Patent Publication Number: US-2023148887-A1

Title: Methods for assessing fractional flow reserve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/047,763, filed Jul. 27, 2018, now U.S. Pat. No. 11,564,581; which claims the benefit of priority under 35 U.S.C. § 119 to U.S. Provisional Application Ser. No. 62/541,069, filed Aug. 3, 2017, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to medical devices, and methods for using medical devices. More particularly, the present disclosure pertains to methods for assessing fractional flow reserve. 
     BACKGROUND 
     A wide variety of intracorporeal medical devices have been developed for medical use, for example, intravascular use. Some of these devices include guidewires, catheters, and the like. These devices are manufactured by any one of a variety of different manufacturing methods and may be used according to any one of a variety of methods. Of the known medical devices and methods, each has certain advantages and disadvantages. There is an ongoing need to provide alternative medical devices as well as alternative methods for manufacturing and using medical devices. 
     BRIEF SUMMARY 
     This disclosure provides design, material, manufacturing methods, and use alternatives for medical devices. An example medical device includes a system for determining fractional flow reserve. The system comprises: a pressure sensing guidewire for measuring a first pressure; a second pressure sensing medical device for measuring a second pressure; a processor coupled to the pressure sensing guidewire and coupled to the second pressure sensing medical device; wherein the processor is designed to: generate a plot of the magnitude of the second pressure over time, identify one or more time intervals of the plot that have a slope less than zero, determine a mean of the second pressure, and calculate the ratio of the first pressure to the second pressure when (a) the second pressure is less than or equal to the mean of the second pressure and (b) during the one or more time intervals when the slope of the plot is less than zero. 
     Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire includes an optical pressure sensor. 
     Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire includes a tubular member having a proximal region with a first inner diameter and a distal region with a second inner diameter different from the first inner diameter. 
     Alternatively or additionally to any of the embodiments above, the second pressure sensing medical device includes a catheter with a pressure sensor. 
     Alternatively or additionally to any of the embodiments above, the first pressure, the second pressure, or both are wirelessly transmitted to the processor. 
     Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire is designed to be disposed distal of an intravascular lesion. 
     Alternatively or additionally to any of the embodiments above, the second pressure sensing medical device is designed to be disposed proximal of an intravascular lesion. 
     Alternatively or additionally to any of the embodiments above, the processor is designed to calculate the ratio of the first pressure to the second pressure in the absence of a hyperemic agent. 
     Alternatively or additionally to any of the embodiments above, the processor is coupled to a display. 
     Alternatively or additionally to any of the embodiments above, the display is designed to display the plot. 
     A system for determining fractional flow reserve is disclosed. The system comprises: a pressure sensing guidewire for measuring a distal pressure at a location distal of a lesion; a pressure sensing catheter for measuring an aortic pressure; a processor coupled to the pressure sensing guidewire and coupled to the pressure sensing catheter; and wherein the processor is designed to: generate a plot of the magnitude of the aortic pressure over time, identify one or more time intervals of the plot that have a slope less than zero, determine a mean of the aortic pressure, and calculate the ratio of the distal pressure to the aortic pressure when (a) the aortic pressure is less than or equal to the mean of aortic pressure and (b) during the one or more time intervals when the slope of the plot is less than zero. 
     Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire includes an optical pressure sensor. 
     Alternatively or additionally to any of the embodiments above, the pressure sensing guidewire includes a tubular member having a proximal region with a first inner diameter and a distal region with a second inner diameter different from the first inner diameter. 
     Alternatively or additionally to any of the embodiments above, the processor is designed to calculate the ratio of the distal pressure to the aortic pressure in the absence of a hyperemic agent. 
     Alternatively or additionally to any of the embodiments above, the processor is coupled to a display. 
     Alternatively or additionally to any of the embodiments above, the processor is designed to scale the mean aortic pressure by a scaling factor in the range of 0.75 to 1.25. 
     Alternatively or additionally to any of the embodiments above, the processor is designed to reject time intervals when the aortic pressure is less than a pressure lower bound. 
