PATENT ABSTRACT
An intravascular imaging guidewire which can accomplish longitudinal translation of an imaging plane allowing imaging, by acoustic or light energy, of an axial length of a region of interest without moving the guidewire. The imaging guidewire comprises a body in the form of a flexible elongate tubular member. An elongate flexible imaging core is slidably received within the body. The imaging core includes a shaft having an imaging device mounted on its distal end. The body and the imaging core are cooperatively constructed to enable axial translation of the imaging core and imaging device relative to the body. The body has a transparent distal portion extending an axial length over which axially translatable imaging may be performed. The imaging guidewire has a maximum diameter over its entire length sized to be received within a guidewire lumen of an intravascular catheter.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 09/162,090, filed Sep. 28, 1998, which is a continuation-in-part of U.S. patent application Ser. No. 08/939,315, filed on Sep. 29, 1997 (now U.S. Pat. No. 6,078,831 issued Jun. 20, 2000), which are hereby incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to an intravascular imaging guidewire system and to methods for use and manufacture thereof, and more specifically to an imaging guidewire which can be used to receive a therapeutic catheter having a guide lumen to direct the catheter to a desired position within a vessel of a body.  
         BACKGROUND OF THE INVENTION  
         [0003]    Intraluminal, intracavity, intravascular, and intracardiac treatment and diagnosis of medical conditions utilizing minimally invasive procedures is an effective tool in many areas of medical practice. These procedures are typically performed using imaging and treatment catheters that are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated, such as the femoral artery. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which is used to locate and diagnose a diseased portion of the body, such as a stenosed region of an artery. The catheter may also be provided with a therapeutic device, such as those used for performing interventional techniques including balloon angioplasty, laser ablation, atherectomy and the like. Catheters also are commonly used for the placement of grafts, stents, stent-grafts, etc., for opening up and/or preventing closure of diseased or damaged vessels.  
           [0004]    Catheters having ultrasound imaging and/or therapeutic capabilities are generally known. For example, U.S. Pat. No. 5,313,949, issued to Yock, the disclosure of which is incorporated herein by reference, describes an intravascular ultrasound imaging catheter having an atherectomy cutting device. Generally speaking, there are two predominant techniques used to position the therapeutic catheter at the region of interest within the body. The first technique simply involves directly inserting the catheter into a vessel and advancing the catheter through the branches of the vascular system by pushing and steering the catheter to enter a desired branch as the catheter is moved forward. The use of this technique typically requires that the catheter be equipped with an extremely flexible guidewire at its distal tip that can be aimed in different directions by rotating the catheter or by actuating a steering mechanism.  
           [0005]    The second technique utilizes a separate guidewire that is first positioned within the vascular system such that a distal end of the guidewire extends beyond the region of interest. The guidewire is routed into position by inserting it into a vessel and advancing it through the vascular system by pushing and steering the guidewire similar to the method previously described for a catheter. The catheter being inserted includes a guidewire lumen that is sized to receive the guidewire. The guidewire lumen may extend the entire length of the catheter, or alternatively, the guidewire lumen may be a short length lumen disposed at the distal end of the catheter. Once the guidewire is in place, the therapeutic and/or imaging catheter is routed over the guidewire to the region of interest while holding the guidewire fixed in place.  
           [0006]    The use of a guidewire provides several advantages. Routing a catheter or guidewire through a circuitous path of the complex network of blood vessels to a region of interest can be a tedious and time consuming task. Placement of the guidewire is made even more difficult with increasing vessel occlusion that may occur in the later stages of vascular disease. In addition, many catheter procedures require the use of several different catheters. For instance, an imaging catheter may be initially inserted to precisely locate and diagnose a diseased region. Then, the imaging catheter may be removed and a therapeutic catheter, such as an balloon angioplasty catheter, may be inserted. Additional therapeutic or imaging catheters may be employed as necessary. Accordingly the successive insertion and removal of each of these catheters, called catheter “exchanges,” is required because there is only enough space within the vessels to rout a single catheter at a time. Hence, with the use of a guidewire, the tedious and time-consuming task of routing a device to the region of interest need only be done once. Then, the much easier procedure of routing catheters over the guidewire to the region of interest may be performed as many times as the desired therapy dictates.  
           [0007]    In order to locate the site of interest and facilitate proper placement of the guidewire, and further to observe the site during and after treatment, a guidewire may include an imaging device, commonly a rotating ultrasonic imaging transducer or a phased-array ultrasound transducer. Providing the guidewire with imaging capability may eliminate the need for insertion of an imaging catheter or imaging capabilities in the therapeutic catheters. Hence, an imaging guidewire can reduce the number of catheter exchanges that a physician must do during a surgical procedure.  
           [0008]    Imaging guidewires have been disclosed generally as, for example, in U.S. Pat. No. 5,095,911, issued to Pomeranz, the disclosure of which is incorporated herein by reference. The imaging guidewire disclosed in Pomeranz includes an elongate, flexible body. A housing enclosing a rotating transducer is secured to the distal end of the body. A drive shaft extends through a lumen of the body and is coupled to the transducer. In order to image a different region of interest, the entire guidewire is moved back and forth to position the housing and transducer adjacent the region.  
           [0009]    However, once the physician has carefully placed the imaging guidewire, it is preferable to maintain the guidewire in a fixed position so as not to lose the correct placement of the guidewire. At the same time, it is often desirable to obtain images along an axial length of diseased area. This currently requires axial translation of the imaging device by axially translating the entire guidewire. The problem with advancing and pulling back the imaging guidewire is that the correct placement of the guidewire may be lost and the physician must then spend more time repositioning the guidewire.  
           [0010]    Furthermore, there are significant technical obstacles in producing an imaging guidewire having a sufficiently small diameter to fit within a guidewire lumen of a catheter while at the same time exhibiting the necessary mechanical and electrical characteristics required for placement in the vascular system and generation of high quality images. For instance, on typical catheters sized to be inserted in the smaller coronary vessels, the guidewire lumen preferably is sized to receive a guidewire having a maximum diameter of 0.014″. However, where larger vessels, such as peripheral vessels, are to be imaged, the guidewire lumen may be sized to receive a guidewire having, for example, a maximum diameter of 0.035″. In addition, the guidewire preferably has sufficient flexibility to traverse a tortous path through the vascular system, and also has sufficient column strength, or pushability, to transmit a pushing force from a remote proximal end of the guidewire, along a winding path, to the distal end thereof.  
