Abstract:
A catheter is provided for insertion in the he blood vessel of a patient for ultrasonically imaging the vessel wall. The catheter includes a tubular element and an internally housed drive cable for effective circumferential scan about the catheter of an ultrasonic generating means. Both the tubular element and the drive cable are of a size and flexibility sufficient to permit their introduction into the vessel and subsequent advancement through the vessel to the location of the vessel wall where imaging is desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of co-pending U.S. patent application Ser. No. 10/691,900, filed on Oct. 22, 2003, which is a continuation of U.S. patent application Ser. No. 10/177,897, filed on Jun. 20, 2002 (now U.S. Pat. No. 6,572,554), which is a continuation of U.S. patent application Ser. No. 09/816,586, filed on Mar. 23, 2001 (now U.S. Pat. No. 6,409,673), which is a continuation of U.S. patent application Ser. No. 09/300,168, filed on Apr. 27, 1999 (now U.S. Pat. No. 6,221,015), which is a continuation of U.S. patent application Ser. No. 08/911,635, filed on Aug. 15, 1997 (now U.S. Pat. No. 5,902,245), which is a continuation of U.S. patent application Ser. No. 08/467,178, filed on Jun. 6, 1995 (now U.S. Pat. No. 5,865,178), which is a continuation of U.S. patent application Ser. No. 08/162,412, filed on Dec. 3, 1993 (now U.S. Pat. No. 5,676,151), which is a divisional of U.S. patent application Ser. No. 08/014,906, filed on Feb. 1, 1993 (now U.S. Pat. No. 5,313,949), which is a continuation of U.S. patent application Ser. No. 07/826,260, filed on Jan. 24, 1992 (now abandoned), which is a continuation of U.S. patent application Ser. No. 07/649,048, filed on Feb. 1, 1991 (now abandoned), which is a continuation of U.S. patent application Ser. No. 07/290,533, filed on Dec. 23, 1988 (now U.S. Pat. No. 5,000,185), which is a continuation-in-part of U.S. patent application Ser. No. 06/834,893, filed on Feb. 28, 1986 (now U.S. Pat. No. 4,794,931). The entire disclosures of all of the aforementioned applications are incorporated herein by reference. The present application is related to U.S. patent application Ser. No. 07/290,217, filed on Dec. 23, 1988, commonly assigned herewith, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to a catheter apparatus, system, and method for intravascular two-dimensional ultrasonographic imaging, and more particularly to such an apparatus, system, and method for guiding and monitoring interventional therapy to reduce vascular stenosis.  
         [0003]     Ultrasonic two-dimensional imaging apparatus and systems have heretofore been provided for use in endoscopy for examining the gastrointestinal tract. Such a device is disclosed in U.S. Pat. No. 4,494,549. Such devices, however, have been relatively large and inflexible and are completely unsuitable for use within the vascular system of the human body. In addition, there is no provision for guiding such devices into specific branches of blood vessels.  
         [0004]     There is, therefore, a need for a new and improved catheter apparatus, systems, and methods which can be utilized for performing intravascular two-dimensional ultrasonographic imaging. It would be particularly desirable if such imaging apparatus and methods could be combined with a variety of intravascular therapeutic modalities, such as angioplasty atherectomy, laser ablation, and the like, in order to provide simultaneous imaging and recanalization procedures.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     According to the present invention, a method for imaging the interior of a blood vessel comprises scanning an ultrasonic signal in a preselected pattern about said interior. By receiving ultrasonic energy reflected from the interior surface of the vessel, including any stenosis or occlusion present, an image or profile of the blood vessel may be produced. Conveniently, the ultrasonic signal is generated by a transducer located at the distal end of a vascular catheter comprising a flexible tubular member. The transducer may be manipulated directly to sweep the ultrasonic signal in a desired pattern, including radial, planar, and conical. Alternatively, the transducer may be fixed within the catheter and a reflective surface manipulated to sweep the ultrasonic signal in a desired pattern. The imaging method of the present invention is advantageously combined with interventional therapeutic techniques to reduce vascular stenosis, where the stenosis may be imagined prior to, during, and after intervention to help direct the interventional activity to where it will be most effective.  
         [0006]     In general, it is an object of the present invention to provide a catheter apparatus, system, and method for intravascular two-dimensional ultrasonography.  
         [0007]     Another object of the invention is to provide an apparatus, system, and method of the above character which has a high resolution capability.  
         [0008]     Another object of the invention is to provide an apparatus, system, and method of the above character which can be utilized for assessing endovascular lesions.  
         [0009]     Another object of the invention is to provide an apparatus, system, and method of the above character which can be utilized for monitoring the results of interventional therapy.  
         [0010]     Another object of the invention is to provide an apparatus, system, and method of the above character which can be used with angioplasty, atherectomy, laser ablation, drug deliver, and similar vascular interventional methods and devices.  
