezing region.

[0117] The catheter shown in FIG. 6 also includes a plurality of electrodes 340 arranged on the outer shell 332. The outer shell supports the metallic electrodes and their corresponding wiring (not shown), which can be utilized for sensing or therapeutic purposes as described herein.

[0118] FIG. 7 is an enlarged longitudinal cross-sectional illustration of a distal section of another cryoablation catheter 600, in accordance with various embodiments of the invention.

[0119] The catheter 600 includes a radially-rigid outer body 602 surrounding an elastic inner shell 604. The elastic inner shell is shown in an enlarged configuration and in contact with the outer body 602. The outer body and inner shell are both made of thermally conducting materials as described herein. In a procedure, heat from the tissue is transferred through the outer shell, through the inner shell, and into the cryogen being circulated through the inner shell.

[0120] In embodiments, the inner shell 604 is sealed to a plurality of channels at its proximal end by a plug insert 624. The multi-lumen plug or insert 624 is shown arranged within the proximal end of the outer shell 602 and supporting the channels extending from the intermediate catheter section into the distal inner shell 604. The number and types of channels may vary. In the embodiment shown in FIG. 7, channels include an inflow tube 628, return flow tube 632, pressure tube 634, and a temperature tube 636.

[0121] In embodiments, a thermocouple is located at the distal end of the catheter tip via temperature tube 636. In embodiments, the thermocouple measures the internal temperature of the cooling chamber. An exemplary temperature during operation is around -190°C. This reading can be used to confirm effective cryogen delivery, sufficient vacuum insulation, and confidence that the tip surface has reached its intended therapeutic temperature. In embodiments, the controller is programmed to adjust cryogen delivery through the inflatable member based on the temperature. In embodiments, the controller is programmed to adjust the cryogen delivery through the inflatable member based on the pressure and temperature readings.

[0122] In embodiments, a nozzle 630 is arranged at the distal end of the inflow tube. The nozzle serves to prevent pressure loss along the inlet channel. Additionally, the channels are thermally insulated (e.g., vacuum insulated) as described herein to further inhibit a phase change along the inlet line. The inlet line and nozzle serve to release the cryogen towards the distal halfof the inner shell, more preferably in the distalmost quarter of the inner shell whereas the opening of the return channel 632 is arranged at the proximal end of the inner shell. In this embodiment, under this arrangement, the fresh fluid travels from the distal end to the proximal end of the inner shell. The flowstreams within the inner shell are primarily in the axial direction.

[0123] The multi-lumen insert 624 is shown with a flange or ridge 625 having a proximal side and distal side.

[0124] To seal the inner shell 604 with the insert 624, the proximal region of the inner shell is fitted over the distal end of the insert until it contacts the distal side of the ridge 625.

[0125] To seal the vacuum tube 650 with the insert 624, the distal region of the vacuum tube is fitted over the proximal end of the insert until it contacts the proximal side of the ridge 625.

[0126] The proximal end of the outer shell 602 is then advanced over the inner shell, plug, and vacuum tube assembly, thereby sandwiching both of the inner shell 604 and vacuum tube 650 to the multi-lumen insert 624. Optionally, the inner member and vacuum tube may be heat fused or otherwise sealed to the multi-lumen insert 624. The tight fit and bonding serves to hermetically seal the inner elastic member around the plug and channels.

[0127] In embodiments, an inner sub-assembly comprises the vacuum tube 650; multilumen insert 624 bonded to the end of the vacuum tube; the inflow, return, pressure, thermocouple tubes extending therethrough; and the elastic inner sleeve 604 hermetically sealed to the insert and enclosing the distal sections of the tubes.

[0128] With reference again to FIG. 7, an outermost sleeve 610 is shown surrounding the outer body 602. The outermost sleeve is preferably thermally conductive but electrically non- conductive. An exemplary material of the non-electrically conductive outer sleeve is as described herein.

[0129] Eight ring-shaped electrodes 620 are shown axially spaced along the distal section of the catheter. As described herein, the electrodes are operable for various functions including detecting tissue contact, for example. Although eight electrodes are shown, the number of electrodes may vary.

