Abstract:
In a system for diagnoses of mammary glands and breasts using radiation and ultrasonic waves in combination, images are correlated for easier visual recognition. The system includes an apparatus for acquiring a radiation image of an object projected on a projection surface, acquiring an ultrasonic slice image of the object along a slice surface substantially orthogonal to the projection surface, and generating first image data representing ultrasonic slice images along slice surfaces, second image data representing a radiation image, and location data representing locations of the slice surfaces on the projection surface; an apparatus for correlating and storing those data; and an apparatus for displaying an ultrasonic slice image based on the first image data, and displaying a radiation image, on which a marker indicating a location of the slice surface on the projection surface is shown, based on the second data and the location data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a medical image diagnostic system to be used for diagnoses of breast cancer or the like by imaging mammary glands and breasts by using radiation and ultrasonic waves in combination. Further, the present invention relates to a medical imaging apparatus, a medical image storage apparatus, and a medical image display apparatus to be used in the medical image diagnostic system. 
     2. Description of a Related Art 
     Conventionally, an imaging method using radiation (X-ray, α-ray, β-ray, γ-ray, electron ray, ultraviolet ray, or the like) is utilized in various fields, and particularly, in the medical field, the method is one of the most important means for diagnoses. Radiation images obtained by X-ray imaging (X-ray mammography) of mammary glands and breasts for breast cancer diagnoses are useful for finding calcification as a precursor, but finding calcification may be difficult depending on the age of a subject. Accordingly, it has been studied to use radiation and ultrasonic wave in combination to make diagnoses based on both radiation images and ultrasonic images. X-ray mammography and ultrasonic imaging have the following features, respectively. 
     X-ray mammography is suitable for exposing calcification as one of early symptoms of a cancer, and enables detection with high sensitivity and high resolving power. Especially, in the case where mammary gland tissues have become atrophied and replaced with fat (so-called “fat breast”) as is the case of postmenopausal women, more information can be obtained by X-ray mammography. However, the X-ray imaging has a disadvantage that detection capability of specific natures of tissues (tissue properties) is low. 
     Further, in an X-ray image, mammary glands are expressed in homogeneous soft tissue density, and thus, the detection of tumor mass is difficult for the case where mammary glands have developed (so-called, “dense breast”) as is the case of adolescent to premenopausal women. Furthermore, in X-ray mammography, only two-dimensional images can be obtained in which an object to be inspected as a solid is projected on a plane. On this account, even when a tumor mass is found, it is difficult to grasp information on the locations in the depth direction, size, and so on of the tumor mass. 
     On the other hand, in ultrasonic imaging, specific natures of tissues (e.g., the difference between a cystic tumor and a solid matter) can be detected, and also, a lobular cancer can be detected. Further, real time observation of images and three-dimensional image generation are possible. However, ultrasonic imaging examination often depends on the skill of an operator such as a doctor in accuracy and provides low reproducibility. Further, it is difficult to observe minute calcification in an ultrasonic image. 
     As described above, X-ray mammography examination and ultrasonic imaging examination have both merits and demerits, and it is desirable that both examinations are performed for reliably finding breast cancer. 
     As a related technology, Japanese Patent Application Publication JP-P2005-312770A discloses an ultrasonic diagnostic apparatus capable of displaying ultrasonic images for observation within a body of an object to be inspected with guide images anatomically and precisely corresponding to the ultrasonic images. The ultrasonic diagnostic apparatus includes image processing control means for generating guide images corresponding to anatomic location and orientation of two-dimensional ultrasonic images based on anatomic image data stored as anatomic image data of a human body in advance, and display means for displaying a plurality of various images including the guide images and two-dimensional ultrasonic images. However, JP-P2005-312770A does not disclose that plural images obtained by respectively using plural different imaging modalities are correlated and displayed. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in view of the above-mentioned problems. A purpose of the present invention is, in a medical image diagnostic system to be used for diagnoses of breast cancer or the like by imaging mammary glands and breasts by using radiation and ultrasonic waves in combination, to correlate radiation images and ultrasonic images for easier visual recognition. 