           [0011]    Moreover, if a rotating transducer is utilized, the drive shaft extending to the transducer should have stable torsional transmittance in order to achieve high quality images. Hence, the drive shaft should not only be flexible, but also should be torsionally stiff to limit angular deflection and nonuniform angular velocity that can cause image distortion. The drive shaft also should be mechanically and electrically connectable to a drive unit and to transducer signal processing electronics. The connection preferably is easily disconnectable so that a guidewire lumen of a catheter may be threaded over the proximal end of the guidewire. This requirement also limits the size of the connector on the drive shaft because the connector must also fit through the guidewire lumen. The drive shaft and connector also should provide a high quality transmission of imaging signals between the imaging device and the signal processing equipment.  
           [0012]    Therefore, a need exists for an improved imaging guidewire that overcomes the aforementioned obstacles and deficiencies of currently available guidewires.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention provides an intravascular imaging guidewire, and methods of use and manufacture, which can accomplish longitudinal translation of an imaging plane allowing imaging of an axial length of a region of interest without moving the guidewire thereby maintaining proper positioning of the guidewire to effectively facilitate the introduction of catheters over the guidewire to the proper position. The imaging guidewire disconnectably mates to a drive unit. The drive unit acts as an interface and connects to signal processing equipment which comprises electronics to transmit, receive and process imaging signals to and from the imaging guidewire.  
           [0014]    Accordingly, the imaging guidewire of the present invention comprises a body in the form of a flexible, elongate tubular member. An elongate, flexible imaging core is preferably slidably and rotatably received within the body. Rotation and longitudinal translation of the imaging core is preferred in order to provide a 360° scan, but it is contemplated in the present invention that the imaging core may also be non-rotating, for example an imaging core having a phased-array ultrasound transducer.  
           [0015]    The imaging core includes a rotatable drive shaft having an imaging device mounted on its distal end. The imaging device produces an imaging signal that can be processed by the signal processing equipment to create an image of the feature at which the imaging device is directed. An electrical cable runs through the center of the drive shaft extending from the imaging device at the distal end to a connector attached to the proximal end of the drive shaft. The connector detachably connects the driveshaft to a drive unit and electrically connects the electrical cable to the drive unit and in turn to the signal processing equipment. At least a distal portion of the body through which the imaging device images preferably is substantially transparent to imaging signals received by the imaging device. The transparent portion of the body preferably extends for at least an axial length over which imaging typically will be desirable.  
           [0016]    The body and the imaging core are cooperatively constructed to enable axial translation of the imaging core and imaging device relative to the body. This allows imaging along an axial length of a diseased region in the patient&#39;s body without moving the guidewire body.  
           [0017]    As described above, the imaging guidewire connects to a drive unit. The principle function of the drive unit is to provide an interface between the imaging guidewire and the signal processing equipment. The drive unit, therefore, transmits the imaging signal between the imaging guidewire and the signal processing equipment. In a further aspect of the present invention, in the preferred embodiment comprising a rotating transducer, the drive unit has a motor to rotate the imaging core for providing a 360° scan. In an alternative embodiment, the motor for rotating the imaging core may be part of the signal processing equipment. In this case, the drive unit simply has a drive shaft that is detachably coupled to the motor of the signal processing equipment.  
           [0018]    In a further aspect, a coupling device, such as a slip ring assembly or an innovative inductive or capacitive coupling in accordance with one aspect of the present invention, may be provided in the drive unit or within an associated adapter to transmit the imaging signals from the rotating electrical cable within the guidewire drive shaft to the non-rotating electronics within the drive unit. In an alternative embodiment having the motor in the signal processing equipment, the coupling device may be contained in the signal processing equipment.  
           [0019]    In a particularly innovative alternative embodiment, the connector on the proximal end of the drive shaft is adapted to provide only a mechanical connection to the mating connector on the drive unit or adapter. For a rotating imaging core, the mechanical connection transmits torque from the drive unit or adapter to the imaging core. In this embodiment, the imaging signal is transmitted from the imaging guidewire connector to the drive unit or adapter via a capacitive coupling or inductive coupling. One element of the coupling is disposed on the draft shaft and rotates with the drive shaft. The other element of the coupling is mounted in the drive unit or adapter and may be rotating or non-rotating.  
           [0020]    As is suggested above, in an additional aspect of the present invention, an adapter may be utilized which performs the function of providing an interface between the imaging guidewire and the drive unit. The adapter comprises a connector which mates to the imaging guidewire connector. The imaging guidewire connector plugs into the adapter which in turn mounts into the drive unit. In the preferred embodiment, the adapter makes both the mechanical and the electrical connections to the imaging guidewire. Furthermore, the coupling device of the drive unit may be contained in the adapter instead. In this way, the coupling device transmits the imaging signals from the rotating electrical cable within the guidewire drive shaft to non-rotating electronics within the adapter. Mounting the adapter into the drive unit electrically connects the adapter to the drive unit, for example via mating electrical connectors.  
           [0021]    In the preferred method of using the imaging guidewire of present invention, the imaging guidewire is first inserted percutaneously into a vessel of the vascular system, usually at a site remote from the site of interest within the body. The imaging guidewire is routed to the region of interest by advancing it through the branches of the vascular system by pushing and steering the guidewire as the guidewire is fed into the vessel. The imaging device may be activated during this process to aid in routing the guidewire and locating a diseased region of the body. The imaging guidewire is positioned such that the distal end extends beyond the diseased region with the transparent portion of the body approximately centered at the region of interest.  
           [0022]    Alternatively, a standard guidewire may first be inserted and routed to the region of interest. Then, a catheter having a full-length guidewire lumen is fully inserted over the standard guidewire. The standard guidewire is then removed and the imaging guidewire is inserted through the guidewire lumen to the desired position.  
           [0023]    At this point, in order to image the length of the diseased region, the imaging device may be axially translated forward and back relative to the body which is preferably fixed in place.  
           [0024]    Once the medical condition has been diagnosed and a treatment is chosen, a therapeutic catheter having a guidewire lumen, or a series of therapeutic catheters, may be routed over the guidewire to the diseased region to perform the desired treatment. To facilitate the catheter exchanges over the guidewire, the imaging guidewire is disconnected from the drive unit by simply disconnecting the guidewire connector from the drive unit. Once the exchange is complete, the imaging guidewire is reconnected to the drive unit. The imaging device on the guidewire may further be used to monitor the treatment while it is being performed and/or to observe the treated area after the treatment is completed. Alternatively, if the imaging device cannot image through the therapeutic catheter, the catheter may be pulled back to expose the imaging device.  
           [0025]    Accordingly, it is an object of the present invention to provide an improved imaging guidewire and method of using the same.  
