Patent Publication Number: US-2021177355-A1

Title: Balloon Catheter with Position Sensors

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to invasive medical probes, and specifically to balloon catheters. 
     BACKGROUND 
     A balloon catheter comprises an inflatable balloon at its distal end that can be inflated and deflated as necessary. In operation, the balloon is typically deflated while the catheter is inserted into a body cavity (for example, a chamber of the heart) of a patient, and is then inflated within the cavity in order to perform the necessary procedure, and deflated again upon completing the procedure. 
     For example, U.S. Patent Application Publication 2018/0280658 describes a medical apparatus that includes a probe having a distal end configured for insertion into a body cavity and containing a lumen that opens through the distal end, and an inflatable balloon deployable through the lumen into the body cavity. The medical apparatus also includes a flexible printed circuit board having a first side attached to the exterior wall of the inflatable balloon and a second side opposite the first side, and an ultrasonic transducer mounted on the first side of the flexible printed circuit board and encapsulated between the exterior wall of the balloon and the flexible printed circuit board. In some embodiments, the medical apparatus may include an electrode mounted on the flexible circuit board and configured as a location sensor. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved apparatus and methods for finding the position of a balloon catheter inside the body. 
     There is therefore provided, in accordance with an embodiment of the invention, medical apparatus, including a flexible insertion tube having a distal end configured for insertion into a cavity in a body of a living subject and containing a lumen passing through the insertion tube to the distal end. An inflatable balloon is deployable from the distal end of the insertion tube and configured to be inflated by passage of a fluid through the lumen while the probe is deployed in the cavity in the body. At least one flexible circuit substrate is attached to a surface of the inflatable balloon. One or more electrodes, which include a conductive material, are disposed on an outer side of the at least one flexible circuit substrate so as to contact tissue in the cavity in the body when the balloon is inflated. A spiral conductive trace is disposed on the at least one flexible circuit substrate. 
     In some embodiments, the insertion tube has a proximal end configured for connection to a console, and the apparatus includes electrical wiring coupling the one or more electrodes and the spiral conductive trace to the console. In one embodiment, the apparatus includes signal generation circuitry, which is configured to supply electrical signals via the electrical wiring to the one or more electrodes so as to apply a therapeutic procedure to the tissue with which the one or more electrodes are in contact. 
     Additionally or alternatively, the apparatus includes position sensing circuitry, which is configured to receive, via the electrical wiring, signals that are output by the spiral conductive trace in response to a magnetic field that is applied to the body and to process the signals so as to derive position coordinates of the inflated balloon in the body. In a disclosed embodiment, the magnetic field includes multiple magnetic field components directed along different, respective axes, and the position sensing circuitry is configured to process the signals responsively to the multiple magnetic field components so as to derive both location and orientation coordinates of the inflated balloon in the body. Additionally or alternatively, the apparatus includes one or more magnetic field generators, which are configured to be positioned in proximity to the body and to apply the magnetic field thereto. 
     In some embodiments, the at least one flexible printed circuit substrate includes a plurality of flexible circuit substrates, which are distributed circumferentially around the inflatable balloon, and the one or more electrodes include multiple electrodes disposed respectively on the plurality of the flexible printed circuit substrates. In one such embodiment, the spiral conductive trace includes two or more spiral conductive traces disposed respectively on two or more of the flexible circuit substrates. The apparatus may additionally include position sensing circuitry, which is configured to receive respective signals that are output by the two or more spiral conductive traces in response to a magnetic field that is applied to the body, and to process the respective signals in combination so as to derive position coordinates of the inflated balloon in the body. 
     In a disclosed embodiment, the distal end of the flexible insertion tube is configured for insertion into a chamber of a heart of the subject. 
