Abstract:
The present document describes a pressure guidewire comprising a shaft tube, a tip portion and a fiber optic pressure sensor. The shaft tube comprises a middle section and a sensor housing extending distally relative to the middle section, the sensor housing having a distal end. The tip portion extends distally relative to the shaft tube. The pressure sensor is embedded in the sensor housing. The sensor housing defines a cavity, inside the sensor housing, which is distal relative to the pressure sensor and delimited at a proximal end thereof by the pressure sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is filed as a continuation application of U.S. patent application Ser. No. 14/138,392 filed on Dec. 23, 2013, which is a continuation of U.S. patent application Ser. No. 14/030,425 filed Sep. 18, 2013, which is a continuation of U.S. patent application Ser. No. 13/389,319 filed Feb. 7, 2012, which is the U.S. national phase application of PCT/CA2011/001257, filed Nov. 9, 2011, and entitled “GUIDEWIRE WITH INTERNAL PRESSURE SENSOR”, which claims priority of U.S. Provisional Application Ser. No. 61/411,722, filed on Nov. 9, 2010, the contents of which are hereby incorporated herein by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    (a) Field 
         [0003]    The subject matter disclosed generally relates to guidewires for catheter use. More particularly, it relates to pressure guidewire technology. 
         [0004]    (b) Related Prior Art 
       Conventional Guidewires 
       [0005]    Conventional guidewires are made using solid rods. They may be made using a combination of different materials such as hard tempered stainless steel and nitinol. Stainless steel provides good pushability and torquability, and is relatively cheap, while the nitinol provides good yield strength, i.e., does not permanently deform. Nitinol is nickel/titanium alloy having superelastic properties as known by those skilled in the art. One consideration in designing guidewires is that welding nitinol to stainless steel is extremely challenging. 
         [0006]    Typical guidewires comprise three main parts as described below. 
         [0007]    The first part is the proximal section. For coronary use, the proximal section, i.e., the length prior to the last 25 to 40 cm, is made typically of 0.014″ outside diameter (OD) stainless steel. Nitinol is not preferred in this section because it does not provide a good pushability and torquability and it is fairly expensive. This section always resides in the catheter guide, hence not directly into the blood vessel. In use, a portion of this section is outside the patient&#39;s body and is controlled by the person using the guidewire. The typical length of the proximal section is 140 cm or longer. 
         [0008]    The second part is the middle section. The middle section is the following 25 to 40 cm of flexible wire, before the tip portion, i.e., the third portion extending further over another 3 to 4 cm. The middle section is the section that navigates within the coronary arteries. Guidewires may use a nitinol wire of about 0.0095″ OD over this section. In order to improve the navigability within the vessel, i.e., having the ability to be threaded through sharp corners within vessels, the distal 1 to 3 cm portion of the middle section, may be slightly tapered, the outside diameter being reduced roughly from 0.0095″ to 0.007″. This taper allows the guidewire to bend with a circular shape, as opposed to a parabolic shape in the case where the outside diameter is uniform. This section can be bent quite seriously when navigating into the vessels and hence, shape retaining is a desirable feature, although not a necessary one. 
         [0009]    The third part is the tip section. The tip is the last 3 to 4 cm of the guidewire. It is made with a very thin tapered, or shaped otherwise, spring tempered or hardened stainless steel core wire. The core wire is surrounded by tungsten, platinum, palladium or another wire winding providing smooth radiopaque tip. Tip section can be pre-shaped prior to use by physician to ease the navigation in any given circumstance. 
         [0010]    Guidewire features are:
       Good trackability: Guidewire can be threaded through tortuous vessels;   Good pushability: Guidewire can be pushed through tortuous vessels and through stenosis;   Good torque: Guidewire can be smoothly rotated to orient the tip within the vessel;   Soft tip: Guidewire is atraumatic for vessels; and   Good support: A balloon catheter can be slid over the guidewire without the guidewire prolapsing or kinking.       