           [0026]    A further object of the present invention is to provide an improved imaging guidewire that can image along an axial length of a region of interest while maintaining a fixed guidewire position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is a schematic diagram of an intravascular imaging guidewire system in accordance with the present invention.  
         [0028]    [0028]FIG. 1(A) is a partial cross-sectional view of an imaging guidewire in accordance with the present invention.  
         [0029]    [0029]FIG. 1(B) is a partial cross-sectional view of an imaging core in accordance with the present invention.  
         [0030]    [0030]FIG. 1(C) is a cross-sectional view of an imaging device that may be coupled to an imaging core in accordance with the present invention.  
         [0031]    [0031]FIG. 2 is an expanded cross-sectional view of the proximal region of the imaging guidewire as designated in FIG. 1(A).  
         [0032]    [0032]FIG. 2(A) is a cross-sectional view of a mating connector that may be used with the imaging guidewire connector shown in FIG. 2.  
         [0033]    [0033]FIG. 2(B) is a partial view of an imaging core having another imaging guidewire connector.  
         [0034]    [0034]FIG. 2(C) is a partial view of an imaging core having still another imaging guidewire connector.  
         [0035]    [0035]FIG. 2(D) is a schematic view of a connector that may mate with the connectors shown in FIGS.  2 (B) and  2 (C).  
         [0036]    [0036]FIG. 2(E) is a schematic view of another connector that may mate with the connectors shown in FIGS.  2 (B) and  2 (C).  
         [0037]    [0037]FIG. 2(F) is a circuit schematic illustrating a capacitive coupling in accordance with the present invention.  
         [0038]    [0038]FIG. 2(G) is a cross-sectional view of a portion of a capacitive coupling in accordance with the present invention.  
         [0039]    [0039]FIG. 2(H) is an enlarged cross-sectional view of a female portion of the capacitive coupling shown in FIG. 2(G).  
         [0040]    [0040]FIG. 2(I) is an enlarged cross-sectional view of a male portion of the capacitive coupling shown in FIG. 2(G).  
         [0041]    [0041]FIG. 2(J) is an illustration of a preferred type of electrode contact that may be used within a capacitive coupling in accordance with the present invention.  
         [0042]    [0042]FIG. 2(K) is an illustration of another preferred type of electrode contact that may be used within a capacitive coupling in accordance with the present invention.  
         [0043]    [0043]FIG. 2(L) is an electrical schematic of an inductive coupling that may be used in accordance with the present invention.  
         [0044]    [0044]FIG. 2(M) is an illustration of the inductive coupling shown in FIG. 2(L).  
         [0045]    [0045]FIG. 2(N) is an illustration of a female portion of the inductive coupling shown in FIG. 2(M).  
         [0046]    [0046]FIG. 2(O) is an illustration of a male portion of the inductive coupling shown in FIG. 2(M).  
         [0047]    [0047]FIG. 3 is an expanded cross-sectional view of the region as designated in FIG. 1.  
         [0048]    [0048]FIG. 4 is a partial cross-sectional view of an alternative imaging guidewire in accordance with the present invention.  
         [0049]    [0049]FIG. 5 is an expanded cross-sectional view of the region as designated in FIG. 4.  
         [0050]    [0050]FIG. 6 is a partial cross-sectional view of another alternative imaging guidewire in accordance with the present invention.  
         [0051]    [0051]FIG. 7 is an expanded cross-sectional view of the region as designated in FIG. 6.  
         [0052]    [0052]FIG. 8 is a partial cross-sectional view of another alternative imaging guidewire in accordance with the present invention.  
         [0053]    [0053]FIG. 9 is an expanded cross-sectional view of the region as designated in FIG. 8.  
         [0054]    [0054]FIG. 10 is a partial cross-sectional view of yet another alternative imaging guidewire in accordance with the present invention.  
         [0055]    [0055]FIG. 11 is an expanded cross-sectional view of the region as designated in FIG. 10.  
         [0056]    [0056]FIG. 12 is a partial cross-sectional view of still another alternative imaging guidewire in accordance with the present invention.  
         [0057]    [0057]FIG. 13 is an expanded cross-sectional view of the region as designated in FIG. 12.  
         [0058]    [0058]FIG. 14 is a partial cross-sectional view of another alternative imaging guidewire in accordance with the present invention.  
         [0059]    [0059]FIG. 15 is an expanded cross-sectional view of the region as designated in FIG. 14.  
         [0060]    [0060]FIG. 16 is a cross-sectional view of still another embodiment of the imaging guidewire in accordance with the present invention.  
         [0061]    [0061]FIG. 17 is an illustration of a motor drive unit (MDU) that may be used with an imaging guidewire in accordance with the present invention.  
         [0062]    [0062]FIG. 18 is a perspective view of a telescoping adapter in accordance with the present invention.  
         [0063]    [0063]FIG. 19 is a perspective view of the telescoping adapter shown in FIG. 18 in an extended position.  
         [0064]    [0064]FIG. 20 is a cross-sectional view of the adapter of FIG. 18.  
         [0065]    [0065]FIG. 21 is a cut-away view of a collet assembly that may be used in an adapter in accordance with the present invention.  
         [0066]    [0066]FIG. 22 is a perspective view of a contact housing and stationary pawl of the collet assembly shown in FIG. 21.  
         [0067]    [0067]FIG. 23 is a perspective view of a rotary pawl and connector assembly of the collet assembly shown in FIG. 21.  
         [0068]    [0068]FIG. 24 is an illustration of an imaging core engaging mechanism used within the collet assembly shown in FIG. 21.  
         [0069]    [0069]FIG. 25 is a cut-away view of a portion of the collet assembly shown in FIG. 21.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0070]    Turning now to the drawings, FIG. 1 is a schematic diagram of an intravascular imaging guidewire system  5  in accordance with a preferred embodiment of the present invention. The system  5  comprises a imaging guidewire  10  which is adapted to be inserted into a lumen of the body and preferably within the vascular system of the body. The imaging guidewire  10  detachably connects to an adapter  150 . The adapter  150  plugs into a motor drive unit  152 . The drive unit  152  is connected to signal processing equipment  154 . Below, various exemplary embodiments of each of these subsystems of the imaging guidewire system  5  will be described with reference to the drawings. While the exemplary embodiments of the imaging guidewire system  5  that are described herein include both an adapter  150  and a separate motor drive unit  152 , it is to be understood that the functionality and essential structure of the adapter  150  may be integrated into the motor drive unit  152 , thereby eliminating the adapter  150  from the guidewire system  5 . In that case, the imaging guidewire  10  would detachably connect directly to the motor drive unit  152 .  
