Patent Publication Number: US-2021161409-A1

Title: Microcatheter sensor design for minimizing profile and impact of wire strain on sensor

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 14/595,884, filed Jan. 13, 2015, which claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Patent Application No. 62/012,628 filed on Jun. 15, 2014. The present application also claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Patent Application No. 62/068,052 filed on Oct. 24, 2014 and titled MICROCATHETER SENSOR DESIGN FOR MINIMIZING PROFILE AND IMPACT OF WIRE STRAIN ON SENSOR. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to methods and systems for determining a pressure gradient across a lesion of a vessel for calculating a Fractional Flow Reserve. 
     BACKGROUND OF THE INVENTION 
     The severity of a stenosis or lesion in a blood vessel may be assessed by obtaining proximal and distal pressure measurements relative to the given stenosis and using those measurements for calculating a value of the Fractional Flow Reserve (FFR). FFR is defined as the ratio of a first pressure measurement (P d ) taken on the distal side of the lesion and to a second pressure measurement taken on the proximal side of the lesion usually within the aorta (P a ). Conventionally, a sensor is placed on the distal portion of a guidewire or FFR wire to obtain the first pressure measurement P d , while an external pressure transducer is fluidly connected via tubing to a guide catheter for obtaining the second or aortic (AO) pressure measurement P a . Calculation of the FFR value provides a lesion specific index of the functional severity of the stenosis in order to determine whether the blockage limits blood flow within the vessel to an extent that treatment is needed. An optimal or normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and in need of an interventional treatment. Common interventional treatment options include balloon angioplasty and/or stent implantation. 
     If an interventional treatment is required, the interventional device, such as a balloon catheter, is tracked over a guide wire to the site of the lesion. Conventional FFR wires generally are not desired by clinicians to be used as guide wires for such interventional devices. Accordingly, if an intervention treatment is required, the clinician generally removes the FFR wire, inserts a conventional guide wire, and tracks the interventional device to the treatment site over the conventional guide wire. 
     The mounting of a pressure sensor on the distal end of a catheter, such as a microcatheter makes it difficult to isolate the pressure sensor from bending stresses experienced as a result of interaction between the pressure sensor and the housing of the catheter. Due to the high sensitivity and size of the pressure sensor used in this application, any stress placed on the pressure sensor can cause a distortion of the sensor resulting in an incorrect pressure reading or bend error. Accordingly, there remains a need for a microcatheter to obtain pressure measurements suitable for use in calculating an FFR value for a given stenosis, whereby the clinician may use a conventional or preferential guidewire instead of a FFR guidewire. In addition, there remains a need for a FFR microcatheter to minimize both the profile of the catheter and the bending stresses experienced by the pressure sensor. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments hereof relate to a catheter, such as a pressure measurement catheter, including an elongate shaft having a proximal end optionally coupled to a handle or luer fitting and a distal end having a distal opening. The elongate shaft further includes a proximal portion, an intermediate portion, and a distal portion having a distal tip. In the proximal portion of the elongated shaft, a shaft wall may define two separate lumens: a guide wire lumen and a second or pressure sensor wire lumen, extending parallel to each other or side-by-side along the proximal portion. The distal portion of the elongate shaft is configured to receive a guidewire in a distal portion of guidewire lumen thereof. The pressure sensing wire may extend to the distal portion of the elongate shaft to be coupled to a pressure sensor mounted on the distal tip for measuring a pressure of a fluid within lumen of vessel. The pressure sensor wire is disposed within a pocket formed adjacent to the pressure sensor thereby minimizing the profile of the catheter. 
     Embodiments hereof also relate to a catheter, such as a measurement catheter, including an elongate shaft having a proximal end optionally coupled to a handle or luer fitting and a distal end having a distal opening. The elongate shaft further includes a proximal portion, an intermediate portion, and a distal portion having a distal tip. In the proximal portion of elongated shaft, shaft wall may define two separate lumens: a guide wire lumen and a second or pressure sensor wire lumen, extending parallel to each other or side-by-side along the proximal portion. The distal portion of the elongate shaft is configured to receive a guidewire in a distal portion of the guidewire lumen thereof. The pressure sensing wire lumen may extend to the distal portion of the elongate shaft to be coupled to a pressure sensor mounted on the distal tip for measuring a pressure of a fluid within lumen of vessel. A flexible interconnect has one end coupled to the pressure sensor and another end coupled to the pressure sensor wire in order to electrically couple the pressure sensor with the pressure sensor wire. Flexible interconnect not only reduces the profile of the catheter, but also helps to isolate the pressure sensor from the bending stresses applied to the catheter by allowing the pressure sensor and the pressure sensor wire to move independently from one another. 
