Patent Publication Number: US-2020275897-A1

Title: Control device, radiography system, medical imaging system, control method, and control program

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2019-036751, filed Feb. 28, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a control device, a radiography system, a medical imaging system, a control method, and a non-transitory storage medium storing a control program. 
     Related Art 
     A radiography apparatus has been known which irradiates an object, such as the breast of a subject, with radiation emitted from a radiation source and detects the radiation transmitted through the object with a radiation detector to capture a radiographic image. 
     In addition, an ultrasonography apparatus has been known which scans the breast of a subject using an ultrasound probe and scans the breast with ultrasonic waves to capture an ultrasound image of the breast. 
     JP2009-028381A and JP2012-170718A disclose an apparatus that can capture both a radiographic image and an ultrasound image of the breast. In JP2009-028381A and JP2012-170718A, the radiographic image and the ultrasound image are captured in a state in which the breast is compressed. 
     In general, in a case in which the breast is compressed by a compression member, the subject feels pain. In a case in which the radiographic image and the ultrasound image are continuously captured as in the technique disclosed in JP2009-028381A and JP2012-170718A, the time for which the subject feels pain may increase since the time for which the breast is compressed increases. Therefore, a technique for effectively relieving the pain of the subject is required. 
     SUMMARY 
     The present disclosure has been made in view of the above-mentioned problems and an object of the present disclosure is to provide a control device, a radiography system, a medical imaging system, a control method, and a non-transitory storage medium storing a control program that may effectively relieve the pain of a subject. 
     In order to achieve the object, according to a first aspect of the present disclosure, there is provided a control device comprising: a compression control unit that, in a case in which continuous imaging that captures a radiographic image of a breast compressed by a compression member and then captures an ultrasound image of the breast while maintaining the compressed state is performed, performs control to set a force of the compression member compressing the breast to a first force in the capture of the radiographic image and to change the force of the compression member compressing the breast from the first force to a second force lower than the first force in the capture of the ultrasound image. 
     According to a second aspect of the present disclosure, in the control device according to the first aspect, the second force may be set such that an amount of change in a thickness of the breast in a case in which the compressed state is changed from a state in which the breast is compressed with the first force to a state in which the breast is compressed with the second force is equal to or less than a predetermined amount of change. 
     According to a third aspect of the present disclosure, in the control device according to the first or second aspect, in a case in which the force is changed from the first force to the second force, the compression control unit may perform control to continuously reduce the force from the first force to the second force. 
     According to a fourth aspect of the present disclosure, in the control device according to the first or second aspect, in a case in which the first force is equal to or less than a predetermined value, the compression control unit may perform control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to a fifth aspect of the present disclosure, the control device according to the first or second aspect may further comprise an acquisition unit that acquires mammary gland amount information indicating an amount of mammary gland in the breast. In a case in which the amount of mammary gland indicated by the mammary gland amount information is equal to or less than a predetermined amount of mammary gland, the compression control unit may perform control to change the force of compressing the breast in the capture of the ultrasound image from the first force to the second force. In a case in which the amount of mammary gland indicated by the mammary gland amount information is more than the predetermined amount of mammary gland, the compression control unit may perform control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to a sixth aspect of the present disclosure, the control device according to the first or second aspect may further comprise an acquisition unit that acquires region information indicating a mammary gland region in the breast on the basis of the radiographic image. In a case in which a size of the mammary gland region indicated by the region information is equal to or less than a predetermined size, the compression control unit may perform control to change the force of compressing the breast in the capture of the ultrasound image from the first force to the second force. In a case in which the size of the mammary gland region indicated by the region information is greater than the predetermined size, the compression control unit may perform control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to a seventh aspect of the present disclosure, the control device according to the first or second aspect may further comprise an acquisition unit that acquires mammary gland amount information indicating an amount of mammary gland in the breast. In a case in which the amount of mammary gland indicated by the mammary gland amount information is equal to or more than a predetermined amount of mammary gland, the compression control unit may perform control to change the force of compressing the breast in the capture of the ultrasound image from the first force to the second force. In a case in which the amount of mammary gland indicated by the mammary gland amount information is less than the predetermined amount of mammary gland, the compression control unit performs control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to an eighth aspect of the present disclosure, the control device according to the first or second aspect may further comprise an acquisition unit that acquires region information indicating a mammary gland region in the breast on the basis of the radiographic image. In a case in which a size of the mammary gland region indicated by the region information is equal to or greater than a predetermined size, the compression control unit may perform control to change the force of compressing the breast in the capture of the ultrasound image from the first force to the second force. In a case in which the size of the mammary gland region indicated by the region information is less than the predetermined size, the compression control unit may perform control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to a ninth aspect of the present disclosure, in the control device according to the first or second aspect, in a case in which the capture of the radiographic image is tomosynthesis imaging that irradiates the breast with radiation emitted from a radiation source at different irradiation angles and captures a radiographic image at each irradiation angle using a radiation detector, the compression control unit may perform control to change the force of compressing the breast in the capture of the ultrasound image from the first force to the second force. In a case in which the capture of the radiographic image is an imaging method other than the tomosynthesis imaging, the compression control unit may perform control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to a tenth aspect of the present disclosure, in the control device according to any one of the first to ninth aspects, in a case in which a time for which the breast is compressed with the first force is equal to or greater than a predetermined value, the compression control unit may perform control to change the force of compressing the breast in the capture of the ultrasound image from the first force to the second force. In a case in which the time for which the breast is compressed with the first force is less than the predetermined value, the compression control unit may perform control to maintain the force of compressing the breast in the capture of the ultrasound image at the first force, instead of changing the force to the second force. 
     According to an eleventh aspect of the present disclosure, in the control device according to any one of the first to tenth aspects, the compression control unit may perform control to change the force from the first force to the second force by moving the compression member in a decompression direction. 