         [0011]     Another object is to provide an apparatus, system, and method capable of selective cannulation of branch vessels.  
         [0012]     Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a side elevational view partially in cross-section of a catheter apparatus incorporating the present invention.  
         [0014]      FIG. 2  is an enlarged cross-sectional view of the distal extremity of the apparatus shown in  FIG. 1 .  
         [0015]      FIG. 2A  is a detail view illustrating an alternate mounting of a crystal transducer to provide a conical sweep pattern.  
         [0016]      FIG. 2B  is an alternate embodiment of the distal extremity of the apparatus shown in  FIG. 1 , modified to be inserted over a movable guidewire and with the cutting direction reversed.  
         [0017]      FIG. 3  is an enlarged cross-sectional view of an intermediate portion of the apparatus shown in  FIG. 1 .  
         [0018]      FIG. 4  is an enlarged cross-sectional view taken along the line of  4 - 4  of  FIG. 1 .  
         [0019]      FIG. 5  is an isometric view of the crystal assembly which forms a part of the apparatus shown in  FIG. 1 .  
         [0020]      FIG. 6A  is a schematic block diagram of the electrical and electronic apparatus utilized in the system.  
         [0021]      FIG. 6B  is a schematic block diagram of the electrical and electronic apparatus with a micromotor at the distal extremity of the catheter.  
         [0022]      FIG. 7  is a two-dimensional display of an ultrasonogram which can be obtained with the apparatus and system shown in  FIGS. 1-6 .  
         [0023]      FIG. 8  is an enlarged cross-sectional view of another embodiment of a catheter apparatus incorporating the present invention.  
         [0024]      FIG. 9  is a cross-sectional view taken along the liens of  9 - 9  of  FIG. 8 .  
         [0025]      FIG. 10  is an enlarged cross-sectional view of still another embodiment of a catheter apparatus incorporating the present invention.  
         [0026]      FIG. 10A  is a detail view illustrating an alternate configuration of a reflective surface to provide a conical sweep pattern.  
         [0027]      FIG. 10B  is an alternate embodiment of the distal extremity of the catheter apparatus of  FIG. 10 , modified to provide a fixed ultrasonic transducer located proximally of a reflective surface on a cutter.  
         [0028]      FIG. 11  is an enlarged cross-sectional view of another embodiment of the catheter apparatus incorporating the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     In general, the catheter apparatus of the present invention includes a flexible tubular element which is adapted to be inserted into a blood vessel in the vascular system and a flexible rotatable elongate element which is disposed in the tubular element. In a first embodiment, an ultrasonic transducer is carried at the distal end of the flexible rotatable elongate element, and electrical circuitry carried at the distal end of the flexible tubular element is connected to the ultrasonic transducer for supplying signals to and receiving signals from the transducer. In a second embodiment, a reflective surface is carried by the distal end of the flexible rotatable elongate element, and the ultrasonic transducer is mounted in the distal tip of the flexible tubular element so that signals generated by the transducer will be reflected by the reflective surface. In both embodiments, a transmitter is provided for supplying signals to the ultrasonic transducer and a receiver is provided for receiving signals from the ultrasonic transducer. A motor drive is usually provided for rotating the flexible elongate element along manual rotation may also be employed. By rotating the flexible elongate element, the transducer signal can be swept in a desired pattern, either directly by the transducer in the first embodiment, or indirectly by the reflective surface in the second embodiment. Timing and control circuitry is provided for controlling the operation of the transmitter and receiver and optionally the motor drive. A display is provided which is operated under the control of the timing and control circuitry for displaying he image information that is received by the receiver.  
         [0030]     The catheters of the present invention may further include interventional capability for recanalization of occluded regions within the imaged blood vessel. Recanalization is intended to refer to both the opening of total occlusions, as well as broadening of the vessel lumen in partial occlusions. Catheters combining ultrasonic imaging capability with atherectomy devices for severing of stenotic material are described in detail hereinafter. The methods of the present invention, however, are not limited to atherectomy and include a wide variety of other interventional techniques that may be performed with vascular catheters. Suitable interventional techniques include balloon angioplasty, laser ablation angioplasty, balloon embolectomy, aspiration embolectomy, heat probe ablation, abrasion, drilling, therapeutic ultrasound, and the like. Also, the catheters may be adapted for introducing clot-dissolving drugs, such as tissue plasminogen activator, streptokinase, urokinase, and the like, in order to reduce the stenosis, as well as platelet receptor blockers and drugs which limit cell multiplication in order to inhibit restenosis. Conveniently, perfusion lumens and ports may be provided in the catheter to provide for the administration of such drugs.  
