Patent Publication Number: US-2009227867-A1

Title: Ultrasonograph

Description:
TECHNICAL FIELD 
     The present invention relates to an ultrasonic diagnostic apparatus for use in medical applications and more particularly relates to an ultrasonic diagnostic apparatus for measuring a vascular wall. 
     BACKGROUND ART 
     An ultrasonic diagnostic apparatus is used to monitor an internal tissue of a subject by irradiating him or her with an ultrasonic wave and analyzing the information contained in its echo signal. For example, a conventional ultrasonic diagnostic apparatus that has been used extensively converts the intensity of an echo signal into its associated pixel luminance, thereby presenting the subject&#39;s structure as a tomographic image. In this manner, the internal structure of the subject can be known. The ultrasonic diagnostic apparatus can be used to make a noninvasive checkup on an internal tissue of a subject, and therefore, is now an indispensable device at any clinical spot along with X-ray CT and MRI. 
     Recently, the number of people suffering from arteriosclerosis has been on the rise and carotid echo has been carried out more and more often using an ultrasonic diagnostic apparatus to diagnose arteriosclerosis. It is known that the carotid artery has a three-layer structure consisting of intima, media and adventitia that are stacked in this order. In carrying out a carotid echo, the combined thickness of the intima and the media (or intima-media thickness, which will be abbreviated herein as “IMT”) is measured and used as an index to arteriosclerosis. According to Non-Patent Document No. 1, if the IMT is 1.1 mm or more, the carotid is determined to have abnormally thickened. The IMT is manually measured with a length measuring function on a tomographic image, which is usually provided for any ultrasonic diagnostic apparatus. The IMT may be measured sometimes at only one spot and sometimes at multiple spots. In the latter case, the maximum or average of those multiple measured values may be used as an index.  FIG. 12  shows how the IMT of a carotid artery is measured with a conventional ultrasonic diagnostic apparatus. Specifically,  FIG. 12  shows a tomographic image as viewed on a plane that is parallel to the axis of the vascular wall (i.e., a vertical cross section of the vascular wall). In  FIG. 12 , the six + signs indicate manually set points. At the central pair of set points indicated by “1”, the distance between the two + signs is 0.5 mm. On the other hand, at each of the other two pairs of set points indicated by “ 2 ” and “ 3 ”, the distance between the two + signs is 0.4 mm. 
     Meanwhile, as an alternative method for diagnosing arteriosclerosis, some people are attempting recently to track the motion of a subject&#39;s tissue more precisely and evaluate the strain and the elasticity, viscosity or any other attribute property of the tissue mainly by analyzing the phase of the reflected echo signal. 
     Patent Document No. 1 discloses a method for tracking precisely the motions of two very small regions on a vascular wall in one cardiac cycle, sensing a slight variation in the thickness (i.e., the magnitude of strain) that is superposed on a significant oscillation due to the heartbeat and calculating a local elasticity based on the magnitude of strain and blood pressure difference. Patent Document No. 1 also discloses an apparatus for displaying a spatial distribution of elasticities as an image. To track those very small regions on a vascular wall, a phase difference tracking method as disclosed in Patent Document No. 2 is used. Hereinafter, a method for tracking a subject&#39;s tissue as disclosed in Patent Document No. 1 will be described with reference to  FIGS. 13(   a ) and 13( b ). As shown in  FIG. 13(   a ), an ultrasonic wave is transmitted from a probe  101  toward the blood vessel  111  of a subject  110  and an echo reflected from the blood vessel  111  is received at the probe  101 . Two measuring points A and B are set on the vascular wall and the signals received from those measuring points A and B are analyzed by the method disclosed in Patent Document No. 2, thereby tracking the motions of the measuring points A and B. 
     The blood vessel  111  repeatedly contracts and dilates through cardiac cycles. More specifically, the blood vessel  111  dilates rapidly in a systolic phase but contracts slowly in a diastolic phase.  FIG. 13(   b ) shows the tracking waveforms TA and TB of the measuring points A and B along with an electrocardiographic complex ECG. As the blood vessel  111  dilates, the measuring points A and B move rapidly. But after that, the measuring points A and B slowly go back to their original locations. The difference between the tracking waveforms TA and TB is represented as a waveform W showing a variation in thickness between the measuring points A and B. Supposing the variation in the thickness variation waveform is ΔW and the reference thickness between the measuring points during initialization is Ws, the magnitude of strain ε between the measuring points A and B is calculated by the following Equation (1): 
       ε=Δ W/Ws    (1) 
     Supposing the blood pressure difference at this time is ΔP, the radial elasticity Er between the measuring points A and B is given by the following Equation (2): 
         Er=ΔP/ε=ΔP·Ws/ΔW    (2) 
     Therefore, by measuring the elasticity Er for multiple spots on a tomographic image, an image representing the distribution of elasticities can be obtained. 
     Non-Patent Document No. 2 discloses a method for calculating the circumferential elasticity of a blood vessel, representing a more accurate physical property than the radial elasticity thereof. According to Non-Patent Document No. 2, the circumferential elasticity is given by the following Equation (3): 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     where h 0  is the initial radial thickness of the overall vascular wall and r 0  is initial radius of the blood vessel. 
       FIG. 14  illustrates a picture to be presented on a monitor screen when the artery is inspected with an ultrasonic diagnostic apparatus. On the screen, an elasticity image  201  representing the distribution of elasticities is superimposed on the posterior wall portion  230  (i.e., a portion of the vascular wall that is more distant from the skin surface) of a tomographic image  200 . 
