Abstract:
A urinary catheter is configured for avoiding heat buildup in, or even cooling, surrounding tissues when the prostate is subjected to treatment radiation such as ultrasound. The catheter includes a region transparent to ultrasound, and through which a cooling fluid (e.g., chilled water) may, in some embodiments, be recirculated during treatment. This region spans the prostate when the catheter is fully inserted (with the tip residing in the patient&#39;s bladder and a terminal balloon inflated to avoid retraction of the catheter).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates, generally, to ultrasound treatment of the prostate gland and, more specifically, to systems and methods for regulating temperature during focused ultrasound therapy. 
       BACKGROUND 
       [0002]    Certain types of body tissues, such as tumors, can be destroyed by heat. One way to apply thermal energy to internal body tissue is to focus high-intensity ultrasound waves into the tissue using, e.g., a phased array of piezoelectric transducer elements. Such treatment can ablate the tissue and thereby reduce or even eliminate the need for invasive surgery to remove it. For effective treatment, it is important that a sufficient thermal dose be reached during each ultrasound application to ablate or otherwise destroy the portion of the target tissue being heated. At the same time, it is important to regulate the temperature to avoid painful or damaging heat build-up in healthy tissues surrounding the target tissue, or even excessive heat in the target tissue. For example, ultrasound treatment of the prostate gland can involve eradicating a malignant lesion or selectively removing tissue to treat benign prostatic hyperplasia (BPH). In either case, excessive heat can injure the patient by destroying healthy tissue, such as the urethra and/or the urethral sphincter. 
         [0003]    During prostate treatment, a urinary catheter such as a Foley device is typically passed through the patient&#39;s urethra and into his bladder. The Foley catheter has two separate channels, or lumens, one of which allows urine collected through a distal port to drain out into a collection bag. The other lumen permits inflation of a balloon, also located at the distal end, to fix the catheter position within the body (e.g., retaining the end of the catheter within the bladder). Foley catheters are commonly made from silicone or natural rubber (latex) with wall thicknesses of 2-3 mm. They are very flexible in the transverse direction and very strong in the longitudinal direction, i.e., no guide wire is required to introduce or to extract the catheter. Unfortunately, they also absorb about 95% of ultrasonic radiation incident thereon and, as a result, are strongly heated by the treatment beam. That heat may be sufficient to destroy urethral tissue and surrounding prostate tissue (which typically is not the tissue to be ablated). As a result, the risk of injury can preclude the use of ultrasound as a treatment modality altogether if catheterization is required. 
         [0004]    Accordingly, there is a need for urinary catheters that avoid the risk of catheter-induced patient injury during prostate-treatment procedures. 
       SUMMARY 
       [0005]    The present invention provides, in various embodiments, a urinary catheter configured to permit large ultrasound power levels to be applied to the prostate without harm to surrounding tissues. In various embodiments, the catheter includes a region that, with the catheter in place, spans the region through which ultrasound is applied and is substantially (e.g., at least 90%, or 95%, or in some cases 99%) transparent to ultrasound energy. In some embodiments only this portion of the catheter is transparent to ultrasound and the rest of the catheter is constructed of more traditional materials, while in other embodiments, substantially the entire catheter is made of the material transparent to ultrasound. 
         [0006]    The catheter may also be configured to permit a cooling fluid (e.g., chilled water) to be recirculated through the ultrasound-spanning region during treatment. In general, this region of the catheter spans the prostate when the catheter is fully inserted (with the tip residing in the patient&#39;s bladder and a terminal balloon inflated to avoid retraction of the catheter). 
         [0007]    Accordingly, in a first aspect, the invention pertains to catheter configured for evacuating urine from a patient during a prostate procedure. In various embodiments, the catheter comprises an elongated tube for insertion through the patient&#39;s urinary tract. The tube has an outer wall and a urine-evacuation lumen therethrough and comprises a plurality of adjacent regions through which the urine-evacuation lumen passes. In particular, a distal region is configured for insertion into the patient&#39;s bladder and includes a terminal urine entry port in fluid communication with the urine-evacuation lumen and an inflatable balloon for retaining the port within the bladder. At least a prostate-spanning region, proximally adjacent to the distal region and having a length sized to span the patient&#39;s prostate gland with the balloon inflated and the urine entry port within the patient&#39;s bladder, is substantially transparent to ultrasound. 
