Abstract:
The invention relates to a sensor and guide wire assembly ( 20 ) for intravascular measurements of physiological variables in a living body, comprising a core wire ( 21 ) and a sensor element ( 22 ). The sensor and guide wire assembly ( 20 ) comprises further a jacket ( 25; 35; 45 ) provided with a first opening ( 26; 36; 46 ), in which at least a portion of the sensor element ( 22 ) is arranged, and a second opening ( 27; 37; 47 ), in which a portion of the core wire ( 21 ) is arranged, the first opening ( 26; 36; 46 ) and the second opening ( 27; 37; 47 ) being separated from each other.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to sensor and guide wire assemblies, in which a sensor element is mounted at the distal end of a guide wire for intravascular measurements of physiological variables in a living body, and in particular to the mounting arrangement of the sensor element.  
       BACKGROUND OF THE INVENTION  
       [0002]     Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. Re. No. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon.  
         [0003]     As is recognized in U.S. Pat. Nos. 6,112,598 and 6,167,763, which also are assigned to the present assignee, a potential problem with this kind of guide wire mounted sensor is the occurrence of so-called bending artefacts. A bending artefact is a change in the output signal from the sensor that is induced by a bending of the guide wire, rather than being induced by a change in the physical environment surrounding the sensor. For a sensor and guide wire assembly like the one disclosed in U.S. Pat. Re. No. 35,648, this means that when the guide wire is bent, the bending of the guide wire imposes a strain on the sensor element, which thereby is deflected or stretched (or contracted). The deflection of the sensor element is then transferred to a deformation of the pressure sensitive device; and, according to well-known principles, the output from the Wheatstone bridge will thereby be affected by the bending of the guide wire.  
         [0004]     According to U.S. Pat. Nos. 6,112,598 and 6,167,763, a solution to this problem is to mount the sensor element in a cantilevering fashion such that the pressure sensitive end of the sensor element does not contact any structure other than its mount. These two patents disclose several embodiments with different ways of mounting the sensor element such that bending forces are not exerted on the pressure sensitive end of the sensor element. A common feature of these embodiments is that an elongated, essentially rectangular sensor chip is mounted in a recess in the core wire in such a way that the proximal end of the chip is attached to the core wire, while the distal end of the sensor chip protrudes into the recess such that a clearance is provided below the distal portion of the chip where the pressure sensitive device (e.g. a membrane) is provided.  
         [0005]     In the U.S. patent application Ser. No. 10/611,661, which is assigned to the present assignee, a clearance is also provided below the distal portion of the sensor chip, but here the chip has been provided with an extra mounting base, which at a proximal portion of the sensor chip protrudes downwards for mounting to the core wire and which thereby creates a clearance below a distal portion of the chip.  
         [0006]     A principally different solution to the bending artefact problem is presented in the U.S. patent application Ser. No. 10/622,136, which also is assigned to the present assignee. Here the sensor chip is provided with a recess, which will act as a hinge or articulation when the core wire is bent. By the provision of this articulated portion, the pressure sensitive portion of the sensor element is not constrained to adapt to bending deformations of the core wire, which prevents such deformations from being transferred to the pressure sensitive device.  
         [0007]     The entire contents of all of the above-described documents are incorporated herein by reference.  
         [0008]     Although sensor and guide wire assemblies provided with sensor chips designed and mounted according to the different teachings of the above-listed documents in practise have proven to work well, the design of a sensor and guide wire assembly can be improved, not least from a manufacturing point of view.  
       SUMMARY OF THE INVENTION  
       [0009]     A sensor element of a sensor and guide wire assembly comprises an elongated, essentially rectangular chip with a pressure sensitive member in the form of a membrane made from polysilicon provided thereon. This sensor chip is arranged in a short tube, also referred to as a jacket or sleeve. According to the prior art, the jacket is hollow and accommodates besides the sensor chip also a portion of a core wire and at least one electrical lead connected to the pressure sensitive member. In order to protect and fixate the sensor element and the core wire inside the jacket, the jacket can also be filled with a suitable material such as silicone.  
         [0010]     An object of the present invention is to provide a new and improved design for a jacket or sleeve, which is a member of a sensor and guide wire assembly, in such a way that, when a sensor chip is mounted in the jacket or sleeve, the sensor and guide wire assembly will have the same or better characteristics regarding resistance against bending artefacts. Preferably, the sensor and guide wire assembly should at the same time be easier and thereby cheaper to manufacture.  
         [0011]     These objects are achieved with a sensor chip and a sensor and guide wire assembly according to the present invention.  