     According to a twelfth aspect of the present disclosure, in the control device according to any one of the first to eleventh aspects, the force of compressing the breast is a compression force of compressing the entire breast. The first force may be a first compression force and the second force may be a second compression force. 
     According to a thirteenth aspect of the present disclosure, in the control device according to any one of the first to eleventh aspects, the force of compressing the breast may be a compression pressure which is a compression force per unit area. The first force may be a first compression pressure and the second force may be a second compression pressure. 
     In order to achieve the object, according to a fourteenth aspect of the present disclosure, there is provided a radiography system comprising: a mammography apparatus that includes a radiation source, a radiation detector, and a compression member that compresses a breast disposed between the radiation source and the radiation detector and captures a radiographic image of the breast in the compressed state using the radiation detector; and the control device according to any one of the first to thirteenth aspects that controls the mammography apparatus. 
     In order to achieve the object, according to a fifteenth aspect of the present disclosure, there is provided a medical imaging system comprising: the radiography system according to the fourteenth aspect; and an ultrasonography apparatus that captures an ultrasound image of the breast compressed by the compression member of the mammography apparatus in the radiography system. 
     In order to achieve the object, according to a sixteenth aspect of the present disclosure, there is provided a medical imaging system comprising: a medical imaging apparatus that includes a radiation source, a radiation detector, and a compression member which compresses a breast disposed between the radiation source and the radiation detector, that captures a radiographic image of the breast in the compressed state using the radiation detector, and that captures an ultrasound image of the breast in the compressed state; and the control device according to any one of the first to thirteenth aspects that controls the medical imaging apparatus. 
     In order to achieve the object, according to a seventeenth aspect of the present disclosure, there is provided a control method including: capturing a radiographic image of a breast compressed by a compression member with a first force; changing the force of the compression member compressing the breast from the first force to a second force lower than the first force while maintaining the compressed state; and performing continuous imaging by capturing an ultrasound image of the breast compressed by the compression member with the second force. 
     In order to achieve the object, according to an eighteenth aspect of the present disclosure, there is provided a non-transitory storage medium storing a program that causes a computer to perform a control processing, the control processing including: capturing a radiographic image of a breast compressed by a compression member with a first force; changing the force of the compression member compressing the breast from the first force to a second force lower than the first force while maintaining the compressed state; and performing continuous imaging by capturing an ultrasound image of the breast compressed by the compression member with the second force. 
     A control device according to the present disclosure is a control device including a processor. In a case in which continuous imaging that captures a radiographic image of a breast compressed by a compression member and then captures an ultrasound image of the breast in the compressed state is performed, the processor performs control to set a force of the compression member compressing the breast to a first force in the capture of the radiographic image and to change the force of the compression member compressing the breast from the first force to a second force lower than the first force in the capture of the ultrasound image. 
     According to the present disclosure, it is possible to effectively relieve the pain of the subject. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically illustrating an example of the overall configuration of a medical imaging system according to a first embodiment. 
         FIG. 2  is a block diagram illustrating an example of the configuration of a console and a mammography apparatus according to the first embodiment. 
         FIG. 3  is a side view illustrating an example of the outward appearance of the mammography apparatus according to the first embodiment. 
         FIG. 4  is a diagram illustrating tomosynthesis imaging performed by the mammography apparatus according to the first embodiment. 
         FIG. 5  is a diagram illustrating an example of a configuration in a case in which a compression force is detected by load applied to a motor in the first embodiment. 
         FIG. 6  is a functional block diagram illustrating an example of the function of the mammography apparatus according to the first embodiment. 
         FIG. 7  is a block diagram illustrating an example of the configuration of an ultrasonography apparatus according to the first embodiment. 
         FIG. 8  is a block diagram illustrating an example of the configuration of an image storage system according to the first embodiment. 
         FIG. 9  is a flowchart illustrating an example of the flow of a compression control process of the mammography apparatus according to the first embodiment. 
         FIG. 10  is a functional block diagram illustrating an example of the function of mammography apparatuses according to Modification Examples 6 to 9. 
         FIG. 11  is a block diagram illustrating an example of the configuration of a console and a mammography apparatus according to a second embodiment. 
         FIG. 12  is a diagram illustrating a pressure sensor. 
         FIG. 13  is a functional block diagram illustrating an example of the function of a mammography apparatus according to a second embodiment. 
         FIG. 14  is a diagram schematically illustrating an example of the overall configuration of a medical imaging system according to a third embodiment. 
         FIG. 15  is a block diagram illustrating an example of the configuration of a console and a medical imaging apparatus according to the third embodiment. 
         FIG. 16  is a side view illustrating an example of the outward appearance of the medical imaging apparatus according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. Each of the embodiments does not limit the invention. In each of the embodiments, for example, a case in which an object of interest of the present disclosure is the mammary gland will be described. 
     First Embodiment 
     In this embodiment, an aspect in which a compression force of compressing the entire breast is an example of the force of compressing the breast according to the present disclosure will be described. 
     First, an example of the overall configuration of a medical imaging system according to this embodiment will be described.  FIG. 1  is a diagram illustrating an example of the overall configuration of a medical imaging system  1  according to this embodiment. 
     As illustrated in  FIG. 1 , the medical imaging system  1  according to this embodiment comprises a radiography system  2 , an ultrasonography apparatus  16 , and an image storage system  18 . 
     First, the configuration of the radiography system  2  will be described. The radiography system  2  includes a mammography apparatus  10  and a console  12 .  FIG. 2  is a block diagram illustrating an example of the configuration of the mammography apparatus  10  and the console  12 .  FIG. 3  is a side view illustrating an example of the outward appearance of the mammography apparatus  10  according to this embodiment. 
     The mammography apparatus  10  according to this embodiment irradiates the breast of a subject as an object with radiation R (for example, X-rays) to capture a radiographic image of the breast. In addition, the mammography apparatus  10  may be an apparatus that captures the image of the breast of the subject not only in a state in which the subject stands up (standing state) but also in a state in which the subject sits on, for example, a chair (including a wheelchair) (sitting state). 