         [0008]    A cooling region, coextensive with the prostate-spanning region, comprises a fluid chamber fluidically isolated from and surrounding the urine-evacuation lumen and in thermal contact with the outer wall of the catheter. A proximal region is proximally adjacent to the cooling region, and includes (i) within the outer wall of the catheter, an inlet conduit in fluid communication with the fluid chamber for conducting a fluid thereto and and outlet conduit in fluid communication with the fluid chamber for conducting a fluid therefrom, and (ii) interfaces for fluidly coupling the urine-evacuation lumen to a collection container and the inlet and outlet conduits to a cooling and recirculation pump. 
         [0009]    In various embodiments, the outer wall in the prostate-spanning region comprises or consists essentially of a hard polymeric material, e.g, MYLAR or a rigid polyurethane. The fluid chamber may be coaxial with the urine-evacuation channel. For example, the fluid chamber may have an annular cross-section and is bounded by an outer surface of the urine-evacuation channel and an inner surface of the outer wall. Alternatively, the fluid chamber may have a pair of concentric channels separated by a porous membrane, where an outer channel of the fluid chamber is interfaced to the inlet conduit and an inner channel of the fluid chamber is interfaced to the outlet conduit. In other embodiments, the fluid chamber comprises a plurality of tortuously arranged channels. 
         [0010]    In another aspect, the invention relates to a system for evacuating urine from a patient during a prostate procedure and cooling the prostate. In various embodiments, the system comprises a catheter comprising an elongated tube for insertion through the patient&#39;s urinary tract. The tube has an outer wall and a urine-evacuation lumen therethrough and comprises a plurality of adjacent regions through which the urine-evacuation lumen passes. A distal region is configured for insertion into the patient&#39;s bladder and includes a terminal urine entry port in fluid communication with the urine-evacuation lumen and an inflatable balloon for retaining the port within the bladder; a cooling region is proximally adjacent to the distal region and has a length sized to span the patient&#39;s prostate gland with the balloon inflated and the urine entry port within the patient&#39;s bladder; the cooling region comprises a fluid chamber fluidically isolated from and surrounding the urine-evacuation lumen and in thermal contact with the outer wall of the catheter. A proximal region is proximally adjacent to the cooling region and includes, within the outer wall of the catheter, an inlet conduit in fluid communication with the fluid chamber for conducting a fluid thereto and and outlet conduit in fluid communication with the fluid chamber for conducting a fluid therefrom. The system further includes a recirculation assembly configured to circulate a cooling fluid through the fluid chamber of the catheter without disturbing a flow of urine through the urine-evacuation lumen. In various embodiments, the recirculation assembly comprises a cooling unit and a pumping apparatus for pumping fluid from the cooling unit through the inlet conduit and from the outlet conduit to the cooling unit. 
         [0011]    In some embodiments, the pumping apparatus comprises (i) a first pump fluidly connected to the inlet conduit for pumping therethrough fluid from the cooling unit, (ii) a second pump fluidly connected to the outlet conduit for pumping therefrom fluid to the cooling unit, and (iii) a controller for operating the pumps at different rates to promote mixing through the fluid chamber. The outer wall of the catheter in the second region may comprise or consist essentially of a hard polymeric material. 
         [0012]    The fluid chamber of the catheter may be coaxial with the urine-evacuation channel. For example, the fluid chamber may have an annular cross-section and is bounded by an outer surface of the urine-evacuation channel and an inner surface of the outer wall. Alternatively, the fluid chamber may have a pair of concentric channels separated by a porous membrane, where an outer channel of the fluid chamber is interfaced to the inlet conduit and an inner channel of the fluid chamber is interfaced to the outlet conduit. In other embodiments, the fluid chamber comprises a plurality of tortuously arranged channels. 
         [0013]    In various embodiments, the fluid chamber of the catheter is coaxial with urine-evacuation channel. If desired, the catheter may include a temperature sensor and the system may include a controller, responsive to the temperature sensor, for controlling the pumping apparatus and the cooling unit. 
