Abstract:
When measurement of a circumference (abdominal circumference of a fetus) on an ultrasonic image is started, a first mobile marker for designating a major axis start point of an ellipse to be measured is displayed. After the major axis start point is designated, a second mobile marker for designating a major axis end point of the ellipse to be measured and a standard range display graphic are displayed. The standard range display graphic comprises two ellipses in which the major axis start point and second mobile marker constitute a major axis or minor axis and the circumferences are configured to be a lower limit and upper limit of the abdominal circumference. A user can designate the major axis end point while recognizing the positional relationship between the standard range display graphic and the outline of an abdominal cross section. Furthermore, a minor axis end of the ellipse to be measured can be designated using the standard range graphic as a guide.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to an ultrasound image processor, and in particular to an ultrasound image processor which executes measurement of a circumferential length of an ellipse shape designated on an ultrasound image. 
       BACKGROUND 
       [0002]    An ultrasound image is formed by an ultrasound diagnostic apparatus which transmits and receives ultrasound to and from a subject. The ultrasound image is used for various examinations and measurements. For example, in order to check a growth state of a fetus, an abdominal circumferential length of the fetus is measured. In this measurement, on an ultrasound image (B-mode image) including a cross section of the abdomen of the fetus, a circumferential length of an outline of an abdominal cross section is measured. 
         [0003]    Measurement of the circumferential length on the ultrasound image is generally achieved by a user such as a doctor designating an ellipse shape along an outline of an abdominal cross section of a fetus on an ultrasound image displayed on a display, and calculating the circumferential length of the ellipse shape. For example, the user moves a marker displayed on the ultrasound image using a trackball or the like, and designates ends of the major axis of the abdominal cross section by the marker. Then, the user designates at least one end of the minor axis. With such a process, the circumferential length of the designated ellipse shape is calculated. 
         [0004]    There may be cases where a large number of artifacts (noise) exist in the ultrasound image. In such cases, the cross sectional outline becomes unclear on the ultrasound image, and it becomes difficult for the user to accurately designate the ellipse shape. If correct designation of the ellipse shape becomes impossible, a problem of erroneous measurement may result in the measurement of the circumferential length. 
         [0005]    A technique for supporting the positioning of a measurement point on the ultrasound image is disclosed. For example, Patent Document  1  discloses that, in a distance measurement of a fetal biparietal diameter, a guide showing a normal range of growth of the fetus is displayed on a screen. The guide includes a line showing a direction passing from the starting point through an end point determining marker, and a line pair including two lines which are orthogonal to the line, which are relatively short, and which show an upper limit and a lower limit of a normal range. The user can use the displayed guide as an estimate, to designate the position of the end point. With such a configuration, erroneous designation of the end point position is prevented. 
       CITATION LIST 
     Patent Literature 
       [0006]    Patent Document 1: JP 4149015 B 
       SUMMARY 
     Technical Problem 
       [0007]    Similar to the measurement of distance on the ultrasound image, in the circumferential length measurement for measuring a circumferential length of an ellipse shape by designating the ellipse shape such as the measurement of the abdominal circumferential length, support for the position designation of the ellipse shape is required. 
         [0008]    An advantage of the present disclosure lies in supporting a position designation of an ellipse shape in an ultrasound image processor which measures a circumferential length of the ellipse shape designated on an ultrasound image. 
       Solution To Problem 
       [0009]    According to one aspect of the present disclosure, there is provided an ultrasound image processor comprising: a measurement unit that measures a circumferential length of an ellipse shape to be measured having a first axis designated on an ultrasound image as one of a major axis and a minor axis, and a second axis which is then designated as the other of the major axis and the minor axis; a marker displaying unit that displays a first axis end point designating marker which moves on the ultrasound image in response to a user operation for designating an end point of the first axis after a starting point of the first axis is designated; and an index figure displaying unit that displays, at least before the end point of the first axis is designated and on the ultrasound image, an index figure having positions of the starting point of the first axis and the first axis end point designating marker as points of reference and showing a standard range of the circumferential range of the ellipse shape to be measured. 
         [0010]    According to the above-described configuration, a position of a measurement target ellipse is designated by designation of the major axis and the minor axis. First, a starting point of a first axis which is a major axis or a minor axis is designated. After the starting point of the first axis is designated, an index figure is displayed on the ultrasound image along with a first axis end point designating marker for designating an end point of the first axis. The index figure is a figure having points of reference on positions of the starting point of the first axis and the first axis end point designating marker. For example, the index figure is of an ellipse shape having the positions of the starting point of the first axis and the first axis end point designating marker as ends of the major axis or the minor axis. The user can use the positional relationship between the outline of the measurement target and the index figure on the ultrasound image as an estimate, to designate the position of the first axis end point designating marker. With such a configuration, the user&#39;s load upon designating the end point of the first axis can be reduced. Alternatively, precision of the designated position of the end point of the first axis can be improved. 
         [0011]    By continuing the display of the index figure even after the designation of the end point of the first axis, it is possible to support, with the index figure, the designation of a starting point of a second axis. The index figure can be represented in various forms, so long as the index figure can show a standard range for the circumferential length of the measurement target. 
         [0012]    According to another aspect of the present disclosure, the index figure includes a first two-dimensional figure having an ellipse shape having a direction from the starting point of the first axis through the first axis end point designating marker as one of a major axis direction and a minor axis direction and having, as a circumferential length, a value based on a lower limit value of the standard range, and a second two-dimensional figure having an ellipse shape having a direction from the starting point of the first axis through the first axis end point designating marker as one of a major axis direction and a minor axis direction and having, as a circumferential length, a value based on an upper limit value of the standard range. 