[0130] FIG. 8 is a partial perspective longitudinal cross section of the distal section of the cryoablation catheter shown in FIG. 7. FIG. 8 more clearly depicts the interface of the tubesextending through the insert 624 and enclosed within the inner elastic shell 604.

[0131] FIG. 8 also more clearly illustrates the gap or space between the balloon 604 and the body 607.

[0132] In embodiments, various implementations are operable to collect data within the space between the inner balloon and outer body, and particularly to monitor preferential filling, control balloon behavior, and or enhance procedural safety.

[0133] In embodiments, a sensor is integrated in the gap. Distributed pressure sensors or MEMS devices are embedded along the outer tube or balloon wall and can detect localized pressure changes, helping identify early or asymmetric inflation. For example, fiber optic strain sensors can monitor dynamic expansion or contact against the outer tube, revealing points of high stress or uneven filling. Impedance-based sensors (e.g., electrodes on inner / outer walls) can track fluid conductivity during fill, offering insight into fluid front progression and completeness of inflation. Miniature temperature or flow sensors may be added to detect cryogenic cooling patterns, especially useful in cryoablation procedures.

[0134] In embodiments, balloon designs including, for example, segmented or multi- lobed balloons can allow for shape control based on inflation sequence or pressure differentials. Asymmetric balloons can be engineered to expand preferentially in certain directions — this can be useful for steering or conforming to anatomy. Internal channeling or zoned compliance can be built into the balloon to facilitate controlled bending, turning, or sealing. For example, a balloon may include a pre-set expanded shape that creates a bend by 30-90 degrees, a spiral, a ring-shape, or other geometry. The balloon bend is then imposed onto the distal section of the apparatus.

[0135] In embodiments, the controller is programmed and operable to control timing and inflation (or partial inflation). In some implementations, a controller algorithm is executed on a processor in the controller that can time inflation in stages, allowing sensors to verify partial fill and adjust rates dynamically. Partial inflation protocols are programmed to shape the balloon for navigation through tortuous anatomy or to prepare the site before full inflation. Timed or pulsed inflation is performed to obtain real-time feedback before reaching full pressure, minimizing risk of rupture. Expected pressure signatures during partial fill can be compared to expected historical pressure signatures. If the real-time pressure signature is outside of a threshold value or correlation, an alert is generated or the procedure can be halted.

[0136] In embodiments, both intraluminal balloon pressure and the gap pressure in the surrounding space is monitored and indicative if the balloon is contacting the outer tube or expanding too freely. This dual pressure monitoring also serves to regulate upstream pressure to prevent over-inflation or backflow. In embodiments, the differential pressure is used as feedback in a closed-loop control system to automatically adjust inflation based on sensor readings.

[0137] Indeed, there are a number of different useful techniques associated with monitoring the interface and spacing between the balloon and outer shield. By combining these sensing and control strategies, the balloon system can be made more responsive, safer, and intelligent, especially in delicate applications like cryoablation where precision and reliability are critical.

[0138] Embodiments of the invention described herein behave differently than conventional balloon apparatuses. Without intending to be bound to theory, a system with an internal balloon that contacts a non-expandable outer shell would exhibit distinct temperature, pressure, and flowrate signatures compared to unconstrained or rigid-only designs.

[0139] The pressure curve is unique. For embodiments, during inflation, the internal balloon expands until it contacts the shell, resulting in a delayed pressure rise. Once contact occurs, pressure increases more sharply and stabilizes — creating a two-phase pressure curve: Phase 1: Gradual pressure increases during free expansion; Phase 2: Rapid pressure increases after full contact This inflection point in the pressure curve is a key indicator of balloon-to- shell engagement.

[0140] The flow signature is unique. For embodiments, an initially higher flowrate would occur due to volume expansion of the balloon. As the balloon contacts the outer shell, the available volume ceases to increase, and the flowrate drops — resulting in a decaying flowrate curve that stabilizes after full contact. Flowrate vs. time curve would show a distinct downward inflection aligned with the pressure curve transition.