     A method for determining fractional flow reserve is disclosed. The method comprises: disposing a pressure sensing guidewire distal of an intravascular lesion; measuring a distal pressure with the pressure sensing guidewire; disposing a pressure sensing catheter in a vascular region; measuring an aortic pressure with the pressure sensing catheter; wherein a processor is coupled to the pressure sensing guidewire and coupled to the pressure sensing catheter; wherein the processor is designed to: generate a plot of the magnitude of the aortic pressure over time, identify one or more time intervals of the plot that have a slope less than zero, and determine a mean of the aortic pressure; and calculating a ratio of the distal pressure to the aortic pressure when (a) the aortic pressure is less than or equal to the mean of the aortic pressure (b) during the one or more time intervals when the slope of the plot is less than zero. 
     Alternatively or additionally to any of the embodiments above, measuring a distal pressure with the pressure sensing guidewire includes measuring the distal pressure in the absence of a hyperemic agent, wherein measuring an aortic pressure with the pressure sensing catheter includes measuring the aortic pressure in the absence of a hyperemic agent, or both. 
     Alternatively or additionally to any of the embodiments above, calculating a ratio of the distal pressure to the aortic pressure includes calculating the ratio of the distal pressure to the aortic pressure in the absence of a hyperemic agent. 
     The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which: 
         FIG.  1    schematically illustrates an example system for assessing fractional flow reserve. 
         FIG.  2    graphically depicts blood pressure values over time. 
         FIG.  3    is a partial cross-sectional side view of a portion of an example medical device. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
     DETAILED DESCRIPTION 
     For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification. 
     All numeric values are herein assumed to be modified by the term “about”, whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (e.g., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. 
     The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include one or more particular features, structures, and/or characteristics. However, such recitations do not necessarily mean that all embodiments include the particular features, structures, and/or characteristics. Additionally, when particular features, structures, and/or characteristics are described in connection with one embodiment, it should be understood that such features, structures, and/or characteristics may also be used connection with other embodiments whether or not explicitly described unless clearly stated to the contrary. 
     The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
     During some medical interventions, it may be desirable to measure and/or monitor the blood pressure within a blood vessel. For example, some medical devices may include pressure sensors that allow a clinician to monitor blood pressure. Such devices may be useful in determining fractional flow reserve (FFR), which may be understood as a ratio of the pressure after, or distal, of a stenosis (e.g., the distal pressure, P d ) relative to the pressure before the stenosis and/or the aortic pressure (e.g., the aortic pressure, P a ). In other words, FFR may be understood as P d /P a . 
     An example system  100  for assessing/determining FFR is schematically represented in  FIG.  1   . The system  100  may include a first pressure sensing medical device  10 . In at least some instances, the first pressure sensing medical device  10  may take the form of a pressure sensing guidewire  10 . Some additional detail regarding the form of the guidewire  10 , provided as an example, is disclosed herein. In other instances, the first pressure sensing medical device  10  may be a catheter or other type of pressure sensing medical device. The pressure sensing guidewire  10  may be utilized to measure blood pressure distal of an intravascular stenosis, e.g., the distal pressure P d . The first pressure sensing medical device  10  may be coupled to a linking device  70 . In some instances, this may include directly attaching the first pressure sensing medical device  10  to the linking device  70 . In other instances, another structure such as a connector cable (not shown) may be used to couple the first pressure sensing medical device  10  to the linking device  70 . When the first pressure sensing medical device  10  is coupled to the linking device  70 , a first pressure data  72  may be communicated between the first pressure sensing medical device  10  and the linking device  70 . It is noted that in  FIG.  1   , a line is drawn between the first pressure sensing medical device  10  and the linking device  70  to represent the coupling of the first pressure sensing medical device  10  and the linking device  70 . In addition the line between the first pressure sensing medical device  10  and the linking device  70  is labeled with reference number  72  in order to represent the transmission of the first pressure data  72  (and/or the first pressure data  72  itself). In at least some instances, the first pressure data  72  is the distal pressure P d . 
     The system  100  may also include a second pressure sensing medical device  74 . In at least some instances, the second pressure sensing medical device  74  may take the form of a pressure sensing catheter. However, other devices are contemplated including pressure sensing guidewires or other devices. The second pressure sensing medical device  74  may be utilized to measure blood pressure proximal of an intravascular stenosis and/or the aortic pressure, e.g., the aortic pressure P a . The second pressure sensing medical device  74  may also be coupled to the linking device  70  and may communicate a second pressure data  76  between the second pressure sensing medical device  74  and the linking device  70 . It is noted that in  FIG.  1   , a line is drawn between the second pressure sensing medical device  74  and the linking device  70  to represent the coupling of the second pressure sensing medical device  74  and the linking device  70 . In addition the line between the second pressure sensing medical device  74  and the linking device  70  is labeled with reference number  76  in order to represent the transmission of the second pressure data  76  (and/or the second pressure data  76  itself). In at least some instances, the second pressure data  76  is the aortic pressure P a . 