         [0031]     A first exemplary construction of a catheter apparatus  11  constructed in accordance with the principles of the present invention comprises an elongate tubular assembly  12  includes an elongate flexible tubular element  13  which is provided with four lumens  14 ,  16 ,  17 , and  18  with the lumen  14  serving as a torque tube, lumen  16  serving as a balloon tube, and lumens  17  and  18  serving as infusion tubes or lumens as hereinafter described. The tubular element  13  may conveniently be formed as a single extrusion which provides the four lumens, with the lumens  14  and  16  being substantially circular in cross-section, and the lumens  17  and  18  being arcuate in shape with the configuration of each being determined by three arcs with one of the arcs being concentric with the outer diameter of the tubular element  13  and with the two smaller arcs being concentric with lumens  14  and  16 , respectively.  
         [0032]     A braided shield  21  is provided on the exterior of the tubular element  13  and takes the form of one or more layers of braided strands  22  formed of suitable magnetic material, such as an electrical shield. A cover tube  23  covers the braided shield  21  and extends the length of the tubular element  13 . The cover tube  23  can be formed of a suitable material such as a heat shrinkable plastic which is shrunk tightly onto the braided shield  21  and provides a smooth outer surface so the tubular assembly  12  can readily enter a vessel of the vascular system of a patient.  
         [0033]     A work performing device such as an atherectomy or cutting device of the type described in European patent application 163 502 may be provided in the distal extremity of the tubular assembly  12 . A suitable cutting device is described in said European application and consists of a housing  27  that is provided with a cutout  28 . A rotary cutter  29  is rotatably disposed within the housing  27  and is provided with a hub  31  that is secured to a flexible rotatable torque cable  32 . The cable  32  is disposed in and extends through the torque tube lumen  14 . The torque cable  32  is formed of a suitable material such as stainless steel. The housing  27  is provided with a rounded tip  33  having a recess  34  which is adapted to receive material which is removed by the rotary cutter  29  as the cutter  29  is advanced as hereinafter described. A spring tip guide or guidewire  36  capable of being shaped is secured to the rounded tip  33  and extends forwardly therefrom and serves to guide or steer the housing  27  as the tubular assembly  12  with the cutting device  26  secured thereto is introduced into the vessel of the vascular system of the patient. As shown, the spring tip guide  36  can be secured to the rounded tip  33  by suitable means, such as solder  37 . It thus can be seen that the guidewire  36  is associated with the housing  27 . Alternatively, a movable guidewire  38  ( FIG. 2B ) can be utilized to facilitate steering of the catheter  11  into the desired vessel of the patient.  
         [0034]     A balloon  41  of an expandable type is optionally secured to the housing in a region opposite the cutout  28  and has its distal extremity bonded around the tip  33  by suitable means, such as an adhesive  42 . As shown in  FIG. 2 , the balloon  41  underlies substantially the entire length of the housing  27 . The balloon  41  is in communication with a balloon tube  43  that extends through the balloon tube lumen  16  in the tubular element  13 . The balloon tube  43  is provided with a lumen  44  through which a medium can be introduced for inflating the balloon  41  and removed for deflating the balloon  41 . The proximal extremity of the balloon  41  and the proximal extremity of the housing  27  are secured to the distal extremity of the tubular assembly  12  by suitable means, such as heat shrinkable tubing  46 .  
         [0035]     A system  49  is provided at the distal end  49  of catheter  11  for imaging the region in which the work performing device is located, said system usually being a two-dimensional ultrasound image system. The system  49  includes an ultrasonic transducer, such as a single crystal  51  (see  FIG. 5 ), which is mounted on the hub  31  and is secured thereto by suitable mans such as an adhesive. The crystal  51  is part of an assembly  52 . The crystal  51  should be capable of operating at a frequency range of 5 to 50 megahertz and typically can be formed of a suitable material such as barium titanate or cinnabar. As can be seen from  FIG. 5 , the crystal  51  has a rectangular block-like configuration and has two opposed surfaces covered by metallic conducting films  53  and  54  formed of a suitable material such as chrome or gold. The material of the films can be formed of a foil or can be in the form of films evaporated or sputtered onto the opposite surfaces of the crystal  51 . The films  53  and  54  serve as electrodes and are connected to connecting wires  56  and  57  by suitable means, such as solder. Means is provided for damping out the oscillations from the backside of the crystal  51  and takes the form of a rectangular block  58  formed of a suitable backing material. The baking material can be formed in a conventional manner so as to cancel out oscillations from the side of a crystal in which the backing material is disposed.  
         [0036]     The present invention, however, is not limited to the use of piezoelectric crystal oscillators as the ultrasonic transducer, and organic electrets such as polyvinylidene difluoride (PVDF) and vinylidene fluoride-trifluoroethylene copolymers may also find use. PVDF is particularly suitable as a transducer at higher frequencies, typically at or above 40 MHz.  