     Embodiments hereof also relate to a catheter, such as a measurement catheter, including an elongate shaft having a proximal end optionally coupled to a handle or luer fitting and a distal end having a distal opening. The elongate shaft further includes a proximal portion, an intermediate portion, and a distal portion having a distal tip. In the proximal portion of elongated shaft, shaft wall may define two separate lumens: a guide wire lumen and a second or pressure sensor wire lumen, extending parallel to each other or side-by-side along the proximal portion. The distal portion of the elongate shaft is configured to receive a guidewire in a distal portion of the guidewire lumen thereof. The pressure sensing wire lumen may extend to the distal portion of the elongate shaft to be coupled to a pressure sensor mounted on the distal tip for measuring a pressure of a fluid within lumen of vessel. The pressure sensor and the pressure sensor wire are spaced apart by a gap. The shaft wall is metalized to electrically couple the pressure sensor with the pressure sensor wire. The gap not only reduces the profile of the catheter, but also helps to isolate the pressure sensor from the bending stresses applied to the catheter by allowing the pressure sensor and the pressure sensor wire to move independently from one another. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of embodiments hereof as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
         FIG. 1  is a broken view of a system for measuring FFR with a distal portion thereof shown within a vessel including a lesion, the system including a measurement catheter including a pressure sensor and a guidewire, in accordance with an embodiment hereof. 
         FIG. 2  is a broken view of the catheter of  FIG. 1  in partial longitudinal cross-section. 
         FIG. 3  is a cross-sectional view of the catheter taken along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is a longitudinal cross-sectional view of the distal portion of the catheter of  FIG. 1 . 
         FIG. 5A  is a longitudinal cross-sectional view of one example of the distal portion of the catheter of  FIG. 1 . 
         FIG. 5B  is a longitudinal cross-sectional view of another example of the distal portion of the catheter of  FIG. 1 . 
         FIG. 6A  is a longitudinal cross-sectional view with an interposer shown in the distal portion of the catheter of  FIG. 1 . 
         FIG. 6B  is a top view of the distal portion of the catheter of  FIG. 6A . 
         FIG. 7  is a longitudinal cross-sectional view of one example of the distal portion of the catheter of  FIG. 1 . 
         FIG. 8  is a longitudinal cross-sectional view of an optional embodiment of of the distal portion of the catheter of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. While the disclosure refers to illustrative embodiments for particular applications, it should be understood that the disclosure is not limited thereto. Modifications can be made to the embodiments described herein without departing from the scope of the present disclosure. Those skilled in the art with access to this disclosure will recognize additional modifications, applications, and embodiments within the scope of this disclosure and additional fields in which the disclosed examples could be applied. Therefore, the following detailed description is not meant to be limiting. Further, it is understood that the systems and methods described below can be implemented in many different embodiments of hardware. Any actual hardware described is not meant to be limiting. The operation and behavior of the systems and methods presented are described with the understanding that modifications and variations of the embodiments are possible given the level of detail presented. 
     References to “one embodiment,” “an embodiment,” “in certain embodiments,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” and “distally” are positions distant from or in a direction away from the clinician. “Proximal” and “proximally” are positions near or in a direction toward the clinician. 
     With reference to  FIG. 1 , a pressure measurement catheter  10  is shown with a proximal portion thereof outside of a patient and a distal portion thereof positioned in situ within a lumen  12  of a patient vessel  14  having a stenosis or lesion  16 . In an embodiment hereof, the vessel  14  is a blood vessel such as but not limited to a coronary artery. Lesion  16  is generally representative of any blockage or other structural arrangement that results in a restriction to the flow of fluid through lumen  12  of vessel  14 . Lesion  16  may be a result of plaque buildup, including without limitation plaque components such as fibrous, fibro-lipidic (fibro fatty), necrotic core, calcified (dense calcium), blood, fresh thrombus, and mature thrombus. Generally, the composition of lesion will depend on the type of vessel being evaluated. In that regard, it is understood that embodiments hereof are applicable to various types of blockage or other narrowing of a vessel that results in decreased fluid flow. 