 
       Pressure Guidewire 
       [0016]    A pressure guidewire is one that includes a tip pressure sensor. Trade-offs are necessary to route the sensor lead wire(s) through the guidewire, resulting in sub-optimal mechanical design. Existing pressure guidewires typically comprises four main parts as described below. 
         [0017]    The first part is the proximal section. The proximal section is made with a stainless steel hypotube (aka the proximal tube) having typical OD of 0.014″. There are three sensor lead wires that are routed through the proximal tube to connect to tip sensor. 
         [0018]    The second part is the middle section. A solid core is welded to the proximal section on one end, and to a sensor housing on the other end. This solid rod is typically 27 cm long. The three wires of typical piezo-resistive sensor run through the proximal tube and on the wall of the core along the 27 cm. The three wires are finally directed within the sensor housing (described below) to be connected to the sensor. 
         [0019]    The solid core and three wire assembly are protected either by providing a polyimide tube covering the assembly, by providing a spiral wound wire or other method for the assembly. The foregoing covering method provides minimal mechanical benefit and therefore they are used mostly as a protective sheath. 
         [0020]    The third part of the pressure guidewire is the sensor housing. The sensor housing is made with a hypotube with internal diameter (ID) accommodating the tip sensor and an OD that is the continuity of the proximal section OD. An opening is provided to the sensor housing to let blood communicate with tip sensor. 
         [0021]    The fourth part of the pressure guidewire is the tip section. The tip section is provided at the end of the sensor housing. A conventional tip section can be used as there is no wire to be passed therethrough. 
         [0022]    The critical part of above described pressure guidewires is the middle section (second part above). Wall thickness of polyimide or wire winding added to the size of the sensor lead wires that runs along the solid core compromise the use of optimal solid core. More specifically, the solid core is usually too thin for delivering adequate pushability and torquability on one hand, and adequate support for a balloon catheter on another hand. 
       SUMMARY 
       [0023]    The device described herein optimizes the mechanical performance; mode specifically it improves the pushability, torquability, trackability and catheter support in the case of a pressure guidewire. 
         [0024]    As a first basic consideration, mechanical performance of prior pressure guidewires can be improved if instead of routing the sensor leads through a region toward the perimeter of the guidewire, therefore relying on a thin solid core for the transfer of torque, the sensor leads are routed through the center. It is known that contribution to torque transfer from the central part of a rod is lower than the contribution from the periphery of the same and therefore, it is optimal sacrificing the central portion rather than its periphery. This way, the torque per available surface area is maximized. 
         [0025]    The size of the distal portion of such a hypotube, the portion that navigates within the coronaries, that delivers optimal flexibility and torquability may however be susceptible to kinking, as it would have to be a fairly thin hypotube if made of stainless steel. It is then useful to provide a mechanism that protects this otherwise vulnerable section against the risks of kinking. Protection against kinking is very suitably provided by the continuity of a proximal hypotube extending over, but being cut with a spiral or other pattern. 
         [0026]    The use of a nitinol tube, instead of stainless steel tube, within the middle section of the guidewire would reduce the risk of kinking. The joining of nitinol is however a challenging process and there is a risk of leaving any of the guidewire distal parts within the blood vessel. It is then also desirable to provide a safety mechanism for retaining any of the distal parts of guidewire in case the joining of nitinol was to fail. 
         [0027]    The presence of a continuous shaft from the very proximal end of the guidewire, up and after the sensor housing provides safety features critical for medical devices. 
         [0028]    Manufacturability is another consideration, where the guidewire device needs to be produced in large quantity at the lowest possible cost. Having a minimal amount of parts surely contributes minimizing the manufacturing cost, as well as ease of assembly. 
         [0029]    According to an embodiment, there is provided a pressure guidewire comprising: a shaft tube comprising: a proximal section providing pushability to the pressure guidewire; a middle section extending further relative to the proximal section, the middle section being cut according to a cut pattern thereby resulting in greater flexibility in the middle section than in the proximal section; and a sensor housing extending further relative to the middle section; an inner hypotube installed substantially within the middle section; a pressure sensor communication means routed to the sensor housing through the proximal section and the middle section; and a tip pressure sensor embedded within the sensor housing and communicatively connected to the pressure sensor communication means. 
