Patent Publication Number: US-2015080726-A1

Title: Ultrasonic diagnostic apparatus, positional information acquiring method, and computer program product

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 12/688,259, filed Jan. 15, 2010, which claims the benefit of priority from the prior Japanese Patent Application No. 2009-10246, filed on Jan. 20, 2009. The entire contents of the above-identified applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an ultrasonic diagnostic apparatus, a positional information acquiring method, and a computer program product. 
     2. Description of the Related Art 
     Among conventional technologies, an ultrasonic diagnostic apparatus is advantageous in its operational ease and noninvasiveness without the possibility of exposure to radiation, to other medical diagnostic imaging devices such as an x-ray diagnostic device and an x-ray computer tomograph. The ultrasonic diagnostic apparatus is therefore widely used in examination and diagnosis of various parts of body tissues such as heart, liver, kidney, mammary gland, and muscles in today&#39;s medicine. 
     The ultrasonic diagnostic apparatus transmits an ultrasonic wave to a subject from an ultrasound probe, and generates an ultrasonic image based on the reflection wave of the ultrasonic wave reflected from the inner tissues of the subject. 
     In recent examinations incorporating an ultrasonic diagnostic apparatus such as ultrasonic breast examinations that are recommended for early detection of breast cancer, an ultrasound probe needs to be moved and rolled on the breast surface by a doctor or a clinical laboratory technician to find an optimal position for observation of a lesion. Thus, for the doctor to recognize the position of the lesion indicated in an ultrasonic image, it is important to obtain positional information of the ultrasound probe at the time of generating the ultrasonic image. 
     To obtain the positional information of the ultrasound probe, an ultrasonic diagnostic apparatus has been developed, in which a magnetic field generation coil that generates a magnetic signal is attached to a bed on which a subject lies and the ultrasound probe is provided with a magnetic sensor (see JP-A 2006-246974 (KOKAI) and JP-A 2007-244575 (KOKAI), for example). In such an ultrasonic diagnostic apparatus, the magnetic sensor that detects the magnetic signal generated by the magnetic field generation coil calculates coordinates of the position of the magnetic sensor with respect to the magnetic field generation coil so that the positional information of the ultrasound probe can be obtained. 
     Furthermore, an ultrasonic diagnostic apparatus in which the ultrasound probe is provided with an optical sensor has also been developed to obtain the positional information of the ultrasound probe (see, for example, “Development of System for Detecting Position of Breast Examination Probe Incorporating Color Sensor”, The 81st Annual Scientific Meeting of the Japan Society of Ultrasonics in Medicine, S283, May, 2008). In such an ultrasonic diagnostic apparatus, the optical sensor reads a color pattern fixed onto the area of the subject that is to be examined so that the positional information of the ultrasound probe can be obtained. 
     The positional information of the ultrasound probe obtained in this manner is displayed, for example, as a body mark on the monitor together with an ultrasonic image so that the doctor who conducts an image diagnosis easily recognizes the position of the examination region in the ultrasonic image that is being viewed. A body mark is a brief description that roughly indicates the position and orientation of the ultrasound probe that is placed on the subject at the time of generating an ultrasonic image. 
     According to the above conventional technologies, however, the positional information of the ultrasound probe cannot be easily acquired. More specifically, with the above conventional technologies, because a positional sensor such as a magnetic sensor and an optical sensor needs to be additionally arranged in the ultrasound probe, the structure of the ultrasonic diagnostic apparatus becomes complicated, which increases the cost of production. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, an ultrasonic diagnostic apparatus includes an ultrasound wave control unit that performs control in such a manner that a depth of an ultrasonic wave emitted from an ultrasound probe is set to a value deeper than an observation region of a subject; an image generating unit that generates a plurality of ultrasonic images in chronological order based on a reflection wave of the ultrasonic wave emitted by the ultrasound probe in accordance with the control performed by the ultrasound wave control unit; a positional information acquiring unit that acquires motion information from the ultrasonic images generated by the image generating unit in chronological order, identifies a left organ or a right organ that is being scanned by the ultrasound probe based on an intensity ratio of heartbeat-related motion components and respiration-related motion components in the motion information that is acquired, and acquires an identification result as positional information; and a display control unit that performs control in such a manner than the positional information acquired by the positional information acquiring unit on a predetermined displaying unit. 
     According to another aspect of the present invention, an ultrasonic diagnostic apparatus includes an ultrasound wave control unit that performs control in such a manner that a depth of an ultrasonic wave emitted from an ultrasound probe is set to a value deeper than an observation region of a subject and that three-dimensional scanning is conducted with the ultrasonic wave; an image generating unit that generates three-dimensional ultrasonic images based on a reflection wave of the ultrasound wave emitted by the ultrasound probe in accordance with the control performed by the ultrasound wave control unit; a positional information acquiring unit that detects through image analysis a rib extending direction depicted in the three-dimensional ultrasonic images generated by the image generating unit, and acquires the rib extending direction that is detected, as positional information of the ultrasound probe; and a display control unit that performs control in such a manner that the positional information acquired by the positional information acquiring unit is displayed on a predetermined displaying unit. 
