Patent Publication Number: US-2023157662-A1

Title: Ultrasound image analysis apparatus, ultrasound diagnostic apparatus, and control method for ultrasound image analysis apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2021-191286 filed on Nov. 25, 2021. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ultrasound image analysis apparatus that performs analysis on an ultrasound image obtained by imaging a breast of a subject. 
     In addition, the present invention also relates to an ultrasound diagnostic apparatus including the ultrasound image analysis apparatus and a control method for the ultrasound image analysis apparatus. 
     2. Description of the Related Art 
     In related art, an ultrasound diagnostic apparatus using ultrasound images has been put into practical use in a medical field. In general, an ultrasound diagnostic apparatus includes an ultrasound probe in which a transducer array is provided and an apparatus main body connected to the ultrasound probe. An ultrasound beam is transmitted from the ultrasound probe toward a subject, an ultrasound echo from the subject is received by the ultrasound probe, and a reception signal is electrically processed. Thereby, an ultrasound image is generated. 
     A composition of a fat tissue and a mammary gland tissue in a breast varies from person to person, while an anatomical structure of a breast is common. In the mammary gland tissue, a main mammary duct branches into extralobular mammary ducts, which are connected to numerous lobules. A stroma is present around the lobules, and the mammary gland tissue includes the stroma. It is known that there are two types of stromata around lobules: a peripheral stroma and an edematous stroma. The peripheral stroma is present along a structure from the lobule to the mammary duct, and includes many collagen fibers. On the other hand, the edematous stroma fills a space between the peripheral stromata. In the edematous stroma, substrates are rich, and collagen fibers, fat, and the like coexist. The edematous stroma includes less collagen fibers as compared with the peripheral stroma. 
     In recent years, a concept of risk management for individual patients has spread. On the other hand, it is known that a ratio of a mammary gland region in a breast, particularly, a high density of mammary glands, is a cancer risk factor. The ratio of the mammary gland region in a breast can be measured by using a mammography apparatus. 
     In addition, in Su Hyun Lee et al. “Glandular Tissue Component and Breast Cancer Risk in Mammographically Dense Breasts at Screening Breast US”, Radiology, Volume  301 , Oct. 1, 2021, it is reported that a cancer is likely to occur in a case where a ratio of a glandular tissue component (GTC) region including mammary ducts, lobules, and peripheral stromata in the mammary gland region is high even though the mammary gland region is almost the same. That is, in addition to the ratio of the mammary gland region in the breast, a ratio of the GTC region in the mammary gland region can be a risk factor. This implies a higher risk in patients with less advanced lobular retraction. 
     However, in the mammography apparatus, the peripheral stroma and the edematous stroma cannot be distinguished, and the entire mammary gland tissue is observed as whitish. As a result, a ratio of the GTC region in the mammary gland region cannot be measured. 
     JP2020-18694A discloses an ultrasound diagnostic apparatus that extracts a mammary gland region by detecting a boundary in a depth direction of an ultrasound image and detects a lesion portion existing in the mammary gland region. 
     SUMMARY OF THE INVENTION 
     However, the ultrasound diagnostic apparatus disclosed in JP2020-18694A aims to detect a lesion portion in the mammary gland region, and is not interested in dividing the mammary gland region into finer tissues. As a result, there is a problem that a cancer risk of the mammary gland region cannot be estimated. 
     The present invention has been made to solve such problems in the related art, and an object of the present invention is to provide an ultrasound image analysis apparatus capable of estimating a cancer risk of a mammary gland region based on an ultrasound image. 
     Another object of the present invention is to provide an ultrasound diagnostic apparatus including such an ultrasound image analysis apparatus and a control method for an ultrasound image analysis apparatus. 
     In order to achieve the above objects, according to an aspect of the present invention, there is provided an ultrasound image analysis apparatus including: a mammary gland region detection unit that detects a mammary gland region from an ultrasound image obtained by imaging a breast of a subject; a glandular tissue component region extraction unit that extracts a glandular tissue component region including mammary ducts, lobules, and peripheral stromata in the mammary gland region detected by the mammary gland region detection unit; and a glandular tissue component region ratio calculation unit that calculates a ratio of the glandular tissue component region to the mammary gland region. 
     The mammary gland region detection unit may detect the mammary gland region by image recognition of the ultrasound image. In this case, the ultrasound image analysis apparatus may further include a breast region detection unit that detects a breast region located between a skin and a pectoralis major muscle from the ultrasound image. The mammary gland region detection unit may recognize a front boundary line and a rear boundary line in the breast region detected by the breast region detection unit, and may detect a region between the front boundary line and the rear boundary line, as the mammary gland region. 
     Alternatively, the mammary gland region detection unit may detect the mammary gland region from the ultrasound image by using deep learning. 
     The glandular tissue component region extraction unit may extract the glandular tissue component region by binarizing the mammary gland region of the ultrasound image by using a brightness threshold value. 
     The glandular tissue component region extraction unit may extract the glandular tissue component region from the mammary gland region of the ultrasound image by using deep learning. 
     The glandular tissue component region ratio calculation unit may calculate the ratio of the glandular tissue component region to the mammary gland region based on the number of occupied pixels of the mammary gland region and the number of occupied pixels of the glandular tissue component region in the ultrasound image. 
     The mammary gland region detection unit may detect the mammary gland region from each of a plurality of the ultrasound images obtained by imaging the breast of the subject at a plurality of predetermined locations of the breast of the subject. 
     The glandular tissue component region extraction unit may extract the glandular tissue component region from each of the mammary gland regions of the plurality of ultrasound images. 
     The glandular tissue component region ratio calculation unit may calculate the ratio of the glandular tissue component region to the mammary gland region in each of the plurality of ultrasound images. 
     The glandular tissue component region ratio calculation unit may calculate an average value of ratios of the glandular tissue component regions to the mammary gland regions in the plurality of ultrasound images. 
     The ultrasound image may be a three-dimensional ultrasound image, and the glandular tissue component region ratio calculation unit may calculate the ratio of the glandular tissue component region to the mammary gland region based on a volume of the mammary gland region detected by the mammary gland region detection unit and a volume of the glandular tissue component region extracted by the glandular tissue component region extraction unit. 
     According to another aspect of the present invention, there is provided an ultrasound diagnostic apparatus including: a monitor that displays an ultrasound image obtained by imaging a breast of a subject; and the ultrasound image analysis apparatus, in which the mammary gland region detection unit detects the mammary gland region from the ultrasound image, and the glandular tissue component region ratio calculation unit displays the calculated ratio of the glandular tissue component region to the mammary gland region on the monitor. 
     Further, the ultrasound diagnostic apparatus may further include a mammary gland region ratio calculation unit that calculates a ratio of the mammary gland region to the breast region and displays the calculated ratio on the monitor. In this case, the glandular tissue component region extraction unit may extract the glandular tissue component region in the mammary gland region only in a case where the ratio of the mammary gland region calculated by the mammary gland region ratio calculation unit is higher than a set value. 
     Preferably, the glandular tissue component region extraction unit extracts the glandular tissue component region by binarizing the mammary gland region of the ultrasound image by using a brightness threshold value, and displays a binarized image obtained by binarizing the mammary gland region on the monitor. 
     The brightness threshold value may be a constant value. 
     The glandular tissue component region extraction unit may detect an edge of the glandular tissue component region in the ultrasound image, and may automatically set the brightness threshold value based on a change in brightness value at the detected edge. 
     The ultrasound diagnostic apparatus may further include: a histogram creation unit that creates a histogram of brightness of the mammary gland region in the ultrasound image and displays the created histogram on the monitor. The brightness threshold value may be set by a user based on the histogram, the binarized image, and the ultrasound image which are displayed on the monitor. 
     The ultrasound diagnostic apparatus may further include: a breast schematic diagram generation unit that generates a schematic diagram of the breast on which a plurality of predetermined locations are plotted and displays the schematic diagram on the monitor. 
