Abstract:
A motorized scanhead device is capable of rotating an array transducer through 360 degrees of angular rotation in a manner such as to provide acquisition of images in successive scanning planes arranged around the principal axis of the device. The device can be incorporated in endoscopes (e.g., transesophageal endoscopes), laparoscopes, endocavity or intracavity probes so as to provide an expanded angle of vision or to render 3D images, without the need for external movement of the device. The motorized scanhead device includes a motor that is isolated from the transducer signal interconnections in order to minimize electrical discharges associated with motor operation and to provide more room between an associated probe housing and the scanhead device.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to ultrasonic diagnostic scanheads and, more particularly, to a motorized scanhead device capable of rotating an array transducer through 360 degrees of rotation to provide image acquisition.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     Ultrasonic imaging apparatus dedicated to endocavity or intracavity operations are well known especially in diagnostic applications such as celioscopy, TE Transesophageal Echography, laparoscopy, and transvaginal and transrectal applications. In addition, probes for intraluminal or intravascular use are very similar except for their smaller diameter. All of these apparatus has a common characteristic, viz., an ultrasonic scanhead is assembled at the distal tip of the probe so as to allow imaging of regions of the tissue being examined which are located remotely and cannot be directly accessed.  
         [0003]     With respect to the endocavity modalities currently being practiced, the existing apparatus are typically provided with either a fixed array transducer or a dual transducer or a moving array transducer for multiplane or volume rendering operations. In many cases, the array transducer is mounted longitudinally with respect to the probe axis and can, therefore, provide scanning of a lateral scanning plane to provide a sector scan. In some circumstances, it is desirable for the transducer to be able to rotate around its longitudinal axis so as to acquire multiplane information or to track a target (e.g., cysts or a biopsy needle). Currently, this action can be carried out by either rotating the probe or the transducer. However, such rotation of the probe may cause significant discomfort to the patient and present risks during manipulation.  
         [0004]     Imaging apparatus having a transducer tip capable of rotation with reference to the probe handle have been disclosed, for example, in U.S. Pat. No. 5,413,107 to Oakley and U.S. Pat. No. 5,681,263 to Flesch. An articulated ultrasonic probe for endoscopic examination having rotation means for the articulated section of the probe is disclosed in the Oakley patent. In this patent, an array transducer is mounted at the distal tip of the endoscope tube. The distal portion can be steered in four different directions by actions manually exerted on control cables through commands provided at the handle of the probe. The transducer head is enabled to rotate by the use of a bellows attached to a rigid tube through which the movement is transmitted. The use of the rigid tube in combination with the bellows allows the apparatus to be rotated even in an articulated position. However, as long as the rigid tube provides sheathing externally if the endoscope, any movement of the transducer will be directly communicated to the external medium and this can lead to patient discomfort and a risk of wounding or other damage to the organ in contact with the probe. Further, sealing problems and problems with disinfection of the instrument may also occur with the use of seals.  
         [0005]     An improvement in the probe of the Oakley patent is disclosed in the Flesch patent wherein the transducer tip is made to rotate internally by cable control. Neither a transmission tube nor a bellows is therefore required. The movement of the transducer only affects the articulated portion of the probe apparatus, thus decreasing patient discomfort and the risk of injury to the tissue.  
         [0006]     However, the devices of both patents discussed above still suffer drawbacks and disadvantages. The latter include, for example, the interdependence between the articulation mechanism and the rotation of the transducer (and the corresponding variation of resistance torsion stiffness versus the angle of articulation), the inaccuracy induced by movement of the transducer combined with the effect of friction, and the lack of compatibility with precision 3D acquisition or real time volume image rendering.  
         [0007]     Endoscope probes providing rotating of the transducer mounted inside of the probe are disclosed in U.S. Pat. No. 4,374,525 to Baba. In this patent, an ultrasonic diagnostic apparatus for an endoscope includes a bendable insertable section of the endoscope that is equipped with an ultrasonic transducer at the distal tip. The tip comprises a liquid bath in which is immersed a rotating transducer unit. The transducer unit is assembled to a drive shaft having a hollow space for passing the transducer interconnections to the handle. Because the shaft and the transducer are rotated, slip ring devices are used for transmitting the electrical signals from the moving shaft to the external electrical connectors for the probe. Articulation of the transducer tip is provided by hinges disposed behind the transducer assembly. It is therefore apparent that this approach cannot be practically applied to devices that include an array transducer wherein hundreds of transducer interconnections are required.  