         [0071]    Referring to FIGS.  1 (A)- 3 , an imaging guidewire  10  is depicted according to one embodiment of the present invention. In general, the guidewire  10  preferably is flexible enough to traverse a circuitous path through the vascular system, and yet has sufficient pushability to transmit a pushing force from a remote proximal end  12  of the guidewire  10 , along a winding path, to a distal end  14  of the guidewire  10 . The imaging guidewire  10  also preferably has sufficient torsional stiffness to reliably transmit rotational force applied at the proximal end  12  to the distal end  14  so that the guidewire  10  can be steered through the branches of vessels of the vascular system. However, those skilled in the art will recognize that the required functional characteristics of the guidewire  10  will vary from application to application. Thus, while the above-described functional characteristics are presently preferred, such characteristics need not be inherent in all embodiments of a guidewire in accordance with the present invention.  
         [0072]    The imaging guidewire  10  comprises a guidewire body  16  in the form of a flexible, elongate tubular member that slidably and rotatably houses an elongate, flexible, rotating imaging core  18 . The imaging guidewire  10  has a substantially uniform diameter and no component along the entire length of the guidewire  10  exceeds a predetermined diameter. This maximum diameter is preferably 0.035″ because guidewire lumens of typical catheters sized to be inserted into peripheral vessels are sized to receive a guidewire having a maximum diameter of 0.035″. The overall length of the guidewire  10  varies depending on the intended application but may preferably range between 40 cm and 300 cm.  
         [0073]    The guidewire body  16  includes a main body  20  having a proximal end  22  and a distal end  24 . The main body  20  extends from a connector  40  of the imaging core  18  at its proximal end  22  to a predetermined distance, preferably approximately 15 to 20 cm, from the distal end  14  of the guidewire  10  at its distal end  24 . The main body  20  is preferably formed of nitinol hypotube because it exhibits strength and flexibility properties desired in a guidewire body. Nitinol is also preferred because it minimizes kinking, has a convenient transition temperature below which it transitions to a “soft” state, and is a memory metal such that it returns to its original shape after being bent under specific temperature conditions. Those skilled in the art would appreciate that other materials including other superelastic materials, other metal alloys, and plastics may also be used. It is to be understood that where nitinol is specified as the preferred material, other materials, including alternative superelastic materials, metal alloy, composite materials and plastics may also be utilized. For example, it is contemplated that the main body  20  may be formed of braided polyimide, polyethylene, peek braids, or stainless steel. The nitinol main body  20  preferably has an outer diameter of approximately 0.035″.  
         [0074]    An imaging portion  26  of the guidewire body  16  is connected to the distal end  24  of the main body  20  and extends to the distal end  14  of the guidewire body  16 . The imaging portion  26  is substantially transparent to imaging signals transmitted and/or received by an imaging device  42  of the imaging core  18 . In a preferred form, the imaging portion  26  is formed of a polyethylene plastic tube that is interference fit onto the distal end  24  of the main body  20 . Alternatively, any other suitable attachment method may be employed such as adhesives, mechanical connectors, etc. In further alternative embodiments, the imaging portion  26  may be coextruded, multi-layer, or composite. As examples, the imaging portion  26  may be polyester, nylon, polymeric strands, or metal braid with a long pitch.  
         [0075]    A floppy tip  28  preferably is placed inside, and at the distal end, of the imaging portion  26 . The floppy tip  28  is designed to prevent trauma to the aorta and to assist in maneuvering the imaging guidewire  10  through a patient&#39;s vessels. In some embodiments, the floppy tip  28  can be aimed in different directions by rotating the catheter or by actuating a steering mechanism (not shown). The floppy tip  28  is preferably formed from a flexible coil spring that is radiopaque so as to be visible under fluoroscopy. The floppy tip  28  is held in place by thermally forming the imaging portion  26  over the floppy tip  28  or alternatively using any other suitable attachment technique such as adhesives, press fit, connectors, fasteners, etc. Alternatively, the floppy tip  28  may be a coil in a polymer, a tungsten core with a polyethylene cover, or a standard guidewire tip such as those produce by Lake Region, Inc.  
         [0076]    In an alternative form, the guidewire  10  is constructed without the floppy tip  28  leaving the distal extremity greater flexibility. In this case, a radiopaque maker band is placed at the distal end of the imaging portion  26 .  
         [0077]    The imaging core  18  principally comprises a tubular drive shaft  44  having an imaging device  46  attached to a distal end of the drive shaft  44  and the connector  40  attached to a proximal end of the drive shaft  44 . The drive shaft  44  may be composed of a single tubular member (not shown), or preferably, it may be several elements attached together as shown in FIGS.  1 (A)- 2 . The drive shaft  44  is preferably formed of a nitinol tube having an outer diameter of approximately 0.022″, and in some currently preferred embodiments, such as that illustrated in FIG. 2, may include a telescoping section  48 .  
         [0078]    The telescope portion  48  acts as a telescoping extension of the drive shaft  44  and preferably is of a length approximately the same as the desired length of axial translation of the imaging device  42 , preferably around 15 cm. The telescope portion  48  is connected to the connector  40  at its proximal end (shown in FIG. 2) and extends distally to a distal end that is attached to a proximal end of a drive cable  50  (shown in FIG. 3). The drive cable  50  is preferably of a counter-wound, multi-filar coil construction as best shown in FIG. 3 and described in U.S. Pat. No. 4,951,677, to Crowley et al., the disclosure of which is incorporated herein by reference. The telescope portion  48  is attached to the drive cable  50  using a coupler  52  (shown in FIG. 3). One end of the coupler  52  is attached to the telescope portion  48  using an interference fit. The interference fit may be accomplished by cooling the nitinol telescope portion  48  below its transition temperature such that it becomes soft. The coupler  52  is then slid onto the telescope portion  48  and when warmed above the transition temperature, a secure interference fit results. The other end of the coupler  52  is attached to the drive cable  50 , preferably using an adhesive, although any suitable attachment means is contemplated. The coupler  52  also functions as a stop which interferes with a stop collar  46  (shown in FIG. 2) attached to the inside of the proximal end  22  of the main body  20  which limits the proximal axial translation of the imaging core  18  relative to the guidewire body  16 . The stop collar  46  may also be interference fit into the nitinol main body  20  using the same method just described for attaching the coupler  52  to the telescope portion  48 .  