     In order to accomplish the above-mentioned purpose, a medical image diagnostic system according to one aspect of the present invention includes a medical imaging apparatus for acquiring a radiation image of an object to be inspected projected on a projection surface by applying radiation to the object, acquiring an ultrasonic slice image of the object along a slice surface substantially orthogonal to the projection surface by transmitting ultrasonic waves toward the object and receiving ultrasonic echoes reflected by the object, and generating first image data representing plural ultrasonic slice images along plural slice surfaces, second image data representing at least one radiation image, and location data representing locations of the plural slice surfaces on the projection surface; a medical image storage apparatus for correlating and storing the first image data, the second image data, and the location data generated by the medical imaging apparatus; and a medical image display apparatus for displaying at least one ultrasonic slice image along at least one slice surface based on the first image data loaded from the medical image storage apparatus, and displaying at least one radiation image, on which a marker indicating a location of the at least one slice surface on the projection surface is shown, based on the second image data and the location data loaded from the medical image storage apparatus. 
     According to the present invention, the ultrasonic slice image along the slice surface substantially perpendicular to the projection surface of the radiation image is displayed and the radiation image, on which the location of the slice surface on the projection surface is indicated, is displayed, and therefore, the radiation image and the ultrasonic image are correlated for easier visual recognition. Thereby, detection capabilities of two different imaging modalities can be mutually complemented, and easier grasping of spatial locations and higher detection capability of diseased issues can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a medical image diagnostic system according to one embodiment of the present invention; 
         FIG. 2  is a block diagram showing a detailed configuration of a medical imaging apparatus according to one embodiment of the present invention; 
         FIG. 3  is a side view showing an appearance of an imaging unit of the medical imaging apparatus shown in  FIG. 2 , 
         FIG. 4  is a block diagram showing a configuration of a medical image storage apparatus according to one embodiment of the present invention; 
         FIG. 5  shows an example of radiation images and ultrasonic images displayed on the display unit; 
         FIG. 6  shows a first example of a procedure of scanning the object by moving an ultrasonic probe; 
         FIG. 7  shows a second example of the procedure of scanning the object by moving the ultrasonic probe; 
         FIG. 8  shows a third example of the procedure of scanning the object by moving the ultrasonic probe; and 
         FIG. 9  is a diagram for explanation of correlations between the plural partial images. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be explained in detail with reference to the drawings. The same reference numbers are assigned to the same component elements and the description thereof will be omitted. 
       FIG. 1  is a block diagram showing a configuration of a medical image diagnostic system according to one embodiment of the present invention. As shown in  FIG. 1 , the medical image diagnostic system  100  includes a medical imaging apparatus  110 , a medical image storage apparatus  140 , and a medical image display apparatus  150 . Further, the medical image diagnostic system  100  may include imaging modalities such as an MRI apparatus  120  and a CT apparatus  130 , an image interpretation report creation terminal  160 , and an image interpretation report server  170 . These apparatuses are connected to one another via a network such as LAN (local area network). Furthermore, the medical image diagnostic system  100  may be connected to an RIS (radiology information system). 
     The medical imaging apparatus  110  has an imaging unit  111  for performing radiation imaging and ultrasonic imaging, an imaging control section  112  for controlling imaging operation in the imaging unit  111 , and an interface unit  113  for communication between the medical image storage apparatus  140  and so on and itself via the network. 
     The medical image storage apparatus  140  is a server for PACS (Picture Archiving and Communication System) for storage and management of image data acquired by various imaging modalities such as the medical imaging apparatus  110 , MR apparatus  120 , and CT apparatus. 
     The medical image display apparatus  150  has display units  151  and  152  as high-definition displays (viewers), a display control unit  153  for controlling image display operation in the display units  151  and  152 , an operation unit  154  for an operator to operate for selection of image display contents, and an interface unit  155  for communication between the medical image storage apparatus  140  and so on and itself via the network. 
     The image interpretation report creation terminal  160  is an apparatus for an image interpretation doctor to use for creating image interpretation reports while viewing the medical images displayed on the medical image display apparatus  150 . The report data representing the image interpretation reports created by the image interpretation doctor is stored in the image interpretation report server  170 . 
       FIG. 2  is a block diagram showing a detailed configuration of a medical imaging apparatus according to one embodiment of the present invention. The medical imaging apparatus has both a function of a radiation mammography apparatus for applying radiation to a breast, detecting the radiation transmitted through the breast, and thereby, generating a radiation image, and a function of an ultrasonic diagnostic apparatus for transmitting ultrasonic waves to the breast, receiving ultrasonic echoes reflected within the breast, and thereby, generating ultrasonic images. As below, the case of using an X-ray as radiation will be explained, however, α-ray, β-ray, γ-ray, electron ray, ultraviolet ray, or the like may be used. 