[0141] The temperature signature is unique. For embodiments, once the balloon makes full contact with the non-expandable shell, improved thermal coupling leads to a sharper drop in outer wall temperature, as thermal transfer becomes more efficient. Temperature gradient across the balloon would flatten after contact, indicating stable heat conduction from the inner cryogen to the shell.

[0142] Together, these signatures — particularly the inflection points in pressure and flowrate curves — can serve as indirect indicators of full balloon deployment and contact with the outer shell, which is critical for performance verification and safety in cryogenic applications.

[0143] In contrast, the absence of the outer non-expanding shell would result in the inner inflatable member having more gradual changes in pressure, flow, and temperature during the latter phase of balloon expansion.

[0144] In embodiments, a step of confirming contact between the inner balloon and the outer shell is performed. For embodiments, pressure sensors or strain gauges are embedded along the outer shell can detect balloon expansion and verify full surface contact. Alternatively, impedance-based sensing or fiber optic strain sensing can be used to monitor changes in mechanical interaction at the interface, ensuring the balloon is properly deployed and in full thermal contact during operation.

[0145] There are a number of advantages to have an internal balloon that contacts a non- cxpandablc shell including, without limitation:

[0146] Improved thermal transfer: A thin, conformable balloon wall minimizes thermal resistance, allowing more efficient cryogen-to-tissue cooling.

[0147] Cryogen containment: The balloon contains the circulation within the therapeutic section, enabling localized, targeted cooling.

[0148] Double fault safety: The balloon provides the first containment layer, while the outer shell serves as a secondary barrier — offering redundancy against cryogen leakage and enhancing patient safety.

[0149] An additional benefit of using a balloon is the ability to perform a pre-cooling or priming step before full inflation. This controlled inflation phase allows initial contact verification, enables sensor feedback on balloon deployment, and stabilizes the thermal environment before full cryoablation. This step can improve both procedural reliability and therapeutic precision by confirming system readiness and proper interface engagement.

[0150] Additionally, in embodiments, the end gap between the balloon tip and the shell tip is important and carefully controlled. The gap defines the extent to which the inner balloon is radially and axially constrained at its distal end. If the interface is loose or oversized, the balloon can expand into this unsupported region during pressurization, leading to localized bulging. Thisis important along the distal therapeutic section where precise control of balloon expansion is necessary. Over time or under cyclic loading, this uncontrolled expansion can accelerate material fatigue, increase the risk of rupture, and reduce the mechanical reliability of the device.Therefore, minimizing the end gap — or designing it with intentional, well-defined geometry — helps maintain structural integrity, ensures predictable balloon behavior, and supports consistent therapeutic performance.

[0151] FIG. 9 is an enlarged cross section of the catheter 600, taken along line 8-8, of FIG. 7. The cross section shown in FIG. 9 is within the articulation or elbow region of the catheter.

[0152] A tubular multi-lumen articulation segment 654 is shown surrounding the vacuum tube 650 and includes a main channel 657 and two side lumens 674, 675 on diametrically opposite sides of the main channel. The lumens hold wires 672, 673 which are operable to articulate the distal section of the catheter by pulling and pushing on the wires. The tubular multi-lumen tubular articulation segment 654 maintains the locations of the pull wires relative to one another for accurate articulation.

[0153] Vacuum tube 650 is shown surrounding the inflow tube 628, return flow tube 632, pressure tube 634, and a temperature tube 636.

[0154] Rectangular tubes 660 are shown within the tubular articulation segment 654 for holding the electrical conductors extending to the electrodes 620 described above.

[0155] An outer shaft 640 is shown surrounding the multi-lumen tubular articulation segment 654.

[0156] FIG. 10 is an enlarged cross section of a proximal region of the catheter 600. The proximal section shares many of the components of the articulation section described above in connection with FIG. 9 except the proximal section does not include the multi-lumen tubular articulation segment 654. Independent tubes 670, 671, optionally floating, are shown for supporting the pull wires contained therein. In embodiments, the space between the outer shaft 640 and the vacuum tube 650 is also evacuated for further thermally insulating the working channels from the physician and environment.