         [0079]    The imaging device  42  is attached to the distal end of the drive cable  50 , as is shown in FIGS.  1 (A)- 1 (C). The imaging device  42  may be any type device that creates a high quality imaging signal of the body tissue to be imaged, but is preferably an ultrasound imaging device. The imaging device  42  includes a housing  54  into which an ultrasound transducer  56  is mounted. The design, construction and use of ultrasound imaging devices is generally known in the art and therefore a detailed description is not included herein. The ultrasound transducer  56  is oriented to image in a radially outward direction and when rotated with the drive shaft  44  creates a 360° radial scan of the surrounding tissue. Alternatively, the ultrasound transducer  56  may be oriented such that it images in a forward looking or backward looking direction or any angle in between.  
         [0080]    To transmit the imaging signal from the imaging device  56  to the connector  40 , a coaxial cable  58  is attached to the imaging device  42  which runs down the center of the drive shaft  44  where the other end of the coaxial cable  58  is attached to the connector  40 . The connector  40  detachably connects to the adapter  150 .  
         [0081]    Turning again to FIG. 2, an innovative connector  40  will be described in detail. Overall, the connector  40  is cylindrically shaped and has a maximum diameter not exceeding the diameter of the remainder of the guidewire  10 , which is preferably 0.035″ in diameter. The distal end of the connector  40  is composed of a conductive ring  60  which is attached to the proximal end of the telescope portion  48  by an interference fit as shown, or by any other suitable attachment method. The conductive ring  60  is filled with conductive epoxy  62  through a fill hole  80  to cover the outer lead  64  of the coaxial cable  58  thereby electrically connecting the conductive ring  60  to the outer lead  64  and completing one pole of the imaging device  42  circuit. The conductive ring  60  may have a second hole  82  to observe the amount of epoxy being inserted to ensure that it does not overfill and electrically connect to a second conductor  66 . The second conductor  66  has a stepped tubular section  70  and a ball-shaped end  72 . The stepped tubular section  70  is covered with an insulator  74  such as a piece of shrink tubing. The stepped tubular section  70  covered with the insulator  74  inserts into the conductive ring  60  and is bonded in place using an adhesive such as cyanoacrylate. The insulator  74  electrically insulates the conductive ring  60  from the second conductor  66 . The inner lead  68  and insulation  76  of the coaxial cable  58  extend through the first conductive epoxy  62  and through the stepped tubular section  70 . The inner lead  68  further extends into a cavity in the ball-shaped end  72 . The cavity in the ball-shaped end  72  is filled with a second conductive epoxy  78  to conductively connect the second conductor  66  to the inner lead  68  completing the other pole of the imaging device  42  circuit.  
         [0082]    Hence, connector  40  provides a detachable electrical and mechanical attachment to the adapter  150  and in turn to the drive unit  152  and the signal processing equipment  154 . The detachability feature allows the guidewire  10  to be quickly and easily disconnected so that catheters may be inserted over the guidewire  10  and, then just as easily, the guidewire  10  can be reconnected.  
         [0083]    [0083]FIG. 2(A) depicts an exemplary mating connector  176  with the connector  40  inserted into it. The mating connector  176  is installed in the adapter  150  as will be described in detail below. The mating connector  176  includes a first contact  178  which is preferably a cylindrical multi-contact socket connector. The first contact  178  comprises a cylindrical body  180  which houses at least one, but preferable a plurality of, spring-loaded bands  182 . The spring-loaded bands  182  and body  180  are formed of an electrically conductive material such as copper alloy. The first contact  178  receives the conductive ring  60  of the guidewire connector  10  and preferably provides sufficient contact friction to drive the rotation of the imaging core  18 . If needed a locking mechanism, such as a key and slot, may be provided on the connector  40  and the mating connector  176  to prevent slippage when the connectors  40  and  176  are being rotated. A second contact  184  forms the proximal portion of the connector  176  and is preferably a small bellows type connector. When the guidewire connector  40  is connected to the mating connector  176 , the conductive ring  60  contacts the first contact  178 , and the ball shaped end  72  contacts the second contact  184 , thereby electrically connecting the imaging guidewire  10  to the adapter  150  and drive unit  152 .  
         [0084]    [0084]FIG. 2(B) shows a partial view of an imaging core  18  having another exemplary imaging guidewire connector  156 . The guidewire body  16  is not shown in FIG. 2(A). It should be appreciated that the structure shown in FIG. 2(A), as well as any of the other connectors describe herein, are contemplated to be used on any of the disclosed guidewires with at most minor modifications. The connector  156  is attached to the proximal end of the drive shaft  44  of the imaging core  18 . Generally, the connector  156  is similar to a typical shield connector. The connector  156  is cyclindrically shaped and has a maximum diameter not exceeding the diameter of the guidewire, which is preferably 0.035″. The connector  156  comprises a cylindrical conductive shell  158  which is attached to the proximal end of the drive shaft  44 . A portion of the shell  158  is filled with conductive epoxy  160  thereby electrically connecting the shell  158  to the outer lead  64  of the coaxial cable  58 . A flex circuit  162  printed on polyimide, for example, is rolled into a tube and inserted into the proximal end of the shell  158 . The flex circuit  162  has a conductive trace printed on the interior surface of the tubular flex circuit  162  and the polyimide exterior serves as an insulator between the conductive trace and the shell  158 . The flex circuit  162  may be bonded in place using any known suitable means such as epoxy adhesive.  
         [0085]    Still another exemplary connector  170  is shown in FIG. 2(C) and is identical to the mating connector  156  except that the flex circuit  162  is replaced by a braided contact  172 . The braided contact  172  may be formed using a piece of polyimide tubing with stainless steel or copper braiding embedded in the tubing, with the braid slightly exposed in the inner diameter.  
         [0086]    An exemplary mating connector  164  which connects to the connectors  156  and  170  is shown in FIG. 2(D). The mating connector  164  is installed in the adapter  150  as described below. The mating connector  164  includes a cone tipped spring contact  166  which is adapted to be inserted into the opening of the connectors  156  and  170  described above and contacts the flex circuit  162  or braided contact  172 , respectively. A flat wire slip contact  168  is disposed radially outward from the spring contact  166  so that it contacts the outside of the shell  158  of the connectors  156  and  170  when the connectors are mated. The slip contact  168  may alternatively be replaced by a cylindrical multi-contact socket connector (not shown).  
         [0087]    [0087]FIG. 2(E) provides an alternative mating connector  174  which is identical to the mating  164  except that the cone tipped spring contact  166  is replaced with a rolled split pin contact  176 . The split pin contact  176  has the advantage that it can compress inward as it contacts the inner diameter of the connectors  156  and  170  when the connectors are mated. Again, the slip contact  168  may be substituted with a multi-contact socket connector (not shown).  