     The ultrasound diagnostic apparatus may further include: an imaging guide unit that guides a user to perform imaging of the ultrasound images at the plurality of predetermined locations. 
     Preferably, the glandular tissue component region ratio calculation unit stores the calculated ratio of the glandular tissue component region in a tag associated with the ultrasound image. 
     The glandular tissue component region ratio calculation unit may display, on the monitor, a past ratio of the glandular tissue component region that is calculated based on the past ultrasound image of the subject, together with a latest ratio of the glandular tissue component region that is calculated based on the latest ultrasound image of the subject. 
     Preferably, the ultrasound diagnostic apparatus further includes: an ultrasound probe; and an image generation unit that generates the ultrasound image obtained by imaging the breast of the subject by transmitting and receiving an ultrasound beam to and from the subject using the ultrasound probe. 
     According to still another aspect of the present invention, there is provided a control method for an ultrasound image analysis apparatus, the method including: detecting a mammary gland region from an ultrasound image obtained by imaging a breast of a subject; extracting a glandular tissue component region including mammary ducts, lobules, and peripheral stromata in the mammary gland region; and calculating a ratio of the glandular tissue component region to the mammary gland region. 
     According to the present invention, it is possible to estimate a cancer risk of a mammary gland region by detecting, via a mammary gland region detection unit, a mammary gland region from an ultrasound image obtained by imaging a breast of a subject, extracting, via a glandular tissue component region extraction unit, a glandular tissue component region including mammary ducts, lobules, and peripheral stromata in the mammary gland region, and calculating, via a glandular tissue component region ratio calculation unit, a ratio of the glandular tissue component region to the mammary gland region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating a configuration of an ultrasound diagnostic apparatus according to an embodiment 1 of the present invention. 
         FIG.  2    is a block diagram illustrating an internal configuration of a transmission/reception circuit according to the embodiment 1. 
         FIG.  3    is a block diagram illustrating an internal configuration of an image generation unit according to the embodiment 1. 
         FIG.  4    is a diagram illustrating an ultrasound image obtained by imaging a mammary gland region of a subject. 
         FIG.  5    is a diagram illustrating an ultrasound image including a mammary gland region in which a GTC region is imaged. 
         FIG.  6    is a diagram illustrating a binarized image obtained by binarizing the mammary gland region by using a brightness threshold value. 
         FIG.  7    is a flowchart illustrating an operation according to the embodiment 1. 
         FIG.  8    is a block diagram illustrating a configuration of an ultrasound diagnostic apparatus according to an embodiment 2. 
         FIG.  9    is a flowchart illustrating an operation according to the embodiment 2. 
         FIG.  10    is a block diagram illustrating a configuration of an ultrasound diagnostic apparatus according to an embodiment 3. 
         FIG.  11    is a flowchart illustrating an operation according to the embodiment 3. 
         FIG.  12    is a block diagram illustrating a configuration of an ultrasound diagnostic apparatus according to an embodiment 4. 
         FIG.  13    is a diagram illustrating a configuration of a breast schematic diagram generated in the embodiment 4. 
         FIG.  14    is a diagram illustrating a breast schematic diagram with a probe mark. 
         FIG.  15    is a flowchart illustrating an operation according to the embodiment 4. 
         FIG.  16    is a block diagram illustrating a configuration of an ultrasound diagnostic apparatus according to an embodiment 5. 
         FIG.  17    is diagram illustrating a breast schematic diagram and an imaging guide displayed on a monitor in the embodiment 5. 
         FIG.  18    is diagram illustrating another breast schematic diagram and an imaging guide displayed on a monitor in the embodiment 5. 
         FIG.  19    is a flowchart illustrating an operation according to the embodiment 5. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
     A description of components to be described below is based on a representative embodiment of the present invention. On the other hand, the present invention is not limited to such an embodiment. 
     Note that, in this specification, a numerical range represented by using “to” means a range including numerical values described before and after “to”, both ends inclusive, as a lower limit value and an upper limit value. 
     In this specification, it is assumed that terms “identical” and “same” include an error margin which is generally allowed in the technical field. 
     Embodiment 1 
       FIG.  1    illustrates a configuration of an ultrasound diagnostic apparatus  1  according to an embodiment 1 of the present invention. The ultrasound diagnostic apparatus  1  includes an ultrasound probe  2  and an apparatus main body  3 . The ultrasound probe  2  and the apparatus main body  3  are wired-connected to each other via a cable (not illustrated). 
     The ultrasound probe  2  includes a transducer array  21  and a transmission/reception circuit  22  connected to the transducer array  21 . 
     The apparatus main body  3  includes an image generation unit  31  connected to the transmission/reception circuit  22  of the ultrasound probe  2 . A display control unit  32  and a monitor  33  are sequentially connected to the image generation unit  31 , and an image memory  34  is connected to the image generation unit  31 . In addition, a breast region detection unit  35 , a mammary gland region detection unit  36 , a glandular tissue component (GTC) region extraction unit  37 , and a GTC region ratio calculation unit  38  are sequentially connected to the image memory  34 , and the GTC region extraction unit  37  and the GTC region ratio calculation unit  38  are connected to the display control unit  32 . In addition, the mammary gland region detection unit  36  is connected to the GTC region extraction unit  37 . 
     Further, an examination result memory  39  is connected to the GTC region ratio calculation unit  38 . 
     A main body control unit  40  is connected to the image generation unit  31 , the display control unit  32 , the image memory  34 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , and the examination result memory  39 . An input device  41  is connected to the main body control unit  40 . In addition, the transmission/reception circuit  22  of the ultrasound probe  2  is connected to the main body control unit  40 . 
     A processor  42  is configured by the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , and the main body control unit  40 . 
     Further, an ultrasound image analysis apparatus  4  is configured by the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , and the main body control unit  40  in the processor  42 . 
     The transducer array  21  of the ultrasound probe  2  includes a plurality of ultrasound transducers which are one-dimensionally or two-dimensionally arranged. Each of these transducers transmits an ultrasound wave according to a drive signal supplied from the transmission/reception circuit  22 , receives a reflected wave from a subject, and outputs an analog reception signal. Each transducer is configured by, for example, forming electrodes on both ends of a piezoelectric body such as a piezoelectric ceramic represented by lead zirconate titanate (PZT), a polymeric piezoelectric element represented by poly vinylidene di fluoride (PVDF), or a piezoelectric single crystal represented by a lead magnesium niobate-lead titanate solid solution (PMN-PT). 
     The transmission/reception circuit  22  transmits an ultrasound wave from the transducer array  21  and generates a sound ray signal based on the reception signal acquired by the transducer array  21  under a control of the main body control unit  40 . As illustrated in  FIG.  2   , the transmission/reception circuit  22  includes a pulser  23  connected to the transducer array  21 , an amplification unit  24  sequentially connected in series to the transducer array  21 , an analog digital (AD) conversion unit  25 , and a beam former  26 . 
     The pulser  23  includes, for example, a plurality of pulse generators, adjusts a delay amount of each drive signal based on a transmission delay pattern which is selected according to a control signal from the main body control unit  40  such that ultrasound waves to be transmitted from the plurality of transducers of the transducer array  21  form ultrasound beams, and supplies each drive signal with the adjusted delay amount to the plurality of transducers. In this way, in a case where a voltage having a pulse shape or a continuous wave shape is applied to the electrodes of the transducers of the transducer array  21 , the piezoelectric body expands and contracts. Thereby, ultrasound waves having a pulse shape or a continuous wave shape are generated from each transducer, and thus an ultrasound beam is formed from a composite wave of these ultrasound waves. 
     The transmitted ultrasound beam is reflected by an object such as a portion of a subject, and an ultrasound echo propagates toward the transducer array  21  of the ultrasound probe  2 . The ultrasound echo which propagates toward the transducer array  21  in this way is received by each transducer included in the transducer array  21 . At this time, in a case where the propagating ultrasound echo is received, each transducer included in the transducer array  21  expands and contracts. Thereby, a reception signal as an electrical signal is generated, and these reception signals are output to the amplification unit  24 . 