         [0012]     According to the invention, a sensor and guide wire assembly comprises a sensor element in the form of a generally rectangular and rather thin sensor chip having a pressure sensitive device provided thereon. The pressure sensitive device can be in the form of a membrane, which covers a small recess in the upper side at a first end of the sensor chip and which has piezoresistive elements mounted thereon. The sensor element is disposed in a first separate longitudinal opening or hole in a jacket or sleeve. The jacket or sleeve comprises further a second separate longitudinal opening or hole, in which a portion of a core wire is accommodated.  
         [0013]     By arranging the sensor chip and the core wire in separate compartments in a jacket, the sensor chip is virtually independent of movements of the core wire; and in particular bending deformations of the core wire will not be transferred to the sensor chip. By this arrangement, it is not necessary to provide the core wire with a special mounting structure, such as a recess or a flattened portion. In comparison with sensor and guide wire assemblies according to the prior art, this arrangement allows the manufacturing of a sensor and guide wire assembly to be made simpler and cheaper.  
         [0014]     In a first embodiment of a jacket according to the present invention, the longitudinal opening for accommodating a sensor chip is cylindrical, whereas the longitudinal opening has been given a rectangular cross-section in a second embodiment of the invention. In a third embodiment, separate openings for respectively the sensor chip and the core wire have been accomplished by a partition wall that divides the interior of a jacket into two semi-circular compartments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  illustrates schematically the general design of a sensor and guide wire assembly according to the prior art.  
         [0016]      FIG. 2  illustrates an example of a mounting arrangement for the sensor element of the sensor and guide wire assembly shown in  FIG. 1 .  
         [0017]      FIG. 3  illustrates a portion of a sensor and guide wire assembly comprising a jacket according to the present invention.  
         [0018]      FIG. 4  shows the cross-section of the jacket of  FIG. 3 .  
         [0019]      FIG. 5  shows the cross-section of a second embodiment of a jacket according to the present invention.  
         [0020]      FIG. 6  shows the cross-section of a third embodiment of a jacket according to the present invention.  
         [0021]      FIG. 7  is a perspective view of a fourth embodiment of a jacket according to the present invention.  
         [0022]      FIG. 8  is a cross-section of the fourth embodiment of a jacket according to the invention.  
         [0023]      FIG. 9  is a perspective view of a fifth embodiment of a jacket according to the present invention.  
         [0024]      FIG. 10  is a cross-section of a sixth embodiment of a jacket according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     For better understanding of the context in which the present invention is going to be used, a sensor and guide wire assembly  1  of a conventional design is illustrated in  FIG. 1 . The sensor guide  1  comprises a hollow tube  2 , a core wire  3 , a first coil  4 , a second coil  5 , a jacket or sleeve  6 , a dome-shaped tip  7 , a sensor element or chip  8 , and one or several electrical leads  9 . The proximal end of the first coil  4  is attached to the distal end of the hollow tube  2 , while the distal end of the first coil  4  is attached to the proximal end of the jacket  6 . The proximal end of the second coil  5  is connected to the distal end of the jacket  6 , and the dome-shaped tip  7  is attached to the distal end of the second coil  5 . The core wire  3  is at least partly disposed inside the hollow tube  2  such that the distal portion of the core wire  3  extends out of the hollow tube  2  and into the second coil  5 . The sensor element  8  is mounted on the core wire  3  at the position of the jacket  6 , and is through the electrical leads  9  connected to an electronic unit (not shown in the figure). The sensor element  8  comprises a pressure sensitive device in the form of a membrane  10  (not visible in the figure), which through an aperture  11  in the jacket  6  is in contact with a medium, such as blood, surrounding the distal portion of the sensor guide  1 .  
         [0026]     Although not shown in the figure, the sensor element  8  further comprises an electrical circuitry, which in a Wheatstone bridge-type of arrangement is connected to one or several piezoresistive elements provided on the membrane  10 . As is well known in the art, a certain pressure exerted on the membrane  10  from the surrounding medium will thereby correspond to a certain stretching of the membrane  10  and thereby to a certain resistance of the piezoresistive elements mounted thereon and, in turn, to a certain output from the sensor element  8 . It should therefore be clear that it is highly preferable that this output from the sensor element  8  does not change due to factors that are not related to a real change in the physical properties of the surrounding medium. As was mentioned above, one such factor is so-called bending artefacts, the source of which is that a bending of the sensor guide  1  is transferred to a deformation of the membrane  10 . Here, the discussion above about piezoresistive elements coupled in a Wheatstone bridge-type of arrangement should only be seen as an illustrative exemplification; in short, the basic problem is that a pressure sensitive device, such as a membrane, can be influenced by a bending of a sensor guide.  