         [0008]     An arrangement which avoids positioning of the moving member between the transducer and the handle of the probe is disclosed in U.S. Pat. No. 4,375,818 to Suwaki. This patent discloses an ultrasonic diagnostic apparatus associated with an optical system for the examination of the coeliac cavity. In one embodiment, an alternative form of the apparatus is provided wherein a motorization or drive means, e.g., a motor, is housed within the foremost portion of the distal tip. A driving mechanism is disposed between the transducer and the motor. The transducer is immersed in a liquid bath and gaskets are used for preventing leakage of liquid. In this patent, providing transducer interconnections does not present a problem, and a passageway forl cables for the motor power supply is provided underneath a chamber containing the transducer. However, this approach still has a number of shortcomings that prevent complete rotation of the transducer. These include the presence of the electrical connections for the motor. Further, there is a risk of liquid leakage through the motor shaft and this makes such an apparatus unreliable for use in continuous operation (as is required in 3D rendering operations).  
         [0009]     An arrangement wherein an array transducer is rotated with reference to its longitudinal axis is disclosed in U.S. Pat. No. 5,085,221 to Ingebrigtsen. This patent discloses a TE transducer head comprising a cylindrical housing, an end cap, a motor coupled to an array transducer to provide rotation thereof, a position sensor axially aligned with the motor, and a set of flexible cables for providing electrical connections to the array transducer. Although his patent does not disclose the coupling mode between the array transducer and the end cap, it can be assumed that an internal space within the housing is filled with coupling liquid for the transmission of acoustic energy to the medium. The transducer head can also be plugged to an endoscope or probe housing using an interconnection interface provided at the proximal end of the device. As provided in a preferred embodiment, the back side or rear of the array transducer is connected to a first flexible cable that is, in turn, connected to a second flat cable or conductor adaptor. Direct drive of the transducer provided by the motorization means (e.g., motor) and controlled by the position sensor enables the apparatus to be compatible with 3D acquisition or with real time volume rendering. However, the approach disclosed in this patent suffers at least two major limitations. First, the transducer cannot perform a complete rotation (because of the interconnection cables). Second, the rotation velocity of the transducer will be significantly slowed by the liquid resistance of the coupling liquid used in this type of transducer.  
         [0010]     In U.S. Pat. No. 5,176,141 to Bom, a disposable catheter probe is disclosed for intraluminal applications. In one preferred embodiment, a motor or motorization means is disposed at the distal portion (tip end) of the apparatus, and provides rotation of an acoustic mirror that laterally steers the ultrasonic energy issued from a transducer arranged along the longitudinal axis of the probe. No movement of the transducer is required to obtain a cylindrical scanning image and, in general, the rotational speed of the acoustic mirror can be set to be as high as desired. On the other hand, rotation of the acoustic mirror as described in the patent requires the use of a liquid chamber for acoustically coupling the ultrasonic energy. This results in a need for dynamic seals for protection of the motor, and such seals often exhibit a lack of reliability and durability. Another shortcoming of this approach concerns the positioning of the transducer. This positioning does not permit the assembly of linear arrays due to the lack of room in the lateral dimension. Thus, this approach is not suitable for use in volume acquisition modalities.  
         [0011]     Others endoscopes and intravascular ultrasound (IVUS) devices provide for rotating the transducer by use of a driveshaft driven by a remotely located motorization means (e.g., a motor located in the handle of the probe). This method results in non-uniform angular velocity so that the rotational speed must be corrected by a position sensor co-located with the transducer as well as dedicated servo-control electronics to ensure precise positioning of the transducer when rotated. For example U.S. Pat. No. 6,019,726 to Webb discloses a method for correcting the non-uniform velocity of a transducer.  
         [0012]     Given the state of the art of ultrasonic endoscopic/intraluminal probes as described above, there is obviously a-need for an ultrasonic scanhead dedicated to such a probe which is capable of providing transducer rotation through angles of up to 360 degrees.  
       SUMMARY OF THE INVENTION  
       [0013]     One object of the invention is to provide a probe providing transducer rotation through angles up to 360 degrees using an arrangement wherein linear arrays are mounted in axial alignment with the probe body without a rotation or drive means mounted between the transducer and the probe handle.  