     There is also provided, in accordance with an embodiment of the invention, a method for position sensing, which includes providing a flexible insertion tube having a distal end configured for insertion into a cavity in a body of a living subject and containing a lumen passing through the insertion tube to the distal end. An inflatable balloon is coupled to be deployed from the distal end of the insertion tube and inflated by passage of a fluid through the lumen while the probe is deployed in the cavity in the body. At least one flexible printed circuit substrate is attached to a surface of the inflatable balloon. A conductive material is deposited on the at least one flexible circuit substrate so as to form one or more electrodes on an outer side of the flexible circuit substrate, whereby the one or more electrodes contact tissue in the cavity in the body when the balloon is inflated, and to form a spiral conductive trace on the at least one flexible circuit substrate. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, pictorial illustration of a system for electrophysiological measurement and treatment in the heart, in accordance with an embodiment of the present invention; and 
         FIG. 2  is a schematic side view of the distal end of a balloon catheter deployed in a chamber of the heart, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Balloon catheters are widely used in invasive therapeutic and diagnostic procedures, particularly inside chambers of the heart. Various methods are known in the art for finding the coordinates of the catheter and the balloon at its distal end within the heart. A magnetic sensor in the distal end of the catheter may be used to find the location and orientation coordinates of the catheter itself, and thus of the proximal end of the balloon, which is attached to the catheter. This sort of measurement is generally not sufficient, however, to give an accurate indication of the coordinates of the distal side of the balloon and of the electrodes that are disposed around the outer surface of the balloon, because the shape and size of the balloon change substantially as a function of inflation pressure within the balloon and of contact pressure between the outer surface of the balloon and the tissue in the heart. 
     In some balloon catheterization systems, such as the system described in the above-mentioned U.S. Patent Application Publication 2018/0280658, the location of the balloon is estimated by measuring the impedance between an electrode on the balloon and electrodes on the body surface. Such methods, however, are inaccurate, and enable the system to estimate only the location coordinates of the balloon, and not the orientation. 
     In response to this deficiency in systems that are known in the art, embodiments of the present invention provide a balloon catheter with additional magnetic position sensors, in the form of one or more spiral conductive traces on the surface of the balloon. (The term “spiral,” as used in the present description and in the claims, refers to a path that winds around a central point, with each successive turn of the path approaching or receding from the central point, depending on the direction in which the path is traversed. The turns of the spiral may be curved or rectangular or have any other suitable shape.) Each such spiral trace acts as a coil, and outputs an electrical signal when placed in a magnetic field. The electrical signals from these coils can be processed to find both the location and orientation of the entire balloon, including the distal side of the balloon, regardless of variations in the size and shape of the balloon due to internal and external pressures. 
     In the disclosed embodiments, medical apparatus comprises a flexible insertion tube configured for insertion into a cavity in a body of a living subject, such as a chamber of the heart. An inflatable balloon is deployed from the distal end of the insertion tube, with at least one flexible circuit substrate attached to the surface of the balloon. One or more electrodes, which comprise a conductive material, are deposited or otherwise disposed on the outer side of the flexible circuit substrate, along with a spiral conductive trace, which serves as a coil. In some embodiments, multiple flexible circuit substrates are distributed circumferentially around the balloon, with electrodes and spiral conductive traces formed one some or all of the circuit substrates. Once the distal end of the insertion tube is in place in the cavity in the body, the balloon is inflated by passage of a fluid through a lumen in the insertion tube, and thus contacts tissue in the cavity in the body. 
     To find the position (location and orientation) coordinates of the inflated balloon, a magnetic field is applied to the body. Position sensing circuitry receives and processes the signals output by the spiral conductive traces in order to derive the position coordinates. Because of space and size constraints, the coils formed by the spiral conductive traces generally have small diameter (for example, about 2 mm) and relatively few turns, and therefore may output only weak signals. When spiral conductive traces are formed on multiple flexible circuit substrates, the respective signals can be processed in combination in order to derive position coordinates with improved signal/noise ratio and thus enhanced accuracy. 