     In some instances, the linking device  70  may communicate with a hemodynamic system  78  (e.g., a hemodynamic display system  78 ). When doing so, data representative of the distal pressure P d  (represented by reference number  80 ) may be communicated to the hemodynamic system  78  and data representative of the aortic pressure P a  (represented by reference number  82 ) may be communicated to the hemodynamic system  78 . In some instances, both connections between the linking device  70  and the hemodynamic system  78  (e.g., for communicating P d  and P a ) may be wired connections. In other instances, one or both of the connections may be wireless connections. In still other instances, both P d  and P a  may be communicated along a single wired connection. 
     In some instances, the linking device  70  may also communicate with a processing and/or display system  84 . When doing so, data representative of the distal pressure P d  and data representative of the aortic pressure P a  (both the distal pressure P d  and the aortic pressure P a  data are represented by reference number  86  in  FIG.  1   ) may be communicated to the processing and/or display system  84 . In at least some instances, P d  and P a  may be communicated between the linking device  70  and the processing and/or display system  84  using a wireless connection. In other instances, one or both of P d  and P a  may be communicated between the linking device  70  and the processing and/or display system  84  with a wired connection. 
     The processing and/or display system  84  may include a processor  88 . The processor  88  may be an integrated component of the processing and/or display system  84  (e.g., the processor  88  may be disposed within the same housing as the processing and/or display system  84 ) or the processor  88  may be separate component of the processing and/or display system  84  and coupled therewith. The processor  88  may be coupled to the first pressure sensing medical device  10  and coupled to the second pressure sensing medical device  74  such that pressure measurements (e.g., P d  and P a ) may be received by the processor  88  from the first pressure sensing medical device  10  and the second pressure sensing medical device  74 . The processor  88  may be designed to and/or otherwise be capable of performing a number of calculations, executing instructions, etc. For example, the processor may be designed to calculate/determine the mean distal pressure P d  (e.g., as measured by the first pressure sensing medical device  10  over one or more cardiac cycles), calculate/determine the mean aortic pressure P a  (e.g., as measured by the second pressure sensing medical device  74  over one or more cardiac cycles), plot the distal pressure P d  and/or the aortic pressure P a  over time, calculate/determine the slope of the plot of the distal pressure P d  and/or the slope of the plot of the aortic pressure P a  (e.g., at various points along the plot), or the like. A display  90  may be coupled to or otherwise integrated with the processing and/or display system  84 . The display  90  may display various data received from first pressure sensing medical device  10  and the second pressure sensing medical device  74 , plots of the pressure data as generated by the processor  80 , etc. 
     When determining FFR, it may be desirable to measure a change or drop in pressure across a stenosis while under a maximum flow condition (e.g., hyperemia). Thus, a number of interventions that are performed to assess FFR include the administration of hyperemic agents such as adenosine to cause maximum flow conditions. For a number of reasons (e.g., patient comfort, extended procedure time, technical challenges associated with mixing adenosine for intravascular administration, cost, etc.), it may be desirable to reduce the use of hyperemic agents. Pressure measurements performed under a resting condition conduction are typically referred as resting indices. An example of such a measurement is resting P d /P a  in which the ratio is computed with data from the whole cardiac cycle. Disclosed herein are methods for assessing/determining FFR that can be performed in the absence of hyperemic agents including adenosine. 
     The maximum coronary flow occurs during the diastolic period of the cardiac cycle. Therefore, measurements of P d  and P a  during a diastolic period may provide a ratio closer to FFR (e.g., a better approximation of FFR) than that obtained from the whole cardiac cycle. In addition to resting P d /P a , some methods for assessing FFR may include computing P d  and P a  during time windows from the diastolic period. For example, some interventions such as instantaneous wave-free ratio and/or iFR™ may attempt to measure FFR during diastole. Such methods may require accurate measurement of waveform timing and/or synchronization with an ECG, which may complicate the process for assessing/determining FFR. Disclosed herein are methods for assessing/determining FFR by monitoring P d  and P a  during specific windows during the diastolic period of the cardiac cycle. The methods for assessing/determining FFR disclosed herein are relatively straightforward to implement such that FFR can be assessed/determined in a timely manner that enhances the comfort for the patient and that does not require unnecessary additional processes and/or synchronization. 
