Abstract:
An integrated x-ray and ultrasound medical imaging system is provided, wherein a radiation detection means and ultrasound transducer may be disposed for scanning movement for image acquisition along either the same or substantially coincidental paths. The radiation detection means and ultrasound transducer may be advantageously located on the same side of the imaged body portion. The x-ray and ultrasound imaging operations may be sequential, partially overlapping, or synchronous. By virtue of the noted arrangement, increased accuracy and medical efficiencies can be realized.

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical imaging systems, and more particularly, to an improved system that combinatively employs x-ray imaging and ultrasound imaging in a manner that yields enhanced accuracy and multiple efficiencies. 
     BACKGROUND OF THE INVENTION 
     The advantages of early detection of potential lesions and suspicious masses within bodily tissue have been well-established. Increasingly, screening for common cancers of the breast, lung, colon, and prostate has gained support and acceptance in the medical community, but improvements in the sensitivity and specificity of the techniques remain key and are readily identifiable objectives. 
     Of particular interest is the area of mammographic screening. After a given age or maturity, normally beginning at age 40, it is common for women to undergo periodic examinations, wherein film-based and/or digital x-ray screening mammograms are obtained. While significant advances have been made, current screening approaches may provide mammograms with insufficient “sensitivity” to allow for the detection of the presence of a potential lesion, thereby resulting in a “false negative”. Further, current screening approaches may provide mammograms with insufficient “specificity” to allow for accurate characterization of detected suspicion tissue masses, thereby potentially resulting in “false positives”. 
     Presently, in the event of an equivocal screening mammogram, a callback examination may be conducted, wherein a diagnostic mammogram is obtained and/or an ultrasound imaging procedure is performed, thereby entailing another patient office visit, additional medical personnel time and increased cost. More particularly, an ultrasound examination may be utilized (e.g. as opposed to a biopsy) to rule out the presence of a solid mass. In this regard, current practice can entail free-hand ultrasound imaging during which a specialist manipulates a hand-held probe relative to a patient&#39;s breast while viewing a display to obtain depth-profile information. As may be appreciated, the ability to mentally correlate such depth-profile information with the location of a potential lesion/suspicious mass visualized on an x-ray image can be quite challenging, thereby sometimes compromising characterization efforts. Moreover, such procedures are time consuming and entail significant expertise. These considerations present significant limitations to the realization of increased efficacies and efficiencies of practice. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, a primary objective of the present invention is to provide a medical imaging system that reduces instances of undetected malignancies (e.g. false negatives) and/or falsely characterized non-malignancies (e.g. false positives) by providing increased sensitivity and specificity. 
     Another objective of the present invention is to provide a medical imaging system that reduces the need of callbacks for patients undergoing screening examinations. 
     Yet another objective of the present invention is to provide a medical imaging system that improves overall efficiencies in the delivery of medical screening services. 
     A further objective of the present invention is to provide a medical imaging system that is patient and user-friendly in implementation, including in particular patient screening applications. 
     One or more of the above objectives and additional advantages are realized by the present invention. An inventive apparatus includes a radiation source for transmitting a radiation signal through a selected region of a patient&#39;s body, and a radiation detection means for receiving a portion of the radiation signal passing through the selected body region and providing a first image signal responsive thereto. Further, the apparatus includes at least one ultrasound transducer for sending/receiving an ultrasound signal into/from the selected region of the patient&#39;s body and providing a second image signal responsive thereto. The radiation detection means and ultrasound transducer may be disposed in known spatial relation to a predetermined imaging frame of reference in which the selected body region may be immobilized, wherein the first and second image signals may be readily correlated and otherwise processed for the generation and display of images to medical personnel (e.g. specialists located at a patient screening site or a networked location). 
     More particularly, and in one aspect, the inventive apparatus may be provided so that the radiation detection means and ultrasound transducer are each operable for scanning movement relative to the selected body region along the same or substantially coincidental paths during image acquisition (e.g. parallel, linear or arcuate paths). In this regard, the radiation detection means and ultrasound transducer may each be of a width that is less than a width of the selected body region, wherein the noted scanning movement allows the entirety of the selected body region to be progressively, or incrementally, imaged with enhanced results. For example, the radiation signal may be substantially focused upon and scanned in synchronous relation with the radiation detection means to reduce scattering effects and otherwise yield high detection quantum efficiencies. Relatedly, it may be preferable for one or both of the radiation detection means and ultrasound transducer to have corresponding lengths that are at least as great as the length of the selected body region. In turn, image acquisition for the entire selected body region may be achieved via a single scanning movement, or pass, of the radiation detection means and/or ultrasound transducer across the width of selected body region, wherein temporal decorrelation effects may be reduced. Alternatively, one or both of the radiation detection means and ultrasound transducer may be of a length that is less than the length of the selected body region, wherein a plurality of scanning movements along parallel paths may be utilized (e.g. via raster, bi-directional or return carriage, unidirectional imaging arrangements). 