         [0014]     It is a further object of the present invention to provide an ultrasonic endoscope/intraluminal probe wherein a motorization means is assembled at an end portion of the probe and wherein a complete cylindrical scanning operation can be performed using a linear array transducer mounted parallel to a lateral surface of the endoscope/intraluminal probe body.  
         [0015]     It is still another object of the present invention to provide a rotating linear array scanhead having improved EMI protection for transducer signals supplied to the external cables.  
         [0016]     It is still a further object of the present invention to provide an ultrasonic scanhead for endoscope/intraluminal probes wherein rotating linear arrays are electrically connected to winding flexible circuits in such a manner as to allow rotation through at least 360 degrees, without any resultant movement of the output portion of the flexible circuits.  
         [0017]     According to one aspect of the invention, there is provided a motorized ultrasonic scanhead device which is capable of providing rotation of an associated array transducer through an angle of 360° or more, so as to enable image acquisition for successive scanning planes being arranged around the principal axis of the device. The device of the invention can be implemented as part of, i.e., can be incorporated in, endoscopes (e.g., transesophageal endoscopes), laparoscopes, endocavity or intracavity probes so as to provide an expanded angle of vision or to render 3D images without the need for external movement of the device. A further aspect of this invention concerns a motorized scanhead wherein the motorization means or motor is isolated from transducer signal interconnections in order to minimize any electrical discharges associated with motor operations and to also provide more room for the assembly between the probe housing and the scanhead device.  
         [0018]     It will be understood that different aspects of the present invention that are disclosed with respect to the principles of the invention can be extended to any type of imaging apparatus having an elongated member or tube terminating in a scanning tip, including endoscopes, intraluminal catheters, endocavity probes and the like.  
         [0019]     Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     FIGS.  1 ( a ),  1 ( b ) and  1 ( c ) are schematic longitudinal cross-sectional views of respective prior art probes providing different modes of transducer movement;  
         [0021]      FIG. 2  is a block diagram of the basic elements of a scanhead assembly in accordance with the invention;  
         [0022]      FIG. 3  is a longitudinal cross section of one preferred embodiment of the ultrasonic scanhead of the invention;  
         [0023]      FIG. 4  is a side elevational view of a scanhead showing external features thereof;  
         [0024]      FIG. 5 ( a ) is a transverse cross-sectional view of one preferred embodiment of the invention incorporating a single array transducer;  
         [0025]      FIG. 5 ( b ) is a transverse cross-sectional view of a further preferred embodiment of the invention incorporating a pair of array transducers mounted in an opposed relation;  
         [0026]      FIG. 6  is a longitudinal cross section of a scanhead in accordance with a further embodiment of the invention;  
         [0027]      FIG. 7 ( a ) is a transverse cross-sectional view taken generally along line A-A of  FIG. 2 ;  
         [0028]      FIG. 7 ( b ) is a transverse cross-sectional view taken generally along line B-B in  FIG. 2 ;  
         [0029]      FIG. 7 © is a transverse cross-sectional view taken generally along line C-C in  FIG. 2 ;  
         [0030]      FIG. 8  is a cross-sectional view of a scanhead in accordance with yet another embodiment of the invention;  
         [0031]      FIG. 9 ( a ) is a longitudinal cross-sectional view of a scanhead in accordance with a further embodiment of the invention, and incorporating a dual flex output;  
         [0032]      FIG. 9 ( b ) is a transverse cross-sectional view of the scanhead of  FIG. 9   a;    
         [0033]      FIG. 10  is a transverse cross section of a cannula showing embedded electrical wires for motor connections;  
         [0034]      FIG. 11  is a longitudinal cross-sectional view of the cannula of  FIG. 10 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Before considering the preferred embodiments of the present invention, reference is made to FIGS.  1 ( a ),  1 ( b ) and  1 ( c ), which show various approaches or modes for providing rotational movement of a transducer in an ultrasonic scanhead, all of which use either a remotely located motor or a motor directly coupled to the transducer to be rotated.  