         [0013]    According to another aspect of the present disclosure, the marker displaying unit displays, after the end point of the first axis is designated, a second axis end designating marker which moves on the ultrasound image in response to a user operation for designating an end of the second axis, and the index figure displaying unit displays a third two-dimensional figure having an ellipse shape having a line segment connecting the starting point of the first axis and the end point of the first axis as one of a major axis and a minor axis and having the second axis end designating marker as an end of the other of the major axis and the minor axis. 
         [0014]    After the end point of the first axis is designated, by displaying, along with the second axis end designating marker, the third two-dimensional figure having an ellipse shape passing through the ends of the first axis and the second axis end point designating marker, it becomes possible for the user to use the third two-dimensional figure as an estimate for designation of the end of the second axis. For example, the end of the second axis can be desirably designated by moving the second axis end designating marker to a position where the third two-dimensional figure and an outline of the measurement target on the ultrasound image coincide with each other, and designating the position as the end of the second axis. 
         [0015]    According to another aspect of the present disclosure, the marker displaying unit initially displays the second axis end designating marker on a straight line passing through a middle point of a line segment connecting the starting point of the first axis and the end point of the first axis and perpendicular to the line segment, and in a range between the first two-dimensional figure and the second two-dimensional figure. 
       Advantageous Effects Of Invention 
       [0016]    According to various aspects of the present disclosure, position designation of an ellipse shape can be supported in an ultrasound image processor which measures a circumferential length of an ellipse shape designated on an ultrasound image. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a schematic diagram of a structure of an ultrasound diagnostic apparatus according to an embodiment of the present disclosure. 
           [0018]      FIG. 2  is a diagram showing a function representing a relationship between a normal range of an abdominal circumferential length and the number of weeks of pregnancy. 
           [0019]      FIG. 3  is a diagram showing an example display on a display before a starting point of a major axis of a measurement target ellipse is designated. 
           [0020]      FIG. 4  is a diagram showing an example display of a standard range displaying figure. 
           [0021]      FIG. 5  shows an example display when a major axis end point designating marker is moved to a candidate position of an end point of the major axis of a measurement target ellipse. 
           [0022]      FIG. 6  shows an example display of a minor axis end designating marker and a measurement target ellipse index. 
           [0023]      FIG. 7  is a diagram showing another example display of the standard range displaying figure. 
           [0024]      FIG. 8  is a diagram showing an example display when a length of a major axis is corrected after a minor axis end of a measurement target ellipse is designated. 
           [0025]      FIG. 9  is a diagram showing an example display when a slope of a measurement target ellipse is changed after the measurement target ellipse is designated. 
           [0026]      FIG. 10  is a diagram showing a rotational movement of a minor axis end marker. 
           [0027]      FIG. 11  is a flowchart showing an example flow of operations of an ultrasound diagnostic apparatus according to an embodiment of the present disclosure. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    An embodiment of the present disclosure will now be described with reference to the drawings. 
         [0029]    An ultrasound diagnostic apparatus  10  is a medical device which is generally equipped in a medical institution such as a hospital, and which executes an ultrasound diagnosis for a subject. The ultrasound diagnostic apparatus  10  forms an ultrasound image used for various examinations and measurements. The ultrasound diagnostic apparatus  10  has a function to measure a circumferential length of an ellipse shape designated on the ultrasound image which is formed. In the present specification, the term “ellipse shape” not only refers to an ellipse in the mathematical sense, but also includes the concept of a shape slightly deformed from an ellipse (such as an oval shape). In the following, the circumferential length measurement function of the ultrasound diagnostic apparatus  10  will be described while exemplifying measurement of an abdominal circumferential length for checking a growth state of a fetus. In the present specification, the ultrasound diagnostic apparatus  10  is one type of an ultrasound image processor. 
         [0030]      FIG. 1  is a schematic diagram of a structure of the ultrasound diagnostic apparatus  10 . A probe  12  is an ultrasound probe which transmits and receives ultrasound to and from a subject. The probe  12  has a transducer array including a plurality of transducers. During transmission, a plurality of transmission signals are supplied from a transmission and reception unit  14  to the plurality of transducers of the transducer array, and the transducers are excited. With this process, an ultrasound beam (transmission beam) is produced. Meanwhile, during reception, when the plurality of transducers of the transducer array receive a reflection echo, in each transducer an acoustic signal is converted into a reception signal, which is an electric signal. A plurality of reception signals thus produced are output to the transmission and reception unit  14 . In the present embodiment, a position and an orientation of the probe  12  are adjusted by the user so that the ultrasound is transmitted to and received from an abdomen of the fetus which is the subject. 
         [0031]    The transmission and reception unit  14  sends, to the probe  12 , a plurality of transmission signals for exciting the plurality of transducers of the probe  12 , to cause generation of the ultrasound at the probe  12 . The transmission and reception unit  14  further executes phasing addition on the plurality of reception signals produced by the plurality of transducers upon reception of the reflection echo, to form beam data arranged in a scanning direction of the ultrasound beam. Phasing addition is a process to electrically form a reception beam. Each beam data set is formed from a plurality of reflection echo signals arranged in a depth direction. As described, the transmission and reception unit  14  has a function of a transmission beam former and a function of a reception beam former. At the downstream of the transmission and reception unit  14 , there is provided a beam data processor including a wave detection circuit or the like, which is not shown in the figures. 