     According to still another aspect of the present invention, a positional information acquiring method includes performing control by an ultrasound wave control unit in such a manner that a depth of an ultrasound wave emitted by an ultrasound probe is set to a value deeper than an observation region of a subject; generating ultrasonic images in chronological order by an image generating unit based on a reflection wave of the ultrasound wave emitted by the ultrasound probe in accordance with the control of the ultrasound wave control unit; acquiring motion information from the ultrasonic images generated by the image generating unit in chronological order, identifying a left organ or a right organ that is being scanned by the ultrasound probe based on an intensity ratio of heartbeat-related motion components and respiration-related motion components in the motion information that is acquired, and acquiring an identification result as positional information by a positional information acquiring unit; and performing control by a display control unit in such a manner that the positional information acquired by the positional information acquiring unit is displayed on a predetermined displaying unit. 
     According to still another aspect of the present invention, a positional information acquiring method includes performing control by an ultrasound wave control unit in such a manner that a depth of an ultrasound wave emitted by an ultrasound probe is set to a value deeper than an observation region of a subject and that three-dimensional scanning is conducted with the ultrasound wave; generating three-dimensional ultrasonic images by an image generating unit, based on a reflection wave of the ultrasound wave emitted by the ultrasound probe in accordance with the control performed by the ultrasound wave control unit; detecting, through image analysis, a rib extending direction depicted in the three-dimensional ultrasonic images generated by the image generating unit, and acquiring the rib extending direction that is detected, as positional information of the ultrasound probe by a positional information acquiring unit; and performing control by a display control unit in such a manner that the positional information acquired by the positional information acquiring unit is displayed on a predetermined displaying unit. 
     According to still another aspect of the present invention, a computer program product having a computer readable recording medium including a plurality of computer executable instructions to execute image processing, wherein the instructions cause a computer to: performing control in such a manner that a depth of an ultrasound wave emitted by an ultrasound probe is set to a value deeper than an observation region of a subject; generating a plurality of ultrasonic images in chronological order based on a reflection wave of the ultrasound wave emitted by the ultrasound probe; acquiring motion information from the ultrasonic images generated in chronological order, identifying a left organ or a right organ that is being scanned by the ultrasound probe based on an intensity ratio of heartbeat-related motion components and respiration-related motion components in the motion information that is acquired, and acquiring an identification result as positional information; and performing control in such a manner that the positional information that is acquired is displayed on a predetermined displaying unit. 
     According to still another aspect of the present invention, a computer program product having a computer readable recording medium including a plurality of computer executable instructions to execute image processing, wherein the instructions cause a computer to: performing control in such a manner that a depth of an ultrasound wave emitted by an ultrasound probe is set to a value deeper than an observation region of a subject and that three-dimensional scanning is conducted with the ultrasound wave; generating three-dimensional ultrasonic images based on a reflection wave of the ultrasound wave emitted by the ultrasound probe; detecting, through image analysis, a rib extending direction depicted in the three-dimensional ultrasonic images that are generated, and acquiring the rib extending direction that is detected, as positional information of the ultrasound probe; and performing control in such a manner that the positional information that is acquired is displayed on a predetermined displaying unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram for explaining a configuration of an ultrasonic diagnostic apparatus according to the present embodiment; 
         FIG. 2  is a diagram for explaining a configuration of an image processing unit according to the present embodiment; 
         FIG. 3  is a diagram for explaining volume data according to the present embodiment; 
         FIG. 4  is a diagram for explaining planes A, B, and C; 
         FIGS. 5A and 5B  are diagrams for explaining a right/left identifying unit; 
         FIG. 6  is a diagram for explaining a process performed by a body mark generating unit by use of the processing results obtained by the right/left identifying unit; 
         FIGS. 7A and 7B  are diagrams for explaining the first method executed by an extending direction detecting unit; 
         FIGS. 8 ,  9 A, and  9 B are diagrams for explaining the second method executed by the extending direction detecting unit; 
         FIGS. 10A and 10B  are diagrams for explaining the position detecting method executed for the ultrasound probe by the extending direction detecting unit; 
         FIG. 11  is a diagram for explaining the process executed by the body mark generating unit by use of the processing results obtained by the extending direction detecting unit; 
         FIG. 12  is a flowchart of the process executed by the ultrasonic diagnostic apparatus according to the present embodiment; 
         FIG. 13  is a diagram for explaining the first modification example of the present embodiment; and 
         FIG. 14  is a diagram for explaining the second modification example of the present embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of an ultrasonic diagnostic apparatus, a positional information acquiring method, and a computer program product according to the present invention are explained in detail below with reference to the 
     First, a configuration of an ultrasonic diagnostic apparatus according to the present embodiment is explained.  FIG. 1  is a diagram for explaining a configuration of an ultrasonic diagnostic apparatus according to the present embodiment. As shown in  FIG. 1 , the ultrasonic diagnostic apparatus according to the present embodiment includes an ultrasound probe  1 , a monitor  2 , an input device  3 , and a main device  10 . 
     The ultrasound probe  1  includes an array of piezoelectric oscillators. These piezoelectric oscillators generate an ultrasound wave in accordance with a drive signal supplied from a transmitting unit  11  of the main device  10 , which is described later, and also receives a wave reflected from a subject P and converts it to an electronic signal. The ultrasound probe  1  includes a matching layer provided on the piezoelectric oscillators, a backing material that prevents an ultrasound wave from propagating from the piezoelectric oscillators to the rear, and the like. 