       FIG. 1  is a schematic, pictorial illustration of a catheter-based system  20  for electrophysiological (EP) sensing and treatment of the heart, in accordance with an embodiment of the present invention. System  20  comprises a catheter  21 , comprising an insertion tube  22  for transvascular insertion into a heart  26  of a patient  28 , who is shown lying on a table  29 . An inflatable balloon  40  is deployed at a distal end  25  of insertion tube  22  (as seen in the inset in  FIG. 1 ). In the pictured embodiment, balloon  40  is applied in a therapeutic procedure, such as ablating tissue around an ostium  51  of a pulmonary vein in the left atrium of heart  26 . Details of the structure and functionality of balloon  40  are described below with reference to  FIG. 2 . 
     The proximal end of catheter  21  is connected to a control console  24  comprising a power source  45 , which typically includes radio-frequency (RF) signal generation circuitry. Power source  45  supplies RF electrical signals via electrical wiring running through insertion tube  22  to electrodes on balloon  40  so as to apply a therapeutic procedure to the tissue with which the electrodes are in contact. For example, depending on the voltage, frequency and power of the RF electrical signals, balloon  40  may be applied in treating arrhythmias in heart  26  by RF ablation or by irreversible electroporation (IRE) of the heart tissue. Additionally or alternatively, electrodes on balloon may be used in EP sensing and mapping of electrical signals in heart  26 . 
     To carry out a therapeutic or diagnostic procedure, a physician  30  first inserts a sheath  23  into heart  26  of patient  28 , and then passes insertion tube  22  through the sheath. Physician  30  advances distal end  25  of insertion tube  22  toward a target location in heart  26 , for example in proximity to ostium  51 , by manipulating catheter  21  using a manipulator  32  near the proximal end of the catheter. During the insertion of insertion tube  22 , balloon  40  is deflated and is maintained in a collapsed configuration by sheath  23 . 
     Once distal end  25  of insertion tube  22  has reached the left atrium in heart  26 , physician  30  retracts sheath  23 , partially inflates balloon  40 , and further manipulates catheter  21  so as to navigate the balloon to the target location within ostium  51  of the pulmonary vein. When balloon  40  has reached the target location, physician  30  fully inflates balloon  40 , so that electrodes disposed circumferentially around the balloon ( FIG. 2 ) contact tissue around the ostium. Console  24  may verify that the electrodes are in good contact with the tissue by measuring the impedance between each of the electrodes and the tissue. Once good contact has been established, physician  30  actuates power source  45  to apply RF power to the tissue. 
     During this procedure, system  20  applies magnetic position sensing in tracking the location and orientation of insertion tube  22  and balloon  40  within heart  26 , and thus guides physician  30  in maneuvering the balloon to the target location (within ostium  51  in the present example) and verifying that the balloon is properly in place. For this purpose, as shown in the inset in  FIG. 1 , distal end  25  of insertion tube  22  contains a magnetic position sensor  39 , in a location slightly proximal to balloon  40 . One or more magnetic field generators  36  are fixed in known positions in proximity to the body of patient  28 , for example under bed  29  as shown in  FIG. 1 . A driver circuit  34  in console  24  applies drive signals to the magnetic field generators so as to produce multiple magnetic field components directed along different, respective axes. During navigation of distal end  25  in heart  26 , magnetic sensor  39  outputs signals in response to the magnetic field components. Position sensing circuitry, such as a processor  41  in console  24 , receives these signals via interface circuits  44 , and processes the signals in order to find the location and orientation coordinates of distal end  25 . These coordinates also indicate the location and orientation of the proximal end of balloon  40 , which is deployed from distal end  25  of insertion tube  22 . 
     In addition, as shown in  FIG. 2 , balloon  40  itself has one or more sensing coils on its surface, in the form of spiral conductive traces. These sensing coils likewise output signals in response to the magnetic fields applied by magnetic field generators  36 . Processor  41  processes these signals in order to derive location and orientation coordinates of the inflated balloon, and specifically of the distal part of the balloon, which contacts the tissue in heart  26 . Processor  41  presents the coordinates of balloon  40  on a display  27 , for example by superimposing a graphical representation of the balloon, in the location and orientation indicated by the position sensors, on a three-dimensional map of the heart chamber in which the balloon is located. 