         [0037]     A male fitting  78  (see  FIG. 1 ) is threaded into the threaded bore  67 . A single arm adapter  81  is mounted in the male fitting  78  and carries an arm  82  having thereon a balloon inflation port  83  that is in communication with the lumen  44  in the balloon tube  43  disposed in the tubular assembly  12 . The single arm adapter  81  is secured to a rotating adapter  86  of a conventional type and through which the tubular assembly  12  extends. Another single arm adapter  87  is mounted in the rotating adapter and is provided with a side arm  88  having an infusion port  89  disposed therein which is in communication with the infusion lumens  17  and  18  provided in the tubular assembly  12 . A tapered fitting  91  is mounted in the single arm adapter  87  and is provided with a threaded bore  92  which carries an O-ring  93  that is adapted to be engaged by a male type fitting  94  to form a liquid-tight seal between the tubular assembly  12  and the torque cable  32  which extends therethrough. The torque cable  32  is secured to a suitable drive member such as a clutch member  98  of the type described in European application 163 502 and U.S. Pat. No. 4,771,774, the disclosures of which are incorporated herein by reference. The clutch member  98  is adapted to be secured to a motor drive means of the type described in U.S. Pat. No. 4,771,774 consisting of a motor drive unit which in the present application is identified as a motor  99  (see  FIG. 6A ). The motor  99  is driven by and is under the control of electronic circuitry forming a part of system  49 . The part of the system  49  shown in block diagram form is substantially conventional and can be of a suitable type such as certain equipment identified as Model 851B manufactured by Advanced Technology Laboratories, Inc., of Bothel, Wash. As shown in  FIG. 6A , such apparatus includes a timing and control block  102  that supplies pulses to a transmitter  103 . The output of the transmitter  103  is supplied through a transmit receive switch  104  which supplies the signals on the conductors  73  and  74  through the slip rings  62  and  63  onto the conductors  56  and  57  connected to the crystal  51 . During the time that the transmitter  103  is supplying high frequency energy to the crystal, the crystal assembly  52  is being rotated by the motor driving the torque cable  32  with the motor  99  being under the control of the timing and control block  102 . The motor  99  is of a type such as an open loop stepping motor or a closed loop servo controlled motor which can be driven by the timing and control block  102 .  
         [0038]     As an alternative to the use of an external motor  99  connected to the cutter  29  by torque cable  32 , it would be possible to construct catheters according to the present invention utilizing micromotors within the distal extremity of the catheter. The micromotors  99 ′ could be attached to directly rotate the cutter and transducer (or reflective surface as described hereinafter) typically by mounting at the end of a nonrotating cable  32 ′ analogous to torque cable  32 , as shown in  FIG. 6B .  
         [0039]     As an alternative to the use of an external motor  99  connected to the cutter  29  by torque cable  32 , it would be possible to construct catheters according to the present invention utilizing micromotors within the distal extremity of the catheter. The micromotors could be attached to directly rotate the cutter and transducer (or reflective surface as described hereinafter) typically by mounting at the end of a nonrotating cable analogous to torque cable  32 .  
         [0040]     The transmitter generates a voltage pulse, typically in the 10 to 50 volt range, for excitation of the transducer crystal  51 . Supplying such voltage pulses to the crystal causes the transducer to produce sonic waves which emanate therefrom into the surrounding tissue structure. Portions of the sonic energy wave are reflected by the tissue structure back to the transducer and the transducer  51  acts as a receiver and picks up the sonic vibrations and converts them into electrical signals which are supplied by the conducting wires  56  and  57  back to the slip rings  62  and  63  through the conductors  73  and  74  and through the transmit receive switch  104  to a receiver  106 . These signals are amplified and supplied to a display unit  107  which includes a CRT screen  108  under the control of the timing and control block  102  to supply an image  109  on the display  108  which can be of the type shown in  FIG. 7 . As can be seen from  FIG. 7 , as viewed through 360°, the vessel wall  111  of the image  109  is shown as indicated, having different cross sections depending upon the buildup of plaque therein. A central region  112  of the image is eclipsed because of the imaging catheter. Alternatively, if desired, only a sector of a lesser angle than 360° can be viewed.  
         [0041]     The catheter apparatus of the present invention can be constructed in various sizes. For example, in a 9 French size, the balloon can have a length of approximately 3 centimeters. Sizes down to 3 French and below can be accomplished with the construction of the present invention. These particular dimensions are exemplary only and not intended to limit the scope of the present invention in any way.  