         [0030]    According to an aspect, the cut pattern comprises a spiral cut pattern. 
         [0031]    According to an aspect, the proximal section, the middle section and the sensor housing are made from a unitary and continuous piece of material. 
         [0032]    According to an aspect, the unitary and continuous piece of material comprises stainless steel. 
         [0033]    According to an aspect, the pressure guidewire further comprises a window through the shaft tube giving access to the inner hypotube for welding, soldering or bonding the inner hypotube within the middle section of the shaft tube. 
         [0034]    According to an aspect, the pressure guidewire further comprises a small piece of material in contact with a wall of the inner hypotube and protruding within the window through the shaft tube, the small piece of material being welded to inner hypotube. 
         [0035]    According to an aspect, the inner hypotube comprises nitinol and the shaft tube comprises stainless steel. 
         [0036]    According to an aspect, the middle section has two ends and comprises two windows, each one of the two windows located at a respective one of the two ends of the middle section and thereby providing two areas for welding, soldering or bonding the inner hypotube within the middle section of the shaft tube. 
         [0037]    According to an aspect, the pressure guidewire further comprises an adhesive or solder for joining the inner hypotube and the shaft tube. 
         [0038]    According to an aspect, the inner hypotube and the shaft tube are made of stainless steel. 
         [0039]    According to an aspect, the inner hypotube comprises a distal portion having a diameter which is profiled, thereby constituting a profiled portion. 
         [0040]    According to an aspect, the tip pressure sensor comprises an optical pressure sensor for measuring a pressure of a fluid in a blood vessel in which the pressure guidewire is inserted. 
         [0041]    According to an aspect, the pressure guidewire further comprises a band to which is fixed the pressure sensor communication means. 
         [0042]    According to an aspect, the sensor housing comprises a window for welding or bonding the band to the shaft tube. 
         [0043]    According to an aspect, the inner hypotube comprises a nitinol hypotube. 
         [0044]    According to an aspect, the distal portion of the profile portion of the inner hypotube is enlarged. 
         [0045]    According to an aspect, both ends of the inner hypotube are bonded to the shaft tube with an adhesive. 
         [0046]    According to an aspect, the pressure sensor communication means comprises an optical fiber. 
         [0047]    According to an aspect, the pressure sensor communication means is also routed within the inner hypotube. 
         [0048]    According to an aspect, the pressure sensor communication means has an end providing a connection to the tip pressure sensor. 
         [0049]    According to an aspect, the pressure guidewire further comprises a soft atraumatic tip extending further relative to the sensor housing. 
         [0050]    According to an embodiment, there is provided a pressure guidewire comprising: a proximal section of shaft tube providing pushability to the pressure guidewire; a middle section of shaft tube being the extension of proximal section, the middle section having greater flexibility than the proximal section; an inner hypotube installed substantially within the middle section and providing middle section with desired mechanical characteristics; a sensor housing extending further relative to middle section; a pressure sensor communication means routed through portion of the sensor housing and through the proximal and middle sections of shaft tube, the pressure sensor communication means having an end; and a tip pressure sensor embedded within sensor housing. 
         [0051]    According to an embodiment, there is provided a pressure guidewire comprising:
       a shaft tube with a proximal section delivering good pushability;   the same shaft tube comprising a middle section having a flexibility, the flexibility of the flexible middle section being provided by way of cutting the hypotube over the middle section;   an inner hypotube installed substantially within the middle section for providing desired mechanical characteristics to the middle section;   the same shaft tube with the distal section cut with a different pattern for offering same rigidity as proximal section for receiving and protecting a tip pressure sensor, and providing a opening for blood pressure to communicate with pressure sensor;   a tip section connected and extending further to the sensor housing; and   a tip pressure sensor located within the sensor housing, with a communication means routed through portion of sensor housing, and inner hypotube and shaft tube.       