     Measurement catheter  10  is shown in  FIG. 2  with a distal portion thereof in longitudinal cross-section. Measurement catheter  10  includes an elongate shaft  18  having a proximal end  20  that may be coupled to a handle or luer fitting  22  and a distal end  24  having a distal opening  26 . Elongate shaft  18  further includes a proximal portion  28 , an intermediate portion  30 , and a distal portion  32  having a distal tip  33 . Although proximal portion  28 , intermediate portion  30 , and distal portion  32  of elongate shaft  18  have been described separately, they are described in such a manner for convenience and elongate shaft  18  may be constructed unitarily such that the portions described are part of a unitary shaft. However, different portions of elongate shaft  18  may also be constructed separately and joined together. 
     In embodiments hereof, elongate shaft  18  or component and/or segments thereof may be formed of polymeric materials, non-exhaustive examples of which include polyethylene terephthalate (PET), polypropylene, polyethylene, polyether block amide copolymer (PEBA), polyamide, fluoropolymers, and/or combinations thereof, either laminated, blended or co-extruded. Optionally, the catheter shaft or some portion thereof may be formed as a composite having a reinforcement material incorporated within a polymeric body in order to enhance strength and/or flexibility. Suitable reinforcement layers include braiding, wire mesh layers, embedded axial wires, embedded helical or circumferential wires, and the like. In one embodiment, for example, at least a proximal portion of elongate shaft  18  may be formed from a reinforced polymeric tube. In other embodiments of an elongate tubular shaft or component in accordance herewith, a proximal segment thereof may be a hypotube of a medical grade stainless steel with outer and inner tubes of a distal segment thereof being formed from any of the polymeric materials listed above. 
     As shown in  FIGS. 2-3 , elongate shaft  18  has a shaft wall  34  defining a guide wire lumen  35  extending therethrough. Guide wire lumen  35  extends through proximal portion  28 , intermediate portion  30 , and distal portion  32 . However, instead of the over-the-wire configuration shown in  FIGS. 1-3 , catheter  10  may have a rapid exchange configuration wherein guide wire lumen  35  extends through distal portion  32  and intermediate portion  30 , and the guidewire exits shaft  18  through a rapid exchange port (not shown) in proximal portion  28 , as would be understood by those skilled in the art. In one embodiment, with reference to the cross-sectional view of  FIG. 3  (taken along line  3 - 3  of  FIG. 2 ), in proximal portion  28  of elongated shaft  18 , shaft wall  34  defines two separate lumens, guide wire lumen  35  and a second or pressure sensor wire lumen  36 , extending parallel to each other or side-by-side along proximal portion  28 . Communication wires  42  are omitted in  FIG. 3  for clarity. Although depicted as circular in cross-section, one or more lumen(s) of elongated shaft  18  may have any suitable cross-section including for example circular, elliptical, rectangular or crescent-shaped. As explained in more detail below, pressure sensing wire lumen  36  may extend to distal portion  32  of elongate shaft  18  to be coupled to a pressure sensor  38 , as shown in  FIGS. 4-5 . In one embodiment, pressure sensor wire lumen  36  may be eliminated wherein a signal from pressure sensor  38  is sent to a computing device  40  other than via a wire  42  in a dedicated pressure sensor wire lumen  36 , such as, but not limited to, wireless transmission or integration of wire  42  into the wall of elongate shaft  18 . In other embodiments of an elongate shaft or tubular component in accordance herewith, pressure sensor wire lumen  36  may be eliminated wherein the shaft or a portion thereof may be formed by a tubular polymeric inner liner overlaid with a power lead layer and a polymeric outer jacket. In such an embodiment, the power leads for the respective pressure sensor of the inner shaft may be wrapped around the respective shaft for all or at least a portion of the shaft and secured in position by the polymeric outer jacket so as to be embedded within the shaft. In another such embodiment, the power lead for the respective pressure sensor of the inner shaft may be straight for a section or for the entire length of the shaft, and secured in position against the inner liner by the polymeric outer jacket so as to be embedded within the shaft. 