     The radiation detection means may comprise an array of radiation detector elements and the ultrasound transducer may comprise an array of ultrasound transducer elements, wherein each of the arrays are positioned or positionable in known spatial relation relative to the imaging frame of reference. Further, the array of radiation detector elements and array of ultrasound transducer elements may be positioned or positionable so that the row(s)/column(s) thereof are disposed in a like relationship relative to their respective scanning travel paths. For example, the element row(s) of each of the arrays may be oriented substantially perpendicular to their corresponding scanning travel paths and the element column(s) of each of the arrays may be oriented substantially parallel to their corresponding scanning travel paths, wherein such scanning travel paths are the same or substantially coincidental. 
     To effect scanning movement, the radiation detection means and ultrasound transducer may be operably interconnected to a common or separate corresponding drive means (e.g. one or more stepper motor(s)) for moving the radiation detection means and ultrasound transducer in a controlled manner relative to the predetermined imaging frame of reference. Preferably, the drive means may be provided so that the radiation detection means and ultrasound transducer may each be scanned at corresponding predetermined and substantially constant velocities, wherein such velocities may be the same or different. For example, the detection means and ultrasound transducer may be driven for at least partially synchronous scanning, preferably at substantially the same, constant velocity. Alternatively, radiation and ultrasound scanning may be conducted sequentially at the same or different corresponding velocities as may be desired due to varying acquisition system bandwidths. 
     The radiation source and radiation detection means may be provided to maintain a substantially fixed distance therebetween throughout scanning. In this regard, the radiation source may be rotatable about and have a focal point located on a substantially fixed axis, and the radiation detection means may be disposed for movement along an arcuate path centered at the focal point of the radiation source during imaging. Further, the ultrasound transducer may also be provided for movement along a coincidental, arcuate path or along a linear path during imaging. 
     In another aspect, the inventive apparatus may be provided so that the ultrasound transducer is disposed for scanning co-movement with and in fixed relation to the radiation detection means. In this regard, the radiation detection means and ultrasound transducer may be physically interconnected or interconnectable. For example, one of the radiation detection means and ultrasound transducer may be supportably carried by the other, wherein the carrier is supportably interconnected to a drive means. Alternatively, the radiation detector and ultrasound transducer may each be interconnected or interconnectable in known spatial relation to a common support member. 
     According to a further aspect of the present invention, the inventive apparatus may be provided so that a selected region of the patient&#39;s body is positionable with (i.) the radiation source on a first side thereof, and (ii.) the radiation detection means and ultrasound transducer on an opposing, second side thereof. In one arrangement, the selected body region may be located in contact relation with a first side of a support layer, wherein the radiation detection means and ultrasound transducer are located or locatable on an opposing second side of the support layer for imaging through the support layer. As may be appreciated, the support layer should be both radiolucent and sonolucent to accommodate the passage of x-ray and ultrasound imaging signals therethrough. Further, an acoustic coupling means may be positioned or positionable in contact relation with both the ultrasound transducer and the second side of the support layer. For example, the acoustic coupling means may be sonolucent and flowable (e.g. conformable) to facilitate an acoustic interface between the ultrasound transducer and support layer. 
     The support layer may be of an arcuate or planar (e.g. flat) configuration and may be of rigid or pliable construction. In turn, to facilitate the maintenance of a contact relationship between the ultrasound transducer, acoustic coupling means, support layer and selected body region, the ultrasound transducer may be disposed for scanning movement along a travel path that substantially coincides with the shape of the support layer (e.g. a coincidental arcuate or linear path). Additionally, to facilitate contact maintenance, the ultrasound transducer may be disposed for movement toward and away from the second side of the support layer during scanning movement. For example, the ultrasound transducer may be biased toward the support layer (e.g. spring-loaded along a slot mount in a support bracket). Further, the ultrasound transducer may be disposed to permit the pitch and/or attitude of the ultrasound transducer (e.g. relative to the support layer) to automatically adjust in response to local shape variations (e.g. variations caused by local tissue variations of a compressed breast deforming a pliable support member). For example, an ultrasound transducer may be mounted to a support bracket via a ball-joint or gimbal arrangement. 
     In yet a further aspect of the present invention, the inventive apparatus may include a processor means for controlling operation of the radiation source, radiation detection means, ultrasound transducer and scanning drive means. More particularly, the processor means may control the drive means to effect scanning movement of and imaging operations by the radiation detection means and ultrasound transducer in a sequential, partially overlapping or substantially synchronous manner. 