         [0032]    An ultrasound image former  16  is formed from, for example, a digital scan converter (DSC), and forms an ultrasound image as a living body image based on the plurality of beam data sets from the transmission and reception unit  14 . In the present embodiment, the ultrasound image formed by the ultrasound image former  16  is a B-mode image, and is in particular an image showing a cross section of the abdomen of the fetus. More specifically, the ultrasound image former  16  produces a display frame data array based on a reception frame data array. One reception frame data set is made of a plurality of beam data sets obtained by one beam scanning. The display frame data array forms the B-mode image as a video image. In the present embodiment, a sequence of ultrasound images sequentially produced by the ultrasound image former  16  are sent to a display processor  30  and an image storage  18 . 
         [0033]    The image storage  18  is a ring buffer which stores a plurality of ultrasound images formed by the ultrasound image former  16 . For example, frames from the most recent frame to a predetermined time in the past are temporarily stored in the ring buffer. Alternatively, an image storage may be provided upstream of the ultrasound image former  16 . In this case, a group of beam data sets before application of the processing performed by the ultrasound image former  16  are stored for each frame. In the present embodiment, the measurement is not executed in real time during operation, but is executed during an image reproduction operation after freeze. More specifically, a plurality of ultrasound images stored in the image storage  18  are reproduced, and a user selects a particular ultrasound image from the reproduced images. The measurement of the abdominal circumferential length is executed in a state where the ultrasound image is displayed on the screen as a static image. 
         [0034]    A controller  20  is formed from, for example, a CPU or a microprocessor, and executes control of each part of the ultrasound diagnostic apparatus  10 . The controller  20  has a plurality of functions which operate in the circumferential length measurement, and these functions are shown in  FIG. 1  as a plurality of blocks. These functions are realized in the present embodiment as software functions. Alternatively, these functions may be realized using hardware such as, for example, electric/electronic circuits, processors, or the like. Alternatively, these functions may be realized as a cooperation of hardware such as a CPU and a processor, and software (program). The blocks will now be described. 
         [0035]    A standard range specifier  22  specifies a lower limit value and an upper limit value of a standard range of the abdominal circumferential length which is the target of measurement. In the present embodiment, the standard range specifier  22  sets a normal range of the abdominal circumferential length calculated from a statistical viewpoint as the standard range. Because the normal range of the abdominal circumferential length differs depending on the number of weeks of pregnancy, the standard range specifier  22  specifies, as the standard range, a lower limit value and an upper limit value of the normal range of the abdominal circumferential length according to the number of weeks of pregnancy. Specifically, the lower limit value and the upper limit value of the standard range of the abdominal circumferential length are specified based on correspondence information showing a correspondence relationship between the lower limit value and the upper limit value of the normal range of the abdominal circumferential length and the number of weeks of pregnancy, and the number of weeks of pregnancy which is input by the user. Alternatively, the lower limit value and the upper limit value of the standard range may be directly input by the user. 
         [0036]    A graphic image former  24  forms various graphic elements displayed in an overlapped manner over the ultrasound image in the circumferential length measurement on the ultrasound image. The graphic elements formed by the graphic image former  24  include a first movable marker which moves on the ultrasound image for designating a starting point of a first axis of an ellipse shape to be measured which is a target of the circumferential length measurement, a second movable marker which moves on the ultrasound image for designating an end point of the first axis of the ellipse shape to be measured, a third movable marker which moves on the ultrasound image for designating an end (starting point or end point) of a second axis of the ellipse shape to be measured, a standard range displaying figure which shows a standard range of the abdominal circumferential length specified by the standard range specifier  22 , or the like. The graphic elements are not limited to those described above, and an image for supporting the circumferential length measurement, such as a figure showing the designated ellipse shape to be measured, may be formed. The group of formed graphic elements are overlapped over the ultrasound image by the display processor  30  and displayed on a display  32 . 
         [0037]    The standard range displaying figure showing the standard range of the abdominal circumferential length is displayed on the display  32  after the starting point of the first axis is designated and before the end point of the first axis is designated; that is, during the process of designating the end point of the first axis. By displaying the standard range displaying figure before the end point of the first axis is designated, it becomes possible to use the standard range displaying figure as an estimate for designating the end point of the first axis. In the present embodiment, a figure of an ellipse shape having a line segment connecting the designated starting point position of the first axis and the first movable marker as a major axis or the minor axis is used as the standard range displaying figure. 
         [0038]    In addition, the standard range displaying figure continues to be displayed even after the end point of the first axis is designated. With such a configuration, the user can use the standard range displaying figure as an estimate in the positioning of the end of the second axis of the ellipse shape to be measured using the third movable marker. 
         [0039]    Details of the standard range displaying figure formed by the graphic image former  24  will be described later with reference to  FIGS. 2 ˜ 9 . 
         [0040]    A measurement unit  26  calculates a circumferential length of the ellipse shape to be measured designated on the ultrasound image. The circumferential length of the ellipse shape to be measured is calculated in consideration of the circumferential length of the ellipse shape to be measured on the ultrasound image and the display scale of the ultrasound image. 
         [0041]    A storage  28  is, for example, a hard disk drive, a ROM, a RAM, or the like, and stores a program for operating various parts of the ultrasound diagnostic apparatus  10 , calculation process results at the ultrasound diagnostic apparatus  10 , or the like. The storage  28  also stores the correspondence information showing the correspondence relationship between the lower limit value and the upper limit value of the normal range of the abdominal circumferential length and the number of weeks of pregnancy, which is referred to by the standard range specifier  22 . The correspondence information may be stored as a function or in a form of a table or the like. 
         [0042]    The display processor  30  executes a process to display, on the display  32 , the ultrasound image formed by the ultrasound image former  16 . In addition, as described above, the display processor  30  overlaps the group of graphic elements formed by the graphic image former  24  over the ultrasound image and displays the resulting image on the display  32 . Further, the display processor  30  may display, on the display  32 , a measurement result of the measurement unit  26  in a form or a report or the like. 