     As illustrated in  FIG. 2 , the mammography apparatus  10  according to this embodiment comprises a control unit  20 , a storage unit  22 , an interface (I/F) unit  24 , an operation unit  26 , a radiation detector  30 , a compression plate driving unit  32 , a compression force detection sensor  33 , a compression plate  34 , a radiation emitting unit  36 , and a radiation source driving unit  37 . The control unit  20 , the storage unit  22 , the I/F unit  24 , the operation unit  26 , the radiation detector  30 , the compression plate driving unit  32 , the compression force detection sensor  33 , the radiation emitting unit  36 , and the radiation source driving unit  37  are connected to each other through a bus  39 , such as a system bus or a control bus, such that they can transmit and receive various kinds of information. 
     The control unit  20  according to this embodiment controls the overall operation of the mammography apparatus  10  under the control of the console  12 . The control unit  20  comprises a central processing unit (CPU)  20 A, a read only memory (ROM)  20 B, and a random access memory (RAM)  20 C. For example, various programs including a compression control processing program  21  which is executed by the CPU  20 A and performs control related to the capture of a radiographic image are stored in the ROM  20 B in advance. The RAM  20 C temporarily stores various kinds of data. 
     The radiation detector  30  detects the radiation R transmitted through the breast which is the object. As illustrated in  FIG. 3 , the radiation detector  30  is provided in an imaging table  40 . In the mammography apparatus  10  according to this embodiment, in a case in which imaging is performed, the breast of the subject is positioned on an imaging surface  40 A of the imaging table  40  by a user such as a doctor or a radiology technician. For example, the imaging surface  40 A with which the breast of the subject comes into contact is made of carbon in terms of the transmission and intensity of the radiation R. 
     The radiation detector  30  detects the radiation R transmitted through the breast of the subject and the imaging table  40 , generates a radiographic image on the basis of the detected radiation R, and outputs image data indicating the generated radiographic image. The type of the radiation detector  30  according to this embodiment is not particularly limited. For example, the radiation detector  30  may be an indirect-conversion-type radiation detector that converts the radiation R into light and converts the converted light into charge or a direct-conversion-type radiation detector that directly converts the radiation R into charge. 
     For example, the image data of the radiographic image captured by the radiation detector  30  and various other kinds of information are stored in the storage unit  22 . Examples of the storage unit  22  include a hard disk drive (HDD) and a solid state drive (SSD). The I/F unit  24  transmits and receives various kinds of information to and from the console  12  using wireless communication or wired communication. The image data of the radiographic image captured by the radiation detector  30  in the mammography apparatus  10  is transmitted to the console  12  through the I/F unit  24  by wireless communication or wired communication. 
     The operation unit  26  is provided as a plurality of switches in, for example, the imaging table  40  of the mammography apparatus  10 . In addition, the operation unit  26  may be provided as a touch panel switch or may be provided as a foot switch that is operated by the user&#39;s feet. 
     The radiation emitting unit  36  comprises a radiation source  36 R. As illustrated in  FIG. 3 , the radiation emitting unit  36  is provided in an arm portion  42  together with the imaging table  40  and a compression unit  46 . In addition, as illustrated in  FIG. 3 , the mammography apparatus  10  according to this embodiment comprises the arm portion  42 , a base  44 , and a shaft portion  45 . The arm portion  42  is supported by the base  44  so as to be movable in the up-down direction (Z-axis direction). The shaft portion  45  connects the arm portion  42  to the base  44 . The radiation source driving unit  37  can relatively rotate the arm portion  42  with respect to the base  44 , using the shaft portion  45  as a rotation axis. 
     In a case in which the mammography apparatus  10  performs tomosynthesis imaging, with the rotation of the arm portion  42 , the radiation source  36 R of the radiation emitting unit  36  is continuously moved to each of a plurality of irradiation positions with different irradiation angles (projection angles) by the radiation source driving unit  37 . In this embodiment, as illustrated in  FIG. 4 , the radiation source  36 R is moved to the irradiation positions t (t=0, 1, . . . , T; in  FIG. 4 , T=5) with different irradiation angles which are arranged at an interval of a predetermined angle θ, that is, the positions where the radiation R is incident on a detection surface  30 A of the radiation detector  30  at different angles. At each irradiation position, the radiation R is emitted from the radiation source  36 R in response to a command from the console  12  and the radiation detector  30  captures a radiographic image. In a case in which the radiography system  2  performs tomosynthesis imaging that moves the radiation source  36 R to each irradiation position t and captures a projection image at each irradiation position t, T projection images are obtained. In this embodiment, the aspect in which the radiation emitting unit  36  is moved to move the radiation source  36 R to the irradiation position t has been described. However, the present disclosure is not limited to this embodiment. For example, the mammography apparatus  10  may be configured to comprise a plurality of radiation sources  36 R corresponding to each irradiation position t. 
     As illustrated in  FIGS. 3 and 5 , the compression plate driving unit  32 , the compression force detection sensor  33 , and the compression plate  34  are provided in the compression unit  46 . Each of the compression unit  46  and the arm portion  42  can be relatively rotated with respect to the base  44 , using the shaft portion  45  as a rotation axis. In this embodiment, gears (not illustrated) are provided in each of the shaft portion  45 , the arm portion  42 , and the compression unit  46 . Each gear is switched between an engaged state and a disengaged state to connect each of the arm portion  42  and the compression unit  46  to the shaft portion  45 . One or both of the arm portion  42  and the compression unit  46  connected to the shaft portion  45  are rotated integrally with the shaft portion  45 . 