     Various embodiments of the inventive apparatus may employ one or more of the above-noted aspects and further additional features. Of note, the inventive apparatus may include a user interface means for displaying a plurality of images of the selected body region that are generated by the processor means utilizing image data obtained from the first and/or second image signals. More particularly, the user interface means may include a display and a user input for controlling the processor means, wherein a first image may be displayed and utilized to select at least a second image. For example, a user input (e.g. a mouse) may be provided to control positioning of a cursor relative to a region of interest on a displayed projection image generated from the x-ray image data (e.g. a projected XY plane image), wherein upon locating the cursor and corresponding user input (e.g. via clicking a mouse button), corresponding cross-cut, z-depth plane images may be generated by the processor means from the ultrasound image dataset and displayed to a user (e.g. YZ and XZ plane images extending through the region of interest). Further, the cursor may be positioned relative to a region of interest on one of the YZ or XZ plane images to obtain a desired XY plane image at a selected Z elevation, wherein such image is generated by the processor means from the ultrasound image dataset. As may be appreciated, the ultrasound image dataset may also be utilized to generate three-dimensional images of a region of interest. 
     In other embodiments a pair of ultrasound transducers may be utilized. For example, a first ultrasound transducer may be disposed on a first side of the selected body region and a second ultrasound transducer may be located on an opposing, second side of the selected body region, wherein the first and second ultrasound transducers are preferably disposed in opposing, aligned relation. More particularly, the first ultrasound transducer may be disposed in contact relation with first acoustic coupling means which is disposed in contact relation with a support layer as described hereinabove. The second ultrasound transducer may be disposed in direction contact with a second acoustic coupling means that is disposed in contact relation with a compression member, wherein the selected body region is immobilized in contact relation between the support layer and the compression member. The utilization of a pair of ultrasound transducer allows for the obtainment of various tissue properties corresponding with the selected body region. For example, an ultrasound signal may be transmitted by the first ultrasound transducer and received by the second ultrasound transducer to yield tissue attenuation and/or signal velocity information, both of which types of information may be utilized to facilitate characterization of tissue masses within the selected body region. 
     In yet further embodiments, an ultrasound image dataset obtained via one or a pair of ultrasound transducers may be processed to obtain Doppler image data. In turn, the Doppler image data may be utilized to measure the direction and velocity of blood flow in a tissue region of interest and to provide a visual display thereof (e.g. a color Doppler image). 
     As may be appreciated, an inventive method is also provided for use in obtaining image data with respect to a selected region of a patient&#39;s body. The inventive method includes the steps of transmitting a radiation signal from a radiation source through the selected body region and moving a radiation detection means along a first path during the transmitting step, wherein the radiation detection means receives a portion of the radiation signal passing through the selected body region and provides a first image signal responsive thereto. The method further includes a step of displacing an ultrasound transducer along a second path, wherein the ultrasound transducer sends/receives an ultrasound signal from the selected body region as it travels along said second path and provides a second image signal responsive thereto. The method may further provide for processing the first and second image signals, and for the selective display of resultant images to medical personnel. 
     In conjunction with the inventive method, the selected body region may be immobilized within a predetermined frame of reference, wherein the transmitting, moving and displacing steps are completed during the immobilization step. Further, the immobilization step may provide for compression of the selected body region. 
     According to one aspect, the method may entail movement of the radiation detection means and displacement of the ultrasound transducer along corresponding first and second paths which are the same or substantially coincidental (i.e. parallel, linear or arcuate paths). By way of example, the radiation detection means and ultrasound transducer may be directly interconnected or interconnectable or to a common support means for driven movement. Additionally, the transmitting step may include scanning the radiation signal across the selected body region synchronous with and in the same direction as the radiation detection means. Further, the radiation signal may be substantially focused upon the radiation detection means during imaging, wherein radiation dosages are reduced and image resolutions are enhanced. 
     In another aspect, the inventive method may provide for positioning of the radiation detection means and ultrasound transducer on the same side of a selected body region of the patient. By way of example, a first side of a support layer may be located adjacent to the selected body region, wherein the radiation detection means and ultrasound transducer may be located on an opposing second side of the support layer for scanning movement. To facilitate ultrasound imaging, acoustic coupling means may be utilized on each side of the support layer. For example, an acoustic coupling member (e.g. a conformable pad containing a flowable acoustic gel) may be interposed between and in direct contact with the first side of the support layer and the selected body region. 
     Further in this regard, an acoustic coupling member (e.g. a conformable pad containing a flowable acoustic gel) may be interposed between the ultrasound transducer and the second side of said support layer in direct contact with each. By way of example, the acoustic coupling member may be interconnected to the ultrasound transducer, wherein the acoustic coupling member slidably engages the support layer during scanning displacement. Alternatively, the acoustic coupling member may be interconnected to the second side of the support layer, wherein the ultrasound transducer slidably engages the acoustic coupling member during scanning displacement. In such an arrangement, processing of the first image signal may include an adjustment to account for x-ray attenuation associated with the passage of the radiation signal through the acoustic coupling member. In one approach, to facilitate such an adjustment, the inventive method may initially provide for transmission of the radiation signal and movement of the radiation detection means along the first scanning path prior to actual imaging of said selected body region. Concomitantly, the radiation detection means may receive a portion of the radiation signal passing through the acoustic coupling member and provide a calibration output signal responsive thereto. In turn, the calibration signal may be stored/utilized in conjunction with the above-noted image processing adjustment. 