     When an ultrasound wave is emitted from the ultrasound probe  1  to the subject P, the emitted ultrasound wave is reflected from the discontinuous planes of acoustic impedances in the body tissue of the subject P, and is received as a reflection wave signal by the piezoelectric oscillators of the ultrasound probe  1 . The amplitude of the received reflection wave signal depends on a difference in the acoustic impedances produced at the discontinuous planes from which the ultrasound wave is reflected. When the emitted ultrasonic pulses are reflected on the surface of the moving blood stream or cardiac wall, the reflection wave signals undergo a frequency shift due to the Doppler effect, in accordance with the velocity components of the ultrasound wave transmission direction in the moving object. 
     The ultrasound probe  1  according to the present embodiment includes an oscillation motor and an oscillation circuit that mechanically oscillate the piezoelectric oscillators, and the subject P can be three-dimensionally scanned by the oscillation of the piezoelectric oscillators. In other words, the operator can automatically obtain three-dimensional reflection wave data (volume data) of the subject P scanned consecutively on multiple sections simply, by touching the subject P with the ultrasound probe  1  according to the present embodiment. Further, when scanning the subject P in three dimensions, distances between the sections can be accurately detected on the basis of the controlled oscillation speed. 
     The present invention is applicable to a two-dimensional ultrasound probe, in which the piezoelectric oscillators are arranged two-dimensionally in a lattice pattern in the ultrasound probe  1 . By use of the two-dimensional ultrasound probe, the ultrasonic diagnostic apparatus can obtain volume data substantially in the same length of time in principle as when obtaining the two-dimensional reflection wave data by a conventional one-dimensional probe. 
     The monitor  2  displays a graphical user interface (GUI) with which the operator of the ultrasonic diagnostic apparatus inputs various setting requests through the input device  3 , and also displays an ultrasonic image generated by the main device  10 . 
     The input device  3  includes a mouse, a keyboard, buttons, a panel switch, a touch command screen, a foot switch, a trackball, and the like. The input device  3  receives various setting requests input by the operator of the ultrasonic diagnostic apparatus, and sends the received setting requests (for example, a region-of-interest setting request) to the main device  10 . For example, when the operator presses the “stop” button or the “freeze” button of the input device  3 , the ultrasound wave transmission and reception is terminated, and the ultrasonic diagnostic apparatus is put into suspend mode. 
     The main device  10  generates an ultrasonic image in accordance with the reflected wave received by the ultrasound probe  1 . As illustrated in  FIG. 1 , the main device  10  includes the transmitting unit  11 , a receiving unit  12 , a B-mode processing unit  13 , a Doppler processing unit  14 , an image processing unit  15 , an image memory  16 , an image synthesizing unit  17 , a control unit  18 , and an internal storage unit  19 . 
     The transmitting unit  11  includes a trigger generating circuit, a delay circuit, a pulsar circuit, and the like, and supplies a drive signal to the ultrasound probe  1 . The pulsar circuit repeatedly generates rate pulses at a predetermined rate frequency to form a transmission ultrasound wave. The delay circuit gives a delay time for each piezoelectric oscillator, which is necessary to concentrate the ultrasound wave emitted by the ultrasound probe  1  into a beam and thereby determine the transmission directional characters, to each rate pulse generated by the pulsar circuit. Furthermore, the trigger generating circuit applies a drive signal (drive pulses) to the ultrasound probe  1  at the timing based on the rate pulses. 
     The transmitting unit  11  has a function of quickly changing the transmission frequencies, the transmission drive voltages, and the like to execute a certain scan sequence, based on the later-described control performed by the control unit  18 . The transmission drive voltages are changed by a linear-amplifier oscillation circuit that can instantaneously change the voltage values or a mechanism that can electrically switch among multiple power units. 
     The receiving unit  12  includes an amplifying circuit, an analog-digital (A/D) converter, an adder, and the like, and executes various processes on the reflection wave signal received by the ultrasound probe  1  to generate reflection wave data. The amplifying circuit amplifies the reflection wave signal and executes a gain correcting process thereon. The A/D converter performs an A/D conversion onto the gain-corrected reflection wave signal and gives the signal a delay time that is necessary to determine the reception directional characteristics. The adder performs addition onto the reflection wave signal processed by the A/D converter and thereby generates the reflection wave data. Through the addition performed by the adder, the reflection components in a direction corresponding to the reception directional characteristics of the reflection wave signal are emphasized. According to the present embodiment, the receiving unit  12  generates three-dimensional reflection wave data. 
     In this manner, the transmitting unit  11  controls the transmission directional characteristics in the transmission of the ultrasound wave, while the receiving unit  12  controls the reception directional characteristics in the reception of the ultrasound wave. 
     The B-mode processing unit  13  receives from the receiving unit  12  the reflection wave data, which is the processed reflection wave signal subjected to the gain correcting process, the A/D converting process, and the adding process, and performs logarithmic amplification and an envelope detecting process to generate data (B-mode data) that expresses the signal intensity in brightness. According to the present embodiment, the B-mode processing unit  13  generates three-dimensional B-mode data from the three-dimensional reflection wave data. 