         [0014]    Still another aspect of the invention pertains to a method for evacuating urine from a patient during a prostate procedure and cooling the prostate. In various embodiments, the method comprises providing a catheter comprising an elongated tube having an outer wall and a urine-evacuation lumen therethrough. The elongated tube includes a plurality of adjacent regions through which the urine-evacuation lumen passes, the regions including (i) a distal region including a terminal urine entry port in fluid communication with the urine-evacuation lumen and an inflatable balloon for retaining the port within the bladder, (ii) a cooling region proximally adjacent to the distal region and comprising a fluid chamber fluidically isolated from and surrounding the urine-evacuation lumen and in thermal contact with the outer wall of the catheter, and (iii) a proximal region proximally adjacent to the cooling region. The method further includes inserting the catheter through the patient&#39;s urinary tract until the distal portion of the catheter reaches the patient&#39;s bladder; inflating the balloon to retain the catheter in position, whereby the urine entry port is held within the patient&#39;s bladder and the cooling region spans the patient&#39;s prostate gland; draining urine from the patient&#39;s bladder via the urine-evacuation lumen; and circulating a cooling fluid through the fluid chamber of the catheter without disturbing a flow of urine through the urine-evacuation lumen. 
         [0015]    In various embodiments, the fluid chamber of the catheter is coaxial with the urine-evacuation channel. For example, fluid chamber of the catheter may have an annular cross-section and be bounded by an outer surface of the urine-evacuation channel and an inner surface of the outer wall. Alternatively, the fluid chamber of the catheter may have a pair of concentric channels separated by a porous membrane, whereby an outer channel of the fluid chamber receives the cooling fluid and an inner channel ejects cooling fluid passing through the porous membrane. In other embodiments, the fluid chamber of the catheter comprises a plurality of tortuously arranged channels. 
         [0016]    The method may further comprise the steps of sensing a temperature of the cooling fluid and, based at least in part thereon, controlling at least one of a cooling unit for the cooling fluid or the prostate procedure. 
         [0017]    The term “substantially” or “approximately” means ±10% (e.g., by weight or by volume), and in some embodiments, ±5%. The term “consists essentially” of means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The foregoing will be more readily understood from the following detailed description of the invention, in particular, when taken in conjunction with the drawings, in which: 
           [0019]      FIGS. 1A and 1B  are sectional views showing the basic operation of a Foley catheter. 
           [0020]      FIG. 2  is an elevation of a catheter in accordance with an embodiment of the present invention. 
           [0021]      FIGS. 3A-3C  axial sections of different segments of the catheter shown in  FIG. 2 . 
           [0022]      FIGS. 4A-4C  are transverse sections through alternative versions of the segment C-C′ shown in  FIG. 3A , taken along the line D-D′. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Refer first to  FIGS. 1A and 1B , which illustrate the basic configuration and operation of a Foley catheter  100 . The catheter passes through the patient&#39;s urinary tract until the distal portion  105  reaches the patient&#39;s bladder  115 , at which point a balloon  120  is inflated (with air or water) to retain the distal end  122  within the bladder. Urine is evacuated through a collection port  110  and conducted through the lumen of the catheter  100 , the proximal end of which is connected to a container (not shown) for collection. A segment  130  of the catheter  100  passes through the patient&#39;s prostate  135 . Because this internal anatomy does not exhibit significant variation, the segment  130  is roughly the same length and in the same location across patients. 
         [0024]      FIG. 2  illustrates a catheter  200  constructed in accordance with the principles of the present invention. Although the length is not shown to scale, the catheter  200  includes a proximal end  205  with a connector or interface  207  configured for attachment to a collection container and a distal end  210  with a collection port as described above. Points along the length of the catheter are labeled for reference in the ensuing discussion. 
         [0025]    The segment A-A, shown sectionally in  FIG. 3A , includes an inflatable balloon  310  and a collection port  312 . A lumen  315  conducts urine through the catheter. Preferably, the lumen  315  is defined by a tube  317  made of an engineering plastic (e.g., KEVLAR, poly ether ketone (PEEK) and polysulfone) that serves both as a urine evacuation channel as well as conferring rigidity to the catheter. A high-strength plastic enables the diameter of the tube to be small without sacrificing rigidity. The diameter of the tube may be, for example, 1.25 mm with a lumen diameter of 0.75 mm. These dimensions are sufficiently small relative to the ultrasound wavelength that ultrasound waves will actually diffract around the tube  317 ). The tube  317  desirably exhibits high flexibility in transverse direction and high rigidity and strength in the longitudinal direction. This allows the catheter  200  to be used without a guide wire. The remainder of the catheter body, including the outer sheath  320 , may be made from a flexible medical-grade polymer such as soft silicone. An interior tube  322 , also made of soft silicone, may span the interior distance between the evacuation tube  317  and the exterior sheath  320 . For ease of presentation, the conventional lumen used to inflate the balloon  310  is not shown or further discussed herein. 