 
         [0058]    According to another embodiment, there is provided a pressure guidewire comprising:
       a shaft tube with a proximal section delivering good pushability;   the same shaft tube comprising a flexible middle section having a flexibilty, the flexibility of the middle section being provided by way of laser cutting the hypotube over the middle section;   an nitinol inner hypotube installed substantially within the middle section for providing desired mechanical characteristics to the middle section;   a nitinol inner hypotube being joined at both ends to corresponding overlapped sections with proximal shaft tube and sensor housing;   the same shaft tube with the distal section cut with a different pattern for offering same rigidity as proximal section for receiving and protecting a tip pressure sensor, and providing a opening for blood pressure to communicate with pressure sensor;   a tip section connected and extending further to the sensor housing; and   a tip pressure sensor located within the sensor housing, with a communication mean routed through portion of sensor housing, and inner hypotube and shaft tube.       
 
         [0066]    Features and advantages of the subject matter hereof will become more apparent in light of the following detailed description of selected embodiments, as illustrated in the accompanying figures. As will be realized, the subject matter disclosed and claimed is capable of modifications in various respects, all without departing from the scope of the claims. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive and the full scope of the subject matter is set forth in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0067]    Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
           [0068]      FIG. 1  is a schematic diagram which illustrates partial side view of an embodiment of the pressure guidewire; 
           [0069]      FIG. 2  is a partial perspective view showing the interfacing portion between the proximal and middle sections of pressure guidewire of  FIG. 1 ; 
           [0070]      FIG. 3  is a partial perspective view showing the interfacing portion between the middle and sensor housing sections of the pressure guidewire of  FIG. 1 ; 
           [0071]      FIG. 4  is a schematic showing the profiling, in part, of the distal end of inner tube of the pressure guidewire of  FIG. 1 ; 
           [0072]      FIG. 5 . is a perspective view showing the tip section of pressure guidewire of  FIG. 1 ; 
           [0073]      FIGS. 6A and 6B  are perspective views showing the small piece fitted to join or interlock nitinol inner tube to shaft tube; and 
           [0074]      FIG. 7  is a schematic diagram showing blood vessels with a cut-out portion in which a pressure guidewire is inserted. 
       
    
    
       [0075]    It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
       DETAILED DESCRIPTION 
       [0076]    Referring now to the drawings, and more particularly to  FIGS. 1 to 6 , there is shown an embodiment of a pressure guidewire  10 . 
         [0077]    The general design for the pressure guidewire shown in  FIG. 1  herein, although it is made of fewer parts than prior art pressure guidewires, it is also made of same four sections, namely, the proximal section  12 , the middle section  14 , the sensor housing section  15  and the tip section  16 . Although, as it will become clear hereinafter, the first three sections  12 ,  14  and  15  are to some extent made of the continuity of the same shaft tube  18 , the above sections of shaft tube  18  may also be called herein after as proximal section  12 , middle section  14  and sensor housing section  15 . 
         [0078]    According to an embodiment, the proximal section  12  is made of a stainless steel hypotube, with an OD of about 0.014″ and by way of non limiting example with an ID of about 0.009″. The proximal section is used to push other more distal sections of the pressure guidewire within the vasculature. The proximal section resides within the guiding catheter at one end, with the other end exiting the patient through the introducer (not shown), therefore allowing the physician to remotely control the pressure guidewire within the blood vessel, such as pushing and torquing the wire. According to an embodiment, the length of the sensor housing  15  is in a range between 1 mm to 3.5 mm. According to an embodiment, the length of the sensor housing 15 is 2.5 mm. 