         [0036]     Referring to  FIG. 1 ( a ), there is shown a schematic cross-sectional first prior art probe  10  including a probe body  10   a  containing a motor-driven drive gear  10   b  that drives an intermediate gear  10   c  that, in turn, drives ring gear  10   d  mounted on a rotatable transducer unit  10   e  so as to extend around the circumference thereof. Transducer unit  10   e  is of conventional construction including a transducer array  10   f  and is mounted such that the longitudinal axis  10   g  thereof extends orthogonal to the longitudinal axis of the probe  10 . The drive mechanism including gears  10   b ,  10   c  and  10   d  converts rotation of drive gear  10   b  into rotation of transducer unit  10   e  around its longitudinal axis  10   g.    
         [0037]     In the prior art probe  12  of  FIG. 1 ( b ), a motor  12   a  drives a transducer unit  12   b  including a transducer array  12   c  and mounted on a motor-driven driveshaft  12   d . The requisite electrical connections to transducer unit  12   b  are indicated at  12   e.    
         [0038]     Referring to  FIG. 1 ( c ), there is shown a prior art probe device  14  including a motor  14   a  which drives transducer unit  14   b  of a disc-shape configuration through an intermediate driveshaft  14   c.    
         [0039]     A scanhead in accordance with the present invention will now be described in connection with  FIG. 2  where a scanhead main body  21  is connected at its proximal end (on the right side as viewed in  FIG. 2 ) to a tubular endoscope/catheter  23  via an interconnect system  24  that can comprise a suitable mechanical connection (e.g., a rod- or thread-like connector) or a suitable adhesive or glue. At the distal end (the left side as viewed in  FIG. 2 ), the scanhead main body  21  is attached to a motorization unit or motor  22  by connection means  25  which can again comprise a suitable mechanical connection or an adhesive. An important feature of the scanhead of  FIG. 2  is that motorization unit  22  is located at the distal end of the scanhead apparatus as illustrated. The tubular body  23  is also connected to an endoscope/catheter handle  26  by connection means  27  which include seals for preventing liquid infiltration. It will be understood that the block diagram of  FIG. 1  is intended to illustrate a basic feature of the invention and should not be interpreted as limiting the invention in any way. For example, a scanhead, main body  21  can also be of a shape other than the cylindrical shape illustrated.  
         [0040]     It will also be understood by those skilled in the art that while important objects of the present invention concern an ultrasonic scanhead for endoscope/catheter use, endoscope/catheter devices are well known per se and no specific description of such endoscope/catheter devices is provided here. In general, any kind of endoscope/catheter device can be used in achieving the objects of the present invention.  
         [0041]     Referring to  FIG. 3  there is shown the internal construction of an ultrasonic scanhead in accordance with a first preferred embodiment. An array transducer  34  that may be of a type having linear or phased arrays is connected to a longitudinally extending flexible interconnection circuit  38  that extends externally from a transducer carrier or mounting member  33 .  
         [0042]     The transducer carrier  33  preferably comprises a molding for one or more array transducers  34  which is made from a resin or resins such as epoxies or polyurethanes. The molding formed by carrier  33  comprises a cylindrical portion having a first diameter which matches the internal diameter of a scanhead housing  30  with a small clearance for receiving a coupling grease or liquid  35 . A second diameter portion is provided on the right side of the carrier  33  as viewed in  FIG. 3  which is of a smaller diameter than the first diameter and serves to provide guidance in positioning the carrier  33  into the housing  30 . A third diameter portion is provided on the left side of the carrier  33  as viewed in  FIG. 3  and is adapted to be coupled to the armature or driveshaft of motorization means or motor  37  so as to provide rotation of the carrier  33 . A hollow bore or through space  36  is also provided in carrier  33  which extends coaxially with respect to the axis of symmetry of the scanhead which provides a passageway for electrical wires  31  of the motor power supply.  
         [0043]     The housing  30  is preferably made of an acoustically transparent material or materials such as TPX™, polysulfone or a high density polyethylene (PE) so as to provide smooth transmission of ultrasonic energy and to avoid reflections of this ultrasonic energy from the material itself.  
         [0044]     In an alternative construction housing  30  can be made from any rigid material (e.g., a polymer or metal can be used in making the housing body) but with the inclusion of a cylindrical acoustically transparent window (not shown) in alignment with the transmitting surface of array transducer  34  during scanning of transducer  34  so that the ultrasonic energy passes through this window.  
         [0045]     Since the electrical wires  31  for energizing motor  37  are placed along the central longitudinal axis of carrier  33 , wires  31  will, therefore, remain static, i.e., do not move. During a scanning operation, the array transducer  34  can be rotated through an angle of 360 degrees, or more, if desired. The motorization means or motor  37  can, for example, be a motor selected from the group consisting of DC, synchronous and stepping motors, is, as shown, mounted axially with respect to the transducer carrier  33  and housing  30 .  