[0157] EXAMPLES

[0158] FIG. 11 is a chart showing temperature and time profiles of a liquid nitrogensystem and ablation catheter as described above in connection with FIGS. 1, 7 respectively, for five different target tip pressures (Ptip). In each test, the tip was placed in 1000 ml water bath initially at body temperature with an active heater to keep the water temperature constant.

[0159] Liquid nitrogen having an initial or inlet temperature of around -180C was circulated through the catheter.

[0160] The pressure at the tip within the inner elastic member was monitored and maintained constant at the target pressure by automatically adjusting the inlet pressure using a programmed controller as described above.

[0161] Temperature of the nitrogen within the tip was recorded over time by thermocouples arranged in the catheter as described above.

[0162] The test results are shown in FIG. 11. Each pressure curve can be characterized by a steep first phase as the inner elastic member is being filled with the working fluid and contacts the outer shell. The internal components of the catheter and surrounding medium appear to start at the temperature of the surrounding medium, and then begin to rapidly cool. Although the pressure curves corresponding to the higher pressures (e.g., 91, 100 psi) drop in temperature rapidly (within 5 seconds) to below -125 C, it is also noteworthy that all curves do so by 20 seconds.

[0163] The temperature time profiles of each curve also reflect a flat second phase in which the temperature is relatively constant. Except for the 60 psi curve, the second portion of each curve is between -125 and -160 C, depending on the tip pressure. This second phase is characterized by the circulating fluid and surrounding medium reaching an equilibrium or steady state of heat transfer in which the desired temperature has been reached. Advantageously, during the second phase, the inlet pressure is anticipated to be modulated to a substantially lower value compared to the initial relatively high pressure (e.g., 400-500 psi) once the surrounding medium and inner catheter components are cooled. Less power is needed to cool the target tissue during the second phase.

[0164] Collectively, the data of FIG. 11 is evidence that maintaining a tip pressure at a constant value of 100 psi (or lower) can provide efficient cooling to a temperature of -125 C or less within 10 seconds, and in some embodiments, within 3 seconds. The testing also shows cooling to -150 C within 8 seconds by maintaining the tip pressure at 100 psi. As describedabove, use of lower pressures during a procedure reduces the chance of cryogen leaks, increases patient safety, and allows for venting directly to the atmosphere, each of which is a meaningful benefit. Additionally, faster cooling rates are achieved by maintaining the pressure at the catheter tip at a constant, relatively low, pressure in accordance with embodiments of the invention described herein.

[0165] ALTERNATIVE EMBODIMENTS

[0166] Aspects of the invention described above can be applied to arrange the inner elastic shell with the outer shell in various configurations including, without limitation, affixing the inner elastic shell to the outer shell. In embodiments, the inner shell can be heat fused to the outer shell.

[0167] Aspects of the invention described above can be applied to circulate a working fluid through a wide variety of thermal implements including, without limitation, flexible catheters, rigid probes, instruments, and devices.

[0168] Aspects of the invention described above can be applied to provide multiple ancillary or pre-cooling heat exchangers, optionally in series, to cool (or warm as the case may be) the working fluid to a target temperature.

[0169] Throughout the foregoing description, and for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the described techniques. It will be apparent, however, to one skilled in the art that these techniques can be practiced without some of these specific details. Although various embodiments that incorporate these teachings have been shown and described in detail, those skilled in the art could readily devise many other varied embodiments or mechanisms to incorporate these techniques. Also, embodiments can include various operations as set forth above, fewer operations, or more operations; or operations in another order than that specifically described above. Additionally, any of the components and steps described herein may be combined with one another in any logical manner except where such components or steps would be exclusive to one another. Accordingly, the scope and spirit of the invention should be judged in terms of the claims, which follow as well as the legal equivalents thereof.