         [0079]    The middle section is the one that faces the most challenging trade-offs. The middle section  14  must not damage the vessel and hence it must be fairly flexible. It must however transmit the torque for better navigability, be stiff enough to deliver a good pushability and provide a good support for an angioplasty balloon. The middle section can be made by extending the proximal section  12  further, but it would be too stiff to navigate within the vessels. On the other hand, the middle section  14  can be softened by cutting the tube as a spiral or other cutting patterns as known by those skilled in the art. Those skilled in the art also know that such cut patterns are achieved using laser, etching and other processes. Spiral cutting the tube would result in a very soft section whether the pitch is high or low, and would not deliver any of the required tensile force and torque response. Other non continuous cut patterns can provide adequate tensile force, but the stiffness is controlled by adjusting the pitch and cut pattern. It is however difficult to provide a smooth and continuous variation of stiffness. There is also a critical safety challenges when torquing such a cut patterned guidewire as the torque induced stresses are concentrated in narrow cut regions of the guidewire, hence potentially provoking guidewire failure. 
         [0080]    Using the device described hereinafter it is possible to control safely the mechanical performance of the middle section  14  by way of a) extending the proximal section  12  further; b) cut this extended section to soften it; and c) combining this cut section with an additional inner hypotube  20  overlapping the whole cut region of middle section  14 , the inner hypotube geometry being chosen such that the desired mechanical characteristics are achieved. The middle section  14  is the continuity of the proximal section  12 , where the portion corresponding to the  27  cm middle section  14  of the shaft tube  18  is cut, such as a spiral cut shaft tubing  22  according to one embodiment. The spiral cut section of the shaft tubing  22  does not provide any significant tensile strength nor does it provide significant bending or torque strength. 
         [0081]    The inner hypotube  20  is inserted within the shaft tube  18  such that it overlaps the middle section  14 , where the tubing is cut. The outside diameter (OD) of the inner hypotube  20  fits the inside diameter (ID) of shaft tube  18  and can be of 0.009″ in an embodiment. The ID of the inner hypotube  20  must accommodates the sensor lead wire, or communication means (not shown in  FIG. 1 ), as is the case of the ID of the shaft tube  18 . Sensor communication means can be made fairly small, especially if optical fiber is used, so the inner hypotube  20  can provide the desired mechanical properties. By way of another non-limiting example, inner hypotube ID can be of 0.005″. 
         [0082]    One problem if such an inner hypotube  20  was used alone is that it may not provide adequate resistance against kinking. In the absence of the spiral cut shaft tubing overlay, or other cut pattern, a more conventional design would involve the addition of an elastomer coating to bring the outer diameter of the inner tube to a similar diameter as that of the shaft tube  18  (i.e., the stainless steel hypotube). However, this would not improve the resistance against kinking, which is a safety consideration. 
         [0083]    Another safety issue is the risk of leaving parts inside the patient as a result of joint failure between inner tube and proximal tube or sensor housing. In case of a joint failure in more conventional designs, such as the one proposed in U.S. Pat. No. 5,085,223 and Patent appl. No. U.S. 2010/0318000, the risk of leaving the distal parts of the guidewire within the blood vessel in case of joint failure is quite important. The proposed design mitigates this risk by providing a spiral cut pattern external tube that covers an inner hypotube, the inner tube providing most of the mechanical characteristics of the middle section. In case of joint failure resulting from applying a pulling force too strongly, the spiral cut tube will collapse over and grip the inner hypotube  20 , thereby bringing along the distal portion of the guidewire. 
         [0084]    The spiral cut shaft tubing  22 , when provided with an inner hypotube  20 , delivers the desired mechanical characteristics. Stiffness (flexibility), torque transfer, pushability and support are provided by the inner hypotube  20 . Inner hypotube  20  dimensions are easily adapted to provide optimal mechanical performance. On the other hand, kink resistance, distal parts safety retainer, and guidewire outside diameter continuity are provided by the spiral cut shaft tubing  22 . It is worth mentioning that kink resistance provided by the spiral cut section is useful mostly in cases where the inner hypotube is not nitinol, e.g., it is useful when inner hypotube is stainless steel. 