     The Doppler processing unit  14  performs a frequency analysis on the speed information of the reflection wave data received from the receiving unit  12 , extracts echo components of the blood stream, the tissue, and the contrast agent that are affected by the Doppler effect, and generates data (Doppler data) by extracting moving body information including the average speed, the dispersion, and the power for different points. According to the present embodiment, the Doppler processing unit  14  generates three-dimensional Doppler data from the three-dimensional reflection wave data. 
     The image processing unit  15  includes an image generating unit  151  that generates an ultrasonic image and a position analyzing unit  152  that analyzes the ultrasonic image generated by the image generating unit  151  and analyzes the positional information of the ultrasound probe  1  on the subject P at the time of generating the ultrasonic image. 
     As an ultrasonic image, the image generating unit  151  generates, from the B-mode data generated by the B-mode processing unit  13 , a B-mode image that expresses the intensity of the reflected wave in brightness, and also generates, from the Doppler data generated by the Doppler processing unit  14 , a Doppler image, which is an average speed image, a dispersion image, a power image, or a combination image thereof indicating the information of the moving body. 
     The image generating unit  151  generally performs a conversion (scan conversion) of a scan line signal string obtained by ultrasonic scanning into a video-format scan line signal string such as for television and thereby generates an ultrasonic image as a display image. In addition to the scan conversion, the image generating unit  151  performs various kinds of image processing by use of image frames after the scan conversion, such as image processing for reconfiguring an average brightness image (smoothing process) and image processing using a differentiation filter in the image (edge emphasizing process). 
     Moreover, when receiving the three-dimensional reflection wave data such as three-dimensional B-mode data and three-dimensional Doppler data, the image generating unit  151  performs volume rendering or the like by use of a three-dimensional reconfiguration algorithm to reconfigure the three-dimensional ultrasonic image. 
     The image generating process of the image generating unit  151  and the analyzing process of the position analyzing unit  152  will be described later. 
     The image memory  16  stores therein ultrasonic images generated by the image generating unit  151 . 
     The image synthesizing unit  17  superimposes character information of various parameters, scales, body marks, and the like onto the ultrasonic image generated by the image generating unit  151  and outputs the image as a video signal to the monitor  2 . 
     The control unit  18  controls the entire process of the ultrasonic diagnostic apparatus. More specifically, the control unit  18  controls the processes performed by the transmitting unit  11 , the receiving unit  12 , the B-mode processing unit  13 , the Doppler processing unit  14 , and the image processing unit  15 , in accordance with the various setting requests input by the operator on the input device  3  and various control programs read from the internal storage unit  19 . The control unit  18  also exercises control so that the ultrasonic image stored in the image memory  16  and the image produced by the image synthesizing unit  17  are displayed on the monitor  2 . 
     The internal storage unit  19  stores therein control programs for the ultrasound wave transmission and reception, image processing, and display processing, and various kinds of data such as diagnostic information (e.g., patient IDs and doctor&#39;s remarks), diagnostic protocols, and various body marks. The internal storage unit  19  is also used as storage of the images stored in the image memory  16 , if necessary. The data stored in the internal storage unit  19  may be transmitted to an external peripheral device by way of a not-shown interface circuit. 
     In this manner, the ultrasonic diagnostic apparatus according to the present embodiment generates an ultrasonic image based on the reflected wave of the ultrasound wave emitted from the ultrasound probe  1 . The main feature of this embodiment resides in that the positional information of the ultrasound probe can be easily acquired at the time of generating the ultrasonic image by the following processes performed by the image generating unit  151  and the position analyzing unit  152 . 
     The processes performed by the image generating unit  151  and the position analyzing unit  152  are explained with reference to  FIGS. 2 to 11 .  FIG. 2  is a diagram for explaining a configuration of an image processing unit according to the present embodiment, and  FIG. 3  is a diagram for explaining the volume data according to the present embodiment.  FIG. 4  is a diagram for explaining planes A, B, and C, and  FIGS. 5A and 5B  are diagrams for explaining the right/left identifying unit.  FIG. 6  is a diagram for explaining the process performed by the body mark generating unit by use of the process result obtained by the right/left identifying unit, and  FIGS. 7A and 7B  are diagrams for explaining the first method executed by the extending direction detecting unit.  FIGS. 8 ,  9 A, and  9 B are diagrams for explaining the second method executed by the extending direction detecting unit, and  FIGS. 10A and 10B  are diagrams for explaining the method of detecting the position of the ultrasound probe executed by the extending direction detecting unit.  FIG. 11  is a diagram for explaining the process performed by the body mark generating unit by use of the process result obtained by the extending direction detecting unit. 
     In the following description, it is assumed that the ultrasound probe  1  three-dimensionally scans the breast of the subject P in an ultrasound breast examination to generate three-dimensional reflection wave data. 
     As illustrated in  FIG. 2 , the image generating unit  151  of the image processing unit  15  according to the present embodiment includes a display image generating unit  151   a  and an analysis image generating unit  151   b . The position analyzing unit  152  of the image processing unit  15  according to the present embodiment includes a right/left identifying unit  152   a , an extending direction detecting unit  152   b , and a body mark generating unit  152   c.    