     In the prior art, to calculate the initial thickness h 0  and initial radius r 0  of the overall vascular wall, the borderline  203  between the vascular flow  207  and the intima  221  of the anterior wall (i.e., a portion of the vascular wall closer to the skin surface)  220 , the borderline  204  between the vascular flow  207  and the intima  231  of the posterior wall  230 , and the borderline  206  between the adventitia  233  of the posterior wall  230  and its surrounding tissue are drawn manually. More specifically, by sensing the boundary between the area of the vascular flow  207  and the area of the intima  221  of the anterior wall  220  that are presented on the monitor screen based on the shades of the tomographic image reflection intensity scale  202 , the operator traces the borderline with the cursor  210  on the monitor screen, thereby determining the borderline  203 . By repeatedly performing similar operations, the other borderlines  204  and  206  can also be drawn.
         Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 2000-229078   Patent Document No. 2: Japanese Patent Application Laid-Open Publication No. 10-5226   Non-Patent Document No. 1: Hiroshi Furuhata, Carotid Echo, Vector Core Inc., 2004, ISBN 4-938372-88-6   Non-Patent Document No. 2: Hideyuki Hasegawa, Hiroshi Kanai et al., “Evaluation of regional elastic modulus of cylindrical shell with non-uniform wall thickness”, J. Med. Ultrasonics, Vol. 28, No. 1 (2001), pp. J3 to J13       

     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, as there are multiple borderlines to draw, it will take a while to establish all of those borderlines. Also, since the initial thickness h 0  and initial radius r 0  of the overall vascular wall are calculated based on the borderlines that have been drawn in this manner, the borderlines should be determined accurately. For that reason, it would impose a heavy burden on the operator to determine the borderlines by moving the cursor by him- or herself. 
     In order to overcome the problems described above, the present invention has an object of providing an ultrasonic diagnostic apparatus that can alleviate the burden on the operator. 
     Means for Solving the Problems 
     An ultrasonic diagnostic apparatus according to the present invention is designed to measure a vascular wall. The apparatus includes: a transmitting section that drives a probe to transmit an ultrasonic wave toward a subject including a blood vessel; a receiving section that receives an ultrasonic echo, produced by getting the ultrasonic wave reflected by the subject, at the probe to generate a received signal; a tomographic image processing section for generating an image signal based on the received signal to present the tomographic image of the subject on a display section; a first borderline generating section for determining a first type of borderline based on the tomographic image presented on the display section; and a second borderline generating section for generating at least one borderline of a second type by translating the first type of borderline. 
     In one preferred embodiment, the ultrasonic diagnostic apparatus further includes a user interface that allows an operator to specify his or her desired location on the tomographic image. 
     In this particular preferred embodiment, the second borderline generating section generates the second type of borderline by translating the first type of borderline to the location that has been specified by the operator with the user interface in accordance with information about the first type of borderline. 
     In a specific preferred embodiment, the first borderline generating section stores, as the information about the first type of borderline, information about a line segment that has been drawn on the tomographic image by the operator with the user interface. 
     In a more specific preferred embodiment, the first borderline generating section generates either a line segment or a polygon as the first type of borderline at the location that has been specified by the operator. 
     In another preferred embodiment, the first type of borderline is located on at least one boundary that is selected from a group of boundaries consisting of boundaries between the intima of the anterior and posterior walls of the blood vessel and vascular flow, boundaries between the media and adventitia of the anterior and posterior walls of the blood vessel, and boundaries between the adventitia of the anterior and posterior walls of the blood vessel and their surrounding tissue. The second type of borderline is located on at least another one of the group of boundaries. 
     In this particular preferred embodiment, the first borderline generating section detects the boundary between the intima of the anterior or posterior wall of the blood vessel and the vascular flow based on the image signal and determines the first type of borderline on the boundary detected. 
     In a specific preferred embodiment, the first type of borderline is located on the boundary between the intima of the anterior or posterior wall and the vascular flow and the second type of borderline is located on the boundary between the media and adventitia thereof. The intima-media thickness of the vascular wall is calculated by reference to the first and second types of borderlines. 
     In a more specific preferred embodiment, the ultrasonic diagnostic apparatus further includes: a tissue tracking section for tracking the motion of a tissue of the subject based on the received signal; and an attribute value calculating section that receives information about the blood pressure of the subject and calculates an attribute value of the tissue based on the motion of the tissue tracked. The attribute value of at least one tissue, which is selected from the group consisting of the intima, media and adventitia of the blood vessel, is calculated with respect to the first and second types of borderlines. 
     In this particular preferred embodiment, the first type of borderline is located on the boundary between the intima and the vascular flow and the second type of borderline is located between the adventitia and the surrounding tissue. By calculating the radius of the blood vessel and the thickness of the vascular wall by reference to the first and second types of borderlines, a circumferential elasticity is calculated as the attribute value. 
     A method for determining the boundaries of a vascular wall using an ultrasonic diagnostic apparatus according to the present invention includes the step of generating a second type of borderline by translating a first type of borderline on a tomographic image of a subject&#39;s blood vessel that has been produced by transmitting and receiving an ultrasonic wave. The first type of borderline is determined so as to be located on at least one boundary that is selected from a group of boundaries consisting of boundaries between the intima of the anterior and posterior walls of the blood vessel and vascular flow, boundaries between the media and adventitia of the anterior and posterior walls of the blood vessel, and boundaries between the adventitia of the anterior and posterior walls of the blood vessel and their surrounding tissue. The second type of borderline is located on at least another one of the group of boundaries. 
     In one preferred embodiment, the method further includes the step of storing, as information about the first type of borderline, information about a line segment that has been drawn on the tomographic image by the operator using a user interface. The step of generating the second type of borderline includes generating the second type of borderline based on the stored information about the first type of borderline. 