         [0085]    As shown by  FIG. 4 , it is also desirable to shape the outside diameter of the inner tube, especially over the last 1 to 3 cm, in order to further improve trackability. In this case, the external diameter of the distal portion of the inner hypotube  20  can be slightly grinded to taper its outer diameter  40  and hence, optimizing mechanical response. 
         [0086]    The very end  41  of the inner hypotube  20 , the portion that fits within the sensor housing section, should be enlarged, e.g., to the same diameter as its proximal section, so as to assure a good joint with the internal wall of the sensor housing section  15  (see  FIGS. 1 ,  5  and  6 ). The very end  41  of the inner hypotube being enlarged assures a better joint for at least two reasons. One is that the gap between the inner hypotube and the internal surface of the sensor housing is minimized, which in turns optimizes the shear strength of the adhesive or soldering in between the sensor housing internal diameter and outside diameter of the very end  41  of inner hypotube. Another important reason is that an enlarged portion will have a much lower internal stress. When using nitinol, the risk of reaching a stress level corresponding to the first plateau of nitinol stress to strain curve as known by those skilled in the art, is much lower. When such first plateau is reached, the strain induced within a nitinol tubing is increasing dramatically, which may provoke a delamination of the adhesive or soldering, which in turn may cause the failure of the joint. 
         [0087]    One method of joining the inner hypotube  20  to the ends of middle section  14  of shaft tube  18  is shown in  FIG. 2 . A window  32  is provided through the wall of the shaft tube  18 , where the inner hypotube  20  is to be welded. The inner hypotube  20  is slid past the window and welded to the middle section  14  using a laser beam or other suitable welding or joining means. The laser beam melts and joins together the edges of the window  32  to the inner hypotube  20  and therefore, secures the two parts together. It is also possible to use the same window  32  to apply adhesive at the joint between the inner and outer tubes. It is also possible to weld the tubes together without such window by heating the outer surface of the outer tube such that it welds to inner tube. Such heat can be generated using a laser, an electron beam or another heat source. 
         [0088]    Similar methods apply for joining the inner hypotube  20  to the other end of middle section  14 , where another window  26  ( FIG. 3 ) is provided at the distal end of middle section  14  of shaft tube  18 . According to an embodiment, the length of windows  32  and  26  is in a range between 0.2 mm to 0.5 mm. According to an embodiment, the length of windows  32  and  26  is 0.3 mm. Both ends of inner hypotube  20  extend a little further past the position of windows  26  and  32 . 
         [0089]    Without the presence of an inner hypotube  20  within the cut middle section  14 , blood may leak inside the shaft tube  18 , which constitutes a fairly large volume, which in turn may cause biocompatibility issues. The presence of the inner hypotube  20  seals off the inside of the shaft tube  18  where it is cut. 
         [0090]    The sensor housing section  15  is made of the very last 2 to 3 mm of the shaft tube  18 . The spiral cut, or other cut patterns, stops some 2 to 3 mm before the end of the shaft tube  18 , where the sensor  34  (see  FIG. 3 ) is to be fitted. A sensor joining window  28  is provided to bond or to fix the sensor  34  within the sensor housing section  15 . Blood pressure is applied to sensor  34  via opening  30 . In the present description, sensor  34  comprises a pressure sensor. According to an embodiment, the length of the opening  30  is in a range between 0.2 mm to 0.5 mm. According to an embodiment, the length of the opening  30  is 0.3 mm. According to an embodiment, the diameter of the sensor joining window  28  is in a range between 0.1 mm to 0.3 mm. According to an embodiment, the diameter of the sensor joining window  28  is 0.2 mm. According to an embodiment, the pressure sensor comprises an optical pressure sensor. 
         [0091]    A radiopaque marker band  36  may be located in the sensor housing section  15  to help in localizing the pressure guidewire in the vessels. The marker band, or otherwise similar non radiopaque band, main purpose is however to allow easy assembly of the sensor within the sensor housing. It is indeed preferable to avoid the application of hard adhesive directly on sensor head. The marker band  36  can be bonded to the pressure sensor communication means (e.g., optical fiber) as a pre-assembly in an environment allowing the control of adhesive flow. The sensor  34  is secured within pressure guidewire by bonding the marker band  36 , or other non radiopaque band, to the sensor housing section  15  using sensor joining window  28 . 