     According to the present embodiment, to analyze the positional information of the ultrasound probe  1 , the depth of the ultrasound wave emitted from the ultrasound probe  1  is automatically set by the control unit  18  deeper than the breast of the subject P who is to undergo the examination, or more specifically, deeper than the ribs of the subject P. For example, when the examination depth is 4 centimeters, the ultrasound probe  1  emits an ultrasound wave down to the depth of “7 centimeters”, and the receiving unit  12  generates three-dimensional reflection wave data corresponding to the analysis depth of “7 centimeters”. 
     Then, as illustrated in  FIG. 3 , the display image generating unit  151   a  uses the three-dimensional B-mode data generated from the three-dimensional reflection wave data of the examination depth as volume display data, and generates from this volume display data an ultrasonic display image (e.g., a volume rendering image and a section image) that is to be displayed on the monitor  2  for the doctor to conduct an image diagnosis. 
     Furthermore, as illustrated in  FIG. 3 , the analysis image generating unit  151   b  uses the three-dimensional B-mode data generated from the three-dimensional reflection wave data of different depths including information of a region deeper than the rib as volume analysis data, and generates from this volume analysis data an ultrasonic analysis image that is used by the position analyzing unit  152  to conduct an image analysis. More specifically, the analysis image generating unit  151   b  generates different section images as ultrasonic analysis images. 
     Three types of sectional surfaces (planes A, B, and C) along which section images are generated from a three-dimensional ultrasonic image in the ultrasonic diagnostic apparatus are now explained. First, as illustrated in  FIG. 4 , the plane A is a sectional surface of the mechanically oscillating ultrasound probe  1  defined by the alignment direction of the piezoelectric oscillators and the ultrasonic transmission direction. As illustrated in  FIG. 4 , the plane B is a sectional surface defined by the alignment direction of the piezoelectric oscillators and the oscillating direction. As illustrated in  FIG. 4 , the plane C is a sectional surface perpendicular to the ultrasonic transmission direction. 
     First, the analysis image generating unit  151   b  generates section images of planes A, B, and C from the volume analysis data that is generated successively in chronological order. It is assumed that the position of the ultrasound probe  1  at this point is fixed to the initial position on the breast of the subject P (for example, 45 degrees downward from the underarm of the subject P) by the operator. 
     Then, the right/left identifying unit  152   a  identifies the right or left breast that is being subjected to the scanning by the ultrasound probe  1 , by use of the section images generated by the analysis image generating unit  151   b  in chronological order. 
     As illustrated in  FIG. 5A , among the cyclic motions in the breast of the subject P, the left breast includes the pulmonary and cardiac motions, while the right breast includes the pulmonary motions only. 
     To identify whether the ultrasonic beam is scanning the left breast or the right breast, the right/left identifying unit  152   a  performs an image analysis on a certain region along the plane A or B at a certain position beneath the ribs, or on the plane C of a certain position beneath the ribs, in chronological order to acquire cyclic motion components, as illustrated in  FIG. 5B . The right/left identifying unit  152   a  thereby identifies the right or left, and calculates the reliability of the identification result. 
     For example, the right/left identifying unit  152   a  extracts feature points from multiple plane-A images in chronological order, and obtains cyclic motion components of the feature points in chronological order. Then, the right/left identifying unit  152   a  makes an identification of the “left” when, among the obtained cyclic motion components, the ratio of the intensity of the motion components in a cycle of approximately 1 second (heartbeat-related motions) to the intensity of the motion components in a cycle of approximately 5 seconds (respiration-related motions) is greater than or equal to a certain percentage (e.g., 60%), while it makes an identification of the “right” when the ratio of the intensity of the motion components in a cycle of approximately 5 seconds (respiration-related motions) to the intensity of the motion components in a cycle of approximately 1 second (heartbeat-related motions) is greater than or equal to a certain percentage (e.g., 600). Thereafter, the right/left identifying unit  152   a  calculates the reliability in accordance with, for example, the intensity ratio that is used in the identification. 
     Then, based on the identification result obtained by the right/left identifying unit  152   a , the body mark generating unit  152   c  generates a body mark, for example, by combining the left or right breast body mark with the probe position mark that indicates the initial position of the ultrasound probe  1 , as illustrated in  FIG. 6 . The body mark generating unit  152   c  obtains these body marks from the internal storage unit  19 . 
     Then, the image synthesizing unit  17  generates a composite image by integrating the display image generated by the display image generating unit  151   a  and the body mark to which the probe position mark is attached by the body mark generating unit  152   c . The monitor  2  displays the composite image generated by the image synthesizing unit  17 , in accordance with the control of the control unit  18 . In this manner, the display image to which the left or right body mark is attached is automatically presented to the operator, without having to manually input the body mark. 
     After the right/left identifying unit  152   a  identifies the right or left, the analysis image generating unit  151   b  generates an image that is used by the extending direction detecting unit  152   b  to detect the rib extending direction by the image processing. More specifically, the analysis image generating unit  151   b  generates different section images in accordance with an extending direction detecting method (the first or second method) executed by the extending direction detecting unit  152   b.    