         [0043]    The display  32  is, for example, a liquid crystal display, and displays the ultrasound image, the group of graphic elements, or the like. An inputter  34  includes a button, a switch, the trackball, or the like, and is used by the user for inputting the number of weeks of pregnancy of the pregnant woman, for moving the first, second, and third movable markers, for designating the ellipse shape to be measured, or the like. 
         [0044]    In the following, the details of the standard range displaying figure showing the standard range of the abdominal circumferential length formed by the graphic image former  24  will be described with reference to  FIGS. 2 ˜ 9  in connection to  FIG. 1 . 
         [0045]      FIG. 2  is a diagram showing a function showing the relationship between the normal range of the abdominal circumferential length and the number of weeks of pregnancy, stored in the storage  28 . Of five graphs shown in  FIG. 2 , a graph  40  at the center is a graph showing an average value of the abdominal circumferential length in each week of pregnancy. A graph  42  below the graph  40  is a graph showing (the average −1.5 SD (Standard Deviation)), and a graph  44  above the graph  40  is a graph showing (the average +1.5 SD). These graphs are calculated based on a measurement results of the abdominal circumferential length in the past. In each week of pregnancy, about 86% of the entirety of fetuses are included between −1.5 SD and +1.5 SD. For example, in the 26th week of pregnancy, about 86.6% of the entirety of fetuses have a size of abdominal circumferential length in a range from about 19 cm to about 22 cm. Thus, in the present embodiment, the range of +1.5 SD is set as the standard range of the abdominal circumferential length, with the value at −1.5 SD as the lower limit value of the standard range and the value at +1.5 SD as the upper limit value of the standard range. The standard range specifier  22  specifies the upper limit value and the lower limit value of the standard range from the function shown in  FIG. 2 , based on the number of weeks of pregnancy which is input by the user. 
         [0046]    A graph  46  positioned further below the graph  42  showing −1.5 SD is a graph showing (the average −2.0 SD), and a graph  48  positioned further above the graph  44  showing +1.5 SD is a graph showing (the average +2.0 SD). In the present embodiment, the range of ±1.5 SD is set as the standard range for the measurement of the abdominal circumferential length, but the standard range is not limited to the range of ±1.5 SD. Currently, in Japan, a criterion for the standard range in the measurement of the abdominal circumferential length of the fetus is ±1.5 SD, but the criterion for the standard range differs from country to country, and may change even in Japan in the future. In addition, in circumferential length measurements other than the measurement of abdominal circumferential length of the fetus, ranges other than +1.5 SD may be set as the standard range. The standard range may be set according to these criteria. 
         [0047]      FIG. 3  is a diagram showing an example display of the display  32  when the measurement of the abdominal circumferential length is started. As shown in  FIG. 3 , on the display  32 , a B-mode image  50  formed by the ultrasound image former  16  is displayed. The B-mode image  50  includes a cross section  52  of the abdomen of the fetus. The abdominal cross section  52  is a cross section viewed from the side of the top of the head, and has an ellipse shape. 
         [0048]    In the present embodiment, the ellipse shape to be measured is an ellipse, and a major axis and the minor axis of the ellipse are designated by the user. When the measurement of the abdominal circumferential length is started, a first movable marker  54  which moves on the B-mode image  50  for designating a starting point of the first axis of the measurement target ellipse is displayed on the display  32 . In the present embodiment, the major axis of the measurement target ellipse is designated as the first axis, and then the minor axis of the measurement target ellipse is designated as a second axis. Alternatively, the minor axis of the measurement target ellipse may be designated first as the first axis. 
         [0049]      FIG. 4  is a diagram showing an example display of the display  32  in a period between the time when the starting point of the major axis of the measurement target ellipse is designated and the time when the end point of the major axis is designated. When the starting point of the major axis of the measurement target ellipse is designated, the first movable marker is fixed at the designated position of the starting point of the major axis, and a major axis starting point marker  60  is displayed at this position. In the present embodiment, in order to distinguish the first movable marker during movement and the major axis starting point marker  60 , these markers are shown with different shapes. 
         [0050]    When the user operates the trackball after the major axis starting point of the measurement target ellipse is designated, a second movable marker  62  for designating the end point of the major axis is displayed. In the present embodiment, the shape of the second movable marker  62  is set identical to that of the first movable marker, but alternatively, different shapes may be employed. Along with the second movable marker  62 , a lower limit value ellipse  56  and an upper limit value ellipse  58  are displayed which have a line segment connecting the major axis starting point marker  60  and the second movable marker  62  as a major axis or a minor axis. The lower limit value ellipse  56  and the upper limit value ellipse  58  form a standard range displaying figure. A circumferential length of the lower limit value ellipse  56  is a value based on the lower limit value of the standard range specified by the standard range specifier  22 . Similarly, a circumferential length of the upper limit value ellipse  58  is a value based on the upper limit value of the standard range specified by the standard range specifier  22 . The circumferential lengths of the lower limit value ellipse  56  and the upper limit value ellipse  58  are determined in consideration of the lower limit value and the upper limit value of the specified standard range, and the display scale of the display  32 . 
         [0051]    As shown in  FIG. 4 , in the present embodiment, of the lower limit value ellipse  56  and the upper limit value ellipse  58 , portions that extend beyond the display range of the B-mode image  50  are not displayed. With such a configuration, it is possible to prevent blockage, by the lower limit value ellipse  56  and the upper limit value ellipse  58 , of the display of various pieces of information displayed outside the display range of the B-mode image  50 . 