     The compression plate  34  according to this embodiment is a plate-shaped compression member and is moved in the up-down direction (Z-axis direction) by the compression plate driving unit  32  to compress the breast of the subject against the imaging table  40 . As illustrated in  FIG. 3 , for the movement direction of the compression plate  34 , the direction in which the breast is compressed, that is, the direction in which the compression plate  34  becomes closer to the imaging surface  40 A is referred to as a “compression direction” and the direction in which the compression of the breast is released, that is, the direction in which the compression plate  34  becomes closer to the radiation emitting unit  36  is referred to as a “decompression direction”. 
     As illustrated in  FIG. 5 , the compression unit  46  comprises the compression plate driving unit  32  including a motor  31  and a ball screw  38  and the compression force detection sensor  33 . The compression force detection sensor  33  has a function of detecting the compression force of the compression plate  34  against the entire breast. In the example illustrated in  FIG. 5 , the compression force detection sensor  33  detects the compression force on the basis of the load applied to the motor  31  as a driving source of the compression plate  34 . The compression plate  34  is supported by the ball screw  38  and the motor  31  is driven to slide the compression plate  34  between the imaging table  40  and the radiation source  36 R. The compression force detection sensor  33  according to this embodiment is a strain gauge, such as a load cell. The compression force detection sensor  33  detects reaction force to the compression force of the compression plate  34  to detect the compression force of the compression plate  34  against the breast. 
     A method for detecting the compression force is not limited thereto. For example, the compression force detection sensor  33  may be a semiconductor pressure sensor or a capacitive pressure sensor. Further, for example, the compression force detection sensor  33  may be provided in the compression plate  34 . 
     It is preferable that the compression plate  34  is optically transparent in order to check positioning or a compressed state in the compression of the breast. In addition, the compression plate  34  is made of a material having high transmittance for the radiation R. It is desirable that the compression plate  34  is made of a material that facilitates the transmission of ultrasonic waves from an ultrasound probe  65  (see  FIG. 7 , which will be described in detail below) of the ultrasonography apparatus  16 . Examples of the material forming the compression plate  34  include resins such as polymethylpentene, polycarbonate, acrylic, and polyethylene terephthalate. In particular, polymethylpentene is suitable as the material forming the compression plate  34  since it has low rigidity, high elasticity, and high flexibility and has suitable values for acoustic impedance that affects the reflectance of ultrasonic waves and an attenuation coefficient that affects the attenuation of ultrasonic waves. The member forming the compression plate  34  is not limited to this embodiment. For example, the member forming the compression plate  34  may be a film-like member. 
     In this example, the compression plate  34  compresses the entire breast. However, the present disclosure is not limited thereto. The compression plate  34  may compress a part of the breast. In other words, the compression plate  34  may be smaller than the breast. For example, a compression plate  34  used for so-called spot imaging which captures a radiographic image of only a region in which a lesion exists is known as the compression plate  34 . 
       FIG. 6  is a functional block diagram illustrating an example of the configuration of the mammography apparatus  10  according to this embodiment. As illustrated in  FIG. 6 , the mammography apparatus  10  according to this embodiment comprises a compression control unit  80 . For example, in the mammography apparatus  10  according to this embodiment, the CPU  20 A of the control unit  20  executes the compression control processing program  21  stored in the ROM  20 B such that the control unit  20  functions as the compression control unit  80 . The mammography apparatus  10  according to this embodiment is an example of a control device according to the present disclosure. 
     Information indicating the compression force which is the detection result of the compression force detection sensor  33  is input to the compression control unit  80  of the mammography apparatus  10 . The compression control unit  80  outputs a command related to the movement of the compression plate  34  to the compression plate driving unit  32 . 
     In a case in which continuous imaging that captures a radiographic image of the breast compressed by the compression plate  34  and then captures an ultrasound image of the breast in the compressed state is performed, the compression control unit  80  performs control to set the compression force of the compression plate  34  against the breast to first compression force in the capture of the radiographic image and to change the compression force of the compression plate  34  against the breast from the first compression force to a second compression force lower than the first compression force in the capture of the ultrasound image. 
     In some cases, the mammography apparatus  10  according to this embodiment performs continuous imaging which captures a radiographic image of the breast compressed by the compression plate  34  and then captures an ultrasound image of the breast. In the case of the continuous imaging, the imaging time for which the breast is continuously compressed by the compression plate  34  is long. Therefore, the compression control unit  80  sets the compression force in the capture of an ultrasound image to be lower than the compression force in the capture of a radiographic image such that the pain of the subject caused by the compression of the breast is relieved. 
     The console  12  according to this embodiment has a function of controlling the mammography apparatus  10  using, for example, an imaging order and various kinds of information acquired from a radiology information system (RIS)  5  through a wireless communication local area network (LAN) and commands input by the user through an operation unit  56 . 
     For example, the console  12  according to this embodiment is a server computer. As illustrated in  FIG. 2 , the console  12  comprises a control unit  50 , a storage unit  52 , an I/F unit  54 , the operation unit  56 , and a display unit  58 . The control unit  50 , the storage unit  52 , the I/F unit  54 , operation unit  56 , and the display unit  58  are connected to each other through a bus  59 , such as a system bus or a control bus, such that they can transmit and receive various kinds of information. 
     The control unit  50  according to this embodiment controls the overall operation of the console  12 . The control unit  50  comprises a CPU  50 A, a ROM  50 B, and a RAM  50 C. For example, various programs including a control processing program  51  (which will be described below) executed by the CPU  50 A are stored in the ROM  50 B in advance. The RAM  50 C temporarily stores various kinds of data. 
     For example, the image data of the radiographic image captured by the mammography apparatus  10  and various other kinds of information are stored in the storage unit  52 . An HDD or an SSD is given as an example of the storage unit  52 . 
     The operation unit  56  is used by the user to input, for example, commands which are related to the capture of a radiographic image and include a command to emit the radiation R or various kinds of information. Therefore, the operation unit  56  according to this embodiment includes at least an irradiation command button that is pressed by the user to input a command to emit the radiation R. The operation unit  56  is not particularly limited. Examples of the operation unit  56  include various switches, a touch panel, a touch pen, and a mouse. The display unit  58  displays various kinds of information. In addition, the operation unit  56  and the display unit  58  may be integrated into a touch panel display. 