     First, the first method executed by the extending direction detecting unit  152   b  is explained. According to the first method, the analysis image generating unit  151   b  generates multiple plane-A images and/or multiple plane-B images by sectioning the volume analysis data generated at a time when the ultrasound probe  1  is placed at the initial position by multiple planes A and/or planes B. In the following explanation, the plane-A images generated by the analysis image generating unit  151   b  are described. 
     As illustrated in  FIG. 7A , the reflection of the ultrasound wave on the rib surface is intense, which makes the brightness of the rib surface region high in a plane-A image that always contains the rib bone of the subject P. In contrast, the region under the rib surface is shown as a shadow with a low brightness in the plane-A image. Furthermore, in the plane-A image, the boundaries of the shadow are drawn in straight lines because they are parallel to the ultrasonic beams. 
     Thus, the extending direction detecting unit  152   b  first performs a smoothing process to remove speckles that appear in the rib surface and the intercostal region outside the shadow in the plane-A image (see ( 1 ) in  FIG. 7A ). 
     Next, the extending direction detecting unit  152   b  performs a boundary extracting process onto the plane-A image that has been subjected to the smoothing process, by use of the Sobel filter to detect the boundary of the rib region and the intercostal region (see ( 2 ) in  FIG. 7A ). The present invention is applicable to the extending direction detecting unit  152   b  that adopts the Hough transform instead of the Sobel filter in the boundary extracting process. 
     Thereafter, the extending direction detecting unit  152   b  extracts the position of the rib edges from the plane-A image that has been subjected to the Sobel filter processing (see ( 3 ) in  FIG. 7A ). In this manner, the extending direction detecting unit  152   b  extracts two edges of the rib bone, as illustrated in  FIG. 7A . When the plane-A image contains two rib bones or more, the extending direction detecting unit  152   b  can distinguish the edges of each rib based on the distances between the edges. 
     The extending direction detecting unit  152   b  performs the above process on each of the plane-A images generated from the same volume analysis data, as illustrated in  FIG. 7B . The extending direction detecting unit  152   b  detects the rib extending direction included in the volume analysis data, in accordance with the special continuity of a rib. 
     The first method is executable when using multiple plane-B images or when using multiple plane-A images and multiple plane-B images. 
     The second method executed by the extending direction detecting unit  152   b  is now explained. According to the second method, the analysis image generating unit  151   b  generates a thickness-added maximum intensity projection (MIP) image beneath the ribs in the plane C from the volume analysis data generated at a certain time when the ultrasound probe  1  is placed at the initial position, as illustrate in  FIG. 8 . 
     Because the thickness-added MIP image of the plane C includes information on the region beneath the ribs, the following feature is observed. The shadow portion under the rib surface (hereinafter, “rib shadow”) has a low brightness in comparison with the projection region of the intercostal tissue. In the thickness-added MIP image of the plane C, the projected intercostal tissue regions and the rib shadows are alternately arranged, as illustrated in  FIG. 8 , and thus the extending directions of the ribs are described as stripes. 
     The extending direction detecting unit  152   b  that executes the second method determines, for example, a center point in the low-brightness region of the thickness-added MIP image of the plane C, and generates a brightness histogram of pixels on each of line segments of interest that pass the center. For example, as illustrated in  FIG. 8 , the extending direction detecting unit  152   b  turns the line segments of interest around the determined center point, and generates a histogram individually for the “line segment of interest 1, the line segment of interest 2, the line segment of interest 3, . . . ”. 
     For example, the extending direction detecting unit  152   b  generates histograms for the line segments of interest 1, 2, and 3, as illustrated in  FIG. 9A . Then, the extending direction detecting unit  152   b  analyzes the generated histograms of the line segments of interest to find the rib extending direction. For example, the extending direction detecting unit  152   b  determines the direction of the line segment of interest 3 in which the low brightness appears with the highest frequency in the histogram as the rib extending direction, as illustrated in  FIG. 9A . 
     When the center point is defined in a high-brightness intercostal tissue region, the extending direction detecting unit  152   b  determines the line segment of interest in which the high brightness appears with the highest frequency as the rib extending direction, as illustrated in  FIG. 9B . 
     The second method is executable if the region above the rib surface is included in the range for generating the thickness-added MIP image of the plane C, as long as the region beneath the ribs is included and the information on the rib shadow can be reflected. The second method is not limited to the use of line segments of interest, but may be used when analyzing the brightness values of all the pixels in the thickness-added MIP image of the plane C to determine the rib extending direction. 
     When the operator moves the ultrasound probe  1  on the breast of the subject P after the rib extending direction at the initial position is detected, as illustrated in  FIG. 10A , to collect new volume data, the extending direction detecting unit  152   b  repeats the rib extending direction detecting process according to the first or second method. 
     For example, the extending direction detecting unit  152   b  detects the rib extending direction according to the first or second method, in volume data 1, 2, and 3, which is volume analysis data collected in chronological order after the rib extending direction at the initial position is detected, as illustrated in  FIG. 10B , and determines the position of the ultrasound probe  1  from the initial position. 