         [0052]    In addition, because the circumferential lengths of the lower limit value ellipse  56  and the upper limit value ellipse  58  are constants, when the distance between the second movable marker  62  and the major axis starting point marker  60  is close, the lower limit value ellipse  56  and the upper limit value ellipse  58  assume shapes elongated in the longitudinal direction. Such a shape cannot be used as a support for positioning the major axis end point, and also complicates the display. Therefore, a configuration may be employed in which, when the distance between the second movable marker  62  and the major axis starting point marker  60  is less than or equal to a predetermined value, the lower limit value ellipse  56  and the upper limit value ellipse  58  are not displayed. 
         [0053]      FIG. 5  shows an example display when the second movable marker  62  is moved to a candidate position of the end point of the major axis of the measurement target ellipse. As can be understood from comparison between  FIGS. 4 and 5 , because the circumferential lengths of the lower limit value ellipse  56  and the upper limit value ellipse  58  are held constant, as the second movable marker  62  is moved to the right, the widths, in the up-and-down direction, of the lower limit value ellipse  56  and the upper limit value ellipse  58  are reduced, and the shapes change to extend toward the right side. In a state where the second movable marker  62  is moved to the major axis end point candidate position, the outline of the abdominal cross section  52  is compared with the positional relationship between the lower limit value ellipse  56  and the upper limit value ellipse  58 , so as to enable the user to judge whether or not the current position of the second movable marker  62  is at an appropriate position as the major axis end point position of the measurement target ellipse. 
         [0054]    As shown in  FIG. 5 , when the outline of the abdominal cross section  52  is located in a region between the lower limit value ellipse  56  and the upper limit value ellipse  58  (a region inside the upper limit value ellipse  58  and outside the lower limit value ellipse  56 ), it is possible to comprehend that the abdominal circumferential length of the fetus which is the subject falls within the standard range before the major axis end point position of the measurement target ellipse is designated. That is, this means that the current position of the second movable marker  62  is at an appropriate position as the end point of the major axis of the measurement target ellipse, and that the major axis starting position of the measurement target ellipse is also designated at an appropriate position. 
         [0055]    In contrast, if the outline of the abdominal cross section  52  is not located in a region between the lower limit value ellipse  56  and the upper limit value ellipse  58 , various possibilities may be considered. First, a case may be considered in which the current position of the second movable marker  62  is not at an appropriate position as the major axis end point of the measurement target ellipse. Secondly, a case may be considered in which the major axis starting point of the measurement target ellipse which is already designated is not at an appropriate position. Thirdly, a case may be considered in which the abdominal cross section  52  included in the B-mode image  50  is not an appropriate cross section. Fourthly, a case may be considered in which the size of the fetus actually falls outside the standard range. When the size of the fetus is not normal, it is typical to again capture the ultrasound image and again measure the size. In other words, in any of the above-described cases, superior measurement result cannot be obtained when the current position of the second movable marker  62  is set as the major axis end point of the measurement target ellipse. Therefore, when the outline of the abdominal cross section  52  is not located in a region between the lower limit value ellipse  56  and the upper limit value ellipse  58 , the user can comprehend that the current position of the second movable marker  62  is not at an appropriate position as the major axis end point of the measurement target ellipse. 
         [0056]    In this manner, according to the present embodiment, the user can comprehend whether or not the end point candidate position is at an appropriate position as the major axis end point of the measurement target ellipse, before the major axis end point of the measurement target ellipse is designated. When the candidate position is not appropriate as the major axis end point of the measurement target ellipse, the user can comprehend it at an early stage, and can execute countermeasures such as review of the major axis end point position or the major axis starting point position of the measurement target ellipse, and re-selection or re-capturing of the ultrasound image at an early stage. Thus, it is possible to reduce the amount of re-doing work by the user, and to reduce the work effort related to the circumferential length measurement. 
         [0057]    In addition, also in a case where the outline of the abdominal cross section  52  is unclear near the major axis end point of the measurement target ellipse, the appropriate major axis end point position can be deduced based on the positional relationship between the outlines of other portions (for example, outline near the minor axis end) and the standard range displaying figure. 
         [0058]    In the present embodiment, the lower limit value ellipse  56  and the upper limit value ellipse  58  are displayed as the standard range displaying figure. Alternatively, various configurations may be employed for the standard range displaying figure, so long as the standard range of the abdominal circumferential length can be shown. For example, the lower limit value ellipse  56  and the upper limit value ellipse  58  may be displayed with broken lines in order for the user to more easily understand the outline of the abdominal cross section  52 , or a portion between the lower limit value ellipse  56  and the upper limit value ellipse  58  may be colored in order for the user to more easily understand the standard range. 
         [0059]      FIG. 6  is a diagram showing an example display after the major axis end point of the measurement target ellipse is designated. When the major axis end point of the measurement target ellipse is designated by the user pressing a determination button or the like, the second movable marker is fixed at the designated end point position, and a major axis end point marker  64  is displayed at this position. When the major axis end point is designated, a third movable marker  66  for designating an end of the minor axis of the measurement target ellipse (starting point or end point) is displayed. Because the third movable marker  66  is for designating an end of the minor axis of the measurement target ellipse, the marker passes through a midpoint of the major axis of the measurement target ellipse (line segment connecting the major axis starting point marker  60  and the major axis end point marker  64 ), and moves in a direction perpendicular to the major axis. The lower limit value ellipse  56  and the upper limit value ellipse  58  continue to be displayed even after the designation of the major axis end point. 