     The I/F unit  54  transmits and receives various kinds of information to and from the mammography apparatus  10 , the RIS  5 , and the image storage system  18  using wireless communication or wired communication. In the radiography system  2  according to this embodiment, the console  12  receives the image data of the radiographic image captured by the mammography apparatus  10  from the mammography apparatus  10  through the I/F unit  54 , using wireless communication or wired communication. 
     Next, the configuration of the ultrasonography apparatus  16  will be described.  FIG. 7  is a block diagram illustrating an example of the configuration of the ultrasonography apparatus  16 . The ultrasonography apparatus  16  is used by the user to capture an ultrasound image of the breast of the subject as the object and is a so-called hand-held ultrasonography apparatus. 
     As illustrated in  FIG. 7 , the ultrasonography apparatus  16  comprises a control unit  60 , a storage unit  62 , an I/F unit  64 , the ultrasound probe  65 , an operation unit  66 , and a display unit  68 . The control unit  60 , the storage unit  62 , the I/F unit  64 , the ultrasound probe  65 , the operation unit  66 , and the display unit  68  are connected to each other through a bus  69 , such as a system bus or a control bus, such that they can transmit and receive various kinds of information. 
     The control unit  60  according to this embodiment controls the overall operation of the ultrasonography apparatus  16 . The control unit  60  comprises a CPU  60 A, a ROM  60 B, and a RAM  60 C. For example, various programs executed by the CPU  60 A are stored in the ROM  60 B in advance. The RAM  60 C temporarily stores various kinds of data. 
     For example, the image data of the captured ultrasound image and various other kinds of information are stored in the storage unit  62 . A specific example of the storage unit  62  is an HDD or an SSD. 
     The ultrasound probe  65  is moved along the upper surface  34 A (see  FIG. 3 , a surface opposite to the surface that comes into contact with the breast of the subject) of the compression plate  34  by the user and scans the breast with ultrasonic waves to acquire an ultrasound image of the breast. Specifically, in a case in which ultrasonography is performed, the ultrasound probe  65  is moved by the user along the upper surface  34 A of the compression plate  34  in a state in which an acoustic matching member (not illustrated), such as echo jelly, is applied onto the upper surface  34 A of the compression plate  34 . 
     The ultrasound probe  65  comprises a plurality of ultrasound transducers (not illustrated) which are one-dimensionally or two-dimensionally arranged. Each of the ultrasound transducers transmits ultrasonic waves on the basis of an applied driving signal, receives ultrasound echoes, and outputs a received signal. 
     For example, each of the plurality of ultrasound transducers is a transducer configured by forming electrodes at both ends of a piezoelectric material (piezoelectric body), such as a piezoelectric ceramic typified by lead (Pb) zirconate titanate (PZT) or a polymeric piezoelectric element typified by polyvinylidene difluoride (PVDF). In a case in which a pulsed or continuous wave drive signal is transmitted to apply a voltage to the electrodes of the transducer, the piezoelectric body is expanded and contracted. Pulsed or continuous ultrasonic waves are generated from each transducer by the expansion and contraction and the ultrasonic waves are combined to form an ultrasound beam. Each transducer receives the propagated ultrasonic waves and is then expanded and contracted to generate an electric signal. The electric signal is output as an ultrasound received signal and is input to the main body (not illustrated) of the ultrasonography apparatus  16  through a cable (not illustrated). 
     The operation unit  66  is used by the user to input, for example, commands or various kinds of information related to the capture of an ultrasound image. The operation unit  66  is not particularly limited. Examples of the operation unit  66  include various switches, a touch panel, a touch pen, and a mouse. The display unit  68  displays, for example, various kinds of information or an ultrasound image corresponding to the received signal from the ultrasound probe  65 . In addition, the operation unit  66  and the display unit  68  may be integrated into a touch panel display. 
     The I/F unit  64  transmits and receives various kinds of information to and from the RIS  5  and the image storage system  18  using wireless communication or wired communication. The image data of the ultrasound image captured by the ultrasonography apparatus  16  is transmitted to the image storage system  18  through the I/F unit  64  by wireless communication or wired communication. 
     Next, the configuration of the image storage system  18  will be described.  FIG. 8  is a block diagram illustrating an example of the configuration of the image storage system  18 . The image storage system  18  stores the image data of the radiographic image captured by the radiography system  2  and the image data of the ultrasound image captured by the ultrasonography apparatus  16 . The image storage system  18  extracts an image corresponding to a request from, for example, the console  12 , the ultrasonography apparatus  16 , and other reading devices (not illustrated) from the stored radiographic images and ultrasound images and transmits the extracted image to the apparatus which is the request source. A specific example of the image storage system  18  is a picture archiving and communication system (PAC S). 
     As illustrated in  FIG. 8 , the image storage system  18  comprises a control unit  70 , a storage unit  72 , and an I/F unit  74 . The control unit  70 , the storage unit  72 , and the I/F unit  74  are connected to each other through a bus  79 , such as a system bus or a control bus, such that they can transmit and receive various kinds of information. 
     The control unit  70  according to this embodiment controls the overall operation of the ultrasonography apparatus  16 . The control unit  70  comprises a CPU  70 A, a ROM  70 B, and a RAM  70 C. For example, various programs executed by the CPU  70 A are stored in the ROM  70 B in advance. The RAM  70 C temporarily stores various kinds of data. 
     The storage unit  72  is a so-called database that stores each of the image data of the radiographic image and the image data of the ultrasound image so as to be associated with, for example, an imaging order or information released to the subject. 
     The I/F unit  74  has a function of transmitting and receiving various kinds of information to and from the console  12  and the ultrasonography apparatus  16  using wireless communication or wired communication. 
