Abstract:
The present invention is generally directed towards an imaging transducer assembly. Generally, the imaging transducer assembly is combined with a sensor of a medical positioning system. In one aspect, the transducer assembly and the sensor share the same voltage source. In another aspect of the invention, the sensor surrounds a portion of the imaging transducer assembly, forming a housing that reinforces the assembly.

Description:
RELATE BACK  
       [0001]     This application is a continuation of application Ser. No. 10/401,901 filed on Mar. 28, 2003, all of which is expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The field of the invention relates to medical imaging systems, and more particularly to an improved imaging transducer assembly.  
       BACKGROUND OF THE INVENTION  
       [0003]     Intraluminal, intracavity, intravascular, and intracardiac treatments and diagnosis of medical conditions utilizing minimally invasive procedures are effective tools 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. For example, U.S. Pat. No. 5,368,035, issued to Hamm et al., the disclosure of which is incorporated herein by reference, describes a catheter having an intravascular ultrasound imaging transducer.  
         [0004]      FIG. 1   a  shows an example of an imaging transducer assembly  1  known in the art. The imaging transducer  1  is typically within the lumen  60  of a guidewire (partially shown), having an outer tubular wall member  5 . The imaging transducer assembly  1  includes a coaxial cable  110 , having a center conductor wire  120  and an outer shield wire  140 , shown in  FIG. 1   b . A conductive wire, having a diameter of approximately 500 microns, is wrapped around the coaxial cable  110 , forming a coil, which functions as a drive shaft  10 . Connected to the distal end of the drive shaft  10  is a stainless steel housing  20 , which serves to reinforce the structure of the imaging transducer assembly  1 . Surrounding the coaxial cable  110 , within the housing  20  is a silver epoxy  30 , a conductive material. Thus, the housing  20  is electrically coupled to the shield wire  140  of the coaxial cable  110  via the epoxy  30 . On the distal end of the silver epoxy  140  is an insulating substance, a non-conductive epoxy  35 .  
         [0005]     On the distal end of the non-conductive epoxy  35  is a layer of piezoelectric crystal (“PZT”)  80 , “sandwiched” between a conductive acoustic lens  70  and a conductive backing material  90 , formed from an acoustically absorbent material (e.g., an epoxy substrate having tungsten particles). The acoustic lens  70  is electrically coupled with the center conductor wire  120  of the coaxial cable  110  via a connector  40  that is insulated from the silver epoxy  30  and the backing material  90  by the non-conductive epoxy  35 . The backing material  90  is connected to the steel housing  20 . It is desirable for the imaging transducer assembly  1  to be surrounded by a sonolucent media. Thus, the lumen  60  of the guidewire is also filled with saline around the assembly  1 . The driveshaft  10 , the housing  20 , and the acoustic lens  70  are exposed to the saline. During operation, the PZT layer  80  is electrically excited by both the backing material  90  and the acoustic lens  70 . The backing material  90  receives its charge from the shield wire  140  of the coaxial cable  110  via the silver epoxy  30  and the steel housing  30 , and the acoustic lens  70 , which may also be silver epoxy, receives its charge from the center conductor wire  120  of the coaxial cable  110  via the connector  40 , which may be silver epoxy as well.  
         [0006]     Turning to  FIG. 1   c , the imaging transducer assembly  1  can be depicted as a simple electric circuit having a voltage source  150 , two terminals, A and B, a load  81  caused by the saline filled in the lumen  60 , and the PZT load  80 . The saline load  81  and the PZT load  80  are charged by the voltage source  150  via the two terminals, A and B, representing the shield wire  140  and the center conductor wire  120  of the coaxial cable  110 , respectively. In addition, transducer control circuitry (not shown), which may include a signal processor to handle imaging signals, may also be coupled with the transducer assembly  1 .  
         [0007]     The imaging transducer is an effective tool for obtaining the cross-sectional image of a blood vessel. However, in some instances, it may be desirable to obtain more information, such as a three-dimensional longitudinal profile of the same blood vessel in addition to the cross-sectional image. Accordingly, an improved imaging transducer assembly would be desirable.  