     In another preferred embodiment, the method further includes the step of generating either a line segment or a polygon as the first type of borderline at the location that has been specified on the tomographic image of the blood vessel by the operator using the user interface. 
     In still another preferred embodiment, the method further includes the step of detecting the boundary between the intima of the anterior or posterior wall of the blood vessel and the vascular flow based on an image signal representing the tomographic image and determining the first type of borderline on the boundary detected. 
     Effects of the Invention 
     According to the present invention, time and trouble to determine the respective boundaries of a vascular wall can be saved and measurements by an ultrasonic diagnostic apparatus can be done in a shorter time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1(   a ) is a block diagram illustrating a configuration for an ultrasonic diagnostic apparatus according to the present invention and  FIG. 1(   b ) is a block diagram illustrating the configuration of its core section. 
         FIG. 2  is a flowchart showing a procedure for determining borderlines using the ultrasonic diagnostic apparatus shown in  FIG. 1 . 
         FIG. 3  illustrates an exemplary picture to be presented on the monitor screen when the procedure shown in  FIG. 2  is adopted. 
         FIGS. 4(   a ) through  4 ( c ) illustrate an exemplary procedure for generating a borderline by translating another borderline. 
         FIGS. 5(   a ) through  5 ( c ) illustrate another exemplary procedure for generating a borderline by translating another borderline. 
         FIGS. 6(   a ) through  6 ( c ) illustrate still another exemplary procedure for generating a borderline by translating another borderline. 
         FIG. 7  is a flowchart showing another procedure for determining borderlines using the ultrasonic diagnostic apparatus shown in  FIG. 1 . 
         FIG. 8  illustrates an exemplary picture to be presented on the monitor screen when the procedure shown in  FIG. 7  is adopted. 
         FIG. 9  is a flowchart showing still another procedure for determining borderlines using the ultrasonic diagnostic apparatus shown in  FIG. 1 . 
         FIG. 10  illustrates an exemplary picture to be presented on the monitor screen when the procedure shown in  FIG. 8  is adopted. 
         FIG. 11  is a flowchart showing yet another procedure for determining borderlines using the ultrasonic diagnostic apparatus shown in  FIG. 1 . 
         FIG. 12  shows an exemplary plane on which an IMT is measured with a conventional ultrasonic diagnostic apparatus. 
         FIG. 13(   a ) illustrates a procedure for calculating the magnitude of strain based on the tracking waveforms at multiple measuring points using a conventional ultrasonic diagnostic apparatus and  FIG. 13(   b ) shows the tracking waveforms at those measuring points. 
         FIG. 14  illustrates a typical elasticity image presented on the screen of a conventional ultrasonic diagnostic apparatus. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           100  control section 
           101  probe 
           102  transmitting section 
           103  receiving section 
           104  tomographic image processing section 
           105  tissue tracking section 
           1 ≢image synthesizing section 
           107  monitor 
           108  elasticity calculating section 
           111  blood pressure manometer 
           112  blood pressure manometer controlling and blood pressure value input section 
           120 ,  121  memory 
           130  user interface 
           150  borderline determining section 
           151  borderline storage section 
           152  second borderline generating section 
           153  first borderline generating section 
           200  tomographic image 
           202  tomographic image reflection intensity scale 
           203  vascular flow-intima borderline on anterior wall of blood vessel 
           204  vascular flow-intima borderline on posterior wall of blood vessel 
           205  media-adventitia borderline on posterior wall of blood vessel 
           206  adventitia-surrounding tissue borderline on posterior wall of blood vessel 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of an ultrasonic diagnostic apparatus according to the present invention will be described with reference to the accompanying drawings. An ultrasonic diagnostic apparatus according to the present invention is used to determine the shape or an attribute value of a vascular wall. In the preferred embodiments to be described below, a boundary between the vascular flow and the intima of the anterior wall of a blood vessel and boundaries between the vascular flow and the intima, between the media and adventitia, and between the adventitia and a surrounding tissue of the posterior wall of a blood vessel are supposed to be determined. However, the present invention is in no way limited to those specific preferred embodiments but is also applicable for use to determine a boundary between the media and adventitia of the anterior wall and a boundary between the adventitia and a surrounding tissue of the anterior wall. 
       FIG. 1(   a ) is a block diagram illustrating a configuration for an ultrasonic diagnostic apparatus as a preferred embodiment of the present invention. The ultrasonic diagnostic apparatus includes a transmitting section  102 , a receiving section  103 , a tomographic image processing section  104 , a tissue tracking section  105 , an image synthesizing section  106 , and an elasticity calculating section  108 . The apparatus further includes a control section  100  for controlling all of these components and a user interface  130 . 
     The user interface  130  is an input device that accepts an operator&#39;s command such as a keyboard, a trackball, a switch or a button. The operator&#39;s command that has been entered through the user interface  130  is input to the control section  100 . The control section  100  may be implemented as a microcomputer, for example, and controls all of those components in accordance with the operator&#39;s commands. In addition, as will be described in detail later with reference to  FIG. 1(   b ), the control section  100  includes a borderline determining section  150  for determining borderlines indicating boundaries between the tissues of a vascular wall. It should be noted that although the control section  100  actually exchanges signals with the respective blocks shown in  FIG. 1(   a ), lines indicating exchange of those signals are not shown in  FIG. 1(   a ) to avoid complications. 