     To further facilitate ultrasound imaging, an acoustic gel or other ultrasound couplant may be applied to the selected body region to be imaged and/or to the support layer prior to imaging to enhance the acoustic interface therebetween. 
     In another aspect of the inventive method, scanning movement of the radiation detection means and scanning displacement of the ultrasound transducer for body imaging may occur in at least a partially overlapping manner. For example, the moving and displacing steps for radiation and ultrasound imaging may be completed in substantial synchronicity. In another approach, scanning movement of the radiation detection means and scanning displacement of the ultrasound transducer for body imaging may be completed sequentially. 
     Additional aspects and advantages of the present invention will become apparent to those skilled in the art upon consideration of the further description provided hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates one embodiment of an imaging system comprising features of the present invention. 
         FIGS. 2A-2C  are cross-sectional front views of an imaging station of the embodiment of  FIG. 1 , wherein progressive tandem, scanning movement of an x-ray detector and ultrasound imager is illustrated. 
         FIG. 3A  is a perspective cutaway and partial exploded assembly view of one imaging assembly embodiment of the system embodiment of FIG.  1 . 
         FIG. 3B  is a perspective cutaway and partial exploded assembly view of another imaging assembly embodiment of the system embodiment of FIG.  1 . 
         FIG. 4  is a cross-sectional front view of another embodiment of an imaging station comprising dual ultrasound transducers. 
         FIG. 5  illustrates an exemplary patient breast located within a predetermined imaging frame of reference and potential image plane views that may be generated. 
         FIG. 6A  illustrates an exemplary projected x-ray image and ultrasound image that may be displayed via use of the radiation image signal and ultrasound image signal obtained in various embodiments of the present invention. 
         FIG. 6B  illustrates various two-dimensional images that may be displayed via use of the radiation image signal and ultrasound image signal obtained in various embodiments of the present invention. 
         FIG. 7  is a high-leveled diagram showing various steps of method embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates one embodiment of an imaging system comprising the present invention. The system includes a monitoring station  10  and imaging station  20  operatively interconnected thereto, e.g. for patient screening and/or follow-up examination. The monitoring station  10  includes a user input keyboard  12  (e.g. for entering patient data), a display  14  and corresponding user input mouse  13  (e.g. for displaying/selecting images), and a processor  16  interconnected to the user input keyboard  12 , display  14  and imaging station  20 . Processor  16  is adapted to receive, process and store image data comprising image signals generated at the imaging station  20 , and to control various operations at the imaging station  20 . The monitoring station  10  may also include a radiopaque and optically transparent shield  18  for shielding medical personnel during observed patient imaging operations at the imaging station  20 . 
     The monitoring station  10  and/or imaging station  20  may be further interconnected or interconnectable in a network arrangement with other user workstations and image processor/storage sites  300 . For example, image data obtained at imaging station  20  may be provided to a networked location (e.g. at a remote site) for high-resolution display and analysis by diagnostic specialists. 
     The imaging station  20  may include an x-ray radiation source  22 , e.g. an x-ray tube, and collimating optics and/or selectable filters  24 , for transmitting a focused radiation signal  26 . By way of example, the radiation signal  26  may comprise a fan-shaped beam. The radiation source  22  may be disposed for controlled rotation about a fixed axis, wherein the radiation signal  26  may be scanned across a selected region of a patient&#39;s body. 
     By way of primary example, a patient&#39;s breast may be located within a predetermined imaging frame of reference located immediately adjacent to an imaging assembly  30 . More particularly, a patient breast may be immobilized between a support layer of the imaging assembly  30  and a compression member  28 . The compression member  28  may be selectively raisable/lowerable relative to the imaging assembly  30 . Further, the radiation source  22 , compression member  28  and imaging assembly  30  may be supportably mounted to an upper station member  21  that is supportably connected to and selectively raisable/lowerable/rotatable relative to a pedestal station member  23 . By virtue of such arrangement, the compression member  28  and imaging assembly  30  may be selectively positioned to accommodate varying patient heights, breast sizes and x-ray imaging angles. 
     As previously noted, radiation signal  26  may be scanned across a selected region of a patient&#39;s body, e.g. a patient&#39;s breast. In this regard, radiation source  22  may be interconnected to a rotatable shaft  25  (e.g. for co-rotation therewith), wherein a focal point of the radiation source  22  is located on a substantially fixed center axis of the rotatable shaft  25 . In turn, a top end of a pendulum member  27  may be interconnected to rotatable shaft  25 , wherein the pendulum member  27  may pivot about the center axis of shaft  25  when shaft  25  rotates. 