     Distal portion  32  of elongate shaft  18  is configured to receive a guidewire  44  in a distal portion of guidewire lumen  35  thereof. Further, as shown in  FIG. 1 , distal portion  32  is sized to extend from a proximal side  46  of lesion  16 , through lesion  16 , and to a distal side  48  of lesion  16  such that distal tip  33  is disposed on distal side  48  of lesion  16 . Accordingly, in an embodiment, distal portion  32  has a length L D  in the range of 25-300 mm. However, length L D  may be any length suitable such that distal portion  32  may extend from proximal side  46  to distal side  48 . Further, because distal portion  32  is configured to extend through lesion  16 , the cross-sectional dimension or profile of distal portion  32  is minimized such as to minimize the disruption of blood flow through lesion  16  in order to obtain an accurate FFR measurement. 
     Distal tip  33  is disposed on distal portion  32  of elongate shaft  18 . In an optional embodiment (not shown), distal tip  33  is disposed on intermediate portion  30  of elongate shaft  18  and is located proximally of distal portion  32 . Distal tip  33  includes pressure sensor  38  for measuring a pressure of a fluid within lumen  12  of vessel  14 , as shown in  FIG. 4 . In the embodiment shown in  FIG. 4 , pressure sensor  38  is disposed in a pocket  50  (See also  FIG. 6B ) of a thickened portion  52  of distal tip  33 . As shown in  FIG. 4 , pocket  50  may be defined by at least one substantially vertical sidewall  54  and substantially horizontal shaft wall  34 . In another embodiment, pocket  50  has at least one sidewall with a curvilinear shape. Pressure sensor  38  may be a piezo-resistive pressure sensor, a piezo-electric pressure sensor, a capacitive pressure sensor, an electromagnetic pressure sensor, an optical pressure sensor, and/or combinations thereof. In one non-limiting example pressure sensor  38  is a micro electromechanical sensor (MEMS) based pressure die measuring about 240 microns by 70 microns by 1100 microns in size. However, other sized pressure sensors may be used. As shown in  FIG. 2 , thickened portion  52  needs to accommodate pressure sensor  38 . Accordingly, thickened portion  52  of elongate shaft  18  causes tip portion  33  to have an outer diameter OD 1  (shown in  FIG. 2 ) which is larger than the outer diameter OD 2  of distal portion  32  of elongate shaft  18 . However, depending on the size of pressure sensor  38 , the outer diameters OD 1  and OD 2  of the elongate shaft  18  could have substantially the same diameter. In one embodiment, outer diameter OD 1  of tip portion  33  is in the range of 0.024 inch-0.040 inch in order to accommodate pressure sensor  38 . However, outer diameter OD 1  may vary depending on the size of pressure sensor  38 , thickness of elongate shaft  18 , and other factors used to determine the diameter or profile of shafts. In an optional embodiment, a cover (not shown) could extend substantially over pocket  50  to protect pressure sensor  38  from contacting the vessel wall while still allowing blood to surround pressure sensor  38 . 
     Pocket  50  is in communication with pressure sensor wire lumen  36  such that any communication wire(s)  42  from pressure sensor  38  may extend from pocket  50  proximally through pressure sensor wire lumen  36 , through a corresponding lumen in luer fitting  22  exiting through proximal port  54  to a computing device  40  coupled to proximal end  56  of communication wire  42 . Proximal end  56  of communication wire  42  may be coupled to computing device  40  via various communication pathways, including but not limited to one or more physical connections including electrical, optical, and/or fluid connections, a wireless connection, and/or combinations thereof. Accordingly, it is understood that additional components (e.g., cables, connectors, antennas, routers, switches, etc.) not illustrated in  FIG. 1  may be included to facilitate communication between the proximal end  56  of communication wire  42  and computing device  40 . In an optional embodiment, computing device  40  is incorporated into catheter  10  or for example, in proximal portion  28 . 