         [0042]     Operation and use of the catheter apparatus, system and method during intravascular ultrasonography can now be briefly described as follows. Let it be assumed that it is desired to utilize the apparatus, system and method of the present invention to remove the atheroma in a blood vessel of a patient. The catheter of the catheter apparatus of the present invention is introduced into a vessel of the patient as, for example, into the femoral artery and introducing the catheter into the artery by the use of the guidewire  36 . The progress of the catheter into the vessel of the patient can be observed under x-ray fluoroscopy. As soon as the cutting device has entered into a region which is desired to remove certain material from the vessel and before a cutting operation is commenced, the atheroma itself can be viewed by operation of the ultrasonic imaging system  49 . This can be accomplished by operating the timing control block  102  to cause operation of the motor  99  which in turn causes rotation of the torque cable  32  and the crystal assembly  52  to scan the interior of the vessel in which the crystal  51  is disposed, usually at a rotation rate in the range from about 100 to 20,000 rpm, more usually from about 500 to 2,000 rpm. An image of what is being scanned will appear on the screen  108  of the display device  107 . Alternatively, the torque cable  32  may be manually rotated (or aimed without rotation) to provide a desired image. Generally, however, motorized rotation will provide a higher definition image. During the time this rotary scanning is taking place, the cable  32  can be advanced to advance the cutter so that the entire region in which the material is to be removed can be scanned. Usually, the cable  32  is advanced incrementally so that distinct cross-sectional images will be successively produced, allowing the operator to determine the length and topography of the region. Alternatively, the entire catheter apparatus  11  may be axially advanced or retracted within the blood vessel lumen to provide a plurality of cross-sectional images to allow assessment of the entire length of the atheroma.  
         [0043]     After the scan, the cable  32  can be retracted slightly (or the catheter  11  repositioned) so that the proximal extremity of the cutout  28  lies at the proximal extremity of the atheroma In order to stabilize the cutting device, the balloon  41  can be inflated so as to urge the cutout  28  of the housing  27  towards the portion of the atheroma it is desired to remove. The motor  99  can then be energized to rotate the cutter  29 . As the cutter  29  is rotated, it can be advanced to progressively remove the material which is disposed within the cutout  28  of the housing  27 . As this material is removed it is pushed forwardly and eventually moves into the recess  34 . The balloon  41  can then be deflated and the catheter apparatus removed from the vessel after which the material which has been deposited in the recess  34  can be removed and the cutting device cleaned for reinsertion into the vessel of the patient for removal of additional material from the vessel if required.  
         [0044]     During the time that the cutting operation is taking place, the cutting operation can be viewed ultrasonically by the rotating crystal  51  that places an image on the screen  108 . From this image it can be ascertained how well the cutter is performing in removing the material and whether or not an additional pass of the cutter is required. It should be appreciated that, if necessary, several passes of the cutter can be made and, if necessary, the catheter assembly can be removed from the vessel of the patient to clean out material which has been removed and deposited in a recess  34 .  
         [0045]     As illustrated in  FIG. 2 , the ultrasonic transducer  51  is oriented to direct the ultrasonic signal in a direction substantially radially outward relative to the axis of the flexible tubular element  13 . It will sometimes be desirable, however, to incline the ultrasonic transducer relative to the tubular axis, as illustrated at  51 ′ in  FIG. 2A . By inclining the transducer  51 ′, the ultrasonic signal is directed at a forward angle α relative to the tubular axis. By rotating the inclined transducer  51 ′, the ultrasonic signal will sweep a conical pattern directed forward of said transducer. The angle α may be in the range from about 10° to 85°, usually being in the range from 20° to 60°. Scanning with a conical sweep is desirable because it can provide forward viewing at or in front of the location where the cut is being made.  
         [0046]     An alternate embodiment  11 ′ of catheter  11  is illustrated in  FIG. 2B . The catheter  11 ′ is similar to that of catheter  11 , except that it is modified to permit insertion of the catheter  11 ′ over a movable guidewire  38  and the cutter  29 ′ is reversed to provide cutting when the cutter is translated in the proximal (rearward) direction. The modifications include providing a penetration  39  in the distal tip of housing  27  and an axially aligned penetration  40  in the cutter  29 ′. The ultrasonic transducer  52 ′ is mounted on the distal end of cutter  29 ′, and torque cable  32 ′ includes an axial lumen. In this way, the catheter  11 ′ is inserted by conventional techniques over guidewire  38 , with the guidewire passing through penetrations  39  and  40  and the lumen of torque cable 32°.  
         [0047]     Another embodiment of the catheter apparatus of the present invention is shown in  FIGS. 8 and 9 . Many of the parts are very similar to the parts utilized in the embodiment of the invention shown in  FIG. 1  and have been given the corresponding numerals. The ultrasonic transducer  52  is mounted in a cavity  53  formed to the rear of the rotary cutter  29 . The distal extremity of the catheter apparatus shown in  FIG. 8 , (i.e., to the left) differs from the apparatus shown in  FIG. 1  in that the conducting wires or leads connected to the ultrasonic crystal  52  are connected to the outside world at a point which is proximal of an adapter  122  whereas in the embodiment shown in  FIG. 1 , the connectors are connected at a point which is distal of the adapters  82  and  88 . Thus, there is shown an adapter  122  which is provided with an arm  123  through which dye injection and pressure measurements can be made and another fitting  124  which can be utilized in inflating and deflating the balloon  41 . Another adapter  126  is provided which is threaded into the proximal end of the adapter  122  and forms a sealing engagement with an O-ring  127  carried by the adapter  122 . The torque cable  32  extends through the adapter  126  and is connected to a clutch member  128 . The clutch member  128  which carries a finger operated member  129  is adapted to be secured to motorized drive means of the type hereinbefore described for causing rotation of the torque cable  32 .  