     Next, the operation of the mammography apparatus  10  according to this embodiment will be described with reference to the drawings. 
     For example, in a case in which the mammography apparatus  10  according to this embodiment receives an imaging order and an imaging start command from the console  12 , the CPU  20 A of the control unit  20  executes the compression control processing program  21  stored in the ROM  20 B to perform the compression control process whose example is illustrated in  FIG. 8 .  FIG. 8  is a flowchart illustrating an example of the flow of a compression control operation of the mammography apparatus  10  according to this embodiment. 
     First, in Step S 100 , the compression control unit  80  determines whether the user has input a compression command through the operation unit  26 . In a case in which the mammography apparatus  10  according to this embodiment captures a radiographic image, first, the user positions the breast of the subject on the imaging surface  40 A of the imaging table  40  of the mammography apparatus  10 . In a case in which the positioning is completed, the user inputs a compression command through the operation unit  26 . In a case in which a compression command has not been input, the determination result in Step S 100  is “No”. On the other hand, in a case in which a compression command has been input, the determination result in Step S 100  is “Yes” and the process proceeds to Step S 102 . 
     Then, in Step S 102 , the compression control unit  80  directs the compression plate driving unit  32  to move the compression plate  34  in the compression direction in response to the compression command such that the breast is compressed with the first compression force between the compression plate  34  and the imaging surface  40 A of the imaging table  40 . 
     The compression of the breast by the compression plate  34  makes it possible to develop the overlap between the mammary gland tissues and to easily determine whether a lesion is a benign lesion or a malignant lesion. In addition, since the breast is compressed and fixed to the imaging table  40  by the compression plate  34 , the body movement of the subject is suppressed. Therefore, it is possible to suppress the blurring of a radiographic image caused by the body movement. Further, since the breast is compressed by the compression plate  34 , the thickness of the breast is reduced. Therefore, it is possible to reduce the amount of radiation emitted to the breast. 
     In a case in which the breast is fixed by the compression plate  34 , the user presses an irradiation command button included in the operation unit  56  of the console  12  to input a command to emit the radiation R. In a case in which the irradiation command is input, the control unit  20  of the mammography apparatus  10  performs control such that the radiation R is emitted from the radiation source  37 R to the breast compressed by the compression plate  34  under the control of the console  12 . Then, the radiation detector  30  generates a radiographic image on the basis of the radiation R transmitted through the breast. The image data of the captured radiographic image is transmitted to the console  12 . 
     Then, in Step S 104 , the compression control unit  80  determines whether the capture of a radiographic image has ended. For example, in a case in which the image data indicating the radiographic image captured by the radiation detector  30  has been transmitted to the console  12 , the compression control unit  80  according to this embodiment determines that the capture of a radiographic image has ended. A method for determining whether the capture of a radiographic image has ended is not limited to this embodiment. For example, a command to end the capture of a radiographic image which has been input through the operation unit  56  of the console  12  may be received. 
     Until the capture of a radiographic image ends, the determination result in Step S 104  is “No”. On the other hand, in a case in which the capture of a radiographic image ends, the determination result in Step S 104  is “Yes” and the process proceeds to Step S 106 . 
     In Step S 106 , the compression control unit  80  determines whether to capture an ultrasound image. For example, in a case in which a command to capture both a radiographic image and an ultrasound image is included in the imaging order or the user inputs a command to capture an ultrasound image through the operation unit  56 , the compression control unit  80  according to this embodiment determines to capture an ultrasound image. 
     In a case in which an ultrasound image is not captured, the determination result in Step S 106  is “No” and the process proceeds to Step S 114 . On the other hand, in a case in which an ultrasound image is captured, the determination result in Step S 106  is “Yes” and the process proceeds to Step S 108 . 
     In Step S 108 , the compression control unit  80  determines whether to change the compression force. Specifically, the compression control unit  80  determines whether to change the compression force of compressing the breast from the first compression force to the second compression force. 
     The development of the mammary gland tissues may be little changed even in a case in which the compression force is reduced to the second compression force after the breast is compressed with the first compression force, which is disclosed in, for example, JP2017-225633A, JP2017-225634A, and JP2017-225635A. These patent publications disclose a technique in which, even in a case in which the compression plate  34  is moved in the decompression direction to reduce the compression force after the breast is compressed with the first compression force, it is difficult for the thickness of the breast to return to the original thickness. Since it is difficult for the thickness of the breast to return to the original thickness and it is possible to maintain the thickness of the breast, the development of the mammary gland tissues is maintained or is little changed. 
     The second compression force may be lower than the first compression force in order to relieve the pain of the subject. In a case in which the compression force against the breast is too low, the thickness of the breast may return to the original thickness and the development of the mammary gland tissues may be different. In a case in which the development of the mammary gland tissues is different between the capture of a radiographic image and the capture of an ultrasound image, for example, the position where calcification appears is changed, which is not preferable. In addition, in a case in which the compression force against the breast is too low, the body movement of the subject is likely to occur. 
     In a case in which the first compression force is relatively low, the second compression force lower than the first compression force may not be preferable for the above-mentioned reasons. Therefore, in the mammography apparatus  10  according to this embodiment, in a case in which the first compression force is equal to or less than a predetermined threshold value, the second compression force is considered to be too low and the capture of an ultrasound image is performed while the first compression force is maintained without being changed to the second compression force. Since the first compression force is relatively low, the pain of the subject is less than that in a case in which the first compression force is high. 
     According to the above-mentioned patent publications, the second compression force is preferably 40% to 70% of the first compression force and is more preferably 50% of the first compression force. Alternatively, the second compression force is preferably 40 N to 100 N lower than the first compression force and is more preferably 50 N lower than the first compression force. In other words, the first compression force is preferably 143% to 250% of the second compression force and is more preferably 200% of the second compression force. Alternatively, the first compression force is preferably 40 N to 100 N higher than the second compression force and is more preferably 60 N higher than the second compression force. In addition, according to the above-mentioned patent publications, it is preferable that the second compression force is in the range of 40 N to 100 N in order to effectively relieve the pain of the subject and to suppress the body movement of the subject. 