       FIG.  2    graphically depicts pressure measurements over a number of cardiac cycles (e.g., one full cycle is depicted plus a portion of another cardiac cycle). In this example, a graphical depiction of P d  (e.g., as measured by the first pressure sensing medical device  10 ) and a graphical depiction of P a  (e.g., as measured by the second pressure sensing medical device  74 ) are shown over time. Also shown is the mean aortic pressure  92 . 
     In order to assess/determine FFR, the processor  88  may be utilized to perform a number of tasks including:
         generating a plot of the magnitude of the distal pressure P d  (e.g., as measured by the first pressure sensing medical device  10  and as depicted in  FIG.  2   ) over time,   generating a plot of the magnitude of the aortic pressure P a  (e.g., as measured by the second pressure sensing medical device  74  and as depicted in  FIG.  2   ) over time,   identifing one or more time intervals of the plot of P a  where the slope of the plot is less than zero,   calculating/determining the mean aortic pressure  92 ,   one or more additional calculations, and/or combinations thereof.       

     In one example, regions of the cardiac cycle are identified where:
         (a) P a  is less than or equal to the mean aortic pressure  92 , and   (b) the slope P a  is less than zero.       

     In another example, regions of the cardiac cycle are identified where:
         (a) P a  is less than or equal to the mean aortic pressure  92  scaled by a scaling factor ranging from 0.5 to 1.5, or about 0.75 to 1.25, or about 0.95 to 1.05 (e.g., regions of the cardiac cycle are identified where P a  is less than or equal to the mean aortic pressure  92  multiplied by the scaling factor), and   (b) the slope P a  is less than zero.       

     In another example, regions of the cardiac cycle are identified where:
         (a) P a  is less than or equal to the mean aortic pressure  92  is scaled by a scaling factor ranging from 0.5 to 1.5, or about 0.75 to 1.25, or about 0.95 to 1.05, and/or   (b) the slope P a  is less than zero, and/or   (c) P a  is higher than a pressure lower bound, which can be determined by one of the following methods:
           i) a fixed negative offset with a range of −10 mmHg-−100 mmHg from the mean aortic pressure  92 ,   ii) a relative negative offset from the mean aortic pressure  92  as computed by 10%-100% of the mean aortic pressure  92 , and/or   iii) a fixed positive offset with a range of 10 mmHg-100 mmHg from the minimum aortic pressure  95 .
 
The mean aortic pressure  92  may be determined for each individual cardiac cycle or across a number of cardiac cycles. Time windows or regions that meet these criteria are believed to be during high flow periods (e.g., during the diastolic period) and are believed to be suitable for use in assessing/determining FFR. Thus, the system  100  can be utilized to assess/determine/calculate FFR during these periods in the absence of hyperemic agents and/or without the need for unnecessary additional processes and/or synchronization. In the graph shown in  FIG.  2   , three time regions  96   a ,  96   b ,  96   c  are defined that meet these criteria. It can be appreciated that in other plots/graphs, fewer or more time regions may be identified. The processor  88  can be utilized to assess/determine/calculate FFR during these time regions  96   a ,  96   b ,  96   c.  
   
               

       FIG.  3    illustrates a portion of the first pressure sensing medical device  10  that may be part of the system  100 . In this example, the first pressure sensing medical device  10  is a blood pressure sensing guidewire  10 . However, this is not intended to be limiting as other medical devices are contemplated including, for example, catheters, shafts, leads, wires, or the like. The guidewire  10  may include a shaft or tubular member  12 . The tubular member  12  may include a proximal region  14  and a distal region  16 . The materials for the proximal region  14  and the distal region  16  may vary and may include those materials disclosed herein. For example, the distal region  16  may include a nickel-cobalt-chromium-molybdenum alloy (e.g., MP35-N). The proximal region  14  may be made from the same material as the distal region  16  or a different material such as stainless steel. These are just examples. Other materials are contemplated. 