     In other words, the extending direction detecting unit  152   b  calculates a relative change of the detected rib extending direction in the volume data 1 and the rib extending direction detected at the initial position, and acquires a relative displacement (rotation angle) with respect to the initial position of the ultrasound probe  1  to determine the position of the ultrasound probe  1  at the time of generating the volume data 1. 
     Similarly, the extending direction detecting unit  152   b  calculates a relative change of the rib extending direction detected in the volume data 2 and the rib extending direction detected in the volume data 1, and acquires a relative displacement (rotation angle) with respect to the fixed position of the ultrasound probe  1  at the time of generating the volume data 1 to determine the position of the ultrasound probe  1  at the time of generating the volume data 2. 
     As illustrated in  FIG. 11 , the body mark generating unit  152   c  rotates the probe position mark from the initial position in chronological order in accordance with the positional information of the ultrasound probe determined for each item of the volume data newly generated by the extending direction detecting unit  152   b.    
     In this manner, the image synthesizing unit  17  generates a composite image by integrating the display image generated by the display image generating unit  151   a  and the body mark whose probe position mark is rotated from the initial position, and the monitor  2  displays the composite image based on the control of the control unit  18 . 
     Next, the process executed by the ultrasonic diagnostic apparatus according to the present embodiment is explained with reference to  FIG. 12 .  FIG. 12  is a flowchart for explaining the process executed by the ultrasonic diagnostic apparatus according to the present embodiment. 
     As illustrated in  FIG. 12 , when receiving a start request for taking a three-dimensional ultrasonic image after the ultrasound probe  1  is placed at the initial position (yes at step S 101 ), the ultrasonic diagnostic apparatus according to the present embodiment collects volume data (volume analysis data) (step S 102 ). According to the present embodiment, the volume analysis data is collected successively in chronological order, with the ultrasound probe  1  fixed to the initial position until step S 108  is completed. 
     Then, the display image generating unit  151   a  generates a display image from the volume display data in the volume analysis data (step S 103 ). The display image generating unit  151   a  successively generates display images for items of the volume display data that are collected in chronological order. The generated display images are synthesized with character information of parameters and scales by the image synthesizing unit  17  and displayed on the monitor  2 . 
     Then, the right/left identifying unit  152   a  identifies the right or left breast that is being scanned, based on the section images that are successively generated by the analysis image generating unit  151   b  from the volume analysis data in chronological order (step S 104 ). In other words, the right/left identifying unit  152   a  calculates the intensity ratio of heartbeat-related cyclic motion components to respiration-related cyclic motion components among the cyclic motion components in the region beneath the ribs of the section images generated in chronological order and thereby identifies the right or left. 
     Thereafter, the extending direction detecting unit  152   b  detects the rib extending direction at the initial position according to the first or second method, based on the volume analysis data generated at a certain time when the ultrasound probe  1  is fixed to the initial position (step S 105 ). 
     Then, the body mark generating unit  152   c  generates a body mark by integrating the body mark of the right or left breast and the probe position mark indicating the initial position of the ultrasound probe  1 , based on the identification result obtained by the right/left identifying unit  152   a  (step S 106 ). 
     Thereafter, the image synthesizing unit  17  synthesizes the latest display image generated by the display image generating unit  151   a  and the body mark generated by the body mark generating unit  152   c  (step S 107 ). The control unit  18  performs control so that the composite image generated by the image synthesizing unit  17  is displayed on the monitor  2  (step S 108 ). 
     When checking the monitor  2  to see the probe-position-mark-attached body mark being displayed, the operator judges whether to continue the image-taking by conducting the rotational scanning of the ultrasound probe  1  or terminate the image-taking. When terminating the image-taking, the operator may press the stop button of the input device  3 . 
     When receiving an image-taking termination request from the operator by way of the input device  3  (yes at step S 109 ), the control unit  18  terminates the process. 
     On the other hand, when an image-taking termination request is not received after step S 108  (no at step S 109 ), the control unit  18  judges whether a new item of volume data (volume analysis data) is collected (step S 110 ). 
     If no new volume data is collected (no at step S 110 ), the ultrasonic diagnostic apparatus is put into standby mode. 
     On the other hand, when a new item of volume data is collected (yes at step S 110 ), the display image generating unit  151   a  generates a display image from the volume display data of the new volume analysis data item (step S 111 ), and the extending direction detecting unit  152   b  detects the rib extending direction from the new volume analysis data item, according to the first or second method (step S 112 ). 
     Then, the extending direction detecting unit  152   b  acquires a relative displacement (rotation angle) with respect to the position of the ultrasound probe  1  at the time of generating the previously collected volume data, based on the relative change of the rib extending direction detected at step S 112  with respect to the rib extending direction previously detected, and thereby determines the position of the ultrasound probe  1  at the time of generating the new volume data item (step S 113 ). When performing the process at step S 113 , the extending direction detecting unit  152   b  determines the position of the ultrasound probe  1  from the relative change of the rib extending direction detected at step S 112  with respect to the rib extending direction detected at the initial position at step S 105 . 
     The body mark generating unit  152   c  generates the body mark by integrating the right or left body mark and the probe position mark indicating the current position of the ultrasound probe  1 , based on the position of the ultrasound probe  1  determined by the extending direction detecting unit  152   b  (step S 114 ). 