         [0088]    Turning now to FIGS.  2 (F)- 2 (P), it will be noted that it is not necessary for a physical connection to be made between the leads of the imaging core  18  and those, for example, of the adapter  150 . Rather, in accordance with one aspect of the present invention a capacitive coupling or an inductive coupling may be provided between the leads of the imaging core  18  and the circuitry of the adapter  150 .  
         [0089]    For example, as is shown in FIGS.  2 (F)- 2 (K), in one embodiment a mating connector  300  may take the form of a capacitive coupling. In such an embodiment, a pair of capacitors  304  and  306  are formed by respective electrode plates  308 - 311  formed within the proximal end of the imaging core  18  and a female receptor  301 . As shown in FIG. 2(I), which illustrates the male, guidewire portion of the connector  300 , a positive lead  312  and a negative lead  314 , which extend from the imaging transducer  56 , may be coupled, via soldering or bonding, to the cylindrical electrode plates  310  and  311  formed within the proximal end of the imaging core  18 . The cylindrical electrode plates  310  and  311  preferably are encased within a ceramic, dielectric material  315 . Further, as shown in FIG. 2(H), the female portion  301  of the connector  300  preferably comprises a pair of cylindrical electrode plates  308  and  309 , a pair of positive and negative leads  316  and  318  coupled respectively to the electrode plates  308  and  309 , a drive sleeve  320 , and a pair of conductive elastomeric sleeves  322  and  324  that are bonded to an inner surface of the electrode plates  308  and  309 . It will be noted that the conductive elastomeric sleeves  322  and  324  are provided to ensure intimate contact between the male and female portions of the connector  300 , and to ensure that very little, if any, air is allowed to reside in the gaps between the electrode plates  308 - 311  that form the capacitors  304  and  306 . Finally, as is shown in FIGS.  2 (J) and  2 (K), the electrode plates  308  and  309  provided within the female portion  301  of the connector  300  may take the form of spring members that allow the female portion  301  of the connector  300  to more securely engage the male portion.  
         [0090]    Turning now to FIGS.  2 (L)- 2 (O), in still a further alternative embodiment, the connector  300  may take the form of an inductive or transformer type coupling. In such an embodiment, a first coil  330  may be provided within proximal end of the imaging core  18  of the guidewire  10 , i.e., within the male portion of the connector  300 , and a second coil  332  may be provided within the female portion  301  of the connector  300 . Those skilled in the art will appreciate that the locations of the coils  330  and  332  may vary from those illustrated in FIGS.  2 (M)- 2 (O) without altering to any significant degree the basic structure and operation of the connector  300 . For example, the coil  332  of the female portion of the connector  300  may be configured to engage an exterior surface of the male portion of the connector, or the coil  332  may be located, for example, within or around an exterior surface of the female portion  301  of the connector  300 . It also will be appreciated that, with respect to the embodiment of the connector shown in FIGS.  2 (L)- 2 (O), it is possible, if desired, for the male and female portions of the connector  300  to rotate as a single unit, possible for the male and female portions of the connector  300  to rotate independently of one another, and possible for only the male portion of the connector to be rotatable within the adapter  150 .  
         [0091]    In view of the foregoing, those skilled in the art will appreciate that any of the above described connectors may be used with an imaging guidewire in accordance with the present invention and, moreover, that portions of the above-described connectors might be combined to provide still additional coupling methodologies. For example, a connector might comprise a physical connection or contact, as described with reference to FIGS.  2 (A)- 2 (E) above, and a capacitive contact or coupling, as described with reference to FIGS.  2 (F)- 2 (K) above.  
         [0092]    Turning again to FIGS.  1 ,  1 (A)- 1 (C),  2  and  3 , the imaging core  18  is slidably and rotatably received within the guidewire body  16  such that the imaging core  18  may be axially translated relative to the guidewire. In this way, the imaging device  42  can be axially translated along the imaging portion  26  of the guidewire body  16  thereby enabling imaging along an axial length of a region of tissue without moving the guidewire body  16 . Hence, the proper positioning of the guidewire  10  within the patient&#39;s body is maintained so that it may effectively serve as a guidewire for the insertion of catheters.  
         [0093]    Prior to inserting the imaging guidewire  10  into a vessel in a body, the imaging guidewire  10  may be filled or flushed with fluid, for example water, to expel air. Residual air in the imaging guidewire  10  can impair imaging especially if using an ultrasound imaging system. The flush may be accomplished by any suitable method such as the Tuohy Borst (aspiration through two valves), providing an open distal (body pressure maintains flush), or simply filling through the proximal end of the imaging guidewire  10 .  
         [0094]    An alternative embodiment of an imaging guidewire  90  is shown in FIGS.  4 - 5 . The imaging guidewire  90  is similar to, and includes many of the features and elements as, the imaging guidewire  10  described above. Throughout the description and figures, like reference numerals refer to like elements and therefore, some elements are not explicitly described for all figures.  
         [0095]    The main differences of the imaging guidewire  90  are the use of a single polymer sheath  94  for the guidewire body  92 , and a modified imaging core  96 . The guidewire body  92  is formed of a single piece polymer sheath  94  having a proximal end  98  and a distal end  100 . Preferred polymer sheath materials include polyimide and PEEK. The sheath  94  extends from the connector  40  to the imaging portion  26  of the guidewire  90 . A nonrotating union collar  104  may be inserted between the rotatable connector  40  and the nonrotating sheath  94  to provide rotation on the internal core and allow non-rotation of the stiffening sleeve (telescope)  106 .  
         [0096]    The imaging core  96  comprises a drive cable  102  having the imaging device  42  attached to its distal end and the connector  40  attached to its proximal end. The drive cable  102  is preferably a counter-wound, multi-filar coil as described above. A stiffening sleeve  106  preferably formed of a flexible tube such as a nitinol tube, is disposed between the drive cable  102  and the sheath  94 . The polymer sheath  94  may not provide sufficient rigidity and pushability to the guidewire and therefore, the stiffening sleeve  106  gives the guidewire these properties. The stiffening sleeve  106  is received into the union collar  104  and extends distally to the imaging device  42 . In an alternative form, the stiffening sleeve  106  could extend distally to a predetermined distance short of the imaging device  42 , preferably about 15 cm short. The stiffening sleeve  106  preferably does not rotate with the drive cable  102 .  
         [0097]    The method of using the imaging guidewire  90  is virtually identical to that described above for imaging guidewire  10 . However, use of the imaging guidewire  90  may allow for extended telescopic action of the guidewire. In some embodiments, as much as, for example, 150 cm of telescopic extension may be provided.  