     The amplification unit  24  amplifies the signal which is input from each transducer included in the transducer array  21 , and transmits the amplified signal to the AD conversion unit  25 . The AD conversion unit  25  converts the signal transmitted from the amplification unit  24  into pieces of digital reception data, and transmits the pieces of reception data to the beam former  26 . The beam former  26  performs so-called reception focus processing by applying and adding a delay to each of the pieces of reception data which is converted by the AD conversion unit  25  according to a sound velocity or a sound velocity distribution which is set based on a reception delay pattern selected according to a control signal from the main body control unit  40 . By this reception focus processing, a sound ray signal obtained by performing phasing addition on each of the pieces of reception data which is converted by the AD conversion unit  25  and narrowing down a focus of the ultrasound echo is acquired. 
     As illustrated in  FIG.  3   , the image generation unit  31  of the apparatus main body  3  has a configuration in which a signal processing unit  51 , a digital scan converter (DSC)  52 , and an image processing unit  53  are connected in series. 
     The signal processing unit  51  performs, on the sound ray signal transmitted from the transmission/reception circuit  22  of the ultrasound probe  2 , correction of attenuation due to a distance according to a depth of a reflection position of the ultrasound wave and then performs envelope detection processing. Thereby, an ultrasound image signal (B-mode image signal), which is tomographic image information related to tissues in the subject, is generated. 
     The DSC  52  converts (raster-converts) the ultrasound image signal generated by the signal processing unit  51  into an image signal conforming to a normal television signal scanning method. 
     The image processing unit  53  performs various required image processing such as gradation processing on the ultrasound image signal which is input from the DSC  52 , and then outputs a signal representing the ultrasound image to the display control unit  32  and the image memory  34 . The signal representing the ultrasound image generated by the image generation unit  31  in this way is simply referred to as an ultrasound image. 
     Under a control of the main body control unit  40 , the display control unit  32  performs predetermined processing on the ultrasound image transmitted from the image generation unit  31 , and displays the ultrasound image on the monitor  33 . 
     The monitor  33  displays the ultrasound image under a control of the display control unit  32 , and includes a display device such as a liquid crystal display (LCD) or an organic electroluminescence (EL) display. 
     The image memory  34  is a memory that stores the ultrasound image generated by the image generation unit  31  under a control of the main body control unit  40 . For example, the image memory  34  can store a plurality of frames of ultrasound images generated by the image generation unit  31  in correspondence with diagnosis on a mammary gland region of a breast of a subject. 
     As the image memory  34 , a flash memory, a hard disc drive (HDD), a solid state drive (SSD), a flexible disc (FD), a magneto-optical (MO) disc, a magnetic tape (MT), a random access memory (RAM), a compact disc (CD), a digital versatile disc (DVD), a secure digital (SD) card, and a recording medium such as a Universal Serial Bus (USB) memory can be used. 
     The breast region detection unit  35  detects a breast region of the subject from the ultrasound image generated by the image generation unit  31 .  FIG.  4    illustrates an example of an ultrasound image obtained by imaging a breast of a subject. The ultrasound image is a tomographic image obtained by bringing a tip of the ultrasound probe  2  into contact with the breast of the subject and performing imaging. A skin S of the subject appears in an upper end of the ultrasound image representing the shallowest portion, and a pectoralis major muscle T appears in a lower portion of the ultrasound image representing a deeper portion. The breast region detection unit  35  can recognize the skin S and the pectoralis major muscle T from the ultrasound image, and detect a deep region between the skin S and the pectoralis major muscle T, as a breast region BR. 
     The mammary gland region detection unit  36  detects a mammary gland region of the subject from the ultrasound image generated by the image generation unit  31 . As illustrated in  FIG.  4   , the mammary gland region detection unit  36  can recognize a front boundary line L 1  located on a shallower side and a rear boundary line L 2  located on a deeper side in the breast region BR detected by the breast region detection unit  35 , and detect a deep region between the front boundary line L 1  and the rear boundary line L 2 , as a mammary gland region M. 
     In order to detect the breast region BR and the mammary gland region M described above, image recognition can be performed using at least one of template matching, an image analysis technique using feature amounts such as adaptive boosting (Adaboost), support vector machine (SVM), or scale-invariant feature transform (SIFT), or a determination model learned by using a machine learning technique such as deep learning. 
     Note that the determination model is a learned model obtained by learning the breast region BR and the mammary gland region M (segmentation) of the breast region BR in a learning ultrasound image obtained by imaging the breast. 
     The GTC region extraction unit  37  extracts a GTC region from the mammary gland region M of the subject that is detected by the mammary gland region detection unit  36 . The GTC region includes mammary ducts, lobules, and peripheral stromata in the mammary gland region M, and an edematous stroma fills a space between the peripheral stromata. In the edematous stroma, substrates are rich and adipocytes coexist. For this reason, in a case where the mammary gland region M is observed in an ultrasound image, the edematous stroma has a high echo level and appears with high brightness. On the other hand, the mammary ducts, the lobules, and the peripheral stromata that are included in the GTC region have relatively low echo levels, and have brightness lower than the brightness of the edematous stroma. 
     For this reason, the GTC region extraction unit  37  binarizes the mammary gland region M of the ultrasound image by using, for example, a brightness threshold value Th. Thus, the GTC region and the edematous stroma in the mammary gland region M are distinguished from each other. Thereby, the GTC region can be extracted. 
     For example, as in the ultrasound image illustrated in  FIG.  5   , in a case where the GTC region R 1  and the edematous region R 2  filled with the edematous stroma coexist in the mammary gland region M, by binarizing the mammary gland region M by using an appropriate brightness threshold value Th, a binarized image as illustrated in  FIG.  6    is obtained. 
     In the binarized image of  FIG.  6   , pixels having brightness values lower than the brightness threshold value Th are represented in black (a shaded regions in  FIG.  6   ), and the pixels form a black portion P 1 . In addition, pixels having brightness values equal to or higher than the brightness threshold value Th are represented in white, and the pixels form a white portion P 2 . The black portion P 1  corresponds to the GTC region R 1 , and the white portion P 2  corresponds to the edematous region R 2 . That is, by binarizing the mammary gland region M, the GTC region R 1  can be extracted as the black portion P 1 . 
     The binarized image created by the GTC region extraction unit  37  is displayed on the monitor  33  via the display control unit  32 . 
     Note that a predetermined constant value can be used as the brightness threshold value Th. 
     In addition, the GTC region extraction unit  37  may perform edge detection on the GTC region R 1  of the ultrasound image by image analysis, and automatically calculate a brightness threshold value Th based on a change in brightness values of a detected edge portion, that is, a change in brightness values of a plurality of pixels from the inside to the outside of the GTC region R 1 . In this way, it is possible to automatically set the brightness threshold value Th suitable for the ultrasound image as an image analysis target, and to acquire a binarized image suitable for the ultrasound image. 
     Further, the GTC region extraction unit  37  can also extract the GTC region R 1  by using a determination model which is learned using a machine learning technique such as deep learning. In this case, a learned model obtained by learning the GTC region R 1  (segmentation) of the mammary gland region M in the learning ultrasound image obtained by imaging the breast is used as the determination model. 
     The GTC region ratio calculation unit  38  calculates a ratio of the GTC region R 1  to the mammary gland region M, and displays the calculated ratio on the monitor  33 . Specifically, the GTC region ratio calculation unit  38  receives the mammary gland region M detected by the mammary gland region detection unit  36  and the GTC region R 1  extracted by the GTC region extraction unit  37 , and calculates a GTC region ratio of the GTC region R 1  to the mammary gland region M. 
     In addition, the GTC region ratio calculation unit  38  stores the calculated GTC region ratio in the examination result memory  39 , as an examination result. 