     In accordance with the instruction given by the control section  100 , the transmitting section  102  generates a high-voltage transmission signal that drives the probe  101  at a specified timing. The probe  101  converts the transmission signal that has been generated by the transmitting section  102  into an ultrasonic wave and sends out the ultrasonic wave toward a subject, and also detects an ultrasonic echo that has been reflected by an internal organ of the subject and converts the echo into an electrical signal. A number of piezoelectric transducers are arranged in the probe  101 . By changing the piezoelectric transducers to use and the timing to apply a voltage to the piezoelectric transducers, the probe  101  controls the angle of deviation and focus of the ultrasonic waves to transmit and receive. The receiving section  103  amplifies the electrical signal generated by the probe  101  and outputs a received signal. Also, the receiving section  103  detects only an ultrasonic wave that has come from a particular position (associated with the focus) or direction (associated with the angle of deviation). 
     The tomographic image processing section  104  includes a filter, a detector, and a logarithmic amplifier, and analyzes mainly the amplitude of the received signal, thereby generating an image signal representing a tomographic image of the subject. The tissue tracking section  105  includes a magnitude of displacement calculating section for analyzing the phase difference between the received signals and calculating the magnitude of displacement of the subject&#39;s tissue in the ultrasonic wave transmitting and receiving directions, and a tracking location calculating section that calculates the new location by adding the magnitude of displacement to the original location. The tissue tracking section  105  tracks the motion of the subject&#39;s tissue in the ultrasonic wave transmitting and receiving directions. 
     The elasticity calculating section  108  calculates an attribute property value such as the magnitude of strain or the elasticity. Specifically, first, the elasticity calculating section  108  calculates the magnitude of strain based on the motion of the subject&#39;s tissue tracked. The elasticity calculating section  108  also receives information about the blood pressure of the subject from the blood pressure manometer  111 . Furthermore, as will be described in detail later, the elasticity calculating section  108  receives information about first and second types of borderlines that have been determined by the borderline determining section  150 , calculates the distance between the borderlines in the subject, and also calculates the radius of the blood vessel and the thickness of the vascular wall. And based on the magnitude of strain, the information about the blood pressure, the radius of the blood vessel, and the thickness of the vascular wall, the elasticity calculating section  108  calculates the radial and circumferential elasticities and outputs them as numerical values or a two-dimensional distribution image. 
     The image synthesizing section  106  synthesizes together the tomographic image and at least one of the elasticity image and the elasticity values and outputs the synthesized image to the monitor  107 . The memory  121  stores the location tracking information (i.e., the motion of the subject&#39;s tissue) and/or the magnitude of strain. With the transmission and reception of the ultrasonic waves by the probe  101  suspended (which will be referred to herein as a “freeze state”), the information stored in the memory  121  is read to re-calculate the elasticity values. On the other hand, the memory  120  stores the image signal. In the freeze state, the image signal representing the tomographic image is read synchronously with the elasticity. 
     Next, the borderline determining section  150  will be described in detail.  FIG. 1(   b ) is a block diagram illustrating the core section of the present invention. The borderline determining section  150  draws a first type of borderline based on the tomographic image presented on the monitor  107  and then generates at least one borderline of a second type by translating the first type of borderline thus determined. 
     For that purpose, the borderline determining section  150  includes a first borderline generating section  153 , a second borderline generating section  152  and a borderline storage section  151 . The first borderline generating section  153  draws a first type of borderline based on the tomographic image and stores information about the first type of borderline in the borderline storage section  151 . This first type of borderline is a line segment to be drawn as a cursor trace by allowing the operator to move the cursor using the user interface  130  such as a mouse while the tomographic image of the subject is being presented on the monitor  107 . 
     The first borderline generating section  153  may regard either a line segment or a polygon, which connects two or more points that have been specified by the operator with the mouse clicked, as the first type of borderline and store its information. Alternatively, the first borderline generating section  153  may obtain a tropic by connecting a plurality of points specified by the operator and regard the tropic as the first type of borderline. Still alternatively, the first borderline generating section  153  may also obtain a spline function that passes a plurality of points specified by the operator and use the spline function as the first type of borderline. The number of borderlines of the first type does not have to be one. If necessary, multiple borderlines may be drawn as borderlines of the first type. 
     In accordance with the information about the first type of borderline that is stored in the borderline storage section  151 , the second borderline generating section  152  translates the first type of borderline to the location specified by the operator, thereby generating a second type of borderline. Optionally, if multiple borderlines of a first group have been determined and stored by the first borderline generating section  153 , then the user interface  130  may select one of those borderlines of the first group stored. 
     The information about the first and second types of borderlines is output to the elasticity calculating section  108 . Based on these pieces of information, the elasticity calculating section  108  figures out the distance between the borderlines in the subject and uses the distance thus obtained to calculate the elasticity. 
     Such functions of the borderline determining section  150  will be described more fully with reference to a tomographic image presented on the monitor  107 . 
       FIG. 2  is a flowchart showing the procedure of determining borderlines between the respective tissues of a vascular wall using a tomographic image that is viewed on a plane parallel to the axis of the blood vessel. First, the ultrasonic diagnostic apparatus transmits and receives ultrasonic waves to/from an internal organ of a subject, thereby getting a tomographic image of his or her vascular wall. As shown in  FIG. 3 , a tomographic image  200  that has been obtained properly shows clearly intima  221 , media  222  and adventitia  223  in the anterior wall  220  and another intima  231 , another media  232  and another adventitia  233  in the posterior wall  230 .  FIG. 3  shows a case where a boss called “atheroma” has been produced between the intima  231  and media  232  of the posterior wall  230  due to the congestion of fat or cholesterol there. To determine the borderlines between the respective tissues of the vascular wall in the state shown in this tomographic image  200 , the ultrasonic diagnostic apparatus is made to enter the freeze state. 