     A bottom end the pendulum member  27  may be interconnected to a drive motor  60  (e.g. a stepper motor), and to an x-ray detector  40  and ultrasound imager  50  comprising imaging assembly  30 . In this regard, the drive motor  60  may be selectively operated to move the x-ray detector  40  and ultrasound imager  50  along corresponding arcuate scanning travel paths. In the illustrated arrangement, operation of drive motor  60  will also effect synchronized scanning of the radiation signal  26  along a coincidental arcuate path by virtue of the operative interconnection of drive motor  60  to radiation source  22  via pendulum member  27  and shaft  25 . 
     Further in this regard, drive motor  60  may comprise an output shaft  62  that travels along a cam surface  70  of a cam member  72  (e.g. mounted to upper station member  21 ) upon rotation of the output shaft  62 . More particularly, an arrangement may be provided as disclosed in U.S. Pat. No. 5,917,881, entitled “DIGITAL SCAN MAMMOGRAPHY APPARATUS UTILIZING VELOCITY ADAPTIVE FEEDBACK AND METHOD”, hereby incorporated by reference, or U.S. Pat. No. 5,526,394, entitled “DIGITAL SCAN MAMMOGRAPHY APPARATUS”, hereby incorporated by reference. 
     Reference will now be made to  FIGS. 2A-2C  for further description of the imaging assembly  30 , as shown in imaging relation to a patient&#39;s breast  100 . As noted above, imaging assembly  30  includes an x-ray detector  40  and ultrasound imager  50 . The x-ray detector  40  receives at least a portion of the radiation signal  26  passing through a patient&#39;s breast  100  and provides a digital x-ray image signal in response thereto. 
     Ultrasound imager  50  transmits/receives ultrasound signals into/from a patient&#39;s breast  100  and provides a digital ultrasound image signal in response thereto. 
     The x-ray detector  40  and ultrasound imager  50  may be located within a housing  32  having a support layer  36 . The x-ray detector  40 , ultrasound imager  50  and drive motor  60  may be interconnected to a bracket member (not shown) that is interconnected to the bottom end of the pendulum member  27 . As noted, the drive motor  60  may be operated to effect radiation signal  26  scanning and scanning displacement of the x-ray detector  40  and ultrasound imager  50  along the same path or substantially coincidental paths relative to the predetermined imaging frame of reference. In that regard, each of radiation source  22 , x-ray detector  40 , ultrasound imager  50  and the drive motor  60  may be operatively interconnected (e.g. via electrical and/or optical lines) to the processor  16  at monitoring station  10 , wherein control signals are provided by processor  16  and image signals are received at processor  16  from the imaging station  20 . 
     In the embodiment shown in  FIGS. 2A-2C , the ultrasound imager  50  and x-ray detector  40  are physically interconnected by a linkage member  82 . The linkage member  80  may be provided so that ultrasound imager  50  and x-ray detector  40  may be selectively interconnected and disconnected (e.g. via mating engagement between complimentary shaft and cylinder members provided on the radiation detector  40  and ultrasound imager  50 , respectively). In another arrangement, two separate bracket members may be interconnected to pendulum member  27  for separate interconnection to x-ray detector  40  and ultrasound imager  50 , respectively. In yet another approach, a single bracket member may be utilized, wherein the x-ray detector  40  and ultrasound imager  50  may be separately disconnected/interconnected thereto for sequential imaging operations. 
     To accommodate x-ray imaging operations, the compression member  28  should be radiolucent. For example, a low density, thermoplastic material may be employed. The support layer  36  of housing  32  should be both radiolucent and sonolucent. For example, a low-density thermoplastic having a relatively small x-ray attenuation coefficient may be employed. In one arrangement, a crystalline, or aliphatic, polymer may be utilized, such as a poly 4-methyl, 1-pentene (i.e. PMP) material, e.g. a material commercially available under the product name “TPX” from Mitsui Plastics, Inc., White Plains, N.Y. 
     As will be further described, ultrasound imager  50  may comprise an ultrasound transducer  52  that transmits and receives ultrasound signals. To facilitate ultrasound operations, the ultrasound transducer  52  may be acoustically coupled to a bottom side of the support layer  36  via an acoustic coupling means  54 . Further, an acoustic coupling means  56  may be utilized to acoustically couple a patient&#39;s breast  100  to a topside of support layer  36 . For example, a standard ultrasound gel (e.g. a glycerin-based gel) gel or other flowable acoustic couplant may be contained within a pad located in contact with or otherwise applied to either or both of the top and bottom sides of support layer  36 . Alternatively, acoustic coupling means  56  may comprise an ultrasound-coupling, solid-disposable membrane, e.g. a SCANTAC membrane offered by Sonotech, Inc. of Bellingham, Wash. As may be appreciated, the use of a gel-containing pad or solid-membrane for acoustic coupling means  56  may reduce or even avoid the need to apply ultrasound couplants directly to a patient&#39;s breast  100 , thereby reducing:set-up and clean-up procedures. 