         [0026]    The interior tube  322  may terminate at or distal to the segment B-B′, which is illustrated in  FIG. 3B  and corresponds generally in terms of axial location to the prostate-spanning segment  130  shown in  FIG. 1B , although it may be longer or shorter depending on the procedure with which the catheter  200  will be used. In the segment B-B′, an outer wall  325  surrounds and defines a hollow interior volume around and coaxial with the evacuation tube  317 . This chamber  328  is filled, during operation, with a recirculating cooling fluid (typically chilled water) to cool the prostate tissue with which the segment B-B′ is in immediate contact. 
         [0027]    The segment B-B′ should be substantially transparent to ultrasound waves and also provide good heat transfer. Thus, the outer wall  325  may be fabricated from very thin plastic with, optionally, a very thin (less than 0.3 mm) layer of silicone thereover. While thin, the outer wall  325  should be rigid in order to avoid radial expansion, which would stress and possibly injure the urinary tract. Suitable materials conferring the necessary rigidity and exhibiting substantial (e.g., &gt;90%) transparency to ultrasound include polyethers such as MYLAR or a MYLAR composition or rigid (i.e., highly crosslinked and based on low-molecular-weight (&lt;1000) polyols with more than two hydroxyl groups) polyurethane, which are strong, facilitating small wall thicknesses; wall thickness is minimized because both acoustic absorbence and heat transfer are inversely proportional thereto. The wall must nonetheless be sufficiently thick to resist deformation during use; typically the wall thickness is less than 5 mm and, in the case of MYLAR or rigid polyurethane, wall thicknesses of 2-3 mm are possible. Other suitable materials include polyethylene terephthalate (PET) and PET modifications as PET-C, polybutadiene terephthalate, etc. It should be stressed that ultrasound transparency and good heat transfer are particularly critical for segment B-B′, so in some embodiments, only this segment is made of a material exhibiting these properties, while the remainder of the catheter may be silicone or latex. In other embodiments, substantially the entire catheter is made of the same material. 
         [0028]    Cooling fluid is delivered to and withdrawn from the chamber  328  by a pair of delivery conduits  330   a,    330   b  in the segment C-C′ as shown in  FIG. 3C , which are fluidically coupled at one end to the chamber  328  via the interface  207  (see  FIG. 2 ) and at the other end to at least one pump  335 . The tubes  330   a,    330   b  are fluidically isolated from the evacuation tube  317 , which empties into a drain or collection bag  338 . The pump  335  is also fluidically connected to a chilling reservoir  340  for the recirculating cooling fluid, and its operation is governed by a controller  345 . The controller  345  may optionally receive signals from, or interrogate, one or more sensors  350  within the catheter. In the illustrated embodiment, the sensor  350  is a temperature sensor (e.g., a thermocouple or thermistor) associated with the withdrawal tube  330   b.  By measuring the temperature of the cooling fluid after it has passed through the chamber, the controller  345  can adjust the rate of recirculation (e.g., increasing the rate to increase cooling efficiency) and/or the level of refrigeration in the reservoir  340  using conventional feedback programming. The sensor can also be used to verify proper operation of the system; for example, a sensed temperature above a threshold may indicate a component failure and signal danger to the patient, alerting the operator or shutting down the application of ultrasound. 