     Therefore, for example, in a case in which the second compression force decided according to the first compression force is equal to or less than a threshold value, the compression control unit  80  according to this embodiment determines not to change the second compression force. For example, the specific threshold value may be determined according to the preferable range of the second compression force, may be determined according to the thickness of the breast compressed by the compression plate  34 , or may be experimentally obtained in advance. 
     In a case in which the second compression force is not changed, the determination result in Step S 108  is “No” and the process proceeds to Step S 112 . On the other hand, in a case in which the second compression force is changed, the determination result in Step S 108  is “Yes” and the process proceeds to Step S 110 . 
     In Step S 110 , the compression control unit  80  compresses the breast with the second compression force using the compression plate  34 . Specifically, the compression control unit  80  directs the compression plate driving unit  32  to move the compression plate  34  in the decompression direction and to stop the movement of the compression plate  34  at the position where the compression force detected by the compression force detection sensor  33  is the second compression force. 
     Preferably, in a case in which the compression force of the compression plate  34  is not changed, the compression control unit  80  transmits information indicating that the compression force of the compression plate  34  is not changed to the console  12 . Preferably, in a case in which the compression force of the compression plate  34  has been changed to the second compression force, the compression control unit  80  transmits information indicating that the change has been completed to the console  12 . 
     In a case in which the information is received, preferably, the console  12  displays information indicating that the capture of an ultrasound image may be started on the display unit  58 . In a case in which the capture of an ultrasound image is started while the compression control unit  80  changes the compression force, there is a concern that the pressure applied to the compression plate  34  will be changed and the detection accuracy of the compression force by the compression force detection sensor  33  will be reduced. As described above, since the timing when an ultrasound image is captured is presented, it is possible to prevent an ultrasound image from being captured while the compression force is changed, which is preferable. 
     The user operates the ultrasonography apparatus  16  to capture an ultrasound image of the breast. Specifically, the user applies an acoustic matching member (not illustrated), such as echo jelly, onto the upper surface  34 A of the compression plate  34 . The user operates the ultrasound probe  65  to scan the upper surface  34 A of the compression plate  34  covered by the acoustic matching member with ultrasonic waves, thereby capturing an ultrasound image. The captured ultrasound image is displayed on the display unit  68  of the ultrasonography apparatus  16 . 
     Then, in Step S 112 , the compression control unit  80  determines whether the capture of an ultrasound image has ended. For example, in the medical imaging system  1  according to this embodiment, in a case in which the capture of an ultrasound image ends, the user inputs a command to release the compression through the operation unit  26  of the mammography apparatus  10 . In a case in which the command to release the compression has been input through the operation unit  26 , the compression control unit  80  determines that the capture of an ultrasound image has ended. 
     In a case in which the capture of an ultrasound image has not ended, that is, in a case in which the command to release the compression has not been input, the determination result in Step S 112  is “No”. On the other hand, in a case in which the capture of an ultrasound image has ended, that is, in a case in which the command to release the compression has been input, the determination result in Step S 112  is “Yes” and the process proceeds to Step S 114 . 
     In Step S 114 , the compression control unit  80  releases the compression of the breast by the compression plate  34  and ends the compression control process. Specifically, the compression control unit  80  directs the compression plate driving unit  32  to move the compression plate  34  in the decompression direction. The compression plate  34  is moved in the decompression direction to release the compression of the breast. 
     A method for determining whether to capture an ultrasound image in Step S 106  of the compression control process in the compression control unit  80  is not limited to the above-mentioned method. For example, a method according to the following Modification Example 1 may be applied. 
     Modification Example 1 
     The compression control unit  80  of the mammography apparatus  10  transmits an inquiry whether to capture an ultrasound image to the console  12  and determines to capture an ultrasound image in a case in which a command to capture an ultrasound image is received as the result of the inquiry. 
     In addition, the timing when it is determined whether to capture an ultrasound image is not limited to the timing of Step S 106 . For example, it may be determined whether to capture an ultrasound image before the compression control process starts. In a case in which it is determined to capture an ultrasound image, the compression control process may be performed. In this case, the process of Step S 106  may be omitted. 
     A method for determining whether to change the compression force of the compression plate  34  in Step S 108  of the compression control process in the compression control unit  80  is not limited to the above-mentioned method. For example, methods according to the following Modification Examples 2 to 9 may be applied. 
     Modification Example 2 
     A correspondence relationship between the first compression force and whether to change the compression force to the second compression force may be determined in advance and the compression control unit  80  may determine whether to change the compression force of the compression plate  34  on the basis of correspondence relationship information indicating the correspondence relationship. In this case, for example, the correspondence relationship information may be stored in the storage unit  22  of the mammography apparatus  10  in advance or may be stored in the storage unit  52  of the console  12 . For example, the compression control unit  80  may use the correspondence relationship information stored outside the radiography system  2 . 
     Modification Example 3 
     The compression control unit  80  may determine whether to change the compression force of the compression plate  34  according to the time for which the breast is continuously compressed with the first compression force by the compression plate  34 . In this embodiment, the time elapsed since the compression plate  34  starts to compress the breast with the first compression force may be measured. In a case in which the measured time is greater than a predetermined threshold value, the compression control unit  80  determines to change the compression force of the compression plate  34 . 
     Modification Example 4 
     The compression control unit  80  may determine whether to change the compression force of the compression plate  34  according to the type of radiography. For example, in a case in which the type of radiography is tomosynthesis imaging, the imaging time may be longer than that in normal imaging. As the imaging time becomes longer, the time for which the breast is compressed by the compression plate  34  becomes longer. Therefore, the necessity of relieving the pain of the subject increases. In addition, in the case of the tomosynthesis imaging, the necessity of suppressing the body movement of the subject while a plurality of radiographic images are captured increases. Therefore, in some cases, the first compression force is relatively high. For this reason, the compression control unit  80  may determine to change the compression force of the compression plate  34  in a case in which the type of radiography is tomosynthesis imaging. 