     Reference is now made to the partial exploded assembly views of  FIGS. 3A and 3B . As illustrated, x-ray detector  40  may include a light scintillator  42  (e.g. comprising a cesium iodide material), a fiber optic plate  44  and a plurality of abutting, charged coupled devices (CCDs)  46 . When assembled, such components may be disposed in adjacent, contact relation on a support member  48  that is interconnected or interconnectable to a support bracket  80  that is interconnected or interconnectable to/disconnectable from the bottom end of pendulum member  27 . As shown, drive motor  60  may also be interconnected to pendulum member  27  via support bracket  80 . As may be appreciated, scintillator  42  produces light in response to the receipt of radiation signal  26 . In turn, such light may be coupled via fiber optic plate  44  to a top surface of the CCDs  46  for detection and signal generation. 
     In the later regard, the CCDs  46  may each comprise an array of light sensitive elements. In one arrangement, each CCD has a 405×2048 array of 27-micron pixels. The CCDs may be operated in a time delay integration (TDI) mode, wherein electronic charge is accumulated and shifted from row-to-row and readout in synchronicity with, but in a direction opposite to, the scanning movement travel path of the x-ray detector  40 . In turn, the resultant radiation image signal may be digitized for storage, processing and image display at monitoring station  10 . 
     Numerous other x-ray detector arrangements may be utilized. For example, such arrangements may include detectors which utilize a light scintillator, photodiodes and thin film transistor (TFT) readout; or detectors employing direct conversion, voltage potential and TFT readout. 
     With further reference to  FIGS. 3A and 3B , it can be seen that the ultrasound transducer  52  may be carried by a support member  58 . Support member  58  may be interconnected or interconnectable to/disconnectable from the support member  48  of radiation detector  40 , e.g. by the linkage member  82  of  FIGS. 2A-2C . In one alternate arrangement, the support member  58  may be separately interconnected or interconnectable to/disconnectable from the pendulum member  27  via a modified or separate support bracket  80 . 
     The ultrasound transducer  52  may comprise an array of ultrasound transducer elements. For example, a plurality of transducer elements with crystals operative in a 7.5-10 MHz frequency range may be employed. As will be appreciated, the ultrasound transducer  52  may transmit/receive an ultrasound signal during pulse/echo operations, wherein a resultant ultrasound image may be output and digitized for storage, processing and image display at monitoring station  10 . 
     The array of ultrasound transducer elements comprising ultrasound transducer  52  may be disposed in parallel relation to the above-noted array of light sensitive elements comprising CCDs  46 . More particularly, the support members  48 , 58  may be provided for interconnection therebetween and/or for separate interconnection to drive means such as drive motor  60 , wherein the orientation of the array of light sensitive elements of CCDs  46  is the same as the orientation of the array of transducer elements of ultrasound transducer  52  relative to their respective scanning travel paths and the imaging frame of reference in which a selected body region is positioned (e.g. array rows/columns are parallel/perpendicular to the scanning paths). As such, regardless of whether x-ray and ultrasound imaging occur simultaneously, in overlapping fashion, or sequentially, the corresponding images may be readily registered in relation to the imaging frame of reference. 
     As may be appreciated, the array of light sensitive elements comprising CCDs  46 , and the array of ultrasound transducer elements comprising ultrasound transducer  52 , may each be of a corresponding width that is less than a width of a selected body region to be imaged. In turn, and by virtue of the scanning movement of the x-ray detector  40  and ultrasound imager  50  relative to the selected body region, the corresponding x-ray image and ultrasound image signals may be processed to yield full-field images of the selected body region. Further in this regard, it may be appreciated that the array of light sensitive elements comprising CCDs  46 , and the array of ultrasound transducer elements comprising ultrasound transducer  52 , may each be of a corresponding length that is greater than the length of a selected body region to be imaged (e.g the anterior-to-posterior dimension of a patient&#39;s breast  100  in FIGS.  2 A- 2 C), wherein x-ray imaging and ultrasound imaging of the selected body region can each be achieved via a single scanning movement of the x-ray detector  40  and ultrasound imager  50 , respectively. Alternatively, either or both of the x-ray detector  40  and ultrasound imager  50  may be of a lesser length; e.g. the array of ultrasound transducer  52  may be of a lesser length, wherein the ultrasound transducer  52  may be disposed for driven movement in a raster-like or return carriage manner for multi-pass imaging (e.g. via bi-directional or unidirectional scanning). 
     Referring now to the specific arrangement illustrated in  FIG. 3A , an acoustic coupling means  54  is shown that includes a coupling pad  55  filled with a sonolucent flowable material (e.g. a hydrogel) located within a tray member  57  (e.g. comprising a sonolucent material), which in turn is positioned in direct contact with the ultrasound transducer  52 . In operation, the coupling pad  55  slidably engages the bottom side of support layer  36  during ultrasound scanning operations. To facilitate such engagement, an acoustic lubricant (e.g. mineral oil) may be applied to the top of the coupling pad  55 . 