         [0092]    A tip section  16  ( FIG. 5 ) is provided at the end of the sensor housing section  15 . A conventional atraumatic tip section  16  shown in  FIG. 3  can be used as there is no sensor lead wire to be passed therethrough. 
         [0093]    Having similar materials for shaft tube  18  and inner hypotube  20 , such as stainless steel, makes the above welding process fairly simple and reliable. It may however be desirable to use dissimilar materials that cannot easily be welded together. For example, it is desirable to use shaft tube  18  made of stainless steel for providing a good pushability, while it is also desirable to use nitinol for the inner hypotube  20  for its superior yield strength and lower elastic modulus. It is well known by those skilled in the art that those two materials are not easily welded together, at least not without an intermediate material. 
         [0094]    The present description also discloses a method for joining together those dissimilar materials.  FIG. 6  shows one method of joining an inner hypotube made of nitinol to a stainless steel middle section  14  hypotube. The inner hypotube  52  is slid within the shaft tube  18  to overlap the cut section, and fed through past the windows  26  and  32  (only window  26  shown in  FIGS. 6A and 6B ). A small piece  50  of nitinol that fits in the windows is machined, inserted into the window  32  to get in contact with the inner hypotube  52  once in place, and laser welded to the inner hypotube  52 , interlocking the two parts together. The small piece  50  then prevents the inner hypotube  52  from sliding within shaft tube  18 . A small amount of adhesive can also be added to eliminate any movement of the small piece  50  relative to shaft tube windows  28  and  32 . 
         [0095]    Another method of joining the above inner hypotube  52  to stainless steel shaft tube  18  is to use an intermediate material, for example nickel, that can be welded to both nitinol and stainless steel. A small piece  50  made of nickel can be laser welded to inner hypotube  52  first. A small hole in the center  51  can be provided to promote heat transfer to inner hypotube  52 . The inner hypotube  52  is then interlocked to proximal section  12  as described above. The edges of the small piece  50  of nickel can then be laser welded to shaft tube  18 . In this case, no direct welding of nitinol to stainless steel occurs and therefore, no brittle interface is created. 
         [0096]    Another method involves the use of adhesive to bond the nitinol inner hypotube  20  to the stainless steel shaft tube  18 . The same parts can also be soldered together and by any other methods known by those skilled in the art. 
         [0097]    It can be appreciated that the design is made with one single uniform part, from proximal section  12  to the sensor housing section  15 , and therefore the guidewire  10  is very smooth with minimum mechanical steps. 
         [0098]    The manufacturability of this design is quite easy and very efficient as the number of parts is minimized. 
         [0099]    The mechanical properties can be optimized by varying the respective wall thicknesses of inner hypotube  20  and shaft tube  18 . 
         [0100]    The pitch of the spiral cut or other laser cut pattern can be varied ideally from a larger pitch to a shorter one when approaching the sensor housing section  15 . Sharp turns are expected to arise in the region of the sensor housing section  15 , near the tip of the guidewire  10  and therefore, it would be best if the pitch of the laser cut pattern was reduced near the sensor housing section  15  to allow a smoother bending of the cut shaft tubing  22 . 
         [0101]    For improved safety, the spiral cut pattern provides a retainer for distal portions of guidewire. Risks of leaving parts inside patient body are therefore minimized. 
         [0102]    There will be an optical connector (not shown) at the very proximal end of the guidewire  10 . 
         [0103]    As known by those skilled in the art, above described pressure guidewire can be coated with different material such as Teflon or hydrophilic coating so as to reduce friction against wall of vessels and/or guiding catheter. 
         [0104]    Now referring to  FIG. 7 , there is shown blood vessels with a cut-out portion in which a pressure guidewire  10  is inserted. 
         [0105]    While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.