         [0048]     As hereinbefore explained, the conducting wires connected to the ultrasonic transducer  52  are braided into the guidewire  32 . Means is carried by the adapter  126  which is adapted to make contact with the conducting wires connected to the crystal  52  and consists of brushes  131  and  132  which are yieldably urged by springs  133  towards the torque cable  32  so as to make contact with the conducting wires or leads carried by guidewire  32 . The springs  133  are held in place by pins  134  which are frictionally seated within the adapter  126 . Conducting wires  136  and  137  are connected to the pins  134 . These wires  136  and  137  are connected into the system in a manner hereinbefore described with the previous embodiments. The operation of this embodiment is very similar to that described in conjunction with the operation of the embodiment shown in  FIG. 1 .  
         [0049]     Operation of this embodiment of the invention is very similar to that hereinbefore described with the principal advantage being that leads which are connected to the crystal and for receiving signals from the crystal are disposed proximally of the two arm adapter  122 .  
         [0050]     As a modification of catheter  121 , cutter  29  could be provided with an abrasive external surface, either in place of or in addition to the forward cutting edge. Such an abrasive surface would be useful to remove atheroma and plaque by contact abrasion.  
         [0051]     Still another embodiment  151  of the catheter apparatus of the present invention is shown in  FIG. 10 . Certain parts of this catheter apparatus  151  are very similar to those hereinbefore described and are identified by the same numbers. Thus there has been provided a housing  27  which has an outwardly facing cutout  28 . A coil spring guide wire  36  is secured to the distal extremity of the housing  27  as shown (although the catheter  151  could easily be adapted to receive a movable guidewire as described above in connection with the embodiment of  FIGS. 1-4 ). The balloon  41  is carried by the housing and has its distal extremity secured to the housing by a band  92 . The balloon  41  is disposed outside of the housing  27  on the side opposite the cutout  28 . A flexible tubular assembly  154  is secured to the proximal end of the housing  27 . A three-arm adapter  152  is mounted on the proximal extremity of the tubular assembly  154 . The tubular assembly  154  comprises a flexible tubular element formed of a suitable material, such as plastic which is provided with a balloon inflation lumen  155  that is in communication with the interior of the balloon  41  and extends into a balloon inflation port  156  provided as a part of the three-arm adapter  152 .  
         [0052]     A crystal  157  is carried by the housing  27  in a stationary position. As shown, the crystal  157  is mounted vertically or in a direction that is at right angles to the longitudinal axis of the housing  27 . It can be mounted in the distal extremity of the housing  27  in a suitable manner such as by an adhesive. A suitable sound absorbing material  158  is provided behind the ultrasonic crystal  157  and fills the space between the crystal  157  and the distal extremity of the housing  27 . A pair of conducting wires  161  are connected to the ultrasonic crystal  157  and extend rearwardly through the housing  27  and are connected into sockets  162  provided in a side arm  163  forming a part of the adapter  152 .  
         [0053]     The flexible tubular element  154  is provided with a large lumen  164  extending the length thereof and which has a rotatable flexible drive cable  166  disposed therein. The flexible torque cable  166  is formed in the manner hereinbefore described and is secured to a generally cylindrical member  167  which as hereinafter described, serves as a reflector mount and also serves to carry a rear-facing rotary cutter  169 . Thus, as shown, the member  167  is provided with a reflective surface  168  which is inclined at an angle of approximately 45° and faces the transducer  157  in such a manner so that sound waves propagated by the transducer impinge upon the surface  168  and are propagated outwardly in a direction substantially transverse, i.e., at right angles, to the longitudinal axis of the housing  27 . A circular cutting edge  169  is provided on the member  167  at the proximal extremity thereof. A truncated conical recess  171  is provided in the proximal extremity of the member  167 . The conical recess  171  can be used as a reservoir for collecting material as it is severed by the circular cutting edge  169 .  
         [0054]     The angle of inclination of the reflective surface  168  relative to the axis of housing  27  may be varied, particularly being increased, as illustrated in  FIG. 10A , where angle β may be in the range from 10° to 85°, usually being in the range from 10° to 40°. By inclining the reflective surface by an angle β less than 45°, the reflected ultrasonic signal will sweep in a rearward conical pattern which allows viewing at or in front of, (i.e., to the right in  FIG. 10 ), the cutting edge  169  of member  167 .  