     As shown in  FIG. 2 , the imaging unit  111  has an X-ray tube  10 , a filter  11 , an X-ray detection unit  12  for detecting an X-ray generated by the X-ray tube  10  and transmitted through an object to be inspected  1 , a compression plate  13  for pressing a breast as the object, a compression plate movement mechanism  14  for moving the compression plate  13 , a pressure sensor  15  for detecting pressure applied to the compression plate  13 , an ultrasonic probe  16  including plural ultrasonic transducers for transmitting and receiving ultrasonic waves, an ultrasonic probe movement mechanism  17  for moving the ultrasonic probe  16 , and a location sensor  18  for detecting location of the ultrasonic probe  16 . 
       FIG. 3  is a side view showing an appearance of the imaging unit of the medical imaging apparatus shown in  FIG. 2 . As shown in  FIG. 3 , the imaging unit  111  has an arm part  2 , a support  3  for movably holding the arm part  2  in the vertical direction (Z-axis direction), and a shaft part  4  for connecting the arm  2  to the support  3 . The arm part  2  is provided with the X-ray tube  10 , the filter unit  11 , the X-ray detection unit  12 , an imaging stage  19  located between the X-ray tube  10  and the X-ray detection unit  12 , the compression plate  13  for pressing the object  1  between the imaging stage  19  and itself, the compression plate movement mechanism  14  for moving the compression plate  13  in the vertical direction (Z-axis direction), and the ultrasonic probe  16 . 
     The X-ray tube  10  and the filter  11  form a radiation emitting section. The X-ray tube  10  emits an X-ray when a tube voltage is applied thereto. The filter  11  is made of a material such as molybdenum (Mo) or rhodium (Rh), and selectively transmits a desired wavelength component of plural wavelength components contained in the X-ray emitted by the X-ray tube  10 . The X-ray detection unit  12  is a flat panel X-ray detector (FPD) for imaging an X-ray image by detecting the X-ray transmitted through the object  1  at plural detection points in a two-dimensional region. The X-ray radiated from the X-ray tube  10  and transmitted through the object  1  is applied to the respective detection points, and thereby, detection signals having magnitudes corresponding to the intensity of the X-ray are outputted from the X-ray detection unit  12 . The detection signals are inputted via a cable to an X-ray imaging control section  30  ( FIG. 2 ). 
     The compression plate  13  is provided in parallel to the imaging stage  19 , and the compression plate movement mechanism  14  moves the compression plate  13  in the Z-axis direction. The pressure sensor  15  detects the pressure applied to the compression plate  13  and a movement control unit  20  ( FIG. 2 ) controls the compression plate movement mechanism  14  based on the detection result. The object (breast)  1  is sandwiched by the compression plate  13  and the imaging stage  19 , and X-ray imaging is performed with the homogeneous thickness of the breast. Thereby, a radiation image of the breast projected on the projection surface (the detection surface of the X-ray detection unit  12 ) is acquired. X-ray imaging is performed at least once for each of the right and left breasts. 
     Here, the compression plate  13  is necessary to be optically transparent for positioning when the breast is compressed or confirmation of the compression state, and desirably formed of a material that transmits the X-ray radiated from the X-ray tube  10  and easily propagates ultrasonic waves to be transmitted from the ultrasonic probe  16 . As a material of the compression plate  13 , a resin such as polymethylpentene having suitable values in acoustic impedance that affects the reflectance of ultrasonic waves and attenuation coefficient that affects the attenuation of ultrasonic waves may be used, for example. 
     The ultrasonic probe  16  includes one-dimensionally or two-dimensionally arranged plural ultrasonic transducers. Each ultrasonic transducer transmits ultrasonic waves to the object based on the applied drive signal, and receives ultrasonic echoes reflected from the object and outputs a reception signal. 
     Each ultrasonic transducer is configured by a vibrator in which electrodes are formed on both ends of a material having a piezoelectric property (piezoelectric material) such as a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate), a polymeric piezoelectric element represented by PVDF (polyvinylidene difluoride), or the like. When a voltage is applied to the electrodes of the vibrator by transmitting pulsed or continuous wave electric signals, the piezoelectric material expands and contracts. By the expansion and contraction, pulsed or continuous wave ultrasonic waves are generated from the respective vibrators, and an ultrasonic beam is formed by synthesizing these ultrasonic waves. Further, the respective vibrators expand and contract by receiving propagating ultrasonic waves and generate electric signals. These electric signals are outputted as reception signals of the ultrasonic waves, and inputted to the ultrasonic imaging control section  40  ( FIG. 2 ) via a cable. 