         [0046]     Preferably, motor  37  is equipped with a hollow shaft  43  that is secured to a third diameter portion of carrier  33  as shown in  FIG. 3  in a manner so as to form an internal passageway for the electrical cables of the motor  37 . Motor  37  is precisely mounted in a support member  41  which, in turn, fits into and, in essence, forms part of the housing  30  through means of a shoulder  34  that provides sealing and guidance in positioning of the overall motor assembly. It is noted that, as illustrated, support member  41  and housing  30  have the same external diameter after assembly. When assembled together, motor  37 , support member  41  and housing  30  are then secured together by an adhesive (e.g., a glue) or by mechanical means.  
         [0047]     The scanhead device as so assembled is then terminated at the distal end by a cap  42  made of a material of the same type as that of support member  41 , and which will seal the housing by its distal tip.  
         [0048]     At the proximal end of the ultrasonic array transducer, an interconnection volume or area  48  is defined or delimited by the transducer carrier  33 , an elongated shaft or axle  45  and the internal cavity of housing  30 . In volume  38  there is disposed an interconnection means  48  which, in a preferred embodiment, comprises flexible circuits coiled around shaft or axle  45  so as to permit the rotation of the transducer  34  without any torsional effect on the flexible circuits comprising interconnection means  48 . The number of turns around shaft or axle  45  necessary to prevent this torsional effect depends on the maximum amplitude of the rotation of transducer  34  and the velocity at which the transducer  34  is to be rotated. Typically, three to five turns of the flexible circuit  48  are sufficient to enable most scanning operations to be carried out. The flexible circuits  48  are secured at one end to the transducer carrier  33  and at the other end to an opening  40  in housing  30 . Opening  40  is sealed, e.g., by a silicon rubber or an adhesive (glue). Once the sealing operation is complete, an external portion  49  of the flexible circuit  48  will consequently be isolated from any movement and/or vibration of the coiled portion of the flexible circuits  48 .  
         [0049]     Further, the area or volume  38  preferably contains an incremental encoding device  53  which is used to detect rotation and rotational speed information with respect to the transducer carrier  33  through use of a conventional encoding disk (not shown) affixed to the proximal end of the carrier  33 . Electrical wires  52  for the encoding device  43  pass through housing  30  and are sealed at the exit point  51 , with, e.g., a flexible glue (such as silicon rubber or the like).  
         [0050]     Acoustic coupling between the transducer  34  and housing  30  is provided by the aforementioned coupling liquid or grease  35  which is preferably of a uniform thickness. Coupling liquid  35  is disposed on thin “window” portion  56  of housing  30 . A space is provided between the surface of transducer  34  and the internal surface of window portion  56  is such as to provide the assembly with capillarity forces that are sufficiently high to maintain the coupling liquid  35  in place during operation. Typically, these surfaces are separated by a distance ranging from 0.1 mm to 0.5 mm. Preferably, the opposing surfaces of housing  30  and transducer  34  that define or delimit the acoustic coupling zone are coated with low surface tension force material or plasma of a nature such as to improve the capillarity effect. Liquids that are well suited for coupling the acoustic energy in biologic tissue include water, paraffin oil, propandiol glycol and the like. Coupling greases or liquids that can be selected for use include silicon types, and these can be mixed with mineral particles so as to increase the frictional properties and acoustic impedance.  
         [0051]     Referring to  FIG. 4 , there is shown a scanhead or probe device in accordance with a preferred embodiment of the invention. The external construction of the scanhead device is illustrated. In  FIG. 4  the device, which is generally denoted  60 , includes a portion A-A which is located at the distal or outermost end of the device and in which the motorization means (not shown) is housed. Distal portion A-A is located adjacent to an intermediate portion B-B in which the ultrasonic transducer (not shown) is located and which is provided with an acoustically transparent window (not shown) for the passage of energizing ultrasonic waves. A proximal portion C-C serves as a junction between the scanhead and the endoscope/catheter device. Portion C-C is an extension of the portion B-B and forms part of the tubular portion of the scanhead device. Portion C-C serves as a receptacle for an interconnection means (not shown) and a position encoder (not shown). Finally, wires  61 ,  62  and a flexible circuit  69  extend from the proximal end of the scanhead to the handle of the probe where they are connected to external cables (not shown).  