     First, in Step S 201 , by moving a cursor  210 , which is displayed on the screen of the monitor  107 , using the user interface  130  such as a trackball or a mouse provided for the ultrasonic diagnostic apparatus, the boundary between the vascular flow  207  and the intima  231  of the posterior wall  230  on the tomographic image  200  is traced with the cursor  210 . As a result, a line segment is drawn as a borderline  204  between the vascular flow  207  and the intima  231  of the posterior wall  230  on the screen. The borderline storage section  151  stores information about the borderline  204  as a first type of borderline. 
     Next, in Step S 202 , a borderline  205  is determined in a similar manner between the media  232  and the adventitia  233  of the posterior wall  230 . The borderline storage section  151  stores information about the borderline  205  as another borderline of the first type. 
     Subsequently, in Step S 203 , the second borderline generating section  152  translates the borderline  205  to the location specified by the operator in accordance with the information about the borderline  205  that is stored in the borderline storage section  151 , thereby generating a borderline  206  on the boundary between the adventitia  233  of the posterior wall  230  and its surrounding tissue. 
     Finally, in Step S 204 , by moving the cursor  210  on the screen of the monitor  107 , the boundary between the vascular flow  207  and the intima  221  of the anterior wall  220  on the tomographic image  200  is traced with the cursor  210 , thereby drawing a borderline  203  between the vascular flow  207  and the intima  221  of the anterior wall  220 . The borderline storage section  151  stores information about the borderline  203  as another borderline of the first type. By following such a procedure, the burden imposed on the operator by tracing boundaries and the time it takes to determine the borderlines can be reduced by one step. 
     In the processing step S 203 , the borderline can be generated by any of various image processing techniques such as copying a line segment on a computer screen and pasting it at a predetermined location. 
       FIGS. 4(   a ) through  4 ( c ) and  FIGS. 5(   a ) through  5 ( c ) show examples of such procedures. In these drawings, regions  501 ,  502  and  503  schematically represent mutually different tissues. 
     First, as shown in  FIG. 4(   a ), a borderline  510  is drawn as a first type of borderline on the boundary between the tissues  501  and  502 . This borderline  510  is obtained as a line segment that has been drawn as a trace of the cursor  210  by allowing the operator to move the cursor  210  along the boundary between the tissues  501  and  502  using the user interface  130 . By determining the borderline  510  in this manner, information about the borderline  510  is stored in the borderline storage section  151 . Alternatively, the operator may also determine the borderline  510  by specifying multiple locations with the cursor  210  and generating a line or a polygon passing all of those specified locations as described above. Still alternatively, the borderline  510  may also be determined by generating either a tropic by a minimum square method or a spline function with respect to the multiple locations specified. 
     After the borderline  510  has been determined in this manner, the second borderline generating section  152  generates a borderline  511 , having the same shape and the same direction as the borderline  510 , at the tip of the cursor  210  in accordance with the operator&#39;s command that has been entered through the user interface  130 . For example, by entering a “copy” command through the user interface  130 , the borderline  511  may be generated and presented on the monitor screen. This borderline  511  is generated based on the information about the borderline  510  stored in the borderline storage section  151  and the location information of the cursor  210 . When the operator moves the cursor  210 , the borderline  511  is also translated. 
     Next, as shown in  FIG. 4(   b ), the operator moves the cursor  210  to a location where a borderline should be generated. In the example shown in  FIG. 4(   b ), the cursor  210  is located on the boundary between the regions  502  and  503  to determine a borderline on the boundary between the regions  502  and  503 . 
     When the cursor  210  is moved to a particular location in this manner, the borderline  510  is translated to that location, thereby generating and displaying a borderline  511  there. 
     Subsequently, if the operator inputs a confirmation command such as a paste command through the user interface  130 , a borderline  512  is established at that location as shown in  FIG. 4(   c ). In this manner, the borderline  512 , generated by translating the borderline  510  that has been drawn by the operator, is determined as the second type of borderline. 
     Alternatively, another procedure may also be adopted. First, as shown in  FIG. 5(   a ), a borderline  510  is drawn as a first type of borderline on the boundary between the tissues  501  and  502 . The borderline  510  is drawn in the same way as already described with reference to  FIG. 4(   a ). 
     After the borderline storage section  151  stores information about the borderline  510  as a first type of borderline, the apparatus changes into a “copy” mode in accordance with an operator&#39;s command that has been entered through the user interface  130 . According to this procedure, the operator can move the cursor  210  to his or her desired location with the user interface  130  without displaying a copy of the borderline  510  on the screen. 
     As shown in  FIG. 5(   b ), the operator has moved the cursor  210  to the location where a borderline should be generated. In the example shown in  FIG. 5(   b ), the cursor  210  is located on the boundary between the regions  502  and  503  to determine a borderline on the boundary between the regions  502  and  503 . After having moved the cursor  210  to his or her desired location, the operator enters a command to generate a copy of the borderline  510  through the user interface  130 . In response, the second borderline generating section  152  generates the borderline  511  by translating the borderline  510  to the location specified with the cursor  210  in accordance with the information about the first type of borderline. 
     Subsequently, if the operator inputs a confirmation command such as an enter command through the user interface  130 , the borderline  512  is established at that location as shown in  FIG. 5(   c ). In this manner, the borderline  512 , generated by translating the borderline  510  that has been drawn by the operator, is determined. 