     The ultrasonic probe  16  may be moved in close contact with the compression plate  13 , or, after insertion of an ultrasonic transmission medium such as echo gel between the compression plate  13  and itself, may be moved apart from the compression plate  13 . In either case, the ultrasonic probe  16  moves along an opposite surface to the pressure surface of the compression plate  13  while keeping acoustic connection (coupling) between the surface and itself. Further, the operator may move the ultrasonic probe  16 , or the ultrasonic probe movement mechanism  17  shown in  FIG. 2  may move the ultrasonic probe  16 . As below, the latter case will be explained. 
     Referring to  FIG. 2  again, the imaging control section  112  has the movement control unit  20  for controlling the compression plate movement mechanism  14 , the ultrasonic probe movement mechanism  17 , and so on, the X-ray imaging control section  30 , the ultrasonic imaging control section  40 , a data storage unit  51 , an image processing unit  52 , a control unit  60 , a storage unit  70 , a display unit  80 , and a console  90 . 
     The location of the ultrasonic probe  16  is detected by the location sensor  18  provided in the ultrasonic probe  16 . The movement control unit  20  grasps the location of the ultrasonic probe  16  based on the output signal of the location sensor  18  and controls the ultrasonic probe movement mechanism  17 . Alternatively, plural location indicators that readily reflect ultrasonic waves are provided on the compression plate  13  or imaging stage  19 , and the movement control unit  20  may grasp the location of the ultrasonic probe  16  based on the contents of ultrasonic slice images represented by B-mode image data sequentially generated by a B-mode image data generating unit  46 . The movement control unit  20  generates location data representing a location of a slice surface (slice location) of an ultrasonic slice image. The location data represents an X-coordinate of the ultrasonic probe  16  at radiation imaging, for example, and is correlated to an X-coordinate in the radiation image. 
     The X-ray imaging control section  30  includes a tube voltage and tube current control unit  31 , a high-voltage generating unit  32 , an A/D converter  33 , and a radiation image data generating unit  34 . In the X-ray tube  10 , the X-ray transparency is determined according to the tube voltage applied between the cathode and the anode, and the amount of X-ray emission is determined according to the time integration of the tube current flowing between the cathode and the anode. The tube voltage and tube current control unit  31  adjusts imaging conditions of the tube voltage, tube current, and so on according to target values. The target values of the tube voltage and the tube current may be manually adjusted by the operator using the console  90 . The high-voltage generating unit  32  generates a high voltage to be applied to the X-ray tube  10  under the control of the tube voltage and tube current control unit  31 . The A/D converter  33  converts analog radiation detection signals outputted from the X-ray detection unit  12  into digital signals (radiation detection data), and the radiation image data generating unit  34  generates radiation image data based on the radiation detection data. 
     The ultrasonic imaging control section  40  includes a scan control unit  41 , a transmission circuit  42 , a reception circuit  43 , an A/D converter  44 , a signal processing unit  45 , and a B-mode image data generating unit  46 . The scan control unit  41  sets frequencies and voltages of the drive signals to be applied from the transmission circuit  42  to the respective ultrasonic transducers of the ultrasonic probe  16  and adjusts the frequency and sound pressure of the ultrasonic waves to be transmitted under the control of the movement control unit  20 . Further, the scan control unit  41  has a transmission control function of transmission directions of ultrasonic beams and selecting transmission delay patterns according to the set transmission directions, and a reception control function of sequentially setting reception directions of ultrasonic echoes and selecting reception delay patterns according to the set reception directions. 
     Here, the transmission delay pattern refers to a delay time pattern to be provided to the plural drive signals for forming an ultrasonic beam in a desired direction with the ultrasonic waves transmitted from the plural ultrasonic transducers of the ultrasonic probe  16 , and the reception delay pattern refers to a delay time pattern to be provided to the plural reception signals for extracting ultrasonic echoes from the desired direction with the ultrasonic waves received by the plural ultrasonic transducers. Plural transmission delay patterns and reception delay patterns are stored in a memory or the like. 