         [0052]     Referring to  FIG. 5 ( a ), there is shown a transverse cross-sectional view of one embodiment of the scanhead of the probe device  60  of  FIG. 4 . In  FIG. 5 ( a ), transducer carrier  63  is mounted for rotation inside of housing  62  and carries a single array transducer  64  including transducer elements  65  and a focusing lens  66 . Electrical connections to transducer elements  65  are indicated at  67 .  
         [0053]      FIG. 5 ( b ) is similar to  FIG. 5 ( a ) except that two oppositely disposed array transducers  64   a  and  64   b  are employed. The other parts common to the two array transducers are similar and are given the same reference numerals with an “a” attached for array transducer  64   a  and with a “b” attached for array transducer  64   b . In a preferred embodiment, the transducer elements  65   a  are of a first configuration and transducer elements  65   b  are of a second, different configuration, and array transducer  64   a  is of a first resonant frequency and array transducer  64   b  is of a second, different resonant frequency.  
         [0054]      FIG. 6  illustrates an advantageous variant of the preferred embodiment wherein a conventional motorization means is mounted so as to provide rotation of a proximally located transducer. The scanhead of  FIG. 5  comprises housing  70  having portions of first and second internal diameters for receiving a transducer  74 . The latter is guided by its proximal shaft  75  into the housing  70 . Transducer  74  is actually molded into a cylindrical shape so as to fit internally within the larger diameter portion of housing  70 . The space remaining between the transducer  74  and the housing  70  is then filled by coupling liquid or grease  76  for promoting good propagation of acoustic energy.  
         [0055]     A position encoder  73  is mounted in the vicinity of the transducer  74  to provide the remote imaging system with accurate information with respect to the position and speed of the transducer  74 .  
         [0056]     An output interconnection means  78  for transducer  74  comprises flexible circuits coiled around the transducer shaft  75 . The interconnection means (flexible circuits)  78  is secured at one end to the transducer mounting portion of housing  70  (not shown) while the other end passes through housing  70  and extends outwardly thereof at  78   a  to enable connection to external cables (not shown).  
         [0057]     Encoder  73  and interconnection means  78  are housed in a space  79  formed by the major diameter portion of the housing  70  and the transducer support portion. In order to provide additional guidance during the assembly of the housing/transducer, a bearing  86  is disposed at the entrance of the smaller diameter portion of the housing  70 .  
         [0058]     The transducer support terminates at the distal end at a reduced diameter portion having mounted thereof at its extremity, a gear  85  which engages a corresponding gear  84  on a motor output gear shaft  89 . In the embodiment illustrated, motorization means  77  is optionally provided with gear reduction gearbox  81  including the output shaft  89  terminated by gear  74 . Gearbox  81  is secured to a support member  71  which is, in turn, affixed to housing  70  so as to form an elongate scanning device including a forwardly or distally located motorization means  77 . It is noted that a proximal portion of support member  71  can be provided with a bearing  76  to provide smoother rotation of the transducer unit  74 .  
         [0059]     The gearing system comprising gears  84  and  85  can be made of plastic so as to reduce operating noise and/or avoid the need for a lubricant such as usually recommended for metal parts. Because the motor shaft  89  is not of a hollow shape as shown in  FIG. 3 , a groove  71   a  in the internal diameter of support member  71  provides a passageway for the electrical power supply wires  88  for the motor  77 . Preferably, the position of the motor  77  with respect to support member  71  is such that gears  84  and  85  mate perfectly once the support member  71  is properly assembled with respect to housing  70 . It will be appreciated that with the arrangement just described, the assembly operation is simplified during manufacturing and the maintenance needed is also reduced.  
         [0060]     A cap  72  is located at the distal end of the scanhead device and covers the distal opening of support member  71  so as to protect the motor  77  and provides smooth terminating shape to the end tip of the device.  