     In the arrangement illustrated in  FIG. 3B , an acoustic coupling means  54  is shown that comprises a coupling pad  59  filled with a sonolucent flowable material (e.g. a hydrogel) interconnected to and extending across the bottom side of support layer  36 . In turn, ultrasound transducer  50  is disposed for sliding engagement with the coupling pad  59  during ultrasound scanning operations. To facilitate such engagement, an acoustic lubricant (e.g. mineral oil) may be applied to the top surface of the ultrasound transducer  52 . 
     In addition the above-noted arrangements, further embodiments may employ varied structural relationships and additional componentry. For example, in some arrangements the ultrasound transducer  52  may be disposed and otherwise driven to follow a substantially linear travel path during scanning operations. Relatedly, support member  36  may be substantially planar, wherein the travel path for the ultrasound transducer  52  is substantially parallel to the plane defined by support layer  36 . In such an arrangement, the x-ray detector  40  may be disposed within imaging assembly  30  to follow a substantially linear travel path or an arcuate travel path. 
     In another modified arrangement, the above-noted support member  58  may be modified to facilitate movement of the ultrasound transducer  52  toward and away from the support layer  36 . More particularly, and by way of example, a modified bracket member  80  may be provided having a slot that extends normal to the bottom side of support layer  36  and within which support member  58  may be mounted for travel toward/away the support layer  36  along the slot. For example, the support member  58  may be spring-loaded, or biased, within the slot towards the support layer  36  so as to facilitate engagement therewith while also allowing for the above-noted sliding engagement between acoustic coupling pad  55  and support layer  36  ( FIG. 3A ) or between the ultrasound transducer  52  and acoustic coupling pad  59  (FIG.  3 B). 
     Additionally, in a further modified arrangement, the support member  58  may be provided to allow a predetermined range of automatic pitch and/or attitude adjustment of ultrasound transducer  52 . Such automatic adjustability may be provided to allow the face of the ultrasound transducer  52  to maintain an optimal interface via the acoustic coupling means  54  with support layer  36 . By way of example, support member  58  may implement a ball-joint or gimbal arrangement which facilitates pivotal movement of the lateral and/or longitudinal axes (e.g. about a common center location) of the ultrasound transducer  52 . Such arrangements may be particularly apt where support layer  36  is of a pliable construction since the orientation of the face of ultrasound transducer  52  may automatically adjust to accommodate local shape changes of the support layer  36  caused by variations in the compressed tissue region to imaged. 
       FIG. 4  illustrates a further embodiment of the present invention. Such embodiment may include the same features as described above in relation to the embodiment of FIG.  1  and  FIGS. 2A-2C  and FIGS.  3 A and/or  3 B, and further includes a second ultrasound imager  90 . By way of example, the second ultrasound imager  90  may be positioned on a side of a patient&#39;s breast  100  that is opposite to the side on which the above-noted ultrasound transducer  50  is located. More particularly, the ultrasound imager  90  may be positioned in contact relation with a top surface of a sonolucent and radiolucent compression member  28 . In turn, an ultrasound transducer  92  may provided with an acoustic coupling member  94  which directly engages the compression member  28 . The ultrasound imager  90  may be interconnected to the above-noted pendulum member  27  so that ultrasound imagers  50  and  90  move in tandem and in opposing faceto-face relation during ultrasound imaging operations. 
     As may be appreciated, multiple ultrasound signals may be transmitted and/or received by the ultrasound imagers  50 , 90  to obtain enhanced ultrasound information. By way of example, the transmission and reception of ultrasound signals between the ultrasound imagers  50 , 90  may yield particular information pertaining to tissue attenuation and signal velocity. 
     Reference is now made to  FIG. 5  which illustrates the positioning of a patient breast  100  within a predetermined frame of reference corresponding with the region located immediately adjacent to the support member  36  of the imaging assembly  30  of  FIGS. 2A-2C . As will be appreciated, the image data comprising the image signal provided by x-ray detector  40  may be utilized to generate a projected XY plane image of the breast  100 . The image data comprising the image signal provided by the ultrasound imager  50  may be utilized to generate YZ plane images, XZ plane images and XY plane images of the patient breast  100 . 
     Further in this regard, and as shown in  FIG. 6A , a projected XY x-ray image and a selected XZ ultrasound image may be displayed at the display  14  of monitoring station  10 . By way of example, a tissue region of interest  102  (e.g. a suspicious mass) may appear in a projected XY plane image. In turn, a user may utilize the input mouse  13  at monitoring station  10  to control the positioning of a display cursor  14   a , wherein the cursor  14   a  may be located on the tissue region of interest  102  in the projected XY plane image. When the curser position is input via mouse  13  (e.g. by a button: click) the illustrated crosscut XZ plane image may be automatically displayed. 