     Thereafter, the image synthesizing unit  17  integrates the display image generated by the display image generating unit  151   a  at step S 111  and the body mark generated by the body mark generating unit  152   c  (step S 115 ), and the control unit  18  performs control so that the composite image generated by the image synthesizing unit  17  is displayed on the monitor  2  (step S 116 ). 
     Then, the system returns to step S 109 , where the control unit  18  judges whether an image-taking termination request is received from the operator by way of the input device  3 . When the image-taking termination request is not received (no at step S 109 ), the ultrasonic diagnostic apparatus executes the operations of step S 110  and the subsequent steps. 
     According to the present embodiment, the analysis image generating unit  151   b  generates section images in chronological order from the volume analysis data that is collected by the ultrasound probe  1  transmitting an ultrasound wave down to the region under the ribs in the ultrasonic breast examination. The right/left identifying unit  152   a  calculates the intensity ratio of the heartbeat-related cyclic motion components to the respiration-related cyclic motion components among the cyclic motion components of the region under the ribs in the chronologically generated section images and thereby identifies the right or left breast that is being scanned. 
     Then, the extending direction detecting unit  152   b  performs an edge extracting process on the plane-A images generated by the analysis image generating unit  151   b  from the same volume analysis data, and thereby detects the rib extending direction (the first method). Alternatively, the extending direction detecting unit  152   b  analyzes the brightness histograms of different line segments of interest in the plane-C thickness-added MIP images generated from the same volume analysis data by the analysis image generating unit  151   b , and thereby detects the rib extending direction (the second method). 
     Furthermore, the extending direction detecting unit  152   b  detects the rib extending direction every time the volume analysis data is collected, and thereby determines the position of the ultrasound probe  1  based on the relative displacement of the extending direction and the initial position of the ultrasound probe  1 . The body mark generating unit  152   c  generates a body mark by integrating the right or left body mark determined based on the identification result obtained by the right/left identifying unit  152   a  and the probe position mark indicating the position of the ultrasound probe  1  determined by the extending direction detecting unit  152   b . Then, the image synthesizing unit  17  generates a composite image by integrating the display image generated by the display image generating unit  151   a  from the volume display data in the observation region of the volume analysis data with the body mark generated by the body mark generating unit  152   c , and this composite image is displayed on the monitor  2 . 
     Thus, the operator does not have to manually set the right or left body mark, and identification of the right or left breast that is being scanned and determination of the position of the ultrasound probe  1  can be conducted only with the image processing executed by the ultrasonic diagnostic apparatus to display the body mark together with the probe position mark. Therefore, the positional information of the ultrasound probe at the time of generating an ultrasonic image can be easily obtained, as described above as the main features of the invention. 
     In addition, the display image from which the region under the ribs is removed is displayed together with the positional information of the ultrasound probe  1  so that the doctor would not be disturbed in the image diagnosis. 
     According to the above embodiment, the position of the ultrasound probe  1  is determined based on the initial position of the ultrasound probe  1  and the relative displacement of the rib extending direction, but the present invention is not limited thereto. The position of the ultrasound probe  1  may be determined based on the detected rib extending direction and the anatomical information of the ribs of a healthy body. This technique is now explained with reference to  FIG. 13 .  FIG. 13  is a diagram for explaining the first modification example of the present embodiment. 
     According to the first modification example, the extending direction detecting unit  152   b  detects the rib extending direction, the curvature of the rib extending direction, and the distance of the ribs from the plane-C thickness-added MIP image generated by the analysis image generating unit  151   b , as illustrated in  FIG. 13 . Then, the extending direction detecting unit  152   b  compares the rib extending direction, the curvature of the rib extending direction, and the distance of the ribs with the skeletal information of a healthy body stored in the internal storage unit  19  to determine the position of the ultrasound probe  1 , as illustrated in  FIG. 13 . 
     In this manner, without setting the initial position of the ultrasound probe  1 , the positional information of the ultrasound probe at the time of generating an ultrasonic image can be readily obtained. 
     According to the present embodiment, the rib extending direction is used for determination of the position of the ultrasound probe  1 , but the present invention is not limited thereto. The rib extending direction may be used for the display of the ultrasonic image. This technique is now explained with reference to  FIG. 14 .  FIG. 14  is a diagram for explaining the second modification example of the present embodiment. 
     According to the second modification example, the extending direction detecting unit  152   b  detects the rib extending direction for each item of the volume analysis data to obtain the relative displacement of the rib extending direction. In accordance with the relative displacement of the rib extending direction, the display image generating unit  151   a  generates a panoramic image by, for example, superimposing the plane-C images generated from different items of the volume display data on one another, as illustrated in  FIG. 14 . 
     In this manner, an ultrasonic image that covers all the area in which the ultrasound probe  1  moves is displayed, and thus the effectiveness of the doctor&#39;s image diagnosis incorporating ultrasonic images can be improved. 
     The structural components of the devices illustrated for the above embodiments are to explain the functional concepts, and therefore the devices may not always be physically configured as illustrated. In other words, the separation and integration of the devices is not limited to the illustration in the actual form, and the entire structure or part of the structure may be functionally and physically separated or integrated in any unit in accordance with various loads, usage conditions, and the like. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.