         [0098]    FIGS.  6 - 7  show an imaging guidewire  10  having an improvement in the transition from the stiffer main body  20  of the guidewire body  16  to the softer, more pliable imaging portion  26  according to the present invention. A relatively large difference in the stiffness of the main body  20  and the imaging portion  26  can create a stress riser at the connection point which tends to cause the more flexible imaging portion  26  to bend sharply and/or kink when the guidewire is routed through small radius paths. To relieve this condition, instead of bonding the imaging portion  26  directly to the main body  20  as described above, a graduated transition  120  comprising a short transition tube  108  is attached to the distal end  24  of the main body  20  and the imaging portion  26  is attached to the other end of the transition tube  108 . The transition tube is made of a material, and is configured, such that it has a stiffness between that of the main body  20  and the imaging portion  26 .  
         [0099]    FIGS.  8 - 9  show an alternative configuration for the graduated transition  120  between the main body  20  and the imaging portion  26  similar to that described with respect to FIGS.  6 - 7 , except that the distal end of the transition tube  110  is left free. The outer diameter of the main body  20  is reduced from that described above to accommodate a full length jacket  112  comprising a thin layer of plastic, preferably polyethylene, to be formed over the entire length of the main body  20 . The preferred reduced thickness of the main body  20  is preferably about 0.032″ corresponding to a jacket  110  thickness of about 0.0015″. The imaging portion  26  and the jacket  112  may be formed from a single varying thickness piece of material. In this configuration, the transition tube  110  is similar in construction and materials to the transition tube  108  described above.  
         [0100]    Another variation of a graduated transition  120  between the main body  20  and the imaging portion  26  is shown in FIGS.  10 - 11 . The imaging guidewire  10  of FIGS.  10 - 11  is identical to that shown in FIGS.  1 - 3  except that the distal end  24  of the main body  20  is constructed in a spiral form  114  with increasing pitch as it extends distally. Then, the imaging portion  26  extends over the spiral form  114 . The spiral form  114  creates a more flexible portion of the main body  20  that performs the graduated transition function similar the that described above.  
         [0101]    FIGS.  12 - 13  depict yet another embodiment of an imaging guidewire  10  having a graduated transition  120 . The imaging guidewire  10  of FIGS.  12 - 13  is identical to that of FIGS.  10 - 11  except that the spiral form  114  is replaced with a tapered finger section  116 .  
         [0102]    Still another embodiment of graduated transition  120  on an imaging guidewire  10  is shown in FIGS.  14 - 15 . In this embodiment, a reinforcing braided section  118  is placed over the connection between the imaging portion  26  and the main body  20 . The braided section  118  may be made of plastic such as polyethylene, co-extruded polymer materials, or any other suitable material. The braided section  118  performs similarly to the graduated transitions described above.  
         [0103]    Except for the varying graduated transition configurations of the guidewire body  16 , the imaging guidewires  10  of FIGS.  6 - 15  are identical to the imaging guidewire described for FIGS.  1 - 3 . In addition, the method of using the imaging guidewires is the same as previously described.  
         [0104]    The stress relief transition from the main body  20  to the imaging portion  26  may also be accomplished by varying the cross-sectional thickness of the main body  20  and/or the imaging portion  26  at the interface of the two tubes. Varying the thickness of the tubes in turn changes the stiffness of the tube. For example, the thickness of the main body  20  and/or the imaging portion  26  may be tapered, stepped or angle cut. Hence, if the main body  20  is made of a stiffer tube than the imaging portion  26 , the main body  20  would be made gradually thinner as it extends distally toward the imaging portion  26 ; and/or the imaging portion  26  would be gradually thickened as it extends proximally toward the main body  20 . An example of the varying thickness transition using a tapered main body and imaging portion  26  is shown in FIG. 16.  
         [0105]    Turning now also to FIGS.  17 - 20 , in one presently preferred form, the imaging guidewire  10  or  90  is capable of disconnectably mating with an adapter  150  which, in turn, couples to a motor drive unit  152 , as is shown in FIG. 1. The motor drive unit  152  may comprise, for example, a model MDU-4 motor drive unit currently distributed by Boston Scientific Corp. Thus, the adapter  150  may be coupled in a conventional manner to the motor drive unit  152 , and the structure and function of the motor drive unit  152  need not be described in detail herein, as the structure and function of the model MDU-4 motor drive unit is believed to be well known in the art. Nonetheless, it should be appreciated that a principal function of the adapter  150  and motor drive unit  152  is to provide a conduit for transmitting an imaging signal from the imaging guidewire  10  or  90  to the signal processing equipment  154 . In addition, the motor drive unit  152  and adapter  150  preferably are configured to provide a mechanical coupling to the imaging guidewire  10  or  90  such that torque may be applied by a motor (not shown) within the motor drive unit  152  via the adapter  150  to the drive cable  50  of the imaging guidewire  10  or  90 . Finally, those skilled in the art will also appreciate that the motor drive unit  152  and adapter  150  may be formed, if desired, as a single unit.  
         [0106]    Turning now in particular to FIG. 17, the motor drive unit  152  may comprise a model MDU-4 motor drive unit manufactured and distributed by Boston Scientific Corp. and preferably includes a case  186  which provides a port  187  for coupling to the adapter  150 . The port  187  provides both a mechanical and an electrical interface between the motor drive unit  152  and the adapter  150 . The motor drive unit  152  and adapter  150  also include various electronic circuits (not shown) for transmitting an imaging signal from the imaging guidewire  10  and  90  to the signal processing equipment  154 . The electronics within the motor drive unit  152  are connected to an electrical cable  190  that extends out of the case  186  of the motor drive unit  152  and is connectable to the signal processing electronics  154  (see FIG. 1) by a connector (not shown).  
         [0107]    While in the currently preferred embodiment a motor (not shown) is provided within the motor drive unit  152 , it will be appreciated that in alternative embodiments a motor for rotating the imaging core  18  may be external to the drive unit  152  and may be a part, for example, of the signal processing equipment  154 . In such embodiments, a motor drive cable may extend out of the case  186  of the motor drive unit  152  and have a connector that is connectable to the motor (not shown). Within the case  186  of the motor drive unit  152 , the motor drive cable would connect to a drive mechanism that, in turn, would transmit rotational torque from the drive cable to a drive mechanism within the adapter  150 .  