     The GTC region ratio cannot be measured by a mammography apparatus. On the other hand, in the ultrasound diagnostic apparatus according to the embodiment 1, the GTC region ratio can be calculated based on, for example, the number of occupied pixels of the mammary gland region M and the number of occupied pixels of the GTC region R 1  in the ultrasound image. Specifically, the GTC region ratio is represented by a ratio of a sum of the number of occupied pixels of all the GTC regions R 1  existing in the mammary gland region M to the number of occupied pixels of the entire mammary gland region M. 
     The GTC region ratio calculation unit  38  may display the calculated GTC region ratio on the monitor  33  by using a numerical value, or may display the calculated GTC region ratio on the monitor  33  by using a pie graph, a bar graph, or the like. 
     The examination result memory  39  is a memory that stores, as an examination result, the GTC region ratio which is calculated by the GTC region ratio calculation unit  38  under a control of the main body control unit  40 . 
     Similar to the image memory  34 , as the examination result memory  39 , a recording medium such as a flash memory, an HDD, an SSD, an FD, an MO disc, an MT, a RAM, a CD, a DVD, an SD card, a USB memory, or the like can be used. 
     Note that the examination result memory  39  may be either a memory integrated with the image memory  34  or a memory separated from the image memory  34 . 
     In addition, the ultrasound image generated by the image generation unit  31  is represented, for example, as image data with a so-called digital imaging and communications in medicine (DICOM) format in which patient identification information is added. The ultrasound image includes a tag for storing accessory information, and the GTC region ratio which is calculated by the GTC region ratio calculation unit  38  can be stored with a tag associated with the ultrasound image. 
     The main body control unit  40  controls each unit of the apparatus main body  3  and the transmission/reception circuit  22  of the ultrasound probe  2  based on a control program or the like which is stored in advance. 
     In addition, a main-body-side storage unit (not illustrated) is connected to the main body control unit  40 . The main-body-side storage unit stores a control program or the like. In addition, as the main-body-side storage unit, for example, a flash memory, a RAM, an SD card, an SSD, or the like can be used. 
     The input device  41  is a device that allows a user to perform an input operation, and includes, for example, devices such as a keyboard, a mouse, a trackball, a touch pad, and a touch sensor overlapped and provided on the monitor  33 . 
     Note that the processor  42  including the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , and the main body control unit  40  is configured with a central processing unit (CPU) and a control program for causing the CPU to perform various processing. The processor  42  may be configured by using a field programmable gate array (FPGA), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a graphics processing unit (GPU), or other integrated circuits (IC), or may be configured by using a combination thereof. 
     In addition, the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , and the main body control unit  40  of the processor  42  can be partially or entirely integrated into one CPU or the like. 
     The ultrasound image analysis apparatus  4  that includes the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , and the main body control unit  40  of the processor  42  may be configured with an FPGA, a DSP, an ASIC, a GPU, or other ICs independently from the image generation unit  31  and the display control unit  32 . 
     Next, an operation of the ultrasound diagnostic apparatus  1  according to the embodiment 1 will be described with reference to a flowchart illustrated in  FIG.  7   . 
     First, in step S 1 , a breast of a subject is imaged by using the ultrasound probe  2 , and thus an ultrasound image is acquired. At this time, under a control of the main body control unit  40 , transmission and reception of ultrasound waves from the plurality of transducers of the transducer array  21  are started according to a drive signal from the pulser  23  of the transmission/reception circuit  22  of the ultrasound probe  2 . The ultrasound echo from the inside of the breast of the subject is received by the plurality of transducers of the transducer array  21 . The reception signal which is an analog signal is output to the amplification unit  24 , and is amplified by the amplification unit  24 . The amplified reception signal is AD-converted by the AD conversion unit  25 , and thus the reception data is acquired. 
     The reception focus processing is performed on the reception data by the beam former  26 , and the sound ray signal generated by the reception focusing processing is transmitted to the image generation unit  31  of the apparatus main body  3 . An ultrasound image representing tomographic image information of the breast of the subject is generated by the image generation unit  31 . At this time, attenuation correction according to a depth of a reflection position of the ultrasound wave and envelope detection processing are performed on the sound ray signal by the signal processing unit  51  of the image generation unit  31 . The sound ray signal is converted into an image signal conforming to a scanning method of a normal television signal by the DSC  52 , and various required image processing such as gradation processing is performed on the image signal by the image processing unit  53 . 
     Subsequently, in step S 2 , the ultrasound image generated by the image generation unit  31  is displayed on the monitor  33  via the display control unit  32 , and is stored in the image memory  34 . 
     Note that, in a case where an ultrasound image is acquired, under a control of the main body control unit  40 , a transmission intensity of the ultrasound wave and a depth range of the ultrasound image displayed on the monitor  33  are adjusted such that the entire breast of the subject, that is, for example, the deep portion between the skin S and the pectoralis major muscle T of the subject illustrated in  FIG.  4   , is fitted into the screen. 
     In a case where the ultrasound image is stored in the image memory  34  in this way, in step S 3 , the ultrasound image is input to the ultrasound image analysis apparatus  4 , and a breast region BR of the subject is detected from the ultrasound image by the breast region detection unit  35 . For example, as illustrated in  FIG.  4   , the deep region between the skin S of the subject appearing in the shallowest portion of the ultrasound image and the pectoralis major muscle T appearing in the deeper portion is detected as the breast region BR. 
     Further, the ultrasound image is input to the mammary gland region detection unit  36  via the breast region detection unit  35 . The mammary gland region detection unit  36  recognizes the front boundary line L 1  and the rear boundary line L 2  in the breast region BR detected by the breast region detection unit  35 , and detects, as the mammary gland region M, the deep region between the front boundary line L 1  and the rear boundary line L 2 . 
     Next, in step S 4 , the GTC region R 1  is extracted from the mammary gland region M by the GTC region extraction unit  37  of the ultrasound image analysis apparatus  4 , the mammary gland region M being detected by the mammary gland region detection unit  36 . At this time, the GTC region extraction unit  37  binarizes the mammary gland region M of the ultrasound image illustrated in  FIG.  5    by using, for example, a brightness threshold value Th as a predetermined constant value, and thus a binarized image as illustrated in  FIG.  6    is acquired. In the binarized image of  FIG.  6   , the black portion P 1  corresponds to the extracted GTC region R 1 , and the white portion P 2  corresponds to the edematous region R 2  filled with the edematous stroma. 
     The binarized image created by the GTC region extraction unit  37  is displayed on the monitor  33  via the display control unit  32 . 
     Subsequently, in step S 5 , the GTC region ratio of the GTC region R 1  to the mammary gland region M is calculated by the GTC region ratio calculation unit  38  of the ultrasound image analysis apparatus  4 , and the GTC region ratio is displayed on the monitor  33  via the display control unit  32 . At this time, the GTC region ratio calculation unit  38  can calculate the GTC region ratio based on a ratio of the number of occupied pixels of all the GTC regions R 1  existing in the mammary gland region M to the number of occupied pixels of the entire mammary gland region M in the ultrasound image. 
     The calculated GTC region ratio is displayed on the monitor  33 , as a numerical value, a pie graph, a bar graph, or the like, and is also stored in the examination result memory  39 , as an examination result. Further, the calculated GTC region ratio can be stored in a tag with a DICOM format by being associated with the ultrasound image, or can be directly transmitted from the ultrasound diagnostic apparatus  1  to an external diagnostic report system or the like via a network. 
     In this way, the GTC region ratio that cannot be measured by the mammography apparatus is displayed on the monitor  33 . 
     By checking the GTC region ratio displayed on the monitor  33 , it is possible to estimate a cancer risk of the mammary gland region of the subject. 
     In addition, by utilizing a so-called picture archiving and communication system (PACS, a medical image management system) or the like, the DICOM in past examinations of the same subject may be acquired, and the past GTC region ratio stored in the DICOM may be obtained. In this case, the GTC region ratio calculation unit  38  can display the past GTC region ratio on the monitor  33  together with the latest GTC region ratio which is calculated based on the latest ultrasound image of the subject. 