         [0061]     In order to make the scanhead compatible with medical uses, the materials used for housing  70 , support member  71  and cap  72  are preferably selected from medical grade plastics such as PEBAX™, TPX™, PEEK™, ULTEM™ and the like. An EMI coating can also advantageously be provided on the internal surface of cap  72  and on support member  71 . This coating is connected to the electrical ground of the imaging system to improve the signal to noise ratio. Similarly, housing  70  may be EMI protected as well. However, care must be taken to avoid an excessive coating thickness in the region of housing  70  at which acoustic waves are transmitted. In this regard, the coating thickness in this region preferably should not exceed a half of a micron. Suitable materials for EMI coating in the region of the acoustic window include copper and gold. The use of an adhesion precursor will further improve the durability of the coating. Shielding products and processes that can be used include coating systems such as Unishield® from Unitech, SuperShield conductive coating from MG Chemicals, and vaporization techniques such as chemical vapor deposition (CVD) including APCVD (atmospheric pressure chemical vapor deposition), LPCVD (low pressure CVD), PACVD (plasma assisted CVD), PECVD (plasma enhanced CVDDV), PCVD (photo CVD), LCVD (laser CVD), MOCVD (metal-organic CVD), CBE (chemical beam epitaxy), CVI (chemical vapor infiltration) and physical vapor deposition (PVD) including sputtering, MBE (molecular beam epitaxy) and thin film growth techniques such as spray coating, electroplating and liquid phase epitaxy.  
         [0062]     FIGS.  7 ( a ) to  7 ( c ) illustrate three different cross-sectional views, A, B and C, of a scanhead generally depicted as in  FIG. 3  and  FIG. 6  which by arrows A, B and C show the locations at which the sections A, B and C are taken. In the view corresponding to section A shown in  FIG. 7 ( a ), a motor  97  is viewed from the rear side thereof, and interconnection pads  97   a  and  97   b  are provided for powering the motor  97  are also illustrated. A support  91  and cap  92  show the manner in which the motor  97  is mounted. A groove  107  is shown in cross section view and includes motor wires  101  adapted to be connected to the motor pads  97   a ,  97   b.    
         [0063]     As shown in  FIG. 7 ( a ), the motor portion of the scanhead can be assembled and disassembled from the scanhead housing simply by first disconnecting motor wires  97   a  and  97   b . Then support member  91  can be safely removed from the housing without any risk of damage to the scanhead. The reverse operation can be carried out by assembling the support member  91  first and then by soldering the wires  97   a  and  97   b  to the motor  97 . This mechanical construction of the scanhead is highly advantageous when applied to surgical ultrasonic devices requiring maintenance operations.  
         [0064]     In embodiments wherein the motor  97  is provided with a hollow shaft through which the wires  97   a ,  97   b  extend, groove  107  is not needed and wires extending from the center of the motor  97  are connected motor pads  97   a  and  97   b.    
         [0065]     Section B, located on the proximal side of section A, is shown in  FIG. 7 ( b ) and is a sectional view of a transducer  104  and a transducer carrier  103 . Modifications and variations that can be applied to this section have been described in FIGS.  5 ( a ) and  5 ( b ), and the transducer  104  shown in  FIG. 7 ( b ) is shown as being embedded in the carrier  103 . Carrier  103  includes a hollow space  106  through which pass the electrical wires for motorization means for the scanhead. Transducer  104  is positioned at the periphery of carrier  103  in such as manner as to contact a coupling medium  105  which acoustically couples ultrasonic energy between the transducer  104  and a housing  100 , through an acoustic window (not shown in  FIG. 7 ( b )).  
         [0066]     It will be understood that while  FIG. 7 ( b ) only shows a single transducer  104  for purposes of simplicity of illustration, a plurality of independent transducers corresponding to transducer  104  can be provided in positions around the periphery of the carrier  103 .  
         [0067]     Referring to  FIG. 7 ( c ), section C is shown which is taken further along the proximal side of the scanhead.  FIG. 7 ( c ) shows, in section, housing  100 , an interconnection flex circuit  108 , a hollow shaft  106  and a space  118  which houses the above described interconnection means (flex circuit)  108  and a position encoder device  113 . In the latter regard, on the bottom side of space  118  there is illustrated schematically the position encoder  113  which is mounted in front of the abovementioned incremental disk (not shown in  FIG. 7 ( c )) preferably attached to the transducer carrier  103 .  