Claims

CLAIMS1. A cryoablation catheter for treating tissue comprising: a proximal shaft; a distal treatment section comprising an outer shell defining an internal chamber, the outer shell being inelastic and non-expandable; an intermediate section having a flexibility greater than the proximal shaft but less than the distal treatment section; a cryoablation element arranged within the internal chamber and comprising an inner shell, the inner shell being elastic and expandable; at least one fluid inflow channel for transporting high pressure fluid into the inner shell within the internal chamber of the distal treatment section; at least one fluid return channel for transporting low pressure fluid away from the inner shell within the internal chamber of the distal treatment section; and wherein the cryoablation element is arranged with the outer shell to contact the outer shell as the fluid circulates through the inner shell, and cooling from the fluid is conducted through inner shell, through the outer shell and to the tissue to be treated.

2. The catheter of claim 1, further comprising an open lumen for receiving a deflection tool, optionally, a pre-shaped, super-elastic metallic stylet.

3. The catheter of claim 1 , wherein the inflow channel is implemented as an inlet tube and extends distally along a majority of the length of the inner shell, and the return channel is implemented as a return tube entering the inner shell and terminating near a proximal end of the inner shell.

4. The catheter of claim 1, further comprising a pressure-sensing tube within the inner shell.

5. The catheter of claim 1, wherein the fluid return channel comprises a larger diameter than the diameter of the fluid inflow channel.

6. The catheter of claim 1, wherein the inflow channel comprises a plurality of orifices shaped and arranged along its length to optimize the flow of the fluid in the axial direction into the inner shell, ensuring uniform temperature distribution throughout.

7. The catheter of claim 1, wherein all the channels are sealed proximally on their exterior and attached to the inner shell thereby forming the internal chamber.

8. The catheter of claim 1, wherein inner shell is spaced from the outer shell by at least 0.1 mm prior to circulating the fluid.

9. The catheter of claim 1, wherein the outer shell is defined by a wall constructed from a flexible material.

10. The catheter of claim 9, further comprising a metallic or plastic braid arranged with the wall, and serving to prevent expansion of outer shell in the radial direction.

11. The catheter of claim 1 , wherein the outer shell comprises an interior surface, and the inner shell is affixed to the interior surface of the outer shell.

12. The catheter of claim 1, further comprising a plurality of metallic electrodes exteriorly disposed on the outer shell.

13. The catheter of claim 12, further comprising at least one conductor channel extending through the distal section, the intermediate section and the proximal shaft for housing conducting wires to each of the metallic electrodes .

14. The catheter of claim 1, wherein the inner shell and outer shell are constructed from a material with enhanced thermal conductivity by incorporating thermal inducers or fillers into a base material of the inner and outer shell.

15. The catheter of claim 1, comprising a first phase during operation, wherein the inner shell is spaced from the outer shell as the inner shell is being filled with the fluid and expands;and a second phase of operation, wherein the inner shell contacts the outer shell, preventing further expansion of the inner shell.

16. The catheter of claim 1, wherein the proximal shaft, intermediate section and outer shell form a first subassembly and the inner shell, inflow and return channels form a second sub-assembly that is advanced as a whole into the first sub-assembly.

17. The catheter of claim 16, wherein the first and second sub-assemblies are arranged and operable to define an annular space distal to the inner shell after the inner shell is expanded during operation, and wherein a second pressure sensor is in fluid communication with the annular space to monitor the pressure within the annular space throughout the operation.

18. The catheter of claim 1, further comprising multi-lumen plug upon which a proximal end of the inner shell is hermetically sealed, and through which the channels extend.

19. The catheter of claim 18, wherein the channels extend through at least a portion of the proximal shaft, through the multi-lumen plug, and into the inner shell, and wherein the channels are enclosed within a vacuum jacket along the proximal shaft.