         [0108]    Turning now in particular to FIGS.  18 - 20 , it is presently preferred that the adapter  150  removably plug into the drive unit  152  via the port  187 . In an exemplary embodiment, the adapter  150  comprises a telescoping cover  202 . The telescoping cover  202  preferably has 2 or more plastic telescoping sections, and 5 telescoping sections  401 - 405  are shown in FIGS. 19 and 20. An adapter connector  204  is disposed on the proximal end of the adapter  150  and mechanically and electrically connects to a drive unit connector (not shown) provided within port  187  (shown in FIG. 17) of the motor drive unit  152 . An adapter flushport  206  is located on the end of the adapter cover  202 . In an exemplary embodiment, the flushport  206  is a T-shaped fitting having a main through port  208  and a side port  210 . Threaded knobs  212  on either side of the through port  208  are provided to compress o-ring seals  406  disposed therein. When compressed, the o-ring seals  406  and  407  fit tightly against an outer wall of an imaging guidewire  10  or  90  that has been inserted into the adapter  150 . The forward o-ring seal  406  may also be compressed against the exterior surface of a catheter (not shown), when the guidewire  10  or  90  is located within a lumen of the catheter. The side port  210  is preferably a luer fitting that allows for typical syringe type coupling to the main through port  208 .  
         [0109]    The telescoping adapter cover  202  protects the imaging core  18  from being openly exposed during pull-back procedures where the imaging core  18  is translated relative to the body  16 . This is important because eliminating such exposure can prevent the imaging signal from being distorted thereby preserving image quality. Moreover, the telescoping adapter cover  150  can be retracted out of the way during catheter exchanges over the guidewire such that the guidewire can be disconnected and reconnected to the adapter.  
         [0110]    Those skilled in the art will appreciate that in alternative embodiments, the adapter  150  may utilize a non-telescoping cover, and that with the exception of lacking a telescoping function, such an adapter would function in virtually the same manner as the adapter  150  shown in FIGS.  18 - 20 .  
         [0111]    Turning now to FIG. 20, there is shown a cross-sectional view of the adapter  150  having a proximal end of a guidewire  10  inserted therein. As shown, the proximal end of an imaging core  18  of the guidewire  10  is inserted into a female portion of a connector (not shown) that is disposed within a collet assembly  408 . The female portion of the connector provided within the collet assembly  408  preferably is of the type described above with reference to FIGS.  2 (A)- 2 (O) above. Thus, it will be appreciated that the female portion of the connector provided within the collet assembly  408  provides both a mechanical and electrical interface between the imaging core  18  of the guidewire  10  and the drive mechanism  410  and electronics (not shown) of the adapter  150 .  
         [0112]    Turning now also to FIG. 21, a collet assembly  408  in accordance with the present invention may comprise, for example, a rotator  450  that engages a drive shaft (not shown) of a motor drive unit  152 , a fixed ferrite  452 , a rotating ferrite  454 , a main collet body  456  and a collet cone  458  having a tapered inner cavity  460 . The rotator  450  is mechanically coupled to the rotating ferrite  454  by a drive shaft tube  462 , and the rotating ferrite  454  is fixedly attached to the main collet body  456 . The collet cone  458  is attached to a distal end of the main collet body  456 . A tapered cavity  464  is defined within the collet cone  458  and the main collet body  456 , and an imaging core engaging mechanism  466  is provided within the tapered cavity  460 .  
         [0113]    Turning now in addition to FIGS.  22 - 25 , the imaging core engaging mechanism  466  comprises a contact housing  468  that is coupled to a stationary pawl  470 , a rotary pawl  472  that has a female portion  168 ,  182  or  301  of a connector mounted therein, and a spring  473  that engages the rotary pawl  472  and a proximal, internal section of the collet main body  456 . In addition, three ball bearings  474  are preferably disposed within respective cavities or recesses  476  formed within a distal end of the contact housing  468 .  
         [0114]    Those skilled in the art will appreciate that the stationary pawl  470 , rotary pawl  472  and spring  473  function in a manner quite similar operating mechanism of a conventional ball point pen. Thus, when the collet assembly  408  is assembled and disposed within an adapter  150 , the proximal end of an imaging guide wire  10  or  90  may be inserted through an opening in the distal end of the adapter  150  and into the collet assembly  408 . As the guidewire  10  or  90  is pushed into the female connector  168 ,  182  or  301  of the collet assembly  408 , the rotary pawl  472  compresses the spring  473  allowing the core engaging mechanism  466  (including the contact housing  468 , stationary pawl  470  and rotary pawl  472 ) to move progressively within the main body  456  of the collet assembly  408  in the direction of the rotator  450 . That movement affords the ball bearings  474  housed within the contact housing  468  additional space within the tapered cavity  460 . As the imaging core engaging mechanism  466  moves further toward the rotator  450 , force is applied by a linear indexing ratchet  476  located on the stationary pawl  470  to a rotary indexing ratchet  478  located on the rotary pawl  472  urging the rotary pawl  472  to rotate about a central axis (not shown) of the collet assembly  408 . However, as shown in FIG. 25, the indexing ratchets  476  and  478  travel within channels  480  formed within an inner wall of the collet main body  456 , until the rotary indexing ratchet  478  escapes the channel  480 . At that time, the rotary indexing ratchet  478  and, thus, the rotating pawl  472  rotate about the central axis of the collet assembly  408 . The rotary indexing ratchet  478  then may engage surface  482  adjacent the channel  480 . When the guidewire  10  or  90  is pushed into the female connector  168 ,  182  or  301  of the collet assembly  408  again, the rotary indexing ratchet  478  disengages the surface  482  and is caused to rotate in a manner such that it may pass into the channel  480 . As the imaging core engaging mechanism  466  moves toward the cone  458 , the ball bearings  474  are driven against the imaging core  18  by the wall of the tapered cavity  460 . Thus, it will be appreciated that, once the imaging core  18  is locked within the imaging core engaging mechanism  466 , pulling on the imaging core  18  in a direction away from the rotator  450  will only cause the imaging core engaging mechanism  466  to more tightly engage the imaging core  18 .  
         [0115]    Now, turning back to FIG. 21, imaging signals provided to the female connector  168 ,  182  or  301  are carried on a pair of wires  490  to a first transformer coil  492 . The signals then are transmitted to a second transformer coil  494  by means of inductive coupling and, from there, the signals may be conveyed to the contacts (not shown) provided within the housing of the adapter  150  for transmission to the motor drive unit  152  and eventually to the processing system  154 .  
         [0116]    In view of the foregoing, the reader will see that the present invention provides an improved imaging guidewire. While the above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as examples of particular embodiments thereof. Many other variations are possible.  
         [0117]    Accordingly, the scope of the present invention should be determined not by the embodiments illustrated above, but rather, the invention is to cover all modifications, alternatives and legal equivalents falling within the spirit and scope of the appended claims.