     Still another procedure may also be adopted. First, as shown in  FIG. 6(   a ), the operator puts the cursor  210  on the boundary between the tissues  501  and  502 . Next, as shown in  FIG. 6(   b ), the operator traces the boundary between the tissues  501  and  502  with the cursor  210 , thereby drawing a line segment  509  indicating a first type of borderline. In the meantime, the borderline determining section  150  automatically draws a trace of points, which are located on the same acoustic line as, but at a predetermined distance from, the cursor  210 , as another line segment  511 . For that purpose, the first borderline generating section  153  gets the location of the cursor  210  and outputs information about that location to the borderline storage section  151 . The operator inputs the interval between the locations of points to be automatically generated and the cursor  210  through the user interface  130 . In the example shown in  FIG. 6(   b ), the borderline between the tissues  502  and  503  should be generated automatically, and therefore, the interval from the boundary between the tissues  501  and  502  to the one between the tissues  502  and  503  is defined by the operator. The second borderline generating section  152  generates the line segment  511  based on the location of the cursor  210  that has been read from the borderline storage section  151  and the interval that has been entered through the user interface  130 . Optionally, the interval may be determined in advance before the series of operations are started in the processing step shown  FIG. 6(   a ). 
     As shown in  FIG. 6(   c ), when the operator finishes tracing the boundary between the tissues  501  and  502  with the cursor  210 , a borderline  510  is established as a first type of borderline. At the same time, a borderline  512  is automatically determined as a second type of borderline. This borderline  512  is a trace of points that are located at a predetermined distance from the location of the cursor  210  that draws the borderline  510 , and therefore, has been obtained by translating the borderline  510 . In this manner, a borderline  510  drawn by the operator and a borderline  512  that is a translated version of the borderline  510  are obtained. 
     As shown in  FIG. 3 , if a blood vessel is viewed on a plane that is parallel to its axis, an anterior wall and a posterior wall are seen with a vascular lumen, where blood flows, interposed, and each of the anterior and posterior walls consists of an intima, a media and an adventitia. In a target region of measurements to be done to calculate an attribute property value of the blood vessel, the boundaries between these tissues should be substantially fixed, i.e., the diameter of the vascular lumen and the thicknesses of the respective tissues should remain approximately the same, unless some disease has occurred there. That is why the boundary between the vascular flow and the intima, the boundary between the intima and media, the boundary between the media and adventitia, and the boundary between the adventitia and a surrounding tissue would be ideally roughly parallel to each other. Even if the axis of the blood vessel is not straight, the diameter of the vascular lumen and the thicknesses of the respective tissues still remain approximately the same, and therefore, the respective boundaries can be obtained by translating one of them to another. 
     For that reason, the second type of borderline generated by the borderline determining section  150  will agree with the actual boundary between the tissues unless the target region is adjacent to a portion with some disease. In this manner, the burden imposed on the operator by forcing him or her to trace the entire boundary and the time it will take to determine the borderlines can be both reduced. Particularly in a situation where a boundary presented on a tomographic image is not so clear, it would not cause so much trouble to the operator to specify only one point as a borderline location but it should be a lot of trouble for the operator to trace such an indefinite boundary entirely with the cursor. According to the present invention, such a burden can be lightened. 
     Also, although the thicknesses of the intima and media of a vascular wall and the diameter of a blood vessel could vary significantly according to the health condition of the given subject or from one person to another, the thickness of the adventitia hardly varies. It is said that at the carotid of a healthy person, the adventitia will have a thickness of approximately 0.3 mm. For that reason, unless the adventitia has any disease, the thickness of the adventitia may be defined in advance and the boundary between the adventitia and a surrounding tissue may be determined at a location that is a predetermined thickness away from the media-adventitia boundary being determined. Then, the burden imposed on the operator can be further alleviated. The adventitia preferably has a thickness of approximately 0.2 mm to approximately 0.4 mm. 
     The second type of borderline determined by the borderline determining section  150  does not have to be located on the boundary between the adventitia and a surrounding tissue but may also be located on any of various other boundaries. Hereinafter, an example in which the second type of borderline is determined somewhere else will be described. 
       FIG. 8  illustrates a tomographic image representing a case where a boss-like disease has occurred on the outer surface of a blood vessel.  FIG. 9  is a flowchart showing the procedure of determining a borderline on the tomographic image shown in  FIG. 8 . 
     First, in Step S 211 , by moving a cursor  210 , which is displayed on the screen of the monitor  107 , using the user interface  130  such as a trackball or a mouse provided for the ultrasonic diagnostic apparatus, the boundary between the vascular flow  207  and the intima  231  of the posterior wall  230  on the tomographic image  200  is traced with the cursor  210 . In this manner, a borderline  204  is drawn between the vascular flow  207  and the intima  231  of the posterior wall  230  on the screen. The borderline storage section  151  stores information about the borderline  204  as a first type of borderline. 
     Next, in Step S 212 , the second borderline generating section  152  translates the borderline  204  in accordance with the information about the borderline  204  that is stored in the borderline storage section  151 , thereby generating a borderline  205  on the boundary between the media  232  and adventitia  233  of the posterior wall  230  as a second type of borderline. 
     Subsequently, in Step S 213 , by moving the cursor  210  on the screen of the monitor  107  using the user interface  130 , the boundary between the adventitia  233  of the posterior wall  230  and a surrounding tissue on the tomographic image  200  is traced with the cursor  210 . In this manner, a borderline  206  is drawn between the adventitia  233  of the posterior wall  230  and the surrounding tissue. The borderline storage section  151  stores information about the borderline  206  as another borderline of the first type. 
     Finally, in Step S 214 , a borderline  203  between the vascular flow  207  and the intima  221  of the anterior wall  220  is drawn in the same way as in Step S 213 . The borderline storage section  151  stores information about the borderline  203  as still another borderline of the first type. 
     By following such a procedure, the burden imposed on the operator by tracing boundaries and the time it takes to determine the borderlines can be reduced by one step. 
       FIG. 10  illustrates a tomographic image of a healthy person&#39;s blood vessel.  FIG. 9  is a flowchart showing a procedure for determining borderlines on the tomographic image shown in  FIG. 10 . 