     In a case where the GTC region ratio is not calculated in the past examination, based on the past ultrasound image acquired in the past examination, the past GTC region ratio may be calculated by the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , and the GTC region ratio calculation unit  38 , and the calculated past GTC region ratio may be displayed on the monitor  33  together with the latest GTC region ratio. 
     In the embodiment 1 described above, the ultrasound image generated by the image generation unit  31  is a two-dimensional ultrasound image. On the other hand, the image generation unit  31  can also generate a three-dimensional ultrasound image of the breast of the subject. After acquiring a plurality of two-dimensional ultrasound images on a plurality of different tomographic planes by performing planar scanning on the subject by using the ultrasound probe  2 , a three-dimensional ultrasound image may be generated based on the plurality of two-dimensional ultrasound images. Alternatively, by using a three-dimensional probe instead of the ultrasound probe  2 , a three-dimensional ultrasound image may be generated in a state where the three-dimensional probe is stationary. 
     The mammary gland region M is detected from the three-dimensional ultrasound image by the mammary gland region detection unit  36 , and the GTC region R 1  is extracted from the mammary gland region M of the three-dimensional ultrasound image by the GTC region extraction unit  37 . The GTC region ratio calculation unit  38  can calculate a GTC region ratio of the GTC region R 1  to the mammary gland region M based on a volume of the mammary gland region M detected by the mammary gland region detection unit  36  and a volume of the GTC region R 1  extracted by the GTC region extraction unit  37 . The calculated GTC region ratio is displayed on the monitor  33 , and is stored in the examination result memory  39 . 
     By calculating the GTC region ratio based on the three-dimensional ultrasound image in this way, it is possible to improve accuracy of estimation of a cancer risk of the mammary gland region M of the subject, and perform diagnosis with higher reliability. 
     In the embodiment 1 described above, as an example of the ultrasound diagnostic apparatus  1 , the configuration including the ultrasound probe  2  and the apparatus main body  3  has been described. On the other hand, the example of the ultrasound diagnostic apparatus including the ultrasound image analysis apparatus  4  is not limited thereto. The ultrasound image analysis apparatus  4  can also be applied to an automatic breast ultrasound apparatus including a transducer assembly and a main body that automatically move while the breast is fixed, such as US2015/0094587A. 
     Further, in the embodiment 1 described above, the ultrasound image analysis apparatus  4  is provided inside the ultrasound diagnostic apparatus  1 . On the other hand, the present invention is not limited thereto. The ultrasound image analysis apparatus  4  can be used separately from the ultrasound diagnostic apparatus  1 . For example, the ultrasound image analysis apparatus  4  may be provided inside a server or the like (not illustrated) connected to a general-purpose ultrasound imaging apparatus via a network, an ultrasound image obtained by imaging the breast of the subject may be transmitted to the server by the general-purpose ultrasound imaging apparatus, and the GTC region ratio may be calculated by the ultrasound image analysis apparatus  4 . Further, for example, as described in JP2008-161283A, JP2019-69319A, and the like, the ultrasound image analysis apparatus  4  may be provided in a mammography apparatus having an ultrasound measurement function, and the GTC region ratio can be calculated inside the mammography apparatus. 
     Embodiment 2 
       FIG.  8    illustrates a configuration of an ultrasound diagnostic apparatus  1 A according to an embodiment 2. In the ultrasound diagnostic apparatus  1 A, an ultrasound probe  2  is connected to an apparatus main body  3 A. The apparatus main body  3 A is obtained by newly adding a mammary gland region ratio calculation unit  61  to the apparatus main body  3  of the ultrasound diagnostic apparatus  1  according to the embodiment 1 illustrated in  FIG.  1    and using a main body control unit  40 A instead of the main body control unit  40 . Other configurations are the same as those of the apparatus main body  3  according to the embodiment 1. 
     The ultrasound diagnostic apparatus  1 A according to the embodiment 2 is configured to calculate not only the GTC region ratio of the GTC region R 1  to the mammary gland region M but also a ratio of the mammary gland region M to the breast region BR and to display the calculated ratios on the monitor  33 . 
     The breast region detection unit  35  and the mammary gland region detection unit  36  are connected to the mammary gland region ratio calculation unit  61 , and the mammary gland region ratio calculation unit  61  is connected to the display control unit  32 , the GTC region extraction unit  37 , and the examination result memory  39 . 
     A main body control unit  40 A is connected to the image generation unit  31 , the display control unit  32 , the image memory  34 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the examination result memory  39 , and the mammary gland region ratio calculation unit  61 . An input device  41  is connected to the main body control unit  40 A. 
     A processor  42 A is configured by the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the main body control unit  40 A, and the mammary gland region ratio calculation unit  61 . 
     The mammary gland region ratio calculation unit  61  receives the detection result of the breast region BR by the breast region detection unit  35  and the detection result of the mammary gland region M by the mammary gland region detection unit  36 , and calculates a ratio of the mammary gland region M to the breast region BR. 
     An operation of the ultrasound diagnostic apparatus  1 A according to the embodiment 2 will be described with reference to a flowchart illustrated in  FIG.  9   . 
     Processing of step S 1  to step S 5  is the same as processing of step S 1  to step S 5  of the flowchart according to the embodiment 1 illustrated in  FIG.  7   . That is, in step S 1 , an ultrasound image is acquired by imaging the breast of the subject, and in step S 2 , the ultrasound image is displayed on the monitor  33 . In step S 3 , the breast region BR is detected from the ultrasound image by the breast region detection unit  35 , and the mammary gland region M is detected by the mammary gland region detection unit  36 . In step S 4 , the GTC region R 1  is extracted from the mammary gland region M by the GTC region extraction unit  37 . In step S 5 , the GTC region ratio of the GTC region R 1  to the mammary gland region M is calculated by the GTC region ratio calculation unit  38 , and the calculated GTC region ratio is displayed on the monitor  33 . 
     Further, in the embodiment 2, subsequently, in step S 6 , a ratio of the mammary gland region M to the breast region BR is calculated by the mammary gland region ratio calculation unit  61  based on the breast region BR detected by the breast region detection unit  35  and the mammary gland region M detected by the mammary gland region detection unit  36 , and the calculated ratio is displayed on the monitor  33  via the display control unit  32  and is stored in the examination result memory  39 , as the examination result. 
     The ratio of the mammary gland region M to the breast region BR is known as a cancer risk factor, and can be measured by a mammography apparatus. On the other hand, according to the ultrasound diagnostic apparatus  1 A of the embodiment 2, the mammary gland region ratio calculation unit  61  can calculate the ratio of the mammary gland region M to the breast region BR based on the ultrasound image generated by the image generation unit  31  without using a mammography apparatus. 
     Therefore, it is possible to estimate a cancer risk of the mammary gland region M of the subject with high accuracy, based on both the GTC region ratio that is calculated by the GTC region ratio calculation unit  38  and the ratio of the mammary gland region M to the breast region BR that is calculated by the mammary gland region ratio calculation unit  61 . 
     In a case where the mammary glands retract and the volume of the breast decreases, fat regions increase on a side shallower than the front boundary line L 1  illustrated in  FIG.  4    and a side deeper than the rear boundary line L 2  illustrated in  FIG.  4   . Further, in a case where fat regions occur between lobes in the mammary gland, the ratio of the mammary gland region M to the breast region BR may decrease. In a case where the ratio of the mammary gland region M to the breast region BR decreases, the cancer risk is also decreased. Thus, the GTC region extraction unit  37  may be configured to extract the GTC region R 1  in the mammary gland region M only in a case where the ratio of the mammary gland region M detected by the mammary gland region ratio calculation unit  61  is higher than a set value. 