         [0027]     To remedy the potentially adverse effects from bending artefacts, several different ways of mounting a sensor element are disclosed in U.S. Pat. Nos. 6,112,598 and 6,167,763, and in  FIG. 2  one of these mounting arrangements is shown.  FIG. 2  illustrates how the sensor chip  8 , whose distal portion is provided with the membrane  10 , is mounted on the core wire  3 . The core wire  3  has been provided with a recess  12  that consists of two portions, a first portion having the purpose of a mounting shelf  13  for receiving the proximal portion of the chip  8  and a second portion  14 , which is deeper than the first portion to allow the distal portion of the sensor chip  8  to protrude freely. The sensor chip  8  is thereby mounted in a cantilevering fashion, without the pressure sensitive distal end of the sensor chip  8  being in contact with any rigid structure. In this known design of a sensor guide, the sensor element  8  is disposed inside the jacket  6 , and is through the electrical leads  9  in contact with an electronic unit (not shown in the figure).  
         [0028]     For the mounting arrangement shown in  FIG. 2 , as well as for the other mounting arrangements according to the prior art, it is the design of the sensor chip or the mounting arrangement, and in particular the design of the core wire, that provides the desired resistance against bending artefacts, while the jacket accommodating the sensor chip and the core wire in all cases has the same tubular shape. In contrast,  FIG. 3  shows a portion of a sensor and guide wire assembly  20  according to the present invention. The sensor guide  20  comprises a core wire  21  and a sensor chip  22 . A distal portion of the sensor chip  22  is provided with a pressure sensitive device in the form of a membrane  23 , and a proximal portion of the sensor chip  22  is through at least one electrical lead  24  in contact with an electronic unit (not shown in the figure). The core wire  21  and the sensor chip  22  are arranged inside a jacket or sleeve  25 , which—as is best seen in  FIG. 4 —comprises a first through hole or opening  26  and a second through hole or opening  27 . The jacket  25  is made of a relatively rigid material such as stainless steel, as opposed to flexible material such as rubber. As is conventional in the art and like all embodiments to be described below, an aperture  28  is provided in the mantle wall of the jacket or sleeve  25 . The pressure sensitive device  23  is through this aperture  28  in contact with the medium (e.g. blood) surrounding this portion of the sensor and guide wire assembly  20 .  
         [0029]     The jacket  25  is typically a few millimeters long. In some applications, the aperture  28  may be covered with a thin or highly flexible membrane (not shown).  
         [0030]     At its proximal end the jacket  25  ends in a portion  29  having a smaller diameter than the main body of the jacket  25 . This end portion  29  serves as a connection piece, to which a proximal coil  30  has been attached. A similar end portion or connection piece  31 , having a smaller diameter than the main body of the jacket  25 , is provided at the distal end of the jacket  25 , and is adapted for attachment to a distal coil  32 . The connection pieces  29 ,  31  are not crucial for the present invention, but since the jacket  25 —because of the off-centre positioning of the second opening  27  in the jacket  25 —is not coaxially arranged around the core wire  21 , the connection pieces  29 ,  31  will ensure that the jacket  25  is centred with respect to the proximal and distal coils  30 ,  32 , something that usually is advantageous.  
         [0031]     During manufacturing of the sensor and guide wire  20  according to the present invention, the sensor chip  22  is positioned inside the first through hole  26 , while the core wire  21  is threaded through the second through hole  27 . The sensor can be fixated in the first hole  26  by means of, for example, gluing or soldering to the upper side of the jacket, or by filling the first through hole  26  with a suitable material such as silicone. The sensor chip  22  is thus not attached to the core wire  21  and does not touch the core wire  21 . Likewise, the jacket or sleeve  25  can be attached to the core wire  21  by means of, for example, gluing or soldering, or by filling the second through hole  27  with a suitable material such as silicone. The dimensions of the openings  26 ,  27  in the jacket  25  can, however, also be closely adapted to the dimensions of the sensor chip  22  and the core wire  21 , respectively, so that no extra measures have to be taken to fixate the sensor chip  22  and/or core wire  21 .  
         [0032]     By arranging the sensor chip  22  in a first through hole  26  and the core wire  21  in a second through hole  27 , the sensor chip  22  is virtually independent of movements of the core wire  21 ; and in particular bending deformations of the core wire  21  will not be transferred to the sensor chip  22  and to the membrane  23 .  
         [0033]     As was indicated above, the shape of a through opening in a jacket or sleeve can according to the present invention be adapted to the shape of the member to be positioned therein.  FIG. 5  illustrates a second embodiment of a sleeve or jacket  35 , in which two through openings  36 ,  37  have been created. Here the first through opening  36  has been given a rectangular cross-section, which is adapted to a rectangular cross-section of a sensor chip (not shown in the figure). Like the embodiment shown in  FIG. 4 , the second through opening  37  has been given a circular cross-section in order to fit to a circular cross-section of a core wire (not shown in the figure), but other cross-section configurations are also possible. A rectangular cross-section, adapted to a core wire having a corresponding cross-section, could, for example, be advantageous in that it would prevent the core wire from rotating inside the jacket.  