20. This catheter of claim 19, wherein the vacuum jacket is hermetically sealed to the multilumen plug.21 . A cryoablation system for ablating a target tissue comprising: a catheter comprising: a proximal shaft, a distal treatment section comprising an internal chamber, at least one fluid inflow channel for transporting high pressure fluid to the internal chamber in the distal treatment section, at least one fluid return channel for transporting low pressure fluid away from the internal chamber of the distal treatment section, wherein the at least one fluid return channel comprises a larger diameter than the diameter of the fluid inflow channel,at least one pressure sensor arranged in the internal chamber of the distal treatment section for measuring the chamber pressure within the internal chamber; a fluid source comprising the fluid at a high initial pressure, and arranged to supply the fluid to the catheter via the fluid inflow channel; a primary cooler for cooling the fluid from the fluid source prior to entering the catheter; a regulator for adjusting the initial pressure to an inflow pressure corresponding to the pressure along the inflow channel; and a controller programmed and operable to maintain the chamber pressure within a target range based on adjusting the inflow pressure.

22. The system of claim 21, wherein the target range is between 50 and 100 psi, and optionally, between 70 and 80 psi.

23. The system of claim 21, wherein the pressure sensor comprises a tube extending from the internal chamber to an electronic sensor operable to provide an electronic signal to be sent to the controller.

24. The system of claim 21, wherein the inflow channel has a diameter ranging from 0.01- .03”, and the return channel has a diameter ranging from 0.04-0.08”.

25. The system of claim 21, wherein controller is programmed with a PID algorithm to maintain the chamber pressure within the target range.

26. The system of claim 21, further comprising a pre-cooler operable to cool the fluid in the inflow channel using energy from the return channel prior to being cooled by the primary cooler.

27. The system of claim 21, wherein the controller is operable to cool the internal chamber to below -150 degrees C within 10 seconds, and optionally, to below -160 degrees C within 15 seconds.

28. The system of claim 21, wherein the inflow pressure during a first phase is in the range of 100 to 500 psi, and the controller is operable to decrease the inflow pressure to less than 100 psi during a second phase, and optionally, wherein the first phase has a duration of less than 10 seconds.

29. The system of claim 21, wherein the inflow channel comprises a distal orifice or a nozzle where the fluid exits the inflow channel and enters the internal chamber.

30. The system of claim 21, wherein the catheter is configured as recited in any one of claims 1-20.

31. The system of claim 21, wherein controller is operable to decrease the temperature to under -150 C within 5 seconds by maintain the target chamber pressure at 100 psi or less.

32. A cryoablation system for ablating a target tissue comprising: a catheter comprising: a proximal shaft, a distal treatment section comprising an internal chamber, a fluid inflow channel for transporting high pressure fluid to the internal chamber in the distal treatment section, at least one fluid return channel for transporting low pressure fluid away from the internal chamber of the distal treatment section, wherein the at least one fluid return channel comprises a larger diameter than the diameter of the fluid inflow channel, a fluid source comprising the fluid at a high initial pressure, and arranged to supply the fluid to the catheter via the fluid inflow channel; a primary cooler for cooling the fluid from the fluid source prior to entering the catheter; a regulator for adjusting the initial pressure to an inflow pressure corresponding to the pressure along the inflow channel; a flowmeter for measuring the fluid delivery flowrate entering the catheter; and a controller programmed and operable to maintain the delivery flowrate within atarget flowrate range based on adjusting the inflow pressure.

33. The system of claim 32, wherein the target flowrate range is between 20 and 90 SLPM.

34. The system of claim 32, further comprising a pressure sensor for measuring chamber pressure within the internal chamber, and a pressure safety module programmed and operable to detect for fluid leaks along the flowpath of the fluid during an ablation.

35. The system of claim 32, wherein controller is programmed with a PID algorithm to maintain the delivery flowrate within the target flowrate range.

36. The system of claim 32, further comprising a pre-cooler operable to cool the fluid in the inflow channel using energy from the return channel prior to being cooled by the primary cooler.

37. The system of claim 32, wherein the inflow channel comprises a distal orifice or a nozzle where the fluid exits the inflow channel and enters the internal chamber.

38. The system of claim 32, wherein the catheter is configured as recited in any one of claims 1-20 above.

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