         [0068]     Still another improvement that can be implemented in the scanhead of the previously described preferred embodiments of  FIG. 3  and  FIG. 6 , is shown in  FIG. 8 .  FIG. 8  is a simplified functional view of a scanhead comprising a housing  120  corresponding to that described, a transducer  124  and a carrier  123 . So as to avoid any wearing contact between the wires  121  which pass through the carrier  123  and the internal cylindrical surface of the carrier  123 , a cannula  132  made from a low friction coefficient material is provided in the hollow space  131  defined by carrier  123 . Cannula  132  is secured to housing  120  so as to remain fixed during the rotation of the transducer  124  and its carrier  123 . A scanhead device equipped with the cannula  132  has the advantage of preventing wearing of wires  121  located therein and, therefore, of increasing the reliability and the lifetime of the scanhead. The scanhead construction of  FIG. 8  is otherwise similar to those described above and thus will not be described further.  
         [0069]     Referring to FIGS.  9 ( a ) and  9 ( b ), there is shown a modification of the abovedescribed preferred embodiments wherein the flexible interconnection circuits or flex circuits are provided on both sides of the transducer carrier. This configuration of the flex circuits is particularly suitable for either a very high density array transducer where the use of dual output flex circuits is mandatory or for a scanhead construction wherein the transducer is to be rotated through an angle less than or equal to 90 degrees. It will be understood that all other features of the preferred embodiments described above are applicable to this embodiments as well.  
         [0070]     In the embodiment of FIGS.  9 ( a ) and  9 ( b ) a housing  134  including a transducer  135  and its carrier  136  are similarly mounted together as described in connection with previous embodiments. Flex circuits  138   a  and  138   b  are located on both sides of the transducer carrier  136  and are coiled around in smaller diameter coils are shown by FIGS.  9 ( a ) and  9 ( b ). Because the flex circuit  138   a  is managed or handled as previously described above in connection with  FIGS. 3 and 6 , flex circuit  138   b  extends from the distal side of carrier  136  and then coiled around the shaft of the carrier  136  and is folded in such a manner as to extend to the region of flex circuit  138   a  and from there to pass through the housing  134 .  
         [0071]     In order to enable the transducer carrier  136  to be rotated without an interference from flex circuit  138   b , carrier  136  is of a truncated diameter and includes a flat portion  137  shown in  FIG. 9 ( b ) so as to provide room for circuit mounting. It is important to note that the flat portion  137  of carrier  136  may be defined according to the amount of rotation of the transducer  135  so that portion  137  can be of a flat shape or a V shape or a curved shape or the like.  
         [0072]     In order to prevent problems associated with the capillarity of the coupling liquid, the distance between the transducer/carrier surface and surface defining the internal diameter of the housing  134  should be carefully selected based on the viscosity of the coupling liquid or grease employed.  
         [0073]      FIGS. 10 and 11  show a further improvement of the scanhead apparatus where a central cannula is designed so as to integrate the electrically conductive wires in its wall thickness, and thus provide the electrical connection for the motor without any wires passing through the hollow space defined within the scanhead apparatus. This space or passage can, therefore, be dedicated to insertion of other surgical instruments for diagnostics, biopsy or treatment. It will be apparent to those of ordinary skill in the art that when such a passage is provided for the insertion of instruments, insertion can be made through the endoscope/catheter probe in a manner so as to enable external access for these instruments (end-finger or lateral openings are compatible).  
         [0074]     Referring specifically to the embodiment illustrated in  FIGS. 10 and 11 , a cannula  142  as shown in  FIGS. 10 and 11  is provided with a shoulder portion  150  that acts as mechanical abutment for mounting the cannula  142 . A cylindrical portion  151  that extends along the transducer carrier  143  includes, in the thickness thereof, embedded conductive wires or traces  148   a  and  148   b . The latter are externally connected to conductive wires  158   a  and  158   b  which may simply be external extensions thereof as indicated by the curved portions that extend beyond the cannula  142  on both sides thereof. A hollow space  149  is provided which has dimensions that are determined to be compatible with standard working channel diameters so as to permit the insertion of surgical instruments therein.  
         [0075]     The use of the cannula  142  illustrated in  FIGS. 10 and 11  enables mounting of a hollow shaft motor type for instrument insertion, as shown in  FIG. 3 . Cannula  142  is preferably made from plastic or composite materials that exhibit non-electrically conductive properties, i.e., insulating materials, so as to provide electrical isolation of the wires or traces  148   a  and  148   b.    
         [0076]     Although the invention has been described above in relation to preferred embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected in these preferred embodiments without departing from the scope and spirit of the invention.