     The transmission circuit  42  generates plural drive signals to be respectively applied to the plural ultrasonic transducers. In this regard, the transmission circuit  42  may adjust the amounts of delay of the plural drive signals and supply the signals to the ultrasonic probe  16  so that the ultrasonic waves to be transmitted from the plural ultrasonic transducers form an ultrasonic beam, or may supply plural drive signals to the ultrasonic probe  16  so that the ultrasonic waves to be transmitted at once from the plural ultrasonic transducers reach the entire imaging region of the object. 
     The reception circuit  43  amplifies the plural ultrasonic reception signals respectively outputted from the plural ultrasonic transducers, and the A/D converter  44  converts the analog ultrasonic reception signals amplified by the reception circuit  43  into digital ultrasonic reception signals. The signal processing unit  45  performs reception focus processing by providing the respective delay times to the plural ultrasonic reception signals based on the reception delay pattern selected by the scan control unit  41 , and adding those ultrasonic reception signals. Through the reception focus processing, sound ray data in which the focal point of the ultrasonic echoes is narrowed is formed. 
     Furthermore, the signal processing unit  45  corrects attenuation of the sound ray data by distance according to the depths of the reflection positions of ultrasonic waves through STC (Sensitivity Time gain Control), and then, performs envelope detection processing with a low-pass filter or the like thereon to generate envelope data. 
     The B-mode image data generating unit  46  performs processing such as logarithmic compression and gain adjustment on the envelope data to generate image data, and converts (raster-converts) the image data into image data that follows the normal scan system of television signals to generate B-mode image data. 
     The data storage unit  51  is configured by a hard disk, memory, or the like, and stores the B-mode image data generated by the B-mode image data generating unit  46 . In this regard, the ultrasonic slice images along the respective slice surface are correlated to location data representing the locations of the slice surfaces (slice locations) and stored. 
     The image processing unit  52  performs necessary image processing such as gradation processing on the B-mode data loaded from the data storage unit  51  to generate first image data for display, and performs necessary image processing such as gradation processing on the radiation image data outputted from the radiation image data generating unit  34  to generate second image data for display. Alternatively, the image processing unit  52  may generate first image data representing ultrasonic images of the right and left breasts within one screen and second image data representing radiation images of the right and left breasts within one screen for comparison and observation of the images of the right and left breasts. The image processing unit  52  outputs the first and second image data to the interface unit  113  together with the ultrasonic slice image location data. 
     The control unit  60  controls the respective parts based on the operation of the operator. The display unit  80  is configured by an LCD display or the like, and used for image confirmation at imaging and display of an operation screen or the like. The console  90  is used by the operator to operate the medical imaging apparatus. So far, the movement control unit  20 , the radiation image data generating unit  34 , the scan control unit  41 , the signal processing unit  45 , the B-mode image data generating unit  46 , the image processing unit  52 , and the control unit  60  are configured by a central processing unit (CPU) and software for allowing the CPU to execute various kinds of processing, however, they may be configured by a digital circuit or analog circuit. The software (program) is stored in the storage unit  70  formed by a hard disk, memory, or the like. Further, the transmission delay patterns and the reception delay patterns to be selected by the scan control unit  41  may be stored in the storage unit  70 . 
     The interface unit  113  transmits the first and second image data and the location data outputted from the image processing unit  52  as data files via the network to the medical image storage apparatus  140  ( FIG. 1 ). 
       FIG. 4  is a block diagram showing a configuration of a medical image storage apparatus according to one embodiment of the present invention. The medical image storage apparatus  140  includes an interface unit  141  for communication between the various imaging modalities, medical image display apparatus, and so on and itself via the network, a data management unit  142  for management of image data and so on transmitted from the medical imaging apparatus  110  ( FIG. 1 ) and other imaging modalities, a display unit  143  as an LCD display or the like for displaying an operation screen and so on, an input unit  144  including a keyboard and a mouse used for inputting various commands and so on, a memory  145  for temporarily storing image data and so on, and a hard disk drive  146  and a hard disk  147  forming a storage unit. The hard disk  147  is a recording medium for storing image data and so on as data files. The hard disk drive  146  records and reproduces the image data and so on in the hard disk  147  under the management of the data management unit  142 . 
     The interface unit  141  receives the first and second image data and the local data obtained by the medical imaging apparatus  110  via the network from the medical imaging apparatus  110  ( FIG. 1 ). The data management unit  142  correlates the first image data representing plural ultrasonic slice images along plural slice surfaces, the second image data representing at least one radiation image, and the location data representing locations of the plural slice surfaces on the projection surface to one another based on those data, and allows the storage unit to store the data. 