     First, in Step S 221 , by moving a cursor  210 , which is displayed on the screen of the monitor  107 , using the user interface  130  such as a trackball or a mouse provided for the ultrasonic diagnostic apparatus, the boundary between the vascular flow  207  and the intima  231  of the posterior wall  230  on the tomographic image  200  is traced with the cursor  210 . In this manner, a borderline  204  is drawn between the vascular flow  207  and the intima  231  of the posterior wall  230  on the screen. The borderline storage section  151  stores information about the borderline  204  as a first type of borderline. 
     Next, in Step S 222 , the second borderline generating section  152  translates the borderline  204  in accordance with the information about the borderline  204  that is stored in the borderline storage section  151 , thereby generating a borderline  205  on the boundary between the media  232  and adventitia  233  of the posterior wall  230  as a second type of borderline. 
     Subsequently, in Step S 223 , the borderline  204  is translated again in accordance with the location information of the borderline  204  that is stored in the borderline storage section  151 , thereby generating a borderline  206  on the boundary between the adventitia  233  of the posterior wall  230  and its surrounding tissue. 
     Thereafter, in Step S 224 , by moving the cursor  210  on the screen of the monitor  107  using the user interface  130 , the boundary between the vascular flow  207  and the intima  221  of the anterior wall  220  on the tomographic image  200  is traced with the cursor  210 . In this manner, a borderline  203  is drawn between the vascular flow  207  and the intima  221  of the anterior wall  220 . 
     By following such a procedure, the burden imposed on the operator by tracing boundaries and the time it takes to determine the borderlines can be reduced by two steps. 
       FIG. 11  is a flowchart showing another procedure for determining borderlines on the tomographic image shown in  FIG. 10 . 
     First, in Step S 231 , by moving a cursor  210 , which is displayed on the screen of the monitor  107 , using the user interface  130  such as a trackball or a mouse provided for the ultrasonic diagnostic apparatus, the boundary between the vascular flow  207  and the intima  231  of the posterior wall  230  on the tomographic image  200  is traced with the cursor  210 . In this manner, a borderline  204  is drawn between the vascular flow  207  and the intima  231  of the posterior wall  230  on the screen. The borderline storage section  151  stores information about the borderline  204  as a first type of borderline. 
     Next, in Step S 232 , the second borderline generating section  152  translates the borderline  204  in accordance with the information about the borderline  204  that is stored in the borderline storage section  151 , thereby generating a borderline  205  on the boundary between the media  232  and adventitia  233  of the posterior wall  230  as a second type of borderline. 
     Subsequently, in Step S 223 , the second borderline generating section  152  translates the borderline  204  again in accordance with the location information of the borderline  204  that is stored in the borderline storage section  151 , thereby generating a borderline  206  on the boundary between the adventitia  233  of the posterior wall  230  and its surrounding tissue as a second type of borderline. 
     In the same way, in Step S 234 , the borderline  204  is translated once again in accordance with the location information of the borderline  204  that is stored in the borderline storage section  151 , thereby generating a borderline  203  on the boundary between the vascular flow  207  and the intima  221  of the anterior wall  220  as another borderline of the second type. 
     By following such a procedure, the burden imposed on the operator by tracing boundaries and the time it takes to determine the borderlines can be reduced by three steps. 
     As described above, by translating a borderline, the burden imposed on the operator to determine at least one borderline and the time it takes to determine that borderline can be reduced. 
     Hereinafter, it will be described with reference to  FIGS. 1(   a ) and  1 ( b ) how to measure an IMT with the ultrasonic diagnostic apparatus of the present invention. First, ultrasonic waves are transmitted and received with the probe  101 , thereby obtaining a series of tomographic images of a vascular wall, which are viewed on a plane parallel to its axis and which are generated consecutively at multiple points in time, and presenting them on the monitor  107  in real time. Meanwhile, the tomographic image data is stored in the memory  120 . Next, in the freeze state, the data is read from the memory  120  and the best tomographic image to measure the IMT is presented on the monitor  107 . 
     By manipulating the user interface  130 , the operator moves the cursor  210  that is displayed on the screen of the monitor  107  and traces the boundary between the vascular flow and the intima of the anterior or posterior wall on the tomographic image on the monitor  107  with the cursor  210 , thereby drawing a first type of borderline. The borderline storage section  151  stores information about this borderline of the first type. 
     Next, if the boundary between the media and adventitia is parallel to the one between the vascular flow and the intima (e.g., if there is no diseased part in the intima or in the media), then the second borderline generating section  152  translates the borderline that has been drawn on the boundary between the vascular flow and the intima, thereby generating a second type of borderline between the media and adventitia at a location corresponding to the boundary between the media and adventitia. On the other hand, if these two boundaries are not parallel to each other (e.g., if there is any diseased part in the intima), the borderline between the media and adventitia is also determined in the same way. That is to say, using the user interface  130 , another borderline of the first type is drawn by moving the cursor  210  on the screen of the monitor  107  and tracing the boundary between the media and adventitia on the tomographic image with the cursor  210 . Also, if the anterior and posterior walls are parallel to each other on the tomographic image, then the second borderline generating section  152  may translate the borderline that has been determined on the anterior or posterior wall, thereby generating a borderline indicating the boundary between the vascular flow and the intima of the anterior or posterior wall or between the media and adventitia thereof. Optionally, the apparatus may also be designed so as to allow the operator to determine, with the user interface  130 , whether a new borderline should be generated by getting the borderline that has been drawn by the operator translated by the second borderline generating section  152  or should be generated by himself or herself using the user interface  130 . The IMT can be calculated based on the interval from the borderline between the vascular flow and the intima to the one between the media and adventitia thus obtained. By adopting such a procedure, the burden and the time-consuming job imposed on the operator by tracing boundaries can be alleviated. In addition, the IMT can be calculated in a shorter time, too. 