         [0029]    The controller  345  may be provided as either software, hardware, or some combination thereof. For example, the system may be implemented on one or more conventional server-class computers, such as a PC having a CPU board containing one or more processors such as the Pentium or Celeron family of processors manufactured by Intel Corporation of Santa Clara, Calif., the 680×0 and POWER PC family of processors manufactured by Motorola Corporation of Schaumburg, Ill., and/or the ATHLON line of processors manufactured by Advanced Micro Devices, Inc., of Sunnyvale, Calif. The processor may also include a main memory unit for storing programs and/or data relating to the methods described above. The memory may include random access memory (RAM), read only memory (ROM), and/or FLASH memory residing on commonly available hardware such as one or more application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), electrically erasable programmable read-only memories (EEPROM), programmable read-only memories (PROM), programmable logic devices (PLD), or read-only memory devices (ROM). In some embodiments, the programs may be provided using external RAM and/or ROM such as optical disks, magnetic disks, as well as other commonly used storage devices. For embodiments in which the functions are provided as one or more software programs, the programs may be written in any of a number of high level languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC, various scripting languages, and/or HTML. Additionally, the software may be implemented in an assembly language directed to the microprocessor resident on a target computer; for example, the software may be implemented in Intel 80×86 assembly language if it is configured to run on an IBM PC or PC clone. The software may be embodied on an article of manufacture including, but not limited to, a floppy disk, a jump drive, a hard disk, an optical disk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gate array, or CD-ROM. 
         [0030]    Depending on parameters such as the dimensions of the chamber  328 , it may be desirable to encourage mixing and avoid the creation of a dead zone toward the distal end of the chamber—i.e., to create a mixing gradient whereby cooling diminishes with distance from the inlets of the delivery conduits  330   a,    330   b.  For example, it is possible to cycle in-flow and out-flow to promote turbulence and hence mixing. For example, the pump  335  may actually be two pumps, each connected to one of the delivery conduits  330   a,    330   b  and both connected to the reservoir  340 . One pump drives cooling fluid into the chamber  328  while the other pumps fluid out of the chamber with the result of generating turbulence. 
         [0031]    Cooling arrangements other than a unitary chamber are also possible. Transverse cross-sections of three representative alternatives are illustrated in  FIGS. 4A-4C . In  FIG. 4A , the open chamber volume is replaced with a plurality of tubes  405  distributed radially around the evacuation lumen  315 . The flow directions of adjacent tubes are different, as indicated by the symbols (+) for the direction into the page and (−) for the direction out of the page. In this way, fresh cooling fluid is distributed radially and symmetrically around the catheter segment. Each of the tubes  405   1  (flow into the page) can be commonly connected to the inlet tube  330   a  (see  FIG. 3C ) and the tubes  405   2  (flow out of the page) can be commonly connected to the outlet tube  330   b.  In one implementation, each adjacent pair of tubes  405  is actually a single tube bent into a U shape at the distal end of the chamber  328  to define a two-level tortuous path therethrough. 
         [0032]    Another arrangement, shown in  FIG. 4B , utilizes a tubular porous barrier  410  concentric with the evacuation lumen  315 , thereby forming an outer sleeve  415  into which cooling fluid is injected via the delivery conduit  330   a  and an inner sleeve  417  from which cooling fluid that has passed through the barrier  410  is withdrawn via the tube  330   b.  The pore size of the barrier  410  is selected to allow a desired circulation rate, and helps distribute fresh cooling fluid through the length of the sleeve  415 . 
         [0033]    With renewed reference to  FIG. 4A , it is possible to utilize a single tube  405  that doubles back at each end of the chamber  328 , defining a tortuous path through the chamber. The degree of cooling will diminish circumferentially from the inlet point, but depending on the circulation rate, this may not be problematic. A simpler tortuous-path alternative to this configuration is shown in  FIG. 4C . Instead of a repeatedly bent internal tube, a series of longitudinal compartments is defined by a series of radial walls  430  symmetrically arranged around the urine-evacuation lumen  315  and extending from the outer wall of the lumen  315  to the inner surface of the wall  325 . (It should be noted that the outer wall  325 , as well as other walls described herein, can have multiple adjacent layers, which are within the scope of the term “wall” as used herein.) The walls  430  extend longitudinally from a barrier at one end of the chamber  328  but are spaced from the barrier at the opposite end in an alternating fashion, so that where a wall does not extend fully to one of the end barriers of the chamber  328 , water will flow around it into the adjacent compartment. Thus, one wall  430  extends to the distal end of the chamber  328  but is spaced from the barrier at the proximal end, the next one is spaced from the barrier at the distal end but extends to the proximal end, and so on. A compartment  435   1  receives cooling fluid from the inlet tube  330   a.  The fluid circulates back and forth through the compartments until it passes through the last compartment  435   10 , which is fluidically connected to the outlet tube  330   b.    
         [0034]    The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. In particular, embodiments of the invention need not include all of the features or have all of the advantages described herein. Rather, they may possess any subset or combination of features and advantages. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.