     The methods and apparatus for magnetic position sensing that are implemented in system  20  are based on those that are used in the CARTO® system, produced by Biosense Webster, Inc. (Irvine, Calif.). The principles of operation of this sort of magnetic sensing are described in detail, for example, in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all hereby incorporated by reference herein in their entireties as though set forth in full. Alternatively, system  20  may implement other magnetic position sensing technologies that are known in the art. 
     In some embodiments, processor  41  comprises a general-purpose computer, with suitable interface circuits  44  for receiving signals from catheter  21  (including low-noise amplifiers and analog/digital converters), as well as for receiving signals from and controlling the operation of the other components of system  20 . Processor  41  typically performs these functions under the control of software stored in a memory  48  of system  20 . The software may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. Additionally or alternatively, at least some of the functions of processor  41  may be carried out by dedicated or programmable hardware logic. 
       FIG. 2  is a schematic side view of balloon  40 , deployed from distal end  25  of insertion tube  22 , in accordance with an embodiment of the invention. Balloon  40  is shown in this figure in its inflated state within ostium  51 . Balloon  40  is typically inflated by passage of a fluid, such as saline solution, through a lumen (not shown) in insertion tube  22 . 
     Balloon  40  is typically formed from a flexible bio-compatible material such as polyethylene terephthalate (PET), polyurethane, nylon, or silicone. Multiple flexible circuit substrates  60  are attached to an outer surface  58  of balloon  40 , for example using a suitable epoxy or other adhesive, and are distributed circumferentially around balloon  40 . Substrates  60  comprise a suitable dielectric material, such as a polyimide, on which electrical traces can be deposited and etched using printed circuit fabrication techniques that are known in the art. Prior to attachment of substrate  60  to outer surface  58 , electrodes  55  are formed on the outer sides of substrates by depositing and etching a suitable conductive material, such as gold. Electrodes  55  will thus contact tissue in heart  26 , such as the tissue of ostium  51 , when balloon  40  is inflated. 
     Spiral conductive traces  66  are deposited on substrates  60  in a similar fashion to electrodes, and serve as magnetic sensing coils  62 . The dimensions of sensing coils  62  are limited by the available space on substrates  60 , for example to about 2×2 mm. For enhanced sensitivity, traces  66  typically have a fine pitch, for example 0.4 mm or less, and may be covered by an insulating coating to prevent short-circuiting of the traces by body tissue and fluids. Electrical wiring  64  couples sensing coils  62  through insertion tube  22  to console  24 , and electrodes  55  are coupled by wiring to the console in similar fashion. (Conductive traces may be formed on both sides of substrate  60 , or deposited in multiple layers on the substrate, using printed circuit fabrication techniques that are known in the art, to enable connection of wiring  64  to the central point of coils  62 .) In the embodiment shown in  FIG. 2 , conductive trace  66  in the form of a recti-linear spiral is connected to or extend as part of trace  68  and trace  70  that extends through the catheter shaft  25  back to the handle so that coil  62  could be used to detect the magnetic field generators as referenced to the patient. Other variations of the coil  62  as well as methods are described and illustrated in Patent Application US20180180684, which is hereby incorporated by reference as if set forth in full, with a copy attached in the Appendix. 
     As explained above, processor  41  receives and processes the signals that are output by sensing coils  62  in response to the magnetic fields produced by magnetic field generators  36 , and thus derives both location and orientation coordinates of the distal side of inflated balloon  40  in heart  26 . In the pictured embodiment, sensing coils  62  are formed on multiple different substrates  60  at different locations around balloon  40 . Processor  41  processes the respective signals that are output by sensing coils  62  on in combination, for example, by finding a directional average of the position coordinates of the multiple sensing coils. Processor  41  is thus able to derive position coordinates of the inflated balloon with enhanced accuracy. 
     Although the embodiments described above relate specifically to ablation therapies in the heart within and around the pulmonary veins, the principles of the present invention may similarly be applied, mutatis mutandis, in other therapeutic and diagnostic procedures within the heart, as well as in other body cavities. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.