     As may be appreciated, monitoring station  10  may be provided to permit enlargement of a selected region of a displayed image. For example, in addition to the illustrated cross-hair configuration of cursor  14   a , cursor  14   a  may comprise a polygonal configuration (e.g. a square or rectangular configuration) that may be positioned to “frame” an enlarged area to be shown in the XZ ultrasound image. 
     In another arrangement, and as shown in  FIG. 6B , a projected XY x-ray image and selected XZ and YZ ultrasound images may be displayed at the display  14  of the monitoring station  10 . Again, a user may employ the input mouse  13  to select a tissue region of interest  102 , wherein the illustrated crosscut, XZ and ZY plane images may be automatically displayed. Then, the cursor  14   a  may be located on the tissue region of interest  102  on either of the XZ plane or ZY plane images, wherein input of the cursor position via mouse  13  may cause an XY plane image (not shown) in the corresponding Z plane to be generated/displayed via use of the ultrasound image data. The various displayable images may be enlarged or otherwise enhanced by processor  16  so as to further facilitate characterization of the tissue region of interest  102  by medical personnel. 
     Reference will now be made to  FIG. 7 , which illustrates general steps of method embodiments comprising the present invention. As shown, prior to a given imaging procedure, processor  16  may cause radiation signal  26  to be scanned across imaging assembly  30  together with driven scanning movement of x-ray detector  40  and ultrasound imager  50 . As a result, corresponding calibration image signals may be provided for subsequent use in image processing (step  200 ), as will be noted below. 
     For patient screening, a patient breast  100  may be immobilized (step  201 ), e.g. the patient breast  100  may be located in contact relation with the support layer  36  of the imaging assembly  30 . For such proposes, the upper member  21  may be raised/lowered/rotated as desired. Then, compression member  24  may be advanced towards the patient breast  100  so as to compress the patient breast  100  within the predetermined imaging frame of reference. 
     Next, processor  16  may cause a pre-scan to be completed by scanning radiation signal  26  and x-ray detector  40 , wherein the resultant x-ray image signal may be processed to determine the location of the edges of the patient breast  100  within the predetermined imaging frame of reference (step  202 ). Optionally, a pre-scan image using ultrasound imager  50  alone may determine the edge of the breast and the composition of the breast, thus providing information for optimizing x-ray imaging exposure parameters. Such breast edge and additional information may be utilized in conjunction with subsequent imaging steps. For example, processor  16  may utilize the breast edge information so as to position the x-ray detector  40  at a location immediately adjacent to a breast edge for imaging. 
     In any case, after the optional pre-scan, the radiation source  22  and x-ray detector  40  may be controlled so as to scan the radiation signal  26  and x-ray detector  40  across the patient breast  100  in tandem, thereby obtaining a radiation image signal (step  204 ). In turn, the radiation image signal may be digitized and the resultant image data may be processed/stored/displayed at the monitoring station  10 . In conjunction with such processing, calibration signal data obtained in step  200  may be employed. 
     In one embodiment, the method may further include the step of scanning the ultrasound imager  50  relative to the patient breast  100  (step  206 ) substantially synchronously with x-ray scanning (step  204 ). In turn, the signal may be digitized and the resultant image data ultrasound image may be processed/stored/displayed at the monitoring station  10 . In conjunction with such processing, calibration signal data obtained in step  200  may be employed. 
     In another embodiment, x-ray imaging and ultrasound imaging may be completed sequentially. For example, after x-ray imaging (step  204 ) the ultrasound imager  50  may be positioned for imaging operations (step  208 ). More particularly, the x-ray detector  40  may be replaced by the ultrasound imager  50 . Alternatively, the ultrasound imager  50  may be displaced from a retracted position to an advanced position relative to the support layer  36  of housing  32 , wherein acoustic coupling means  54  only engages the bottom side of the support layer  36  when located in the advanced position. 
     In any case, once ultrasound imager  50  is properly positioned, the processor  16  may initiate ultrasound scanning operations (step  210 ), wherein the ultrasound imager  50  provides an ultrasound image signal to the processor  16  for image data storage/processing/display. Again, in conjunction with such processing, calibration signal data obtained in step  200  may be employed. 
     As shown by  FIG. 7 , the various methods may also provide for the selected display of x-ray and ultrasound images (step  212 ). For example, and as noted above, such data may be utilized to provide a projected XY plane image and selected XY, XZ and YZ plane images corresponding with a tissue region of interest identified by medical personnel. In turn, such images may be viewed, enhanced, etc. by medical personnel to characterize the tissue region of interest. 
     The embodiments described above are for exemplary purposes only and is not intended to limit the scope of the present invention. Various adaptations, modifications and extensions of the embodiment will be apparent to those skilled in the art and are intended to be within the scope of the invention as defined by the claims which follow.