         [0055]     The three-arm adapter  152  is provided with another arm  173  which serves as an infusion port and which is in communication with the lumen  164  through which the drive cable  166  extends. This lumen  164  opens into the interior of the housing  27  and is in communication with the cutout  28 . Another adapter  176  is threaded into the proximal extremity of the adapter  162  and engages an O-ring  177 . The drive cable  166  extends through the adapter  176  and has its distal extremity secured to the clutch member  128 . As hereinbefore explained, the clutch member  128  can be secured to a motorized drive means (or may be manually rotated) for causing rotational movement of the cutter and mirror member  167 .  
         [0056]     An alternate embodiment  151 ′ of catheter  151  is illustrated in  FIG. 10B . The catheter employs a fixed ultrasonic transducer  157 ′, but cutter  169 ′ is reversed to provide for forward cutting. Forward cutting is often advantageous in that severed stenotic material is less likely to become entangled with the torque cable  166 ′. Ultrasonic transducer  157 ′ will be provided with a central penetration to allow passage of the torque cable  166 ′, and said transducer will be located at the proximal end of housing  27 ′, but otherwise the construction of catheter  151 ′ will be the same as catheter  151 .  
         [0057]     In a further modification, it is possible to secure the ultrasonic transducer  157 ′ onto the torque cable  166 ′. Wires connecting the transducer  157 ′ to the external receiver and transmitter would then be attached to the torque cable  166 ′ and coupled to the outside in a manner similar to that illustrated in  FIGS. 1-4 . The transducer  157 ′ would then translate axially in tandem with the cutter  169 ′ and the mirror  168 ′. By maintaining a fixed distance between the cutter  169 ′ and transducer  157 ′, signal processing to produce an image is simplified.  
         [0058]     Operation of the catheter apparatus  151  shown in  FIG. 10  may now be described as follows. The operation of this device in many respects is very similar to that hereinbefore described with respect to the placement of the catheter in the vessel. The housing  27  can be positioned in the stenosis hereinbefore described and ultrasonic imaging can be carried out by supplying pulses of electrical energy to the ultrasonic transducer  157  which emanates ultrasonic energy and directs the same onto the reflector  168  which reflects the ultrasonic energy up into the tissue surrounding the housing. Rotation of the mirror  168  causes an image to be formed that can be viewed in the manner hereinbefore described. This imaging can be carried out by rotating the cable  166  and at the same time advancing the drive cable  166  throughout the length of the cutout  28  to view the stenosis. After the viewing operation has been accomplished and it is ascertained that it is desirable to remove the material creating the stenosis by use of the work performing device in the form of the cutter member  167 , the cutter member  167  can be advanced to the distal extremity of the cutout  28 . With the cutout  28  in the proper location, the balloon  41  can then be inflated through the balloon inflation port  156  to urge the housing  27  in a direction so that the stenosis enters the cutout. As soon as this has been accomplished, the cutter member  157  can be rotated at a high rate of speed and gradually retracted, (i.e., translated to the right in  FIG. 10 ), to cause the material forming the stenosis to be severed by the blade  169  on cutter member  167  and collected within the recess  171 . This cutting and collecting operation can be continued until the cutter member  167  has been advanced to the extreme proximal position. At this time, the catheter apparatus  151  can be removed and the tissue collected within the recess  171  can be removed. Thereafter, additional insertions of the catheter apparatus can be made and the same cutting operations performed until desired amount of material has been removed from the area of the stenosis to provide for increased blood flow through the vessel.  
         [0059]     Another embodiment of a catheter apparatus  180  incorporating the present invention is shown in  FIG. 11 . The catheter apparatus  180  is utilized solely for imaging purposes and employs a fixed ultrasonic transducer  182  which transmits its signal against a rotating reflective surface  204 . The catheter apparatus  180  is constructed very similar to the catheter apparatus  151  shown in  FIG. 10  with the exception that the cutting mechanism has been eliminated. The use of such a catheter apparatus  180  is desirable where it is unnecessary to provide a cutting function (or other interventional treatment modality). The catheter apparatus  180  also has many parts that are similar to the catheter apparatuses heretofore described. Thus there is provided a housing  27  which carries on its distal extremity a coil spring guide  36 . As before, however, the catheter  180  can also be adapted to be inserted over a movable guidewire within the scope of the present invention. The ultrasonic transducer  182  is provided in the distal extremity of the housing  27  and is disposed vertically or in a direction that is perpendicular to the longitudinal axis of the housing. A sound absorbing backing material  183  is provided in the distal extremity of the housing behind the transducer  182 . Conducting wires or leads  184  are connected to the transducer  182 . The proximal extremity of the housing  27  is connected to the distal extremity of flexible elongate tubular element  186  that is connected to a two-arm adapter  187 . The leads  184  extend through the tubular element  186  and are connected to sockets  188  provided in the arm  189  of the two-arm adapter  187 . The tubular element  186  is provided with a large lumen  191  that carries the drive cable  192 . The drive cable  192  is connected to a clutch member  193  of the type hereinbefore described which is adapted to be driven by motive means in the manner hereinbefore described. The clutch member  193  is provided with a flange  194  that cooperates with a flange  196  on the adapter  187 . The adapter  187  carries an O-ring  197  seated against another flange  198  forming a part of the adapter  187 . The O-ring  197  forms a liquid-tight seal with respect to the drive cable  192 . The clutch member  193  is thus held in a fixed longitudinal position while still permitting rotation of the same. The adapter  187  is provided with a tapered surface  199  adapted to fit into a motor drive means. Alternatively, the clutch member  193  can be adapted for manual rotation. Alternatively, the clutch member  193  can be adapted for manual rotation.  