     Hereinafter, it will be described how to calculate the elasticities. First, ultrasonic waves are transmitted and received with the probe  101 , thereby obtaining a series of tomographic images of a vascular wall, which are viewed on a plane parallel to its axis and which are generated consecutively at multiple points in time, and presenting them on the monitor  107  in real time. Meanwhile, the tissue tracking section  105  tracks the vascular wall tissue. Using the blood pressure values provided by the blood pressure manometer  111 , the elasticity calculating section  108  calculates radial elasticities and gets an image representing the distribution of the radial elasticities presented on the monitor  107 . The tomographic image data and the image data representing the distribution of the radial elasticities are stored in the memories  120  and  121 , respectively. The tomographic images are presented consecutively, while the image representing the distribution of the elasticities is updated once in every cardiac cycle. After having changed the modes of the ultrasonic diagnostic apparatus into the freeze state, the data is read from the memory  121  and the best image representing the distribution of the elasticities and a tomographic image synchronized with that image are read from the memory  120  and presented on the monitor  107 . 
     By manipulating the user interface  130 , the operator moves the cursor  210  that is displayed on the screen of the monitor  107  and traces the boundary between the vascular flow and the intima of the posterior wall on the tomographic image on the monitor  107  with the cursor  210 , thereby drawing a first type of borderline. The borderline storage section  151  stores information about the first type of borderline thus determined. 
     Next, if the boundary between the adventitia of the posterior wall and its surrounding tissue is parallel to the one between the vascular flow and the intima (e.g., if there is no diseased part in the intima or in the adventitia), then the second borderline generating section  152  translates the first type of borderline that has been drawn on the boundary between the vascular flow and the intima, thereby generating a second type of borderline between the adventitia and the surrounding tissue at a location corresponding to the boundary between the adventitia and the surrounding tissue. On the other hand, if these two boundaries are not parallel to each other (e.g., if there is any diseased part in the intima or in the adventitia), the borderline between the adventitia and the surrounding tissue is also determined in the same way. That is to say, using the user interface  130 , another borderline of the first type is drawn by moving the cursor  210  on the screen of the monitor  107  and tracing the boundary between the adventitia and the surrounding tissue on the tomographic image with the cursor  210 . 
     Next, if the boundary between the vascular flow and the intima of the anterior wall is parallel to the one between the vascular flow and the intima of the posterior wall, then the second borderline generating section  152  translates the first type of borderline that has been drawn on the boundary between the vascular flow and the intima of the posterior wall, thereby generating a second type of borderline at a location corresponding to the boundary between the vascular flow and the intima of the anterior wall. On the other hand, if these two boundaries are not parallel to each other, the borderline between the vascular flow and the intima of the anterior wall is also determined in the same way. That is to say, using the user interface  130 , another borderline of the first type is drawn by moving the cursor  210  on the screen of the monitor  107  and tracing the boundary between the vascular flow and the intima of the anterior wall on the tomographic image with the cursor  210 . 
     Based on the interval from the borderline between the vascular flow and the intima of the posterior wall to the one between the adventitia and the surrounding tissue thus obtained, the initial radial thickness h 0  of the overall blood vessel can be calculated. Based on the interval from the borderline between the vascular flow and the intima of the anterior wall to the one between the vascular flow and the intima of the posterior wall thus obtained, the initial radius r 0  of the blood vessel can be calculated. And the circumferential elasticity can be calculated based on these values. By adopting such a procedure, the burden and the time-consuming job imposed on the operator by tracing boundaries can be alleviated. In addition, the circumferential elasticity can be calculated in a shorter time, too. 
     In the preferred embodiments described above, the first borderline generating section generates a line segment or a polygon as the first type of borderline by allowing the operator to draw it with the user interface  130  or specify multiple points. However, the first type of borderline may also be generated automatically. For example, a vascular flow portion and a vascular wall portion of a subject have significantly different acoustic impedances and the image signals thereof have different amplitudes. That is why the boundary between the vascular flow portion and the vascular wall portion, i.e., the boundary between the vascular flow and the intima of the vascular wall, can be detected automatically based on the amplitudes of the image signals. The first borderline generating section may detect the boundary between the vascular flow and the intima of the anterior or posterior wall based on the image signals generated by the tomographic image processing section and may determine the first type of borderline on that boundary. Also, the vascular flow portion would produce a Doppler effect in the reflected echo due to the flow of the blood. For that reason, the first borderline generating section may also detect the boundary between the vascular flow and the intima of the anterior or posterior wall by utilizing a Doppler mode and determine the first type of borderline on the boundary detected. 
     Meanwhile, the acoustic impedances of the intima, media and adventitia included in a vascular wall are not significantly different from each other. For that reason, it could sometimes be difficult to detect them by any of these methods. However, as described above, the boundaries between these tissues in the vascular wall are often parallel to the boundary between the vascular flow and the intima unless there is any diseased part there. In that case, if the operator can specify the boundary between the media and adventitia at an appropriate location by looking at the tomographic image, then the second borderline generating section can translate the first type of borderline, which has been automatically detected and determined, to the location specified by the operator and generate a second type of borderline there. Consequently, the burden imposed on the operator can be lightened significantly and the variations caused by the operators&#39; decisions can be reduced greatly. 
     INDUSTRIAL APPLICABILITY 
     The present invention is effectively applicable to an ultrasonic diagnostic apparatus that estimates the shape or attribute property value of the vascular wall of a subject.