     That is, in a case where the ratio of the mammary gland region M detected by the mammary gland region ratio calculation unit  61  is higher than the set value, the GTC region R 1  is extracted from the mammary gland region M by the GTC region extraction unit  37 , and the GTC region ratio is calculated by the GTC region ratio calculation unit  38 . The calculated GTC region ratio is displayed on the monitor  33 . On the other hand, in a case where the ratio of the mammary gland region M detected by the mammary gland region ratio calculation unit  61  is equal to or lower than the set value, extraction of the GTC region R 1  is not performed by the GTC region extraction unit  37 , and thus calculation of the GTC region ratio is not also performed by the GTC region ratio calculation unit  38 . 
     Embodiment 3 
       FIG.  10    illustrates a configuration of an ultrasound diagnostic apparatus  1 B according to an embodiment 3. In the ultrasound diagnostic apparatus  1 B, an ultrasound probe  2  is connected to an apparatus main body  3 B. The apparatus main body  3 B is obtained by newly adding a histogram creation unit  62  to the apparatus main body  3  of the ultrasound diagnostic apparatus  1  according to the embodiment 1 illustrated in  FIG.  1    and using a main body control unit  40 B instead of the main body control unit  40 . Other configurations are the same as those of the apparatus main body  3  according to the embodiment 1. 
     The ultrasound diagnostic apparatus  1 B according to the embodiment 3 is configured to allow the user to input the brightness threshold value Th which is used in a case where the GTC region extraction unit  37  creates a binarized image. 
     The mammary gland region detection unit  36  is connected to the histogram creation unit  62 , and the histogram creation unit  62  is also connected to the display control unit  32 . 
     A main body control unit  40 B is connected to the image generation unit  31 , the display control unit  32 , the image memory  34 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the examination result memory  39 , and the histogram creation unit  62 . An input device  41  is connected to the main body control unit  40 B. 
     A processor  42 B is configured by the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the main body control unit  40 B, and the histogram creation unit  62 . 
     The histogram creation unit  62  creates a histogram of brightness of the mammary gland region M detected from the ultrasound image by the mammary gland region detection unit  36 , and displays the created histogram on the monitor  33  via the display control unit  32 . 
     An operation of the ultrasound diagnostic apparatus  1 B according to the embodiment 3 will be described with reference to a flowchart illustrated in  FIG.  11   . 
     Processing of step S 1  to step S 3  is the same as processing of step S 1  to step S 3  of the flowchart according to the embodiment 1 illustrated in  FIG.  7   . That is, in step S 1 , an ultrasound image is acquired by imaging the breast of the subject, and in step S 2 , the ultrasound image is displayed on the monitor  33 . In step S 3 , the breast region BR is detected from the ultrasound image by the breast region detection unit  35 , and the mammary gland region M is detected by the mammary gland region detection unit  36 . 
     In the embodiment 3, subsequently, in step S 7 , a histogram of brightness of the mammary gland region M in the ultrasound image is created by the histogram creation unit  62 , and the created histogram is displayed on the monitor  33  via the display control unit  32 . 
     Further, in step S 8 , the mammary gland region M is binarized by the GTC region extraction unit  37  by using an initial value of the brightness threshold value Th, and the binarized image as illustrated in  FIG.  6    is displayed on the monitor  33  via the display control unit  32 . 
     In this way, the histogram created by the histogram creation unit  62 , the binarized image created by the GTC region extraction unit  37 , and the ultrasound image generated by the image generation unit  31  are displayed on the monitor  33 . 
     Next, in step S 9 , whether or not the binarized image is good is determined by the user&#39;s visual comparison of the binarized image displayed on the monitor  33  with the ultrasound image. Specifically, it is determined whether or not the binarized image created by the GTC region extraction unit  37  matches with the ultrasound image generated by the image generation unit  31 . 
     For example, in the binarized image as illustrated in  FIG.  6   , in a case where it is determined by the user that a black portion P 1  properly represents the GTC region R 1  appearing in the mammary gland region M of the ultrasound image as illustrated in  FIG.  5    in the size and the shape, it is determined that the binarized image is good. On the other hand, in a case where it is determined by the user that a black portion P 1  of the binarized image is quite different from the GTC region R 1  appearing in the mammary gland region M of the ultrasound image in the size and the shape, it is determined that the binarized image is not good. 
     In a case where it is determined in step S 9  that the binarized image is not good, the processing proceeds to step S 10 , and a new brightness threshold value Th is input by the user via the input device  41  based on the histogram, the binarized image, and the ultrasound image displayed on the monitor  33 . 
     Thereafter, returning to step S 8 , a binarized image is created by using the new brightness threshold value Th which is input in step S 10  by the GTC region extraction unit  37 , and the binarized image is displayed on the monitor  33 . Further, in step S 9 , whether or not the binarized image is good is determined again by the user. 
     In this way, processing of step S 8  to step S 10  is repeated until it is determined in step S 9  that the binarized image is good. 
     In addition, in a case where it is determined in step S 9  that the binarized image is good, the processing proceeds to step S 4 , and processing of step S 4  and processing of step S 5  are sequentially executed. The processing of step S 4  and the processing of step S 5  are the same as processing of step S 4  and processing of step S 5  in the flowchart according to the embodiment 1 illustrated in  FIG.  7   . That is, in step S 4 , the GTC region R 1  is extracted from the mammary gland region M by using the binarized image by the GTC region extraction unit  37 . In step S 5 , the GTC region ratio of the GTC region R 1  to the mammary gland region M is calculated by the GTC region ratio calculation unit  38 , and the GTC region ratio is displayed on the monitor  33 . 
     As in the embodiment 3 described above, the histogram of brightness of the mammary gland region M that is created by the histogram creation unit  62  is displayed on the monitor  33 , and a new brightness threshold value Th is input by the user based on the histogram, the binarized image, and the ultrasound image displayed on the monitor  33 . Thereby, the GTC region extraction unit  37  can more accurately extract the GTC region R 1  from the mammary gland region M. Therefore, it is possible to estimate a cancer risk of the mammary gland region M of the subject with high accuracy. 
     Embodiment 4 
       FIG.  12    illustrates a configuration of an ultrasound diagnostic apparatus  1 C according to an embodiment 4. In the ultrasound diagnostic apparatus  1 C, an ultrasound probe  2  is connected to an apparatus main body  3 C. The apparatus main body  3 C is obtained by newly adding a breast schematic diagram generation unit  63  to the apparatus main body  3  of the ultrasound diagnostic apparatus  1  according to the embodiment 1 illustrated in  FIG.  1    and using a main body control unit  40 C instead of the main body control unit  40 . Other configurations are the same as those of the apparatus main body  3  according to the embodiment 1. 
     The ultrasound diagnostic apparatus  1 C according to the embodiment 4 is configured to perform imaging of a plurality of ultrasound images at a plurality of predetermined locations of the breast and to calculate the GTC region ratio based on the plurality of ultrasound images. 
     The breast schematic diagram generation unit  63  is connected to the display control unit  32 . 
     A main body control unit  40 C is connected to the image generation unit  31 , the display control unit  32 , the image memory  34 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the examination result memory  39 , and the breast schematic diagram generation unit  63 . An input device  41  is connected to the main body control unit  40 C. 
     A processor  42 C is configured by the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the main body control unit  40 C, and the breast schematic diagram generation unit  63 . 
     In one ultrasound image obtained by bring the ultrasound probe  2  to come into contact with one location of the breast of the subject and imaging the breast of the subject, only a local tomographic plane of the breast can be seen. For this reason, in the ultrasound diagnostic apparatus  1 C according to the embodiment 4, imaging of the ultrasound images is performed by using the ultrasound probe  2  at the plurality of predetermined locations of the breast. 
     Therefore, the breast schematic diagram generation unit  63  generates, for example, a breast schematic diagram (also referred to as a schema or a body mark)  71  as illustrated in  FIG.  13   . The breast schematic diagram  71  illustrated in  FIG.  13    schematically represents a left breast when viewed from the front, and includes a circle-shaped breast region BR and a substantially-triangle-shaped axillary region  73  representing an armpit and extending obliquely upward from the breast region BR. The breast region BR is divided into four regions including an inner upper region A, an inner lower region B, an outer upper region C, and an outer lower region D of the breast. The axillary region  73  is connected to a left oblique upper portion of the outer upper region C. 