         [0060]    An initial position for displaying the third movable marker  66  for designating the minor axis end of the measurement target ellipse may be determined based on the standard range displaying figure. The position designated as the minor axis end of the measurement target ellipse may be considered to be between the lower limit value ellipse  56  and the upper limit value ellipse  58 . Therefore, for example, the initial display position of the third movable marker  66  may be set at a point on a straight line perpendicular to the line segment connecting the major axis starting point marker  60  and the major axis end point marker  64  and passing through the midpoint of the line segment, and positioned between the lower limit value ellipse  56  and the upper limit value ellipse  58 . Desirably, an intermediate point between the lower limit value ellipse  56  and the upper limit value ellipse  58  or a nearby point is set as the initial display position of the third movable marker  66 . With such a configuration, a movement distance of the third movable marker  66  for designating the minor axis end of the measurement target ellipse can be reduced. 
         [0061]    Along with the third movable marker  66 , there is displayed a measurement target ellipse index  68  having the line segment connecting the major axis starting point marker  60  and the major axis end point marker  64  as the major axis and the third movable marker  66  as an end of the minor axis. The measurement target ellipse index  68  is a figure which shows the shape of the measurement target ellipse. When the third movable marker  66  is moved in the up-and-down direction, the shape of the measurement target ellipse index  68  is also changed to extend in the up-and-down direction. 
         [0062]    The user can use the measurement target ellipse index  68  as an estimate when designating the minor axis end of the measurement target ellipse. For example, the user can move the third movable marker  66  to a position where the outlines of the abdominal cross section  52  and the measurement target ellipse index  68  overlap each other, and designate the position as the minor axis end of the measurement target ellipse, to thereby accurately designate the position of the minor axis end. With regard to the minor axis end of the measurement target ellipse, when the position of one of the ends is designated, the position of the other end is automatically determined, and thus, only one of the minor axis ends is designated. When the minor axis end of the measurement target ellipse is designated, the measurement target ellipse is determined. The measurement unit  26  then calculates the circumferential length of the determined measurement target ellipse. 
         [0063]      FIG. 7  is a diagram showing an alternative example of the standard range displaying figure. The lower limit value ellipse  56  and the upper limit value ellipse  58  shown in  FIGS. 4-6  are set as ellipses passing through the major axis starting point marker  60  and the second movable marker  62  (or the major axis end point marker  64 ). In the alternative configuration of  FIG. 7 , a lower limit value ellipse  70  and an upper limit value ellipse  72  are set as ellipses which do not pass through the major axis starting point marker  60  and the second movable marker  62  (or the end point marker), and instead, pass through nearby points of these markers. 
         [0064]    Specifically, an ellipse in which an ellipse having the line segment connecting the major axis starting point marker  60  and the second movable marker  62  as the major axis or the minor axis (hereinafter referred to as a “basic ellipse”) is reduced in similitude (the circumferential length of which is the lower limit value of the standard range) is set as the lower limit value ellipse  70 , and an ellipse in which the basic ellipse is enlarged in similitude (the circumferential length of which is the upper limit value of the standard range) is set as the upper limit value ellipse  72 . Alternatively, an ellipse in which the major axis and the minor axis of the basic ellipse are shortened by the same length may be set as the lower limit value ellipse  70 , and an ellipse in which the major axis and the minor axis of the basic ellipse are lengthened by the same length may be set as the upper limit value ellipse  72 . 
         [0065]    As shown in  FIG. 7 , by displaying the lower limit value ellipse  70  and the upper limit value ellipse  72  passing through points slightly deviated from the major axis starting point marker  60  and the second movable marker  62 , it becomes possible to determine the end point of the major axis of the measurement target ellipse to include, in a region between the lower limit value ellipse  70  and the upper limit value ellipse  72 , the entirety of the outline of the abdominal cross section  52  including regions near the starting point and the end point of the major axis of the measurement target ellipse. 
         [0066]    In the example configuration of  FIG. 7 , the lower limit value ellipse  70  and the upper limit value ellipse  72  are set as ellipses which pass through points slightly deviated from the major axis starting point marker  60  and the second movable marker  62 . Alternatively, a configuration may be employed in which an ellipse having a line segment connecting a point which is deviated by a predetermined value from the position of the second movable marker  62  toward the side of the major axis starting point marker  60  and the major axis starting point marker  60  as the major axis or the minor axis is set as the lower limit value ellipse, and an ellipse in which a line segment connecting a point which is deviated by a predetermined value from the position of the second movable marker  62  toward a side opposite from the major axis starting point marker  60  and the major axis starting point marker  60  as the major axis or the minor axis is set as the upper limit value ellipse. With such a configuration, the lower limit value ellipse  70  and the upper limit value ellipse  72  are ellipses which pass through the major axis starting point marker  60  and a region near the second movable marker  62 . In this case, the end point of the major axis of the measurement target ellipse can be determined to include, in a region between the lower limit value ellipse  70  and the upper limit value ellipse  72 , the outline of the abdominal cross section  52  including a region near the end point of the major axis of the measurement target ellipse. 
         [0067]      FIG. 8  is a diagram showing an example display when the length of the major axis of the measurement target ellipse is corrected after the minor axis end of the measurement target ellipse is designated. The ultrasound diagnostic apparatus  10  has a function to correct the starting point and the end point of the major axis of the measurement target ellipse which are designated, or the minor axis end. In the following, there will be described an example display in the case where the starting point of the major axis is corrected after the minor axis end of the measurement target ellipse is designated. When the length of the minor axis is to be corrected, referring again to  FIG. 6 , the user again designates the minor axis end with the third movable marker  66 . 
