Abstract:
An ultrasonic transmission unit for an imaging/quantitative ultrasound device provides for coaxial transducer crystals which may be operated independently with a first crystal operated alone for quantitative measurement and the first and second crystal operated together to provide a broad illumination for imaging of structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates generally to quantitative ultrasound equipment and in particular, to an ultrasonic transducer providing separate transmission modes for imaging and quantitative measurement.  
           [0004]    Quantitative ultrasound may be used to make measurements of in vivo tissue. In one such device used to assess bone quality, in evaluating conditions such as osteoporosis, an opposed ultrasonic transmitter and ultrasonic receiver are positioned across a body member containing trabecular bone. The heel is often the site of measurement because of its ready accessibility, the relatively thin layers of soft tissue surrounding it, and because the heel bone or os calcis is in significant proportion trabecular bone.  
           [0005]    The ultrasonic signal after passing through the bone and soft tissue is analyzed to assess bone health. The analysis may determine changes in sound speed, attenuation, or other parameters. One such system is described in U.S. Pat. No. 6,027,449, entitled: “Ultrasonometer Employing Distensible Membranes”. This patent is assigned to the assignee of the present case and is hereby incorporated by reference.  
           [0006]    While the earliest quantitative ultrasound devices for bone measurement were limited to providing quantitative output, it was recognized that the ability to, provide an image could be useful in positioning the body member and therefore in obtaining reproducible results in measurements separated over time. Ultrasonic images may be obtained by scanning a single receiving transducer or by dividing an ultrasonic receiver into a number of elements arranged in an array and separately detecting the received ultrasonic signal at each element. The present invention to be described below is applicable to both techniques.  
           [0007]    The separate measurements are analyzed as to speed of sound, or attenuation or another parameter and these analyzed values are mapped to a gray scale and used to produce an image with each gray scale value placed in a picture location (pixel) corresponding to the point of detection of the original ultrasonic signal. The image may be displayed and/or used in an automatic method for identifying a region of interest for quantitative measurement.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    The present inventors have recognized that multi-path interference from ultrasound coming around the bone compromises the quantitative analysis of the ultrasound waves coming through the bone. This “around-the-bone” component increases with the larger sized ultrasonic transmitter necessary to fully “illuminate” the bone for imaging purposes.  
           [0009]    Once the interference reaches the ultrasonic receiver, it is difficult to remove or compensate for its influence. Accordingly, the present invention provides a dual mode ultrasonic transmitter that provides first, small-area, ultrasonic transmitter which produces a localized source of ultrasonic energy for quantitative measurements, and second a larger ultrasonic transducer, used in conjunction with the smaller ultrasonic transducer which produces a large area ultrasonic wave suitable for imaging the bone and the surrounding tissue. These two modes are used as required.  
           [0010]    Specifically then, the present invention provides an imaging/quantitative ultrasonic device having an ultrasonic receiver unit providing a reception aperture of a first predetermined area and an ultrasonic transmission unit having a transmission aperture of a second predetermined area, the ultrasonic transmission unit positioned in opposition across a measurement region from the ultrasonic receiver unit for directing ultrasonic acoustic waves to the reception aperture. The ultrasonic transmission unit further includes a means for independently transmitting ultrasonic acoustic waves from a first and second portion of the transmission aperture. A controller communicates with the ultrasonic transmission unit to alternately transmit ultrasonic waves from (a) only the first of the transmission aperture for preparing a quantitative measurement, and (b) both the first and second portions of the transmission aperture for preparing an image.  
           [0011]    In this way, scattered ultrasound coming around the bone may be minimized in the quantitative measurement while still providing a uniform broad area ultrasonic signal for imaging purposes.  
           [0012]    The ultrasonic transmission unit may have an electrically separate circular transducer and a coaxially annular transducer.  
           [0013]    Thus, the present invention is well adapted to use of standard ceramic transducer technologies.  
           [0014]    The first transducer may have a diameter of substantially one inch.  
           [0015]    In this way, the transducer can be constructed to match the existing ultrasonic densitometry equipment and provide consistent measurement with other machines.  
           [0016]    The ultrasonic receiver may include an array of receiving elements and the controller may communicate with the receiver unit to sequentially (a) detect ultrasonic acoustic waves from only a first portion of the reception aperture when the ultrasonic acoustic waves are being transmitted only from the first portion of the transmission aperture and (b) detect ultrasonic acoustic waves from both the first and the second portion of the reception aperture when the ultrasonic acoustic waves are being transmitted from both the first and second portions of the transmission aperture.  
           [0017]    In this way, the receiver can also be used to discriminate between direct and scattered ultrasound.  