     In some embodiments, the proximal region  14  and the distal region  16  are formed from the same monolith of material. In other words, the proximal region  14  and the distal region  16  are portions of the same tube defining the tubular member  12 . In other embodiments, the proximal region  14  and the distal region  16  are separate tubular members that are joined together. For example, a section of the outer surface of the portions  14 / 16  may be removed and a sleeve  17  may be disposed over the removed sections to join the regions  14 / 16 . Alternatively, the sleeve  17  may be simply disposed over the regions  14 / 16 . Other bonds may also be used including welds, thermal bonds, adhesive bonds, or the like. If utilized, the sleeve  17  used to join the proximal region  14  with the distal region  16  may include a material that desirably bonds with both the proximal region  14  and the distal region  16 . For example, the sleeve  17  may include a nickel-chromium-molybdenum alloy (e.g., INCONEL). 
     A plurality of slots  18  may be formed in the tubular member  12 . In at least some embodiments, the slots  18  are formed in the distal region  16 . In at least some embodiments, the proximal region  14  lacks slots  18 . However, the proximal region  14  may include slots  18 . The slots  18  may be desirable for a number of reasons. For example, the slots  18  may provide a desirable level of flexibility to the tubular member  12  (e.g., along the distal region  16 ) while also allowing suitable transmission of torque. The slots  18  may be arranged/distributed along the distal region  16  in a suitable manner. For example, the slots  18  may be arranged as opposing pairs of slots  18  that are distributed along the length of the distal region  16 . In some embodiments, adjacent pairs of slots  18  may have a substantially constant spacing relative to one another. Alternatively, the spacing between adjacent pairs may vary. For example, more distal regions of the distal region  16  may have a decreased spacing (and/or increased slot density), which may provide increased flexibility. In other embodiments, more distal regions of the distal region  16  may have an increased spacing (and/or decreased slot density). These are just examples. Other arrangements are contemplated. 
     A pressure sensor  20  may be disposed within the tubular member  12  (e.g., within a lumen of tubular member  12 ). While the pressure sensor  20  is shown schematically in  FIG.  3   , it can be appreciated that the structural form and/or type of the pressure sensor  20  may vary. For example, the pressure sensor  20  may include a semiconductor (e.g., silicon wafer) pressure sensor, piezoelectric pressure sensor, a fiber optic or optical pressure sensor, a Fabry-Perot type pressure sensor, an ultrasound transducer and/or ultrasound pressure sensor, a magnetic pressure sensor, a solid-state pressure sensor, or the like, or any other suitable pressure sensor. 
     As indicated above, the pressure sensor  20  may include an optical pressure sensor. In at least some of these embodiments, an optical fiber or fiber optic cable  24  (e.g., a multimode fiber optic) may be attached to the pressure sensor  20  and may extend proximally therefrom. The optical fiber  24  may include a central core  60  and an outer cladding  62 . In some instances, a sealing member (not shown) may attach the optical fiber  24  to the tubular member  12 . Such an attachment member may be circumferentially disposed about and attached to the optical fiber  24  and may be secured to the inner surface of the tubular member  12  (e.g., the distal region  16 ). In addition, a centering member  26  may also be bonded to the optical fiber  24 . In at least some embodiments, the centering member  26  is proximally spaced from the pressure sensor  20 . Other arrangements are contemplated. The centering member  26  may help reduce forces that may be exposed to the pressure sensor  20  during navigation of guidewire and/or during use. 
     In at least some embodiments, the distal region  16  may include a region with a thinned wall and/or an increased inner diameter that defines a sensor housing region  52 . In general, the sensor housing region  52  is the region of distal region  16  that ultimately “houses” the pressure sensor  20 . By virtue of having a portion of the inner wall of the tubular member  12  being removed at the sensor housing region  52 , additional space may be created or otherwise defined that can accommodate the sensor  20 . The sensor housing region  52  may include one or more openings such as one or more distal porthole openings  66  that provide fluid access to the pressure sensor  20 . 
     A tip member  30  may be coupled to the distal region  16 . The tip member  30  may include a core member  32  and a spring or coil member  34 . A distal tip  36  may be attached to the core member  32  and/or the spring  34 . In at least some embodiments, the distal tip  36  may take the form of a solder ball tip. The tip member  30  may be joined to the distal region  16  of the tubular member  12  with a bonding member  46  such as a weld. 