         [0068]    As shown in (A) of  FIG. 8 , when the minor axis end of the measurement target ellipse is designated, a minor axis end marker  80  is displayed at a position of the minor axis end. The measurement target ellipse index  68  in which the position and the size are determined by the major axis starting point marker  60 , the major axis end point marker  64 , and the minor axis end marker  80  continues to be displayed. Further, although not shown in (B) of  FIG. 8 , the lower limit value ellipse  56  and the upper limit value ellipse  58  continue to be displayed. Then, when the user notices that the position of the major axis starting point marker  60  is deviated from the outline position of the abdominal cross section  52  and enters a major axis length correction mode by pressing a correction button included in the inputter  34 , as shown in (B) of  FIG. 8 , the major axis starting point marker  60  is deleted, and the first movable marker  54  is again displayed at or near the position where the major axis starting point marker  60  was displayed. 
         [0069]    In the major axis correction mode also, the lower limit value ellipse  56  and the upper limit value ellipse  58  are displayed. In this case, the displayed lower limit value ellipse  56  is an ellipse having a length of the minor axis (or the major axis) identical to the length of the minor axis of the designated measurement target ellipse index  68 , having the major axis end point marker  64  as an end of the major axis (or the minor axis), and having the circumferential length identical to the lower limit value of the standard range. Similarly, the upper limit value ellipse  58  is an ellipse having a length of the minor axis (or the major axis) identical to the length of the minor axis of the designated measurement target ellipse index  68 , having the major axis end point marker  64  as an end of the major axis (or the minor axis), and having the circumferential length identical to the upper limit value of the standard range. 
         [0070]    As described with reference to  FIG. 5 , in the designation of the position of the major axis end point, the positional relationship between the outline of the abdominal cross section  52  (in particular, the outline near the minor axis) and the lower limit value ellipse  56  and the upper limit value ellipse  58  is used as the estimate for the position designation. In the major axis correction mode, based on a presumption that the setting of the minor axis of the measurement target ellipse index  68  is appropriate, the lower limit value ellipse  56  and the upper limit value ellipse  58  directly show a range which can be considered to be appropriate as the major axis starting point (that is, a range of the major axis starting point where the circumferential length of the measurement target ellipse is within the standard range). The user can correct the major axis starting point position using the lower limit value ellipse  56  and the upper limit value ellipse  58  as an estimate. 
         [0071]    In order to correct the length of the major axis, the first movable marker  54  is moved in a direction of the major axis of the measurement target ellipse. In the example of (B) of  FIG. 8 , the first movable marker  54  is moved toward the left direction to lengthen the length of the major axis. In addition, with the movement of the first movable marker  54  toward the left direction, the shape of the measurement target ellipse index  68 , which continues to be displayed from the time before the designation of the minor axis end, is changed to extend in the left direction. The user can further use the measurement target ellipse index  68  as the estimate for the designation of the corrected starting point position. With the change of the shape of the measurement target ellipse  68  to extend in the left direction, the position of the minor axis end marker  80  which shows the position of the minor axis end of the measurement target ellipse index  68  is also moved. More specifically, for example, when the first movable marker  54  is moved to the left by  2  cm, the minor axis end marker  80  is moved to the left by a half of the distance,  1  cm. In this manner, the minor axis end marker  80  continues to show the end of the minor axis (or the major axis) of the measurement target ellipse index  68 . 
         [0072]    In  FIG. 8 , a case is described where the major axis starting point of the measurement target ellipse is corrected. In a case where the major axis end point is corrected, a similar display as above is shown. In this case, the major axis end point marker  64  is deleted, and the second movable marker is displayed. The lower limit value ellipse  56  and the upper limit value ellipse  58  are displayed while having the minor axes (or the major axes) with identical lengths as the length of the minor axis of the measurement target ellipse index  68 , having the major axis starting point marker  60  as one end of the major axis (or the minor axis), and having the circumferential lengths of the lower limit value and the upper limit value of the standard range, respectively. 
         [0073]    The ultrasound diagnostic apparatus  10  can also correct the slope of the measurement target ellipse.  FIG. 9  is a diagram showing an example display when the slope of the measurement target ellipse is corrected after the measurement target ellipse is designated. Although not shown in (A) of  FIG. 9  also, the lower limit value ellipse  56  and the upper limit value ellipse  58  continue to be displayed. In this case, similar to the example configuration of  FIG. 8 , the user presses the correction button in the display state shown in (A) of  FIG. 9  in which the minor axis end of the measurement target ellipse is designated, to enter a slope correction mode. Similar to the above, as shown in (B) of  FIG. 9 , the major axis starting point marker  60  is deleted and the first movable marker  54  is again displayed. 
         [0074]    In the state of (B) of  FIG. 9 , similar to (B) of  FIG. 8 , the lower limit value ellipse  56  and the upper limit value ellipse  58  are displayed while having the minor axes (or the major axes) of the same length as the minor axis of the measurement target ellipse index  68 , having the major axis end point marker  64  as an end of the major axis (or the minor axis), and having the circumferential lengths of the lower limit value and the upper limit value of the standard range, respectively. The user corrects the slope of the measurement target ellipse index  68  using the lower limit value ellipse  56  and the upper limit value ellipse  58  as an estimate. 