       FIG. 4  is a longitudinal cross-sectional view of distal shaft portion  32  including distal tip  33 . Therein, sensor  38  has a first outwardly facing surface  60 , a second inwardly facing surface  62 , a first distal end  64  and a second proximal end  66 . A diaphragm  58  of sensor  38  is disposed on first surface  60 . Communication wires  42  (for example, 0.0025 inch coated copper wire in a tri-filar configuration) extending from lumen  36  are coupled to an electrical interface, such as an interposer  70  which has first and second surfaces  72 ,  74 . In this embodiment, communication wires form an “S-shape”, such that one end of the communication wires  42  is raised up to the elevated level of first surface  72  of interposer  70 . Second sensor surface  62  is coupled to first surface  72  of interposer  70  (for example, by an adhesive  76 ), thereby disposing interposer between shaft wall  34  of elongate shaft  18  and sensor  38 . 
     Sensor wires  80  (for example, 0.001 inch thick gold wires) have a first end coupled to first surface  72  of interposer  70  and a second end coupled to electrical pads or metallization on first surface  60  of sensor  38 . Similarly to the communication wires, sensor wires may also make an S-shape, such that one end of the sensor wires  80  is raised up to the elevated level of first surface  60  of sensor  38 . Interposer  70  has second surface  74  coupled to shaft wall  34  of elongate shaft  18 . In one embodiment, interposer  70  is coupled to shaft wall  34  by an adhesive  82  having a thickness of about 25 microns. Sensor  38  may be elevated above shaft wall  34  by the thickness of interposer  70  and to some degree by the thickness of the adhesive layers  76  and  82 . 
       FIG. 5A  is a longitudinal cross-sectional view of another example of distal shaft portion  32  including distal tip  33 . In  FIG. 5A , sensor  38  is elevated above shaft wall  34  by a step  90  extending from shaft wall  34 . Sensor  38  is coupled to step  90  by, for example, an adhesive layer  92 . Sensor  38  may be elevated above shaft wall  34  by a distance of about 40-50 microns. In another example, the distance between the sensor  38  and shaft wall  34  is about 25-60 microns. Sensor  38  can be coupled to step  90  at any point along the length of sensor  38 . As shown in  FIG. 5A , sensor  38  is coupled to step  90  at a location that is adjacent first end  64  of sensor  38 . Placement of sensor  38  at this location creates an overhang  94 , such that first end  64  of sensor  38  is spaced apart from shaft wall  34  thereby forming a pocket  96  under first end  64  of sensor  38 . Thus, pocket  96  is defined by step  90 , overhang  94  and shaft wall  34 . In one example, pocket  96  could be further defined by side walls (not shown) extending from shaft wall  34  on either side of pocket  96 , the side walls further extending between step  90  and overhang  94 . In an optional example, step  90  extends substantially along the entire second surface  62  (except for overhang  94 ) of sensor  38  such that second end  62  of sensor is not suspended above shaft wall  34 . 
     In the example of  FIG. 5A , pocket  96  has an opening  98  for receiving communication wire  42  (or any type of electrical coupling such as wiring or an interposer) whereby communication wire  42  is coupled to second surface  62  of sensor  38 . In this case, sensor  38  could be configured (such as by the flip chip or controlled collapse chip connection method) to have electrical pads, solder bumps or other metallization on second surface  62  instead of first surface  60 , in order to provide an electrical coupling between sensor  38  and communication wire  42 . Although, communication wire  42  is shown, other wires such as sensor wire  80  are also receivable within pocket  96 . Thus, by directly coupling communication wire  42  to second surface  62  of sensor  38  within pocket  96 , the example of  FIG. 5A  (as compared with  FIG. 4 ) has eliminated interposer  70 , adhesive layers  76  and  82 , and any additional wiring, such as sensor wire  80 . By eliminating components needed to create an electrical coupling, the profile of thickened portion  52  is reduced or minimized. 
       FIG. 5B  is a longitudinal cross-sectional view of another example of distal shaft portion  32  including distal tip  33 . In this example, sensor  38  is similar to the sensor of  FIG. 4  with the electrical pads or other metallization, and diaphragm  58  both disposed on first surface  60  of sensor  38 . However, in the example of  FIG. 5B , sensor  38  is “flipped” or mounted upside down onto step  90 . In this configuration, communication wire  42  is receivable within pocket  96  and coupled to first surface  60  of sensor  38 . 