     By horizontally inverting the breast schematic diagram  71  illustrated in  FIG.  13   , a breast schematic diagram schematically representing a right breast is obtained. 
     The breast schematic diagram generation unit  63  generates a breast schematic diagram  71  in which the plurality of predetermined locations for imaging the ultrasound images by bring the ultrasound probe  2  come to into contact with the breast are plotted as probe marks  74  as illustrated in  FIG.  14   , by using the inner upper region A, the inner lower region B, the outer upper region C, and the outer lower region D obtained by dividing the breast region BR into four. The generated breast schematic diagram  71  is displayed on the monitor  33 . 
     In the breast schematic diagram  71  of  FIG.  14   , the probe marks  74  are plotted in all the four regions obtained by dividing the breast region BR. The probe mark  74  is represented by a line segment having a predetermined length, and not only indicates a position of each of the plurality of locations with which the ultrasound probe  2  is brought into contact but also indicates a direction of the ultrasound probe  2  which is brought into contact with each location by a direction of the line segment. 
     In the ultrasound diagnostic apparatus  1 C according to the embodiment 4, the breast region detection unit  35  detects the breast region BR from each of the plurality of ultrasound images obtained by performing imaging at the plurality of locations defined by the breast schematic diagram  71 . The mammary gland region detection unit  36  detects the mammary gland region M from the breast region BR of each of the plurality of ultrasound images. The GTC region extraction unit  37  extracts the GTC region R 1  from the mammary gland region M of each of the plurality of ultrasound images. In addition, the GTC region ratio calculation unit  38  calculates a ratio of the GTC region R 1  to the mammary gland region M in each of the plurality of ultrasound images. The calculated ratio is displayed on the monitor  33  via the display control unit  32 . 
     An operation of the ultrasound diagnostic apparatus  1 C according to the embodiment 4 will be described with reference to a flowchart illustrated in  FIG.  15   . 
     First, in step S 11 , a breast schematic diagram  71  as illustrated in  FIG.  14    is generated by the breast schematic diagram generation unit  63 , and the breast schematic diagram  71  is displayed on the monitor  33  via the display control unit  32 . In the breast schematic diagram  71  illustrated in  FIG.  14   , the probe marks  74  are plotted in all the four regions obtained by dividing the breast region BR. 
     In step S 12 , the user confirms the breast schematic diagram  71  displayed on the monitor  33 , and performs imaging of an ultrasound image according to the probe mark  74  plotted in one region of the four regions. That is, the ultrasound probe  2  is brought into contact with the breast of the subject in accordance with the position and the direction indicated by the probe mark  74 . In this state, the plurality of transducers of the transducer array  21  start transmission and reception of ultrasound waves, and ultrasound echoes from the inside of the breast of the subject are received by the plurality of transducers of the transducer array  21 . 
     Processing of step S 1  to step S 5  that is subsequent to step S 12  is the same as processing of step S 1  to step S 5  of the flowchart according to the embodiment 1 illustrated in  FIG.  7   . In step S 1 , an ultrasound image is acquired, and in step S 2 , the ultrasound image is displayed on the monitor  33 . In step S 3 , the mammary gland region M is detected from the ultrasound image. In step S 4 , the GTC region R 1  is extracted from the mammary gland region M. In step S 5 , the GTC region ratio of the GTC region R 1  to the mammary gland region M is calculated, and the calculated GTC region ratio is displayed on the monitor  33 . 
     Thereafter, in step S 13 , it is determined whether or not imaging of ultrasound images at a plurality of predetermined locations is completed. Here, imaging according to a first probe mark  74  of the four probe marks  74  plotted on the breast schematic diagram  71  is completed, and imaging according to the remaining three probe marks  74  is not performed. Thus, it is determined that imaging at the plurality of locations is not yet completed, and the processing returns from step S 13  to step S 12 . 
     In step S 12 , imaging according to a second probe mark  74  is performed. Subsequently, in step S 1  to step S 5 , a GTC region ratio based on the ultrasound image acquired according to the second probe mark  74  is calculated, and the calculated GTC region ratio is displayed on the monitor  33 . Thereafter, in step S 13 , it is determined whether or not imaging at the plurality of locations is completed. 
     Similarly, processing of step S 12 , step S 1  to step S 5 , and step S 13  is repeated until imaging of ultrasound images according to all the four probe marks  74  plotted on the breast schematic diagram  71  is completed. 
     In addition, in a case where it is determined in step S 13  that imaging of ultrasound images according to all the four probe marks  74  is completed, a series of processing is completed. 
     Thereby, the GTC region ratio in each of four tomographic planes corresponding to the four probe marks  74  on the breast schematic diagram  71  is calculated, and the calculated GTC region ratio is displayed on the monitor  33 . 
     By calculating the GTC region ratio based on the plurality of ultrasound images obtained by performing imaging at the plurality of locations, it is possible to improve accuracy of estimation of a cancer risk of the mammary gland region M of the subject, and perform diagnosis with higher reliability. 
     The GTC region ratio calculation unit  38  may display a plurality of GTC region ratios calculated at the plurality of predetermined locations on the monitor  33 . Alternatively, the GTC region ratio calculation unit  38  may calculate an average value of a plurality of GTC region ratios at the plurality of locations and display the average value on the monitor  33  instead of the plurality of GTC region ratios or together with the plurality of GTC region ratios. 
     In the breast schematic diagram  71  illustrated in  FIG.  14   , the probe marks  74  are plotted in all the four regions obtained by dividing the breast region BR. On the other hand, the probe marks  74  may be plotted in two or more regions of the four regions instead of all the four regions. Further, the number of regions obtained by dividing the breast region BR is not limited to four. For example, the breast region BR may be divided into two regions or eight regions. 
     Further, instead of plotting the probe marks  74  in the regions obtained by dividing the breast region BR, as illustrated in  FIG.  13   , only regions such as the inner upper region A, the inner lower region B, the outer upper region C, and the outer lower region D are designated in the breast schematic diagram  71 , and the user may perform imaging of an ultrasound image at a certain position in the designated region. 
     The number of divided regions in the breast schematic diagram  71 , the number of the probe marks  74  to be plotted, and the like may be automatically set by the breast schematic diagram generation unit  63  under a control of the main body control unit  40 C, or may be manually set by the user via the input device  41 . 
     Embodiment 5 
       FIG.  16    illustrates a configuration of an ultrasound diagnostic apparatus  1 D according to an embodiment 5. In the ultrasound diagnostic apparatus  1 D, an ultrasound probe  2  is connected to an apparatus main body  3 D. The apparatus main body  3 D is obtained by newly adding an imaging guide unit  64  to the apparatus main body  3 C of the ultrasound diagnostic apparatus  1 C according to the embodiment 4 illustrated in  FIG.  12    and using a main body control unit  40 D instead of the main body control unit  40 C. Other configurations are the same as those of the apparatus main body  3 C according to the embodiment 4. 
     The ultrasound diagnostic apparatus  1 D according to the embodiment 5 is configured to guide imaging of ultrasound images at a plurality of predetermined locations of the breast. 
     The imaging guide unit  64  is connected to the display control unit  32 . 
     A main body control unit  40 D is connected to the image generation unit  31 , the display control unit  32 , the image memory  34 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the examination result memory  39 , the breast schematic diagram generation unit  63 , and the imaging guide unit  64 . An input device  41  is connected to the main body control unit  40 D. 
     A processor  42 D is configured by the image generation unit  31 , the display control unit  32 , the breast region detection unit  35 , the mammary gland region detection unit  36 , the GTC region extraction unit  37 , the GTC region ratio calculation unit  38 , the main body control unit  40 D, the breast schematic diagram generation unit  63 , and the imaging guide unit  64 . 