           [0018]    The ultrasonic transmission unit and ultrasonic receiver unit may be separated by a distance less than twice the diameter of the reception and transmission apertures.  
           [0019]    Such a separation ensures that a generally planar acoustic wave may be generated for imaging purposes.  
           [0020]    The foregoing features and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a perspective view of an imaging/quantitative ultrasonic densitometer suitable for use with the present invention showing an ultrasonic reception unit and ultrasonic transmission unit opposed across a footwell;  
         [0022]    [0022]FIG. 2 is an exploded perspective view of the ultrasonic transmission unit of FIG. 1 showing the constituent coaxial transducer, coupling plate and compliant water filled bladder;  
         [0023]    [0023]FIG. 3 is a schematic representation of the densitometer of FIG. 1 showing the control of the transmitter unit and the receiver unit by a microprocessor which also controls mechanical subsystems and a display;  
         [0024]    [0024]FIG. 4 is a flow chart showing operation of the present invention in obtaining quantitative and image data; and  
         [0025]    [0025]FIG. 5 is a cross-sectional view taken along line  5 - 5  with a patient&#39;s foot in place showing the generation of scatter during the imaging process. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    Referring to FIG. 1, an imaging/quantitative ultrasonic device  10  includes a housing  12  having a generally upward opening footwell  14  sized to receive a human foot. At the toe end of the footwell  14  on the upper surface of the housing  12  is a display/touch panel  16  allowing data to be entered into or received from an internal computer (not shown in FIG. 1). Flanking the footwell  14  near the heel end of the footwell is an ultrasonic transmitter unit  18  and an ultrasonic receiver unit  20  supporting at their opposed surfaces compliant bladders  22  holding a coupling fluid such as water. The bladders  22  serve to communicate ultrasonic energy from the contained transducers of the transmitter unit  18  through a patient&#39;s foot inserted into the footwell  14  and back out to the contained transducer of the receiver unit  20 .  
         [0027]    Referring now to FIG. 2, the transmitter unit  18  includes a cylindrical, center ultrasonic element  24  coaxially surrounded by an annular, outer ultrasonic element  26 , both fabricated of conventional ultrasonic piezoelectric ceramics as is well known in the art. Alternatively, these elements may be made from one piece of ceramic with a dividing kerf and appropriately positioned independent electrodes. The center ultrasonic element  24  may have a diameter of approximately  25  mm whereas the outer annular ring may have a diameter of approximately  90  mm.  
         [0028]    The ultrasonic elements  24  and  26  are held in a retaining ring  28  mounted to the side of the footwell as shown in FIG. 1. The retaining ring  28  may include fluid channels for the inflation and deflation of the bladders  34  as is well understood in the art.  
         [0029]    A front surface  30  of the ultrasonic elements  24  and  26  are attached to a matching plate  32  providing an impedance coupling between the ultrasonic elements  24  and  26  and water contained within compliant bladder  34 . Matching plate  32  may be, for example, a plate of polyester.  
         [0030]    Referring now momentarily to FIG. 5, each of the center ultrasonic element  24  and the outer ultrasonic element  26  include at least one separate electrode to allow them to be independently activated to produce an ultrasonic signal. In one embodiment, the annular, outer ultrasonic element  26  is driven by a separate buffer amplifier  36  from the center ultrasonic element  24 , the latter which is driven by buffer amplifier  38 . Alternatively, a single buffer amplifier may be used and switched between either the center ultrasonic element  24  alone or the center element  24  plus the outer ultrasonic element  26 .  
         [0031]    The receiver unit  20  comprises a number of receiving elements  40  generally arrayed over a rectangular grid. Signals from each receiving element are collected by one or more multiplexers  42  to be sent out one or more signal leads  44 . The multiplexers  42  are controlled by an external computer signal, as will be described, to allow any individual or combination of receiving element(s)  40  to be read over signal leads  44  to permit scanning over the array of the receiver unit  20  for imaging purposes.  
         [0032]    Referring now to FIG. 3, the imaging/quantitative ultrasonic device  10  provides an internal bus  46  allowing a computer  48  having a processor  50  and memory  52  to communicate both with the transmitter unit  18  and the receiver unit  20 . In this way, the transmitted wave may be controlled according to a program held in memory  52  and the received wave may be processed according to the program in memory  52 . The bus  46  also communicates with the display/touch panel  16  which allows inputting of data to the computer  48  and outputting data from the computer  48  during execution of the program  52 . The bus  46  also allows communication between the computer  48  and the mechanical subsystems  54  such as pumps for inflating the bladders  34  prior to use or deflating the bladders  34  for storage.  
         [0033]    Referring now to FIG. 4, during operation of the program held in memory  52 , at a first step indicated by process block  60 , the computer  48  energizes both buffer amplifiers  36  and  38  (or switches one buffer to connect with both the ultrasonic elements  24  and  26 ) to operate ultrasonic elements  24  and  26  in tandem to produce a generally planar wave  62  (shown in FIGS. 3 and 5) generally for imaging purposes.  
         [0034]    Referring still to FIG. 4, at optional process block  63 , the computer  48  switches the buffer amplifier  38  off (or switches a single buffer amplifier to connect only to the outer ultrasonic element  26 ) to energize only the outer ultrasonic element  26  for the purpose of creating an outer wave passing largely around the os calcis, as indicated by wave  62 . At this time, only outer reception elements  40 ″ of the receiver unit  20  (shown in FIG. 5) are scanned or simultaneously connected together to detect the outer wave  62  and make the necessary measurement typically by combining and averaging of their measured values.  
         [0035]    Referring still to FIG. 4, at process block  66 , the computer  48  switches the buffer amplifier  36  off (or switches a single buffer amplifier to connect only to the center ultrasonic element  24 ) to energize only the center ultrasonic element  24  for the purpose of creating a central wave passing through the os calcis, as indicated by wave  68 . At this time, only central reception elements  40 ′ of the receiver unit  20  (shown in FIG. 5) are scanned or simultaneously connected together to detect the central wave  68  and make the necessary measurement typically by combining and averaging of their measured values.  
         [0036]    At process block  66 , the computer  48  processes the image and quantitative data. This image data may consist of amplitude data or attenuation data such as broadband ultrasonic attenuation (BUA) or speed of sound measurements (SOS), some other acoustic parameter(s), or a combination of any or all mapped to a gray scale (or color) value and a spatial location in the image corresponding to the location of each element(s)  40  in the ultrasonic receiver unit  20 . The image may be displayed on the display/touch panel  16 , and adjustment to the foot position is made, as is described below, and the process repeated as necessary.  
         [0037]    In a first embodiment, the image is generated solely from the data collected at process block  60  and quantitative measurements made solely from the data collected at process block  66 .  
         [0038]    In an alternative embodiment, the data collected at process block  63  may be obtained and used to make a measurement of the scatter ultrasonic energy to refine the quantitative measurements or to image certain structures. Further, the inner ultrasonic element  24  may be used alone for imaging purposes, for example, imaging of the center of the os calcis. Thus generally the invention contemplates obtaining up to three sets of data, data from the inner ultrasonic element  24  alone, data from the outer ultrasonic element  26  alone, and data from both elements, to generate separate image and quantitative information, through combinations of the above.  
         [0039]    The precise location of the central reception elements  40 ′ our outer reception elements  40 ″ may be determined automatically from the developed image of process block  63  by techniques known in the art or may be selected manually from the image by the operator. Thus, the reception pattern may be moved depending on the image so that quantitative measurements are made on the correct region. Alternatively, the operator may move the patient&#39;s foot, based on the image, to align the appropriate region of the foot with the central reception elements  40 ′ and/or the center ultrasonic element  24 . Movement of the foot may be accomplished through the use of a set of shims  17  of predetermined thickness (shown in FIG. 1) fitting into the footwell  14  or by means of a motorized stage supporting the foot but movable by the operator or automatically based on the image. The collected data is processed by the computer  48  using well known techniques, as indicated by process block  70 , to produce a quantitative value output to the display/touch screen  16 .  
         [0040]    Referring now to FIG. 5, although the applicants do not wish to be bound by a particular theory, it is believed that during the generation of the planar wave  62 , scatter or refraction occurring along line  72  causes acoustic energy not passing through a central trabecular region  74  of the os calcis  76  of the human heel  78  to be nevertheless diverted to central reception elements  40 ′ and incorporated into the quantitative measurement. Accordingly, by deactivating the annular, outer ultrasonic element  26  during the quantitative portion of the measurement, this scatter along lines  72  may be reduced in favor of a direct path  80  proceeding from center ultrasonic element  24  through the trabecular region  74  of the os calcis  76  to the central receiving elements  40 ′.  
         [0041]    The present invention provides a simple method of reducing this scatter which may be used alone or in combination with synthetic aperture-type techniques in which the phase of ultrasonic signals received by the elements  40  is used to focus the receiver unit  20  on particular regions of the bone of the os calcis  76 .  
         [0042]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims. For example, the transmitter unit  18  need not be divided into coaxial regions but may provide for any two independently excitable regions that may be used to develop different data for imaging and quantitative measurement.