       FIG. 6A  is a longitudinal cross-sectional view of another example of distal shaft portion  32  including distal tip  33 . In addition to reducing the profile of distal tip  33  to a minimum, isolating sensor  38  from any stress or strain is important because physical or mechanical distortion of sensor  38  can result in an incorrect pressure reading. One source of stress or strain applied to sensor  38  could be from the movement of electrical leads, pressure sensor wire  80 , or communication wire  42  during operation of catheter  10 . To avoid stress and strain from such wiring, one option is to couple one end of a flexible interconnect  100  to communication wire  42  and to couple the other end of flexible interconnect  100  to first surface  60  of sensor  38 , as shown in  FIG. 6A . Flexible interconnect  100  can be manufactured with cross-sectional profiles as low as 25 microns further reducing the profile of distal tip  33 . In one example, sensor  38  is mounted and positioned on one portion of step  102  (which extends from shaft wall  34 ) in such a way as to form a ledge  104  having a top surface  106 . Flexible interconnect  100  can lie against ledge  104  as well as move or slidably curve across top surface  106  of ledge  104  in response to bending forces. Flexible interconnect  100  has elastic and deformable properties that allow flexible interconnect  100  to move, bend and adjust within distal tip  33 . The resilient characteristics of flexible interconnect  100  not only help flexible interconnect  100  to minimize the profile of distal tip  33  but also the stress and strain acting on distal tip  33  are absorbed by flexible interconnect  100 , instead of sensor  38 , further isolating sensor  38  from these bending forces. In addition, flexible interconnect  100  allows sensor  38  and communication wire  42  to move independently from one another, further alleviating the stress and strain being applied to sensor  38 . 
       FIG. 6B  is a top view of the embodiment illustrated in  FIG. 6A  showing flexible interconnect  100  in a curved and compacted configuration to minimize profile of distal tip  33 . As can be seen in  FIG. 6B , electrical wiring  108  (disposed on or within flexible interconnect  100 ) couples communication wire  42  to electrical pads  110  of sensor  38 . Not only does flexible interconnect  100  minimize the profile of distal tip  33 , flexible interconnect  100  also provides a much more stable coupling than, for example, three separate wires coupling communication wire  42  with sensor  38 . In addition, separate wiring would require epoxy or solder at each joint to secure wiring to sensor  38 , thereby adding to the profile of distal tip  33 . 
       FIG. 7  is a longitudinal cross-sectional view of another example of distal shaft portion  32  including distal tip  33 . In the example of  FIG. 7 , distal tip  33  does not have an interposer or sensor wires. Instead, a gap  120  is provided between sensor  38  and communication wire  42 . A top surface  122  of shaft wall  34  which spans the distance of gap  120  is metallized, or electrical leads are etched into top surface  122 . As a result, communication wire  42 , which is in contact with top surface  122 , is electrically coupled to top surface  122  of shaft wall  34 . One way to metalize top surface  122  of shaft wall is to mold distal tip  33  with an appropriately doped polymer. Portions of the polymer are exposed to laser direct structuring technology to activate the polymer for selective plating as well as to create patterns for electrical pad configurations. Once the mold is complete, layers of metallization (typically 5-8 microns thick) are placed into the electrical pad patterns thereby electrically coupling sensor  38  with communication wire  42 . In an optional example, metallization or electrical leads can be integrated within shaft wall  34  and do not need to extend along top surface  122  of shaft wall  34 . 
     By spanning the distance between sensor  38  and communication wire  42 , gap  120  provides a flex region disposed between sensor  38  and communication wire  42 . The flex region bends or twists in response to the catheter&#39;s movement in the patient&#39;s vasculature, which absorbs stress and strain forces that would otherwise be transmitted to sensor  38 . The flex region also allows sensor  38  and communication wire  42  to move independently from one another further reducing the amount of stress and strain forces being transmitted to sensor  38 . As shown in  FIG. 7 , a bonding member  124 , such as a gold wire bond, is coupled between sensor  38  and top surface  122  of shaft wall  34 . More specifically, bonding member  124  has one end  126  coupled to electrical pads  110  of sensor  38 , and bonding member  124  has another end  128  coupled to top surface  122  of shaft wall  34 . Thus, bonding member  124  provides a bridge to electrically couple sensor  38  to communication wire  42  through top surface  122  of shaft wall  34 . 