       SUMMARY OF THE INVENTION  
       [0008]     The improved imaging device is intended for use within the lumen of a blood vessel. Generally, the imaging transducer assembly is combined with a sensor of a medical positioning system.  
         [0009]     In one embodiment, the imaging transducer assembly and the sensor may be electrically charged using a first and second terminal. The imaging transducer assembly may be coupled with a coaxial cable having a center wire and an outer wire, wherein one of the first and second terminals is coupled with the center wire and the other of the first and second terminal is coupled with the outer wire. Further, at least one of the first and second terminals is insulated from any sonolucent media in contact with the imaging transducer assembly. Further, the sensor surrounds the imaging transducer assembly, forming a housing structure to reinforce the assembly.  
         [0010]     In another embodiment, a method includes obtaining the cross-sectional image of a blood vessel and at substantially the same time, obtaining the longitudinal profile of the same blood vessel.  
         [0011]     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     In order to better appreciate how the above-recited and other advantages and objects of the present inventions are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. It should be noted that the components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. However, like parts do not always have like reference numerals. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely.  
         [0013]      FIG. 1   a  is a cross-sectional side view of an imaging transducer assembly known in the art.  
         [0014]      FIG. 1   b  is a cross-sectional view of the coaxial cable within the prior art imaging transducer assembly of  FIG. 1   a.    
         [0015]      FIG. 1   c  is a simplified diagram of an electrical circuit formed by the prior art imaging transducer assembly of  FIG. 1   a.    
         [0016]      FIG. 2   a  is an illustration of a prior art medical positioning system.  
         [0017]      FIG. 2   b  is a simplified diagram of an electrical circuit formed by a sensor of a prior art medical positioning system.  
         [0018]      FIG. 3   a  is cross-sectional side view of an imaging transducer assembly in accordance with an exemplary embodiment of the present invention.  
         [0019]      FIG. 3   b  is a cross-sectional view of a coaxial cable within the imaging transducer assembly of  FIG. 3   a.    
         [0020]      FIG. 3   c  is a simplified diagram of an electrical circuit formed by the imaging transducer assembly of  FIG. 3   a.    
         [0021]      FIG. 4  is a partial cross-sectional side view of a catheter in accordance with an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Described below is an improved imaging transducer assembly.  
         [0023]     In some instances, it may be desirable to be able to obtain not only the cross-sectional image of a blood vessel, but also information such as the three-dimensional longitudinal profile of the same blood vessel. One approach in obtaining such additional information is to use a medical positioning system, which is generally known in the art. Turning to  FIG. 2   a , a prior art medical positioning system  240  is illustrated. The system  240  generally includes a plurality of transmitter and/or receiver nodes  250  that may be arranged around a patient. For instance, the nodes  250  may be arranged on a framework of towers that surround a patient. The system  240  further includes one or more sensors  260 , which are configured to send and/or receive electro-magnetic, or electromechanical, signals to and/or from the transmitter/receiver nodes  250 .  
         [0024]     A sensor  260 , coupled with a guidewire (partially shown), may be placed within the blood vessel of a patient&#39;s body. The signals exchanged between the sensor  260  and the nodes  250  function as navigational signals which, as can be appreciated by one of ordinary skill in the art, may be used to determine the position of the sensor  260  within the patient&#39;s body. In other words, the sensor  260  transmits navigational signals to the nodes  250 , and a processor (not shown) coupled with the nodes  250  determines the position of the sensor  260  based on the signals received by the nodes  250 . Alternatively, or in addition, the nodes  250  may send navigational signals to the sensor  260 , and a processor (not shown) coupled with the sensor  260  determines the position of the sensor  260  within the patient&#39;s body based on the signals sent by the nodes  250 . The medical positioning system  240  can track and record the position of the sensor  260  as it is moved throughout a patient&#39;s blood vessel, thus providing a longitudinal profile of the blood vessel.  
         [0025]     Turning to  FIG. 2   b , the sensor  260  is depicted as a simplified electrical circuit having two terminals, A and B, an “antenna” load, and a load  270 . The antenna is the portion of the sensor  260  where a substantial amount of the navigational signals are sent and/or received. If the sensor  260  is configured to send electromagnetic signals to the nodes  250 , then to facilitate the electromagnetic broadcast, the load  270  may be a voltage source  270 , which charges the antenna via the terminals A and B. Alternatively, if the sensor  260  is configured to receive electromagnetic signals from the nodes  250 , then the load  270  may be sensor circuitry, which may include a signal processor (not shown) to handle navigational signals.  
         [0026]     In one example preferred embodiment of the improved imaging transducer assembly shown in  FIGS. 3   a  and  3   b , a sensor of a medical positioning system may be combined with an imaging transducer to form a transducer/sensor assembly  300 . Turning to  FIG. 3   a , a cross-sectional side view of a transducer/sensor assembly  300  is shown in a lumen  305  of the distal portion of a guidewire or catheter assembly (partially shown) having an outer tubular wall  301 . The transducer/sensor assembly  300  includes a coaxial cable  410 , having a center conductor wire  420 , and an outer shield wire  430 , as shown in  FIG. 3   b . The center conductor wire  420  is insulated from the outer shield wire  430 . In addition, the shield wire  430  is surrounded by an insulating jacket  440 . It should be noted that numerous alternative cable configurations may be used; for example, a cable having “twisted pair” wires may be used instead of a coaxial cable.  
         [0027]     Turning back to  FIG. 3   a , surrounding the coaxial cable  410  is a layer of insulating material, such as a non-conductive epoxy  330 . Surrounding the epoxy  330  is a drive shaft  310 , which is a conductive wire wound around the epoxy  330 /coaxial cable  350  to form a first coil shape  310 . Preferably, the conductive wire is stainless and has a diameter of approximately 500 microns. Thus, the coaxial cable  350  is conductively insulated from the drive shaft  310 .  
         [0028]     The distal end of the transducer/sensor assembly  300  includes an electrically conductive backing material  390 , having a top, bottom and center, which may be formed from an acoustically absorbent material (for example, an epoxy substrate having tungsten particles). The center of the backing material  390  surrounds a shield pellet  400 , which is electrically coupled to the shield wire  430  at the distal end of the coaxial cable  410 . The top of the backing material  390  is coupled to the bottom of a layer of piezoelectric crystal (PZT)  380 . The top of the PZT layer  380  is coupled to a conductive acoustic lens  370 , which may include silver epoxy. The acoustic lens  370  is electrically coupled to the center conductor wire  420  of the coaxial cable  410  via a connector  360 , which may include silver epoxy, surrounding the non-conductive epoxy  330  such that the connector  360  is insulated from the backing material  390 .  
         [0029]     The transducer/sensor assembly  300  further includes a sensor  320  of a medical positioning system. The “antenna” portion of the sensor  320  is an insulated conductive wire  325 . The wire  325  may also have magnetic qualities. The wire  325  is tightly wrapped around a portion of the distal end of the coaxial cable  410  and non-conductive epoxy  330 , and is also tightly wrapped around the distal end of the drive shaft  310 , forming a second coil shape. The second coil shape desirably provides an inductance for the antenna portion of the sensor  320  when charged to increase its ability to send and receive electromagnetic signals. The second coil shape also serves as a housing to reinforce the transducer/sensor assembly  300 . However, it should be noted that the antenna portion of the sensor  320  may have a variety of other shapes and configurations. For example, the antenna portion of the sensor  320  may be a solid structure. The wire  325  is preferably copper and approximately 10 microns in diameter. The small diameter of the wire  325  allows the sensor  320  to have a small impact on the dimensions of the transducer/sensor assembly  300 , thus allowing the transducer/sensor assembly  300  to still work within the lumen  305  of the guidewire or catheter assembly.  