         [0060]     The drive cable  192  has its distal extremity secured to a rotating member  203  which is provided with an inclined reflective surface  204  which serves as a reflector for reflecting ultrasonic energy generated by the transducer  182  in a transverse direction relative to the longitudinal axis of the housing  27 . The angle of inclination of surface  204  may vary, typically between 45° and 85° provide for forward viewing as described above, depending on the sweep geometry desired. As illustrated, the torque cable  192  is unable to axially translate within the lumen  191 . Thus, the reflective surface  204  on rotating member  203  remains in a fixed longitudinal position relative to the housing  27  and cannot be advanced or retracted with respect to the ultrasonic transducer  182 . The reflective surface  204  can, of course, be axially translated within a blood vessel by movement of the catheter  180  as a whole. Also, the catheter  180  could be modified to permit axial translation of the rotating member  203  within the housing  27  (in a manner similar to the previous catheter embodiments), but generally this will be unnecessary.  
         [0061]     The large lumen  191  in flexible elongate tubular element  186  is in communication with a side arm port  206  that forms a part of the two-arm adapter  187 . The housing  27  should be formed of a material that causes minimal attenuation of the ultrasonic signal which is transmitted and received by transducer  182 . Suitable materials include polyethylene, silicone rubber, polyvinyl chloride, polyurethanes, polyesters, natural rubbers, and the like. Alternatively, the housing may be formed of acoustically opaque materials if a cutout  207  (shown by the dashed lines) is provided through which the ultrasonic energy can pass.  
         [0062]     The operation of the catheter apparatus  180  shown in  FIG. 11  is very similar to that hereinbefore described with the exception that the cutting operation is omitted. With this catheter apparatus, the device can be inserted in the same manner as with respect to the other devices hereinbefore described. When the device is in the desired location, as for example, in the stenosis, the stenosis can be imaged ultrasonically by causing the rotating member  203  to be rotated with respect to the crystal  182  to cause ultrasonic energy to be directed upwardly and outwardly through the housing  181  to impinge upon the sidewalls of the vessel in which the catheter apparatus  180  is positioned. If a different longitudinal position is desired to be scanned, the entire catheter apparatus  181  can be shifted longitudinally in the vessel to the desired location. After the ultrasonic imaging has been completed, the catheter apparatus  180  can be removed and other operations performed if desired with other instruments.  
         [0063]     It should be appreciated that if desired, another embodiment of catheter apparatus used solely for imaging can be provided by mounting the crystal at the end of the torque cable as illustrated in  FIG. 8  so that the crystal is rotated about an axis parallel to the longitudinal axis of the housing.  
         [0064]     From the foregoing, it can be seen that a two-dimensional ultrasound image is generated by rotating a crystal or a mirror that is located at the tip of the catheter. Good resolution is obtained because of the relatively high frequency, i.e., 5 to 50 megahertz, that is used. The image that is created is generally perpendicular to the longitudinal axis of the catheter, but may also be in a forward conical pattern, depending on the precise geometry of the transducer and/or mirror. The motor or manual drive means that is utilized for rotating the transducer is external to the patient. Rotation, of the transducer is made possible because of the electrical connection made with the brush contacts. The use of the balloon stabilizes the housing so that the cutting operation can be readily accomplished.  
         [0065]     The apparatus and system of the present invention makes it possible to obtain images in very small vessels and has made it possible to accomplish the same by utilizing the precision driving of a very flexible cable. The catheter apparatus in addition to being capable of imaging is also capable of being steered by the flexible guidewire secured to the tip.  
         [0066]     It is apparent from the foregoing that there has been provided a catheter apparatus, system, and method which is particularly useful for intravascular two-dimensional ultrasonography and which can be utilized with many different types of operations, as for example, in performing atherectomies.