       FIG. 8  is a longitudinal cross-sectional view of an optional embodiment of distal shaft portion  32  having a protective covering or cap  150  disposed about and partially or fully enclosing distal tip  33 . Although cap  150  could partially or fully enclose an embodiment of any distal tip disclosed herein, cap  150  of  FIG. 8  is shown disposed about distal tip  33  of  FIG. 5B . With diaphragm  58  facing inward toward surface  34  instead of being exposed directly to fluid in lumen  12 , distal tip  33  would need at least one opening  160  in cap  110 , preferably, in close proximity to diaphragm  58  to allow ingress of fluid for pressure measurement. In one example, opening  160  would be disposed on the side portion cap  150  (as shown in  FIG. 8 ) such that the opening  160  would be close enough to sensor  38  and diaphragm  58  to provide fluid communication between sensor  38 , diaphragm  58  and lumen  12  of patient vessel  14  thereby allowing a pressure measurement by sensor  38 . Opening  160  can be positioned anywhere on cap  160  and opening  160  can be of any shape or size depending on the desired amount of fluid communication between patient vessel  14  and sensor  38 . 
     A method of measuring FFR using measurement catheter  10  will now be described with reference to  FIG. 1 . As would be understood by those skilled in the art, when measuring FFR a guide catheter (not shown) may be advanced through the vasculature such that the guide catheter is disposed within the aorta with a distal end thereof disposed within the aorta at an ostium of the aorta adjacent the branch vessel  14  within which lesion  16  is located. As shown in  FIG. 1 , guidewire  44  can be advanced intraluminally through the guide catheter, into vessel  14  within lumen  12  to the site of lesion  16 . In the embodiment shown, guidewire  44  is advanced from proximal side  46  of lesion  16  to distal side  48  of lesion  16 , which is also consistent with the direction of the blood flow BF, as indicated by the arrow BF in  FIG. 1 . In an embodiment, vessel  14  is a coronary artery, but vessel  14  may be other vessels in which it may be desirable to measure pressure, and in particular, to measure FFR. 
     Thereafter, as shown in  FIG. 1 , measurement catheter  10  can be tracked or advanced over indwelling guidewire  44  to the target site such that distal end  32  of elongate shaft  18  is positioned distal of lesion  48 . As can be seen in  FIG. 1 , distal tip  33  including pressure sensor  33  can be disposed distally of lesion  16  such that elongate shaft  18  is disposed through lesion  16 . 
     With measurement catheter  10  in place, pressure sensor  33  measures the pressure of blood distal of the lesion within lumen  12 . Accordingly, the pressure measured by pressure sensor  33  is the distal pressure measurement, or P d , used in calculating FFR. In one embodiment, adenosine is administered either intracoronary at the site, bolus, or intravenously by continuous infusion for providing an accurate distal pressure measurement (P d ) for an FFR value. A proximal pressure measurement P a , which is taken in the aorta by an external AO pressure transducer associated with the guide catheter, and a simultaneous pressure measurement P d  taken with pressure sensor  33  of measurement catheter  10  are then obtained to provide the FFR value, i.e., P d /P a , for the lesion. The proximal pressure measurement P a  and distal pressure measurement P d  can be communicated to computing device  40 . Computing device  40 , shown schematically in  FIGS. 1 and 2 , may include such components as a CPU, a display device, an amplification and filtering device, an analog-to-digital converter, and various other components. Computing device  40  may receive the proximal pressure measurement P a  and distal pressure measurement P d , and may process them to provide a continuous display of FFR measurement. 
     When the FFR measurement is completed, measurement catheter  10  may then be completely withdrawn from the patient or repositioned in vivo at another lesion and the process repeated. Pressure-sensing catheters in accordance with embodiments hereof may be used for other than providing proximal and distal pressure measurements (P a , P d ) for calculating an FFR value. For instance, pressure-sensing catheters in accordance with embodiments hereof may be used to provide an in vivo pressure measurement anywhere along the vasculature, or a particular lesion therein. As well, embodiments hereof may be used to provide in vivo pressure measurements, across a heart valve, venous valve or other valvular location within the body where it may be deemed useful. 
     The detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in the context of treatment of blood vessels such as the coronary arteries, the invention may also be used in any other body passageways where it is deemed useful such as but not limited to peripheral arteries, carotid arteries, renal arteries, and/or venous applications. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the detailed description. 
     While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment.