Abstract:
Elastography is used to examine soft tissue of the uterus to detect tumors and to evaluate the strength of the cervix of the uterus based on its elastographic properties.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0001] This invention was made with United States government support awarded by the following agencies: NIH CA 39224. The United States has certain rights in this invention. 
     
    
     
       CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0002]    --  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates to a device for medical imaging and diagnosis and in particular for imaging methods suitable for examining the tissue of the uterus, cervix, and pelvic floor.  
           [0004]    The uterus is a vase-like muscular organ the shape of an upside down pear about two and one-half inches long in non-pregnant women. The narrow neck of the uterus is called the cervix. An examination of the uterus is typically performed by touch (palpation) during which the physician explores the contours of the uterus and cervix using his or her fingers while pressing down on the abdomen. In this way, in some cases, the physician may detect tumors or cysts.  
           [0005]    X-ray imaging methods, including computed tomography (CT), do not work well with the soft tissue of the uterus. Ultra-sound imaging may be employed, however, uterine fibroids and adenomyosis foci appear similar on conventional ultrasound scans making differentiation very difficult for the sonologist. Currently, magnetic resonance imaging (MRI) is the only imaging modality capable of characterizing these two conditions but MRI imaging is expensive, limiting its use as a screening tool.  
           [0006]    Some problems with the uterus are manifest by postmenopausal bleeding which may be caused by a benign etiology (endometrial atrophy, hyperplasia, polyps, or leiomyomas). However, approximately 10-30% of women with menopausal bleeding will be found to have endometrial cancer. Distinguishing between these etiologies is difficult with current imaging technology.  
           [0007]    Pre-term delivery is a complex problem that may result from incompetence of the cervix of the uterus. Although cervical incompetence is believed to be the principal causative factor in approximately 25% of miscarriages, it is difficult to determine which pregnancies might benefit from intervention and what the appropriate intervention might be. For example, the attending physician may recommend cerclage or simply prolonged bed rest.  
           [0008]    A history of pre-term delivery may be used to estimate the chance of pre-term delivery or, alternatively, such a risk may be estimated from the length of the cervix usually measured with a trans-vaginal ultrasound image. However, cervical length has not proven to be a wholly reliable indicator of this condition.  
           [0009]    Pelvic floor disorders, such as incontinence and prolapse, result from failure of the fibromuscular connective tissue sheath that forms the supporting structure for the organs of the deep pelvis. The identification of defects in this support structure is important for surgical planning and repair. At present, MRI imaging provides the only means of assessing these structures, but such imaging is expensive and available only in the larger centers.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    The present inventors propose the use of a new ultra-sound technique termed elastography for assessment of uterine, cervical, and pelvic floor tissue. Elastography produces images closely related to tissue stiffness. When applied to the cervix, tissue stiffness may be an important factor in determining the competence of the cervix. Elastography may also allow differentiation between fibroids and adenomyosis in the uterine wall because adenomyosis is an ingrowth of soft, glandular endometrial tissue into the myometrium of the uterus, likely to be more flexible than fibroids, which are primarily composed of stiff fibrous tissues and muscular bundles and whorls. Further, it is believed that elastography may better highlight one of the features of uterine cancer, the relative rigidity of the neoplastic tissue. In this regard, elastography could distinguish diffuse, stiff endometrial tissue (cancer) from diffuse, soft endometrial tissue (hyperplasia), focal, stiff tissue (leiomyomas), and focal, soft tissue (polyps).  
           [0011]    Specifically then, the present invention provides a method for evaluating the soft tissue of the uterus with respect to measurement of cervical incompetence using the steps of obtaining the first image of the cervix with an ultrasonic acoustic wave, then applying a displacement to the cervix after which a second image of the cervix is obtained to deduce elasticity of the cervix under the displacement. A measurement based on the deduced elasticity, indicating a likelihood of cervical incompetence, may then be output.  
           [0012]    It is therefore one object of the invention to use an imaging modality that can provide a direct measurement of tissue elasticity of the cervix to evaluate cervical competence.  
           [0013]    The displacement of the cervix and the imaging may both be performed by a single ultrasonic probe or a separate probe may be used for ultrasonic measurement and for displacement. In this latter case, the ultrasonic probe may be applied transabdominally. The probe for displacement may be a blunt rod or a balloon within the cervix.  
           [0014]    Thus it is another object of the invention to provide an elastographic characterization of the cervix that may be employed flexibly with a variety of different techniques.  
           [0015]    The output may be a comparison of the elasticity of the cervix with the threshold elasticity deduced from a standard population.  
           [0016]    Thus it is another object of the invention to provide a simple measure of the risk of pre-term delivery.  
           [0017]    The invention may include a step of defining an area of the cervical tissue and combining elasticity measurements over that area, and the output may be related to the combination of the elasticity measurements.  
           [0018]    Thus it is another object of the invention to provide for a robust measurement system that uses multiple measurements over an area.  
           [0019]    The same techniques of displacement and imaging may be applied to the uterus wall to detect and distinguish among abnormal masses. Specifically, a first image of the uterus may be obtained using an ultrasonic acoustic wave and a displacement applied to the uterus after which a second image of the uterus may be taken to deduce elasticity of the uterine wall. An image of the uterus may be produced indicating variations in elasticity associated with possible tumors.  
           [0020]    Thus it is another object of the invention to allow differentiation among masses in the soft tissue of the uterus.  
           [0021]    The same techniques of displacement and imaging may be applied to the fibromuscular tissues of the vaginal wall to detect pelvic floor defects. Specifically, a first image of the connective tissue sheath investing the vagina may be obtained using an ultrasonic acoustic wave and a displacement applied to the vaginal wall after which a second image of the uterus may be taken to deduce elasticity of the vaginal wall. An image of the vagina may be produced indicating variations in elasticity associated with possible connective tissue defects.  
           [0022]    Thus it is another object of the invention to assess the integrity of the pelvic floor and allow identification of support defects in the pelvic floor.  
           [0023]    In one embodiment of the invention, a specialized probe is used to evaluate uterine, cervical tissue or tissue of the pelvic floor, has a balloon sized for insertion into the relevant portion of the uterus or vagina to extend along its length and a pump communicating with the balloon to apply a controlled displacement of the uterine or cervical tissue by inflation of the balloon.  
           [0024]    Thus it is one object of the invention to provide a localized and reproducible distention or compression of the tissue being examined.  
           [0025]    The balloon may include an ultrasound transducer mounted within the balloon for acquiring images through the balloon into the uterine or cervical tissue.  
           [0026]    Thus, it is another object of the invention to provide for improved and localized imaging of the tissue of the uterus.  
           [0027]    In one embodiment of the invention, pressure or force sensors are used to measure the applied pressure. Pressure sensors on the transvaginal probe will be used to measure pressure when compression is applied to the cervix using the probe. Pressure measurements in the balloon will be performed when the pump and balloon is used to apply a controlled displacement of the uterine or cervical tissue by inflation of the balloon.  
           [0028]    In one embodiment of the invention, pressure and strain measurements will be used to obtain quantitative or Young&#39;s Modulus values of the stiffness of the cervix and uterine tissue, using appropriate boundary conditions.  
           [0029]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    [0030]FIG. 1 is a simplified block diagram of an ultrasound scanner suitable for use with the present invention in scanning uterine tissue;  
         [0031]    [0031]FIG. 2 is a graphical representation of an ultrasonic signal received by the ultrasound scanner of FIG. 1 showing the analysis of one waveform of the signal taken at two successive times with a different strain of the uterine tissue showing a shifting of the signals corresponding to such strain;  
         [0032]    [0032]FIG. 3 is a block diagram of the processing of the scan data of FIG. 2 by the ultrasound scanner of FIG. 1 to deduce stiffness using a time-domain analysis technique;  
         [0033]    [0033]FIG. 4 is a figure similar to that of FIG. 3 using a frequency domain analysis technique;  
         [0034]    [0034]FIG. 5 is a representation of the screen of the display of the apparatus of FIG. 1 showing juxtaposed conventional and strain tissue images and, showing tracking cursors for navigation and quantitative display of the strain measurement in numerical and graphical form;  
         [0035]    [0035]FIG. 6 is a cross section of a patient taken along a mid-sagittal plane of the uterus and perineal area showing the use of a transperineal ultrasound probe together with a blunt probe for displacement of the tissue of the cervix;  
         [0036]    [0036]FIG. 7 is a figure similar to that of FIG. 6 showing the use of a blunt of probe of FIG. 6 with a transabdominal ultrasonic probe;  
         [0037]    [0037]FIG. 8 is figure similar to that of FIGS. 6 and 7 showing the use of a transvaginal probe both for ultrasonic acquisition and for tissue displacement;  
         [0038]    [0038]FIG. 9 is a figure similar to that of FIGS. 6-8 showing the use of a transabdominal ultrasonic probe or a transperineal probe with a balloon for displacement of the uterine tissue;  
         [0039]    [0039]FIG. 10 is a detailed view of the uterus of FIG. 9 showing the use of a syringe for inflation and deflation of the balloon placed within the uterus adjacent to an unknown mass;  
         [0040]    [0040]FIG. 11 is a figure similar to that of FIG. 10 showing a smaller balloon for use in displacement of only the cervix as anchored by a secondary balloon and showing a region of interest for cervical characterization;  
         [0041]    [0041]FIG. 12 is a view similar to that of FIG. 10 showing a balloon surrounding a side-looking ultrasonic probe for scanning the uterus while moving within the balloon;  
         [0042]    [0042]FIG. 13 is a simplified cross sectional view of a probe system providing for inflation of a balloon and independent axial movement over the ultrasonic probe of FIG. 12;  
         [0043]    [0043]FIG. 14 is a figure similar to that of FIGS. 10 and 11 showing an embodiment of the balloon for placement in the vagina for measurement of the tissue of the pelvic floor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0044]    Elastography is a known, but new imaging modality that reveals the stiffness properties of tissues, for example, axial strain, lateral strain, Poisson&#39;s ratio, Young&#39;s modulus, or other common strain and strain-related measurements. The strain measurements may be collected over an area and compiled as a two-dimensional array of data, which may then be mapped to a gray scale to form a strain “image”.  
         [0045]    In “quasi static” elastography, two conventional images of the tissue are obtained using ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI). The first image provides a base line of the tissue at a given state of compression or distention and the second image is obtained with the tissue under a different compression or distention. The tissue may be compressed by an external agency such as a probe or the like or may be compressed by its own muscular action, for example, in the case of the heart, or by movement of adjacent organs. Displacement of the tissue between the two images is used to deduce the stiffness of the tissue. Quasi-static elastography is thus analogous to a physician&#39;s palpation of tissue in which the physician determines stiffness by pressing the tissue and detecting the amount that the tissue yields under this pressure.  
         [0046]    In “dynamic” elastography, a low frequency vibration is applied to the tissue and the tissue vibrations accompanying the resulting elastic wave are measured, for example, using ultrasonic Doppler detection.  
         [0047]    Referring now to FIG. 1, the present invention applies elastography to measurements of the uterus and cervix using an ultrasonic imaging system alone or in combination with a stand-alone computer  30 . Generally, the ultrasonic imaging system  10  provides a graphic display  32 , a keyboard  34  for data entry and a cursor control device  36 , such as a mouse, as is well understood in the art for providing user input.  
         [0048]    In a preferred embodiment, the ultrasonic imaging system  10  may make use of a Siemens Antares (commercially available from Siemens Medical Systems, Issaquah, Wash.) with a research interface or a GE Logiq 900 (commercially available from GE Medical Systems, Waukesha, Wis.) with a research interface ultrasound system communicating with a 3.5, 5 or 7.5 Megahertz linear or curvilinear array ultrasound transducer  12  transmitting and receiving a beam  14  of ultrasonic energy along a number of rays  16 . For uterine imaging, as shown, the ultrasound transducer  12  may be placed against the patient&#39;s abdomen for transabdominal imaging. Alternatively, as described below, a transperineal or transvaginal probe of a type generally understood in the art may be used.  
         [0049]    During data acquisition, the ultrasound transducer  12  transmits an ultrasound beam  14  toward the uterus  18  and receives echo data at each of numerous transducer elements. This data is transmitted via cable  20  to the ultrasonic imaging system  10  where it is received and processed by interface circuitry  22 . Alternatively, echo data may be formed into signals representing echoes from along each of the rays  16  and then transmitted to ultrasonic imaging system  10 . In the preferred embodiment, the data may be sampled at least 2-5 times the center frequency or higher, and repeated acquisitions are taken at a frame rate of at least twenty frames per second.  
         [0050]    The processed ultrasound data will be assembled into conventional B-mode images  38  providing a real-time representation of a plane through the uterus  18  according to well-known techniques. Further processing, according to the present invention (as will be described below), may be performed by a processor  33  executing a stored program contained in memory  35  residing either in the standard ultrasonic imaging system  10  or the stand-alone computer  30 .  
         [0051]    Referring now also to FIG. 2, each B-mode image  38  is composed of a series of time-domain signals  56  corresponding approximately with the rays  16 , and having a varying amplitude mapped to brightness of pixels  54  forming the columns of the B-mode image  38 . As such, the time axis of each signal  56  generally reflects distance from the ultrasound transducer  12  to the tissue of the uterus  18 .  
         [0052]    The strain within the tissue of the uterus  18  may be determined by comparing corresponding time-domain signals  56   a  and  56   b  from two sequential ultrasound echo B-mode images  38  measuring the uterine tissue at different degrees of displacement (e.g., compression or distention) as will be described below. As shown, the second time-domain image signal  56   b  exhibits an expansion in time reflecting an expansion or distention of the uterine tissues toward or away from the ultrasound transducer  12 . More generally, the later time-domain image signal  56   b  might represent either relative distention or relative compression with respect to earlier time-domain image signal  56   a.    
         [0053]    A general translation of the tissue of the uterus  18  (rather than local compression or distension) would cause an equal offset between all points in time-domain image signals  56   a  and  56   b . However, the elasticity of the tissue causes local tissue compression or distension, which in turn produces a gradient in the phase offset of the time-domain image signals  56   a  and  56   b  as a function of time and distance from the ultrasound transducer  12 .  
         [0054]    For the example shown, the phase offset  58  between the time-domain image signals  56   a  and  56   b  at early times and hence near the ultrasound transducer  12  will be smaller than the phase offset  60  at later times and for tissue further away from the ultrasound transducer  12 . The rate of change of these displacements at points over the region of the uterus  18  provides a series of strain values having magnitude and sign that is used to produce an elastographic image of the tissue of the uterus  18 .  
         [0055]    Referring to FIG. 3 more specifically, ultrasonic radio frequency (RF) scan data  64  is collected being at least two B-mode images  38  containing successive time-domain image signals  56   a  and  56   b . At process block  65 , these signals are processed to determine tissue displacement along an axis from the ultrasound transducer  12  through the uterus  18 . In principle, short segments of the time-domain image signals  56   a  and  56   b  are analyzed by moving one segment with respect to the other until a best match is obtained and the amount of movement needed for the best match determines tissue displacement. The matching process may be implemented by means of mathematical correlation of the segments.  
         [0056]    The displacement of signal  66  output by process block  65  is further processed by the process block  68 , which determines strain as a gradient of the displacement signal. The strain values  71  may be mapped to an elastographic image  72 .  
         [0057]    As each successive frame is obtained by the system of FIG. 1, a new elastographic image  72  may be obtained by comparing that frame to the predecessor frame to determine displacement as has been described, and thus the strain is relative to the last B-mode image  38 . Alternatively, a base image approximating the uterus  18  uncompressed or at an initial state of compression may be used to produce an elastographic image  72  relative to that base image. More generally a peak or root-mean-square value or other similar measure can be adopted for computing strain.  
         [0058]    Referring momentarily to FIG. 4, alternative algorithms may be used to create the elastographic images  72 . In one such algorithm, the time-domain image signals  56   a  and  56   b  may be received by process block  81  to extract spectra of the time-domain image signals  56   a  and  56   b  using, for example, the well-known fast Fourier transform algorithm. The spectra of the time-domain image signals  56   a  and  56   b  will be shifted according to the Fourier transformation property that causes dilation in a time-domain signal to produce a down-frequency shift in its frequency-domain spectrum. The amount of shift may be determined at process block  83  using correlation techniques similar to those used in process block  65  but executed on the frequency-domain signals.  
         [0059]    The shift between the spectra taken of different segments of the time-domain signals  56   a  and  56   b , centered at increasing time delays, provides a gradient signal to produce elastographic images  72 . While the results are similar to the technique of FIG. 3, this approach may have some advantages in terms of robustness against noise and the like.  
         [0060]    Each of these process blocks may be implemented through a combination of hardware and software in the ultrasonic imaging system  10  and/or the stand-alone computer  30  as is well understood to those of ordinary skill in the art.  
         [0061]    Referring now to FIGS. 3 and 5, the strain values  71  for each pixel  74  of the elastographic images  72  will have a magnitude and sign. The magnitude indicates the amount of the distension or compression of the tissue and the sign indicates whether it is a compression or distention with positive signs normally denoting compression and negative signs by convention noting distension of the tissue. These values may be mapped to colors and displayed in an elastographic image  72 . The elastographic image is that which will be used for detection of tumors or the like.  
         [0062]    Referring now to FIGS. 1 and 5, the processor  33  executing the stored program in memory  35  may juxtapose the conventional B-mode image  38  (typically in a gray scale) next to the elastographic image  72  on the display  32 . The B-mode image  38  shows relatively time invariant qualities of the uterine tissue, such as tissue interfaces, and further provides a higher resolution image of the uterus  18  in which anatomical features may be more readily distinguished. The B-mode images  38  and elastographic image  72  may be static or updated in real time and sized and oriented to show the same region of uterine tissue.  
         [0063]    The program may also provide for a cursor  80  that may be positioned over the B-mode images  38  and a cursor  82  that may be positioned over the elastographic image  72 , respectively, through the use of the cursor control device  36  and keyboard  34 . Cursor  80  and  82 , in any case, are positioned to track each other so as to constantly contain a region of interest  84  centered on the same structure in both the B-mode images  38  and elastographic image  72 . In this manner, the B-mode image  38  may be used to identify particular anatomy of the uterus  18 , for example, the cervix  104  and the strain may be investigated locally by reviewing the region within the cursor  82 .  
         [0064]    A quantitative readout  86  may be provided on the graphic display  32  providing statistics related to the strain of tissue contained in the region of interest of the cursor  82 . In the simplest embodiment, a current average strain relative to the last B-mode image  38  may be displayed or alternatively a peak strain, absolute strain, or average strain magnitude may be displayed. For evaluation of cervical incompetence, the data acquired with the cursor  82  on the cervix  104  may be compared to empirically obtained data representing values for a standard population having known cervical function and the measured data displayed in chart form  90  providing a marker  93  displaying a qualitative indication of how the patient compares to a characterized standard population.  
         [0065]    Referring now to FIG. 6, in a first data collection method, a transperineal ultrasonic probe  100  may be directed toward the uterus  18  so that its rays  16  illuminate the uterus  18  from an inferior direction. A mechanical probe  102 , for example a blunt rod, may then be used to apply compression to the cervix  104  in between acquisition of B-mode images  38 .  
         [0066]    Referring to FIG. 7 in an alternative acquisition technique, a transabdominal ultrasound transducer  12  may be directed to illuminate the uterus  18  from the abdomen, again with the mechanical probe  102  used to provide the necessary tissue displacement.  
         [0067]    Referring to FIG. 8, alternatively, a transvaginal ultrasonic probe  106  may illuminate the uterus  18  from the inferior direction and may fit within the vagina to apply compression directly to the cervix  104  in place of the mechanical probe  102  as previously described.  
         [0068]    In each of these techniques the operator may provide a signal to the ultrasonic imaging system  10  through the keyboard  34  or the like indicating a command to obtain additional B-mode image  38  with displacement and without displacement. This command could also be derived from a sensor that detects or measures the motions of probe  102 . Alternatively, the elastographic images  72  may be generated on a real-time basis as displacement is applied.  
         [0069]    Referring now to FIGS. 9 and 10 displacement of the tissue of the uterus  18  as a whole, as opposed to only the tissue of the cervix  104 , may be accomplished through the use of a balloon-end catheter  110  having a balloon  111  sized to extend substantially the length of the uterus  18 . The balloon  111  of the balloon-end catheter  110  is inserted within the uterus and a first image is obtained. The balloon portion may then be inflated with a saline solution  115  to press outward on the muscle wall of the uterus  18  by using a simple pump  112  such as a syringe attached to tubing  114  connecting to the balloon  111  of the balloon-end catheter  110 . Alternatively multiple images may be taken of different degrees of inflation of the balloon  111 .  
         [0070]    Referring to FIG. 9, the displacement caused by the balloon  111  may be imaged either using a transabdominal ultrasound transducer  12  or the transperineal ultrasonic probe  100  or the transvaginal ultrasonic probe  106  (the latter shown in FIG. 8). It is believed that the displacement will reveal a strain image that may identify localized masses  118  having a stiffness that differs from the general muscle of the uterus  18  which will be apparent in the elastographic image  72  of FIG. 5.  
         [0071]    Referring now to FIG. 15, displacement of the tissue of the vagina  140  as a whole, as opposed to only the tissue of the uterus  18  or cervix  104 , may be accomplished through the use of a balloon-end catheter  142  having a balloon  143  sized to extend substantially the length of the vagina  140 . The balloon  143  of the balloon-end catheter  142  is inserted within the vagina  140  and a first image is obtained. The balloon  143  may then be inflated with a saline solution as described above and a second image obtained. Alternatively multiple images may be taken of different degrees of inflation of the balloon  143 .  
         [0072]    The displacement caused by the balloon  143  may be imaged either using a transabdominal ultrasound transducer  12  or the transperineal ultrasonic probe  100  or the transvaginal ultrasonic probe  106  (the latter shown in FIG. 8) or intravascular ultrasound transducer  128  within the balloon  143  as described above. It is believed that the displacement will reveal a strain image that may identify localized defects having a stiffness that differs from the intact fibromuscular sheath investing the vagina, which will be apparent in the elastographic image. Alternatively, the displacement of the vagina  140  may be done using a mechanical probe  102  or the transvaginal ultrasonic probe  106  as described above.  
         [0073]    Referring now to FIG. 11, a dual-balloon catheter  120  may also be used for cervical measurements having a first balloon  122  at one end of the catheter and sized to extend only through the cervix  104  of the uterus  18 . Positioning of the balloon  122  may be provided by a second balloon  124  removed from the first end that may be inflated in the vaginal canal  126  outside of the cervix  104 , or alternatively with a balloon (not shown) held within the uterus  18  itself. For these measurements, the cursor  80  will be placed on the wall of the cervix  104  to make the necessary composite strain measurements as may be then related to the population at large.  
         [0074]    Referring now to FIG. 12, in a further embodiment, a thin intravascular ultrasound transducer  128  is inserted within the balloon  111  to provide a radial or side-looking beam  14  that may scan the uterus  18  from within the balloon  111  of the balloon-end catheter  110 . This scanning may be performed by rotation of the thin ultrasound transducer  128  about long axis accompanied by translation of the thin ultrasound transducer  128  along its axis. In this way, a composite image of the uterus  18  may be collected on a slice-by-slice basis. Alternatively, the thin ultrasound transducer  128  may be directed manually by the physician to scan the uterus  18  looking for particular elastographic anomalies on a real time display of elastographic images  72 . The saline solution  115  provides a coupling of the ultrasound from the intravascular ultrasound transducer  128  into the tissue of the uterus  18 .  
         [0075]    Referring to FIG. 13, for the above scanning, the balloon-end catheter  110  may include a seal  130  opposed to the balloon  111  removed from the patient. The shaft of the intravascular ultrasound transducer  128  may exit through the seal  130 , which allows a translation and rotation of the intravascular ultrasound transducer  128  without loss of saline solution  115 .  
         [0076]    A T-connection  136  may connect the lumen of the balloon-end catheter  110  to an electric pump  138  providing for a periodic sinusoidal inflation and deflation of the balloon  111  of the balloon-end catheter  110 . Electric pump  138  may be, for example, a rolling diaphragm pump attached through a crank arm to a rotation motor or the like. A separate syringe (not shown) may be used to adjust the mean inflation. A signal may pass from the pump  138  to be received by the ultrasonic imaging system  10  to coordinate its acquisition of images during the deflation and inflation portion of the pump cycles. In this way repeated measurements may be made during the scanning process. A pressure transducer  131  may provide an instantaneous measure of balloon pressure. This pressure measurement allows better reproducibility of the elasticity measurements and/or may allow quantitative measurements such as Young&#39;s modulus to be made using appropriate boundary conditions.  
         [0077]    In one embodiment of the invention, the pump communicating with the balloons described above will be used to apply cyclical or dynamic compression and relaxation at a low frequency (inflation and deflation with saline). Imaging will then be performed transabdominally using tissue Doppler or Tissue Velocity Imaging, to obtain strain and strain rate images, using a scanner such as a GE Vingmed Vivid 5 or Vivid 7 scanner (commercially available from GE Vingmed of Forton, Norway)  
         [0078]    The present invention is applicable to a range of specific techniques for measurement of tissue elasticity including but not limited to Sonoelasticity or Sonoelastography, Dynamic Elastography, MRI elastography any of which may be used to estimate strain, strain rate or Young&#39;s Modulus images all of which should be considered measures of elasticity for the purpose of this application. It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.