         [0075]    The first movable marker  54  is set movable in a rotational direction centered at the position of the major axis end point (position of the major axis end point marker  64 ) of the measurement target ellipse. With this configuration, the slope of the measurement target ellipse is corrected. As shown in (C) of  FIG. 9 , when the first movable marker  54  is rotated around the major axis end point marker  64 , the lower limit value ellipse  56  and the upper limit value ellipse  58  are rotated around the major axis end point marker  64 , following the rotational movement of the fist movable marker  54 . With such a configuration, it is possible for the user to use the lower limit value ellipse  56  and the upper limit value ellipse  58  as an estimate for designating the corrected slope of the measurement target ellipse. In other words, the measurement target ellipse index  68  is rotated so that the outline of the abdominal cross section  52  lies within the region between the lower limit value ellipse  56  and the upper limit value ellipse  58 . 
         [0076]    With the rotational movement of the first movable marker  54 , the measurement target ellipse index  68  which continues to be displayed from the time before the designation of the minor axis end is also rotated following the first movable marker  54 . With such a configuration, the user can further use the measurement target ellipse index  68  in the designation of the slope of the measurement target ellipse. With the rotational movement of the measurement target ellipse index  68 , the position of the minor axis end marker  80  showing the position of the minor axis end of the measurement target ellipse index  68  is also rotated. 
         [0077]      FIG. 10  is a diagram showing the rotational movement of the minor axis end marker  80 . In the example configuration of  FIG. 10 , the first movable marker is rotated around the major axis end point marker  64  from the position  60  to the position  54 . If the rotational angle in this case is θ1, the minor axis end marker is also rotated by the angle θ1 around the major axis end point marker  64  from a position  80   a  to a position  80   b . With this process, the minor axis end marker  80  continues to show the end of the minor axis (or the major axis) of the measurement target ellipse index  68 . 
         [0078]      FIG. 11  is a flowchart showing an example flow of operations of the ultrasound diagnostic apparatus  10 . The steps shown in  FIG. 11  will now be described with reference to  FIG. 1 . 
         [0079]    When the user designates an ultrasound image to be used for circumferential length measurement, and the circumferential length measurement is started at the ultrasound diagnostic apparatus  10 , in step S 10 , the standard range specifier  22  specifies the lower limit value and the upper limit value of the standard range of the abdominal circumferential length of a fetus based on the number of weeks of pregnancy of the pregnant woman which is input by the user. 
         [0080]    In step S 12 , the controller  20  judges whether or not the starting point of the major axis of the measurement target ellipse is designated by the user operating the first movable marker, and whether or not the movement operation of the second movable marker for designating the end point of the major axis of the measurement target ellipse is executed by the user operating the trackball or the like after designating the starting point. 
         [0081]    In step S 14 , the display processor  30  displays the major axis starting point marker at the starting point position of the major axis of the measurement target ellipse. Further, the display processor  30  displays the second movable marker on the ultrasound image, and displays, as the standard range displaying figures, a lower limit value ellipse having the line segment connecting the major axis starting point marker and the second movable marker as the major axis or the minor axis and the lower limit value of the standard range specified in step S 10  as the circumferential length, and the upper limit value ellipse having the line segment connecting the major axis starting point marker and the second movable marker as the major axis or the minor axis and the upper limit value of the standard range specified in step S 10  as the circumferential length. 
         [0082]    In step S 16 , the controller  20  judges whether or not the end point of the major axis of the measurement target ellipse is designated by the user. Until the end point of the major axis is designated, the display processor  30  continues to display the second movable marker and the standard range displaying figure (the lower limit value ellipse and the upper limit value ellipse). 
         [0083]    When the user designates the end point of the major axis of the measurement target ellipse, in step S 18 , the display processor  30  displays the major axis end point marker at the position of the major axis end point. In addition, the display processor  30  displays the third movable marker for designating the minor axis end of the measurement target ellipse. Further, in step S 20 , the display processor  30  displays the measurement target ellipse index showing the shape of the measurement target ellipse. The measurement target ellipse index is an ellipse having a line segment connecting the major axis starting point marker and the major axis end point marker as the major axis, and the third movable marker as the minor axis end. Further, the display of the lower limit value ellipse and the upper limit value ellipse is continued even after the end point of the major axis is designated. 
         [0084]    In step S 22 , the controller  20  judges whether or not the minor axis end of the measurement target ellipse is designated by the user. Until the minor axis end is designated, the display processor  30  continues to display the third movable marker, the lower limit value ellipse, the upper limit value ellipse, and the measurement target ellipse index. 
         [0085]    In step S 24 , the measurement unit  26  measures the circumferential length of the designated measurement target ellipse. 
         [0086]    The present embodiment has been described exemplifying the measurement of the abdominal circumferential length of a fetus. The present disclosure, however, is not limited to such a configuration, and may be applied to any measurement of the circumferential length of an ellipse shape designated on an ultrasound image. In this case, as the table or function showing the lower limit value and the upper limit value of the standard range stored in the storage  28 , a table or function corresponding to the measurement target is prepared. 
         [0087]    In addition, in the present embodiment, the ultrasound diagnostic apparatus  10  is exemplified as an ultrasound image processor. Alternatively, for example, a PC or the like may be used as the ultrasound image processor. In this case, the ultrasound image formed by the ultrasound diagnostic apparatus is sent to the PC, and the PC executes the specification of the standard range, overlapping of the graphic image, measurement of the circumferential length, or the like. 
       REFERENCE SIGNS LIST 
       [0088]      10  ULTRASOUND DIAGNOSTIC APPARATUS;  12  PROBE;  14  TRANSMISSION AND RECEPTION UNIT;  16  ULTRASOUND IMAGE FORMER;  18  IMAGE STORAGE;  20  CONTROLLER;  22  STANDARD RANGE SPECIFIER;  24  GRAPHIC IMAGE FORMER;  26  MEASUREMENT UNIT;  28  STORAGE;  30  DISPLAY PROCESSOR;  32  DISPLAY;  34  INPUTTER.