     The data management unit  142  is configured by a central processing unit (CPU) and software for allowing the CPU to execute various kinds of processing, however, the data management unit  142  may be configured by a digital circuit or analog circuit. The software (program) is stored in the storage unit. 
     The medical image display apparatus  150  shown in  FIG. 1  loads the first and second image data and the location data stored in the medical image storage apparatus  140 , displays at least one ultrasonic slice image along at least one slice surface based on the first image data, and displays at least one radiation image including a marker indicating the at least one slice surface in the projection surface based on the second image data and the location data. 
     For example, the display control unit  153  of the medical image display apparatus outputs the first image data to the display unit  152  and outputs the second image data and the location data to the display unit  151 . Thereby, the ultrasonic image is displayed on the display unit  152 , and the radiation image and the marker are displayed on the display unit  151 . Alternatively, the ultrasonic image, the radiation image, or a synthesized image may be displayed on one display unit. 
     The image processing unit  52  of the medical imaging apparatus shown in  FIG. 2  performs rotation processing and flip (vertical flip) processing of images, and thereby, regarding symmetric organs of the object, generates first image signals representing an ultrasonic slice image of a left tissue along the first slice surface and an ultrasonic slice image of a right tissue along the second slice surface symmetrically with a line segment at a predetermined distance within the object as a central axis. Further, the image processing unit  52  generates second image signals representing a radiation image of the left tissue in which the location of the first slice surface on the projection surface is indicated and a radiation image of the right tissue in which the location of the second slice surface on the projection surface is indicated symmetrically with a line segment at a predetermined distance within the object as a central axis. 
       FIG. 5  shows an example of radiation images and ultrasonic images displayed on the display unit. In this example, ultrasonic images representing right and left breasts are displayed on the display unit  152 , and radiation images representing the right and left breasts and a marker are displayed on the display unit  151 . 
     The image processing unit  52  ( FIG. 2 ) generates first image signals representing an ultrasonic slice image of a left breast (L) along the first slice surface and an ultrasonic slice image of a right breast (R) along the second slice surface symmetrically with respect to the Y-axis direction with a line of the chest wall as a central axis. Further, the image processing unit  52  generates second image signals representing a radiation image of the left breast (L) in which the location of the first slice surface on the projection surface is indicated and a radiation image of the right breast (R) in which the location of the second slice surface on the projection surface is indicated symmetrically with respect to the X-axis direction and the Y-axis direction with a line of the chest wall as a central axis. 
     As shown in  FIG. 5 , in the radiation image displayed on the display unit  151 , the location of the slice surface of the ultrasonic slice image is indicated by the marker (a dashed-dotted line A-A′). An operator is able to move the locations of the markers indicated in the radiation images with respect to the right and left breast together or independently in the vertical direction by operating the operation unit  154  shown in  FIG. 1 . 
     When the operator moves the location of the marker, the display control unit  153  allows the display unit  152  to display an ultrasonic slice image along a slice surface corresponding to the location designated by the marker based on the first image data stored in the medical image storage apparatus  140 . Thereby, the operator is able to observe a region  1   b  of the ultrasonic image corresponding to a region  1   a  of interest in the radiation image. 
     Alternatively, the operator is able to change the ultrasonic images displayed on the display unit  152  with respect to the right and left breast together or independently by operating the operation unit  154  shown in  FIG. 1 . When the operator changes the ultrasonic image, the display control unit  153  changes the location of the marker displayed on the display unit  151  to indicate the location of a slice surface of a new ultrasonic slice image. Thereby, the operator is able to observe the region  1   a  of the radiation image corresponding to the region  1   b  of interest in the ultrasonic image. 
       FIGS. 6-8  show first to third examples of a procedure of scanning the object by moving the ultrasonic probe. The object (breast)  1  is sandwiched between the compression plate  13  and the imaging stage  19 , and the movement control unit  20  controls the ultrasonic probe movement mechanism  17  and the scan control unit  41  so that the ultrasonic probe  16  transmits and receives ultrasonic waves while the ultrasonic probe movement mechanism  17  moves the ultrasonic probe  16 . Thereby, the B-mode image data representing plural ultrasonic slice images of the object  1  along the plural slice surfaces are sequentially generated. Typically, the ultrasonic imaging is performed at least once for the respective right and left breasts. In  FIGS. 6-8 , since the ultrasonic probe  16  is substantially orthogonal to the compression plate  13  and the imaging stage  19 , the respective slice surfaces are substantially orthogonal to the projection surface of X-ray image. 