     The tubular member  12  may include an outer coating  19 . In some embodiments, the coating  19  may extend along substantially the full length of the tubular member  12 . In other embodiments, one or more discrete sections of the tubular member  12  may include the coating  19 . The coating  19  may be a hydrophobic coating, a hydrophilic coating, or the like. The tubular member  12  may also include an inner coating  64  (e.g., a hydrophobic coating, a hydrophilic coating, or the like) disposed along an inner surface thereof. For example, the hydrophilic coating  64  may be disposed along the inner surface of the housing region  52 . In some of these and in other instances, the core member  32  may include a coating (e.g., a hydrophilic coating). For example, a proximal end region and/or a proximal end of the core member  32  may include the coating. In some of these and in other instances, the pressure sensor  20  may also include a coating (e.g., a hydrophilic coating). 
     The materials that can be used for the various components of the system  100  and/or the guidewire  10  may include those commonly associated with medical devices. For simplicity purposes, the following discussion makes reference to the tubular member  12  and other components of the guidewire  10 . However, this is not intended to limit the devices and methods described herein, as the discussion may be applied to other tubular members and/or components of tubular members or devices disclosed herein. 
     The tubular member  12  and/or other components of the guidewire  10  may be made from a metal, metal alloy, polymer (some examples of which are disclosed below), a metal-polymer composite, ceramics, combinations thereof, and the like, or other suitable material. Some examples of suitable polymers may include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM, for example, DELRIN® available from DuPont), polyether block ester, polyurethane (for example, Polyurethane 85A), polypropylene (PP), polyvinylchloride (PVC), polyether-ester (for example, ARNITEL® available from DSM Engineering Plastics), ether or ester based copolymers (for example, butylene/poly(alkylene ether) phthalate and/or other polyester elastomers such as HYTREL® available from DuPont), polyamide (for example, DURETHAN® available from Bayer or CRISTAMID® available from Elf Atochem), elastomeric polyamides, block polyamide/ethers, polyether block amide (PEBA, for example available under the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), Marlex high-density polyethylene, Marlex low-density polyethylene, linear low density polyethylene (for example REXELL®), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), poly paraphenylene terephthalamide (for example, KEVLAR®), polysulfone, nylon, nylon-12 (such as GRILAMID® available from EMS American Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC), poly(styrene-b-isobutylene-b-styrene) (for example, SIBS and/or SIBS 50A), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers thereof, polymer/metal composites, and the like. In some embodiments the sheath can be blended with a liquid crystal polymer (LCP). For example, the mixture can contain up to about 6 percent LCP. 
     Some examples of suitable metals and metal alloys include stainless steel, such as 304V, 304L, and 316LV stainless steel; mild steel; nickel-titanium alloy such as linear-elastic and/or super-elastic nitinol; other nickel alloys such as nickel-chromium-molybdenum alloys (e.g., UNS: N06625 such as INCONEL® 625, UNS: N06022 such as HASTELLOY® C-22®, UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and the like), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® 400, NICKELVAC® 400, NICORROS® 400, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 such as HASTELLOY® ALLOY B2®), other nickel-chromium alloys, other nickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper alloys, other nickel-tungsten or tungsten alloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like); platinum enriched stainless steel; titanium; combinations thereof; and the like; or any other suitable material. 
     In at least some embodiments, portions or all of guidewire  10  may also be doped with, made of, or otherwise include a radiopaque material. Radiopaque materials are understood to be materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. This relatively bright image aids the user of the guidewire  10  in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with a radiopaque filler, and the like. Additionally, other radiopaque marker bands and/or coils may also be incorporated into the design of the guidewire  10  to achieve the same result. 
     In some embodiments, a degree of Magnetic Resonance Imaging (Mill) compatibility is imparted into the guidewire  10 . For example, the guidewire  10 , or portions thereof, may be made of a material that does not substantially distort the image and create substantial artifacts (e.g., gaps in the image). Certain ferromagnetic materials, for example, may not be suitable because they may create artifacts in an MM image. The guidewire  10 , or portions thereof, may also be made from a material that the Mill machine can image. Some materials that exhibit these characteristics include, for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like), nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such as MP35-N® and the like), nitinol, and the like, and others. 
     It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the disclosure. This may include, to the extent that it is appropriate, the use of any of the features of one example embodiment being used in other embodiments. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.