     The imaging guide unit  64  guides imaging of ultrasound images at a plurality of locations indicated by the probe marks  74  in the breast schematic diagram  71 . 
     In the embodiment 5, an order of imaging at a plurality of predetermined locations is set in advance by, for example, the user. The breast schematic diagram generation unit  63  generates a breast schematic diagram  71  in which a probe mark  74  indicating a location at which next imaging is to be performed among the plurality of predetermined locations is plotted, and the breast schematic diagram  71  is displayed on the monitor  33 . 
     As illustrated in  FIG.  17   , the imaging guide unit  64  creates a guide  75 A which corresponds to one probe mark  74 A plotted in the breast schematic diagram  71  and includes a text, for example, “Place the probe here and perform imaging such that the pectoralis major muscle can be seen”, and displays the guide  75 A on the monitor  33 . 
     In a case where imaging according to the probe mark  74 A is completed, as illustrated in  FIG.  18   , the breast schematic diagram generation unit  63  displays, on the monitor  33 , the breast schematic diagram  71  in which a probe mark  74 B indicating a location at which next imaging is to be performed is plotted, and the imaging guide unit  64  creates a guide  75 B which corresponds to the probe mark  74 B and includes a text, for example, “Please perform imaging of this portion next” and displays the guide  75 B on the monitor  33 . 
     In this way, the imaging guide unit  64  guides imaging of ultrasound images corresponding to the probe marks  74  in the breast schematic diagram  71  displayed on the monitor  33 . 
     As illustrated in  FIG.  17    and  FIG.  18   , in a case where the guides  75 A and  75 B are positioned so as not to overlap the probe marks  74 A and  74 B plotted on the breast schematic diagram  71 , the guides  75 A and  75 B can be displayed by being superimposed on a part of the breast schematic diagram  71 . Alternatively, the guides  75 A and  75 B may be displayed at a position separated from the breast schematic diagram  71 . 
     An operation of the ultrasound diagnostic apparatus  1 D according to the embodiment 5 will be described with reference to a flowchart illustrated in  FIG.  19   . 
     First, in step S 11 , as illustrated in  FIG.  17   , a breast schematic diagram  71  in which one probe mark  74 A indicating a location at which first imaging is to be performed among the plurality of predetermined locations is plotted is displayed on the monitor  33  by the breast schematic diagram generation unit  63 . Further, in step S 14 , a guide  75 A corresponding to the probe mark  74 A is displayed on the monitor  33  by the imaging guide unit  64 . 
     Subsequent processing of step S 12  and step S 1  to step S 5  is the same as processing of step S 12  and step S 1  to step S 5  of the flowchart according to the embodiment 4 illustrated in  FIG.  15   . Imaging of an ultrasound image is performed according to the probe mark  74 A of the breast schematic diagram  71 . Further, a GTC region ratio of the GTC region R 1  to the mammary gland region M is calculated, and the GTC region ratio is displayed on the monitor  33 . 
     In step S 5 , the GTC region ratio calculation unit  38  may display a plurality of GTC region ratios calculated at the plurality of predetermined locations on the monitor  33 . Alternatively, the GTC region ratio calculation unit  38  may calculate an average value of a plurality of GTC region ratios at the plurality of locations and display the average value on the monitor  33  instead of the plurality of GTC region ratios or together with the plurality of GTC region ratios. 
     Thereafter, in step S 13 , as in the embodiment 4, it is determined whether or not imaging of ultrasound images at a plurality of predetermined locations is completed. Here, since only the first imaging is completed according to the probe mark  74 A, the processing returns from step S 13  to step S 11 . 
     In step S 11 , for example, as illustrated in  FIG.  18   , a breast schematic diagram  71  in which a probe mark  74 B indicating a location at which second imaging is to be performed among the plurality of predetermined locations is plotted is displayed on the monitor  33  by the breast schematic diagram generation unit  63 . In subsequent step S 14 , a guide  75 B corresponding to the probe mark  74 B is displayed on the monitor  33  by the imaging guide unit  64 . 
     In subsequent step S 12  and step S 1  to step S 5 , the imaging at the second location is performed according to the probe mark  74 B. In addition, a GTC region ratio of the GTC region R 1  to the mammary gland region M is calculated, and the calculated GTC region ratio is displayed on the monitor  33 . Further, in step S 13 , it is determined whether or not imaging at the plurality of locations is completed. 
     In this way, processing of step S 11 , step S 14 , step S 12 , step S 1  to step S 5 , and step S 13  is repeated until all imaging at the plurality of predetermined locations is completed. 
     Further, in step S 13 , in a case where it is determined that all imaging at the plurality of predetermined locations is completed, a series of processing is completed. 
     In this way, the breast schematic diagram generation unit  63  displays, on the monitor  33 , the breast schematic diagram  71  in which the probe mark  74  indicating a location for next imaging is plotted, and the imaging guide unit  64  displays, on the monitor  33 , the guide  75 B corresponding to the probe mark  74  indicating a location for next imaging. Thereby, even in a case of a user who is not skilled in imaging of ultrasound images of a breast, it is possible to accurately and quickly perform imaging and to display the GTC region ratio on the monitor  33 . 
     In the embodiment 5, the apparatus main body  3 D may include a speaker (not illustrated), and the imaging guide unit  64  may provide a voice guide for imaging at the plurality of predetermined locations via the speaker. 
     The method of connecting the ultrasound probe  2  and the apparatus main body  3  in the embodiments 1 to 5 is not particularly limited, and a wired connection method or a wireless connection method may be used. 
     In the embodiments 1 to 5, the ultrasound probe  2  includes the transmission/reception circuit  22 . On the other hand, the apparatus main body  3  may include the transmission/reception circuit  22 . In addition, the apparatus main body  3  includes the image generation unit  31 . On the other hand, the ultrasound probe  2  may include the image generation unit  31 . Further, the image generation unit  31  illustrated in  FIG.  3    includes the signal processing unit  51 , the DSC  52 , and the image processing unit  53 . On the other hand, the ultrasound probe  2  may include only the signal processing unit  51 , and the apparatus main body  3  may include the DSC  52  and the image processing unit  53 . 
     In addition, in the embodiments 1 to 5, as the apparatus main body  3 , a portable or handheld compact apparatus main body can be used, and a stationary apparatus main body can also be used. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               1 ,  1 A,  1 B,  1 C,  1 D: ultrasound diagnostic apparatus 
               2 : ultrasound probe 
               3 ,  3 A,  3 B,  3 C,  3 D: apparatus main body 
               4 : ultrasound image analysis apparatus 
               21 : transducer array 
               22 : transmission/reception circuit 
               23 : pulser 
               24 : amplification unit 
               25 : AD conversion unit 
               26 : beam former 
               31 : image generation unit 
               32 : display control unit 
               33 : monitor 
               34 : image memory 
               35 : breast region detection unit 
               36 : mammary gland region detection unit 
               37 : GTC region extraction unit 
               38 : GTC region ratio calculation unit 
               39 : examination result memory 
               40 ,  40 A,  40 B,  40 C,  40 D: main body control unit 
               41 : input device 
               42 ,  42 A,  42 B,  42 C,  42 D: processor 
               51 : signal processing unit 
               52 : DSC 
               53 : image processing unit 
               61 : mammary gland region ratio calculation unit 
               62 : histogram creation unit 
               63 : breast schematic diagram generation unit 
               64 : imaging guide unit 
               71 : breast schematic diagram 
               73 : axillary region 
               74 ,  74 A,  74 B: probe mark 
               75 A,  75 B: guide 
             S: skin 
             BR: breast region 
             M: mammary gland region 
             L 1 : front boundary line 
             L 2 : rear boundary line 
             T: pectoralis major muscle 
             R 1 : GTC region 
             R 2 : edematous region 
             P 1 : black portion 
             P 2 : white portion