         [0030]     The two ends of the wire  325  are terminals that receive an electric charge. One end  350  of the wire  325  is coupled to the connector  360  that electrically couples the acoustic lens  370  with the center conductor wire  420  of the coaxial cable  410 . The other end  340  of the wire  325  is coupled to the shield wire  430  of the coaxial cable  410 , surrounded and insulated from the drive shaft  310  and the connector  360  by the non-conductive epoxy  330 .  
         [0031]     To facilitate the operation of the imaging transducer portion of the transducer/sensor assembly  300 , the lumen  305  of the guidewire or catheter assembly is preferably filled with a sonolucent media, such as saline. It is desirable to have at least one of the ends  350 ,  340  of the wire  325  of the sensor  320  be insulated from the saline within the lumen  305  because if both ends,  350  and  340 , were exposed to the saline, the semi-conductive nature of the saline might shunt the ends,  350  and  340 , thus undesirably “shorting out” the antenna of the sensor  320 , and/or affecting the signal-to-noise ratio of the navigational signals. In light of this, the transducer/sensor assembly  300  preferably has one end  340  of the wire  325  of the sensor insulated from the drive shaft  310 , backing material  390 , connector  360 , and saline by the non-conductive epoxy  330 . Further, the coil portion of the wire  325  is also insulated from the driveshaft  310  and the saline in the lumen  305  by a non-conductive material. The other end  350  of the wire  325 , however, may be exposed to the saline.  
         [0032]     During the operation of the transducer/sensor assembly  300 , the PZT crystal  380  is electrically excited by both the backing material  390 , charged through the shield wire  430 , and the acoustic lens  370 , charged through the center conductor wire  420 . In addition, the antenna portion  325  of the sensor  320  is also charged by the shield wire  430  and the center conductor wire  420 . If the sensor  320  is configured to send electromagnetic signals to nodes of a medical positioning system (not shown), then the charge may facilitate a broadcast. However, if the sensor  320  is configured to receive electromagnetic signals from one or more nodes of a medical positioning system (not shown), then separate circuitry including a signal processor may be used to filter and extract the desired electromagnetic signals. Thus, turning to  FIG. 3   c , the assembly  300  is depicted as a simplified electric circuit having a voltage source  530 , the load of the PZT layer  380 , the load of the antenna portion  325  of the sensor  320 , which is in parallel with the load of the PZT layer  380 , sensor circuitry  531 , which may include a signal processor (not shown) to receive and process electromagnetic signals, i.e., navigational signals, from the sensor  320 , as would be known to a person of skill in the art, transducer circuitry  532 , which may also include a signal processor (not shown) to process imaging signals from the imaging transducer, and terminals A and B. Terminals A and B represent the center conductor wire  420  and the shield wire  430  of the coaxial cable  410 , respectively. Other features and circuits may also be added as desired.  
         [0033]     Turning to  FIG. 4 , the transducer/sensor assembly  300  may be placed in a distal portion  520  of a guidewire  500 . The guidewire  500  may comprise a guidewire body  302  in the form of a flexible, elongate tubular member, having an outer wall  301 . The guidewire body  302  may be formed of any material known in the art including nitinol hypotube, metal alloys, composite materials, plastics, braided polyimide, polyethylene, peek braids, stainless steel, or other superelastic materials.  
         [0034]     The length of the guidewire  500  may vary depending on the application. In a preferred embodiment, the length of the guidewire  500  is between 30 cm and 300 cm. A catheter (not shown) may be configured to use several different diameters of guidewires  500 . For example, the guidewire  500  may have a diameter of 0.010, 0.014, 0.018, or 0.035 inches. Typically, the diameter of the guidewire  500  is uniform.  
         [0035]     A proximal portion  510  of the guidewire  500  may be adapted to connect to circuitry (not shown) that processes imaging signals from the imaging transducer and/or circuitry (not shown) that processes navigational signals from the sensor  320 ., such circuits being well known.  
         [0036]     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions described herein is merely illustrative, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. For example, this invention is particularly suited for applications involving medical imaging devices, but can be used on any design involving imaging devices in general. As a further example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.