         [0034]     The through openings shown in  FIGS. 4 and 5  are preferably made by drilling, punching or cutting holes in an otherwise solid cylindrical member, which can be made from any suitable material such as metal, plastic or ceramic. Another way of forming separate openings for a core wire and a sensor chip is illustrated in  FIG. 6 . Here a jacket or sleeve  45  comprises a first through opening  46 , which is intended for accommodating a sensor chip (not shown in the figure), in the form of a semi-circular compartment and a second through opening  47 , which is intended for accommodating a core wire (not shown in the figure), also in the form of a semi-circular compartment. The first and second through openings  46 ,  47  are separated by a partition wall  45 a. In addition to the manufacturing techniques mentioned above, other ways of manufacturing a jacket or sleeve having two separate through holes may hereby be considered. For example, the jacket shown in  FIG. 6  can be manufactured by providing a partition wall inside a hollow tubular member. The partition wall could then be glued or soldered to the inner wall of the tubular member  45 . Furthermore, the interior of the tubular member could be divided into two separate compartments having different dimensions, such that each compartment would have a cross-section in the shape of the letter D, but where the two compartments would have different lengths of the straight portions. Like for the two previous embodiments, the space not occupied by the core wire or by the sensor chip could be filled with a suitable material, such as silicone. For example, the space for the sensor chip can be at least partially filled with an elastic compound such that the sensor chip or element floats in the elastic compound, to provide further protection from bending stress.  
         [0035]      FIGS. 7 and 8  illustrate a jacket  55  according to a fourth embodiment of the present invention. This embodiment also includes an aperture  58  through which pressure may be sensed. This embodiment includes two crimps  57   a  and  57   b  in order to retain the core wire (not shown) in the lower portion of the jacket  55 . Crimps  57   a  and  57   b  include members  55   a  and  55   b,  respectively, which protrude from the inner surface of the jacket into the central portion of the jacket in order to retain the core wire (not shown) in a location separate from the location of the sensor chip (not shown).  
         [0036]      FIG. 9  illustrates a jacket  65  according to a fifth embodiment of the present invention. This embodiment is a variation of the embodiment shown in  FIGS. 7 and 8  and includes a crimp  67   a  at an end portion of the jacket  65 . This embodiment also includes a member  65   a  which protrudes from an inner surface of the jacket toward a central portion of the jacket to retain the core wire (not shown) separate from the sensor chip (not shown).  
         [0037]      FIG. 10  illustrates a jacket  65 ′ according to a sixth embodiment of the present invention. In this embodiment  65 ′, two members  65   aa  and  65   bb  protrude from an inner surface of the jacket toward a central portion of the jacket to retain the core wire (not shown) separate from the sensor chip (not shown). These two members are separated by a gap  65   ac.  It should be noted that the embodiments of FIGS.  3  to  6  are similar to the embodiments of FIGS.  7  to  10  in that the embodiments of FIGS.  3  to  6  also include at least one member  25   a,    35   a,  and  45   a  which protrudes from an inner surface of the jacket toward a central portion of the jacket to retain the core wire (not shown) separate from the sensor chip (not shown).  
         [0038]     Before ending the description of preferred embodiments of the present invention it should be mentioned that the two separate openings in a jacket (sleeve or tubular member), which have been described and illustrated as passing all the way through the sleeve (sometimes called through-and-through openings) actually could be closed at least one end. In particular for the sensor chip it is conceivable that the first opening on the distal side (the left hand side in  FIG. 3 ) ends in a closed wall, so that the sensor chip only can be contacted from the proximal side. It is also possible to arrange the sensor chip in such a way that it is not completely enclosed by the jacket, e.g., by having a jacket whose length is shorter than the length of the sensor chip.  
         [0039]     For the invention, the important feature is that a sensor chip is arranged within a first opening (which also could be referred to as a hole, compartment or cavity) in a jacket (sleeve or tube), and that a core wire is disposed within a second opening (which also could be referred to as a hole, compartment or cavity) in the jacket, such that the first and second openings are completely separated from each other (as in the embodiments shown in  FIGS. 4-6 ), or such that the first and second openings are partially separated from each other in such a way that the sensor chip is separated from the core wire (as in the embodiments shown in  FIGS. 7-10 ). With this arrangement, the sensor chip is essentially independent of movements of the core wire; and in particular bending deformations of the core wire will not be transferred to the sensor chip.  
         [0040]     Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below. It should in particular be noted that the improved characteristics of a sensor guide provided with a jacket according to the invention are not dependent on the design of the other parts of the sensor guide. For example, the core wire, to which the jacket is attached, may extend along essentially all the length of the sensor guide, or the core wire may only be provided at the distal portion of the sensor guide.