     In the first example shown in  FIG. 6 , the ultrasonic probe  16  first performs the first scan by transmitting and receiving ultrasonic waves while moving in the positive X-axis direction, then, moves to a predetermined distance in the positive Y-axis direction, and performs the second scan by transmitting and receiving ultrasonic waves while moving in the negative X-axis direction. Such operation is repeated at necessary times, and thereby, plural partial images are acquired over the entire one breast. In the first example, scanning is performed at three times in the X-axis direction, and thus, one ultrasonic slice image is formed by three partial images in the respective slice locations in the X-axis direction. 
     In the second example shown in  FIG. 7 , the ultrasonic probe  16  first performs the first scan by transmitting and receiving ultrasonic waves while moving in the positive X-axis direction, then, moves to a predetermined distance in the negative X-axis direction and the positive Y-axis direction, and performs the second scan by transmitting and receiving ultrasonic waves while moving in the negative X-axis direction. Such operation is repeated at necessary times, and thereby, plural partial images are acquired over the entire one breast. In the second example, scanning is performed at three times in the X-axis direction, and thus, one ultrasonic slice image is formed by three partial images in the respective slice locations in the X-axis direction. 
     In the third example shown in  FIG. 8 , using an ultrasonic probe  16   a  having a substantially large size (the length in the Y-axis direction) compared to the size of the breast, scanning is completed by moving the ultrasonic probe  16   a  once in the positive X-axis direction, and ultrasonic slice images in the respective locations in the X-axis direction are acquired. 
     In the third example shown in  FIG. 8 , since the ultrasonic slice images in the respective locations in the X-axis direction are acquired, the B-mode image data generated by the B-mode image data generating unit  46  represents the respective ultrasonic slice images. On the other hand, since the plural partial images are acquired in the first example shown in  FIG. 6  or in the second example shown in  FIG. 7 , it is necessary to correlate the plural partial images in order to obtain one ultrasonic slice image by synthesizing one set of partial images in each slice location in the X-axis direction. 
       FIG. 9  is a diagram for explanation of correlations between the plural partial images. Here, the case where one ultrasonic slice image is formed by three partial images will be explained. As shown in  FIG. 9 , in slice locations X 1 , X 2 , . . . , X N  in the X-axis direction, partial images K 1 , K 2 , . . . , K N  are acquired by the first scan, partial images L 1 , L 2 , . . . , L N  are acquired by the second scan, and partial images M 1 , M 2 , . . . , M N  are acquired by the third scan. In this case, ultrasonic slice images S 1 , S 2 , . . . , S N  are formed by synthesizing three partial images in the respective slice locations in the X-axis direction. For example, ultrasonic image S 1  is formed by synthesizing the partial image K 1 , the partial image L 1 , and the partial image M 1 . 
     For the purpose, the data storage unit  51  of the medical imaging apparatus shown in  FIG. 2  stores B-mode image data representing plural partial images and information on correlations between the plural partial images. This information includes X-coordinates and Y-coordinates of the ultrasonic probe  16  outputted from the location movement control unit  20  when ultrasonic imaging is performed, for example. The image processing unit  52  forms one ultrasonic slice image by synthesizing one set of partial images represented by the B-mode image data loaded from the data storage unit  51  based on the information on the correlation loaded from the data storage unit  51 . 
     Alternatively, the image processing unit  52  does not necessarily perform the synthesis of partial images, but the data management unit  142  of the medical image storage apparatus shown in  FIG. 4  may store the information on the correlations between plural partial images together with the first and second image data and location data in the storage unit, and the display control unit  153  of the medical image display apparatus shown in  FIG. 1  may synthesize one set of partial images represented by the first image data loaded from the medical image storage apparatus  140  to form one ultrasonic slice image based on the information on the correlation loaded from the medical image storage apparatus  140 . 
     Furthermore, the information on the correlations between plural partial images is not necessarily stored, but the display control unit  153  of the medical image storage apparatus may synthesize one set of partial images represented by the first image data loaded from the medical image storage apparatus  140  to form one ultrasonic slice image by determining the correlations between plural partial images represented by the first image data loaded from the medical image storage apparatus  140  based on the location data, the order of those partial images, and/or contents of those partial images and so on loaded from the medical image storage apparatus  140 .