     Modification Example 5 
     The compression control unit  80  may determine whether to change the compression force of the compression plate  34  in response to a command from the user. For example, in a case in which the subject has input a command to reduce the compression force through the operation unit  26  of the mammography apparatus  10 , the compression force in the capture of an ultrasound image may be changed from the first compression force to the second compression force. In this case, for example, the subject may input the command to reduce the compression force before the capture of an ultrasound image starts, while a radiographic image is being captured, or after an ultrasound image is captured. 
     The way of feeling pain varies depending on the subject. According to this example, in a case in which the subject feels pain while being compressed with the first compression force, the subject may input the command to reduce the compression force. 
     Modification Example 6 
     The compression control unit  80  may determine whether to change the compression force of the compression plate  34  on the basis of the amount of mammary gland in the breast as the object. In a case in which the amount of mammary gland is relatively small, the amount of mammary gland tissues to be developed is small and deformation caused by compression is small. Therefore, for example, even in a case in which the thickness of the breast changes, the deviation of the mammary gland tissues is small. Conversely, in a case in which the amount of mammary gland is relatively large, the amount of mammary gland tissues to be developed is large and deformation caused by compression is large. Therefore, for example, in a case in which the thickness of the breast changes, the deviation of the mammary gland tissues increases. For this reason, in a case in which the amount of mammary gland in the breast is equal to or greater than a threshold value, the compression control unit  80  may determine to change the compression force of the compression plate  34 . 
     A method for deriving the amount of mammary gland in the breast is not particularly limited. For example, the amount of mammary gland in the breast may be derived on the basis of a radiographic image captured in a state in which the breast is compressed with the first compression force by the compression plate  34 . For example, a known method, such as a technique that estimates a mammary gland content on the basis of a radiographic image and a fat image estimated from the radiographic image described in JP2010-253245A, may be used as the method for deriving the amount of mammary gland from the radiographic image. 
       FIG. 10  is a functional block diagram illustrating an example of the configuration of the mammography apparatus  10  in a case in which the amount of mammary gland is derived from a radiographic image. As illustrated in  FIG. 10 , the mammography apparatus  10  according to this modification example further comprises an acquisition unit  82 . For example, in the mammography apparatus  10  according to this embodiment, the CPU  20 A of the control unit  20  executes the compression control processing program  21  stored in the ROM  20 B such that the control unit  20  functions as the acquisition unit  82 . 
     The acquisition unit  82  acquires the amount of mammary gland from the radiographic image captured by the radiation detector  30  and outputs information indicating the amount of the amount of mammary gland to the compression control unit  80 . The compression control unit  80  determines whether the amount of mammary gland is greater than a threshold value on the basis of the input information indicating the amount of mammary gland. In addition, for example, the amount of mammary gland may be derived from the radiographic image by the radiation detector  30  or the acquisition unit  82 . Further, for example, the threshold value used for the determination by the compression control unit  80  may be experimentally obtained in advance. For example, the threshold value may vary depending on the thickness of the breast. 
     Modification Example 7 
     As the aspect in which the compression control unit  80  determines whether to change the compression force of the compression plate  34  on the basis of the amount of mammary gland in the breast as the object, the following aspect may be used: in a case in which the amount of mammary gland in the breast is equal to or less than the threshold value contrary to Modification Example 6, the compression control unit  80  determines to change the compression force of the compression plate  34 . 
     In general, in the capture of an ultrasound image, the ultrasound probe  65  scans a mammary gland region. Therefore, as the mammary gland region becomes larger, the scanning range of the ultrasound probe  65  becomes wider and the imaging time becomes longer. As a result, the time for which the subject feels pain is likely to become longer. For this reason, in a case in which the amount of mammary gland in the breast is equal to or less than the threshold value, the compression control unit  80  may determine to change the compression force of the compression plate  34 . 
     The configuration and the method described in Modification Example 6 may be applied as the configuration of the mammography apparatus  10  and a method for deriving the amount of mammary gland in this modification example. 
     Modification Example 6 and this modification example are opposite aspects. Therefore, for example, Modification Example 6 may be applied in a case in which importance is attached to the development of the mammary gland and Modification Example 7 may be applied in a case in which importance is attached to the pain of the subject. In addition, for example, any one of Modification Example 6 or Modification Example 7 may be applied according to the thickness of the breast compressed by the compression plate  34 . The threshold value used in Modification Example 6 and the threshold value used in Modification Example 7 may be different values or the same value. 
     Modification Example 8 
     The compression control unit  80  may determine whether to change the compression force of the compression plate  34  according to the mammary gland region of the breast as the object. As the amount of mammary gland becomes larger, the size of the mammary gland region tends to become larger. As described in Modification Example 6, in a case in which the amount of mammary gland is large and the compression force is changed, the development of the mammary gland tissue may vary. Therefore, in a case in which the size of the mammary gland region is equal to or greater than the threshold value, the compression control unit  80  may determine to change the compression force of the compression plate  34 . 
     A method for deriving the size of the mammary gland region is not particularly limited. For example, mammary gland tissue pixels corresponding to the mammary gland tissues are detected from the radiographic image and a region in which the number of detected mammary gland region pixels is equal to or greater than a predetermined value is derived as the mammary gland region. A method for detecting the mammary gland tissue pixel is not particularly limited. For example, a technique described in JP2010-253245A can be applied. In a case in which the technique described in this patent publication is applied, first, a radiographic image is divided into a breast image and a direct region. Then, a pectoral muscle region is extracted from the breast image. Then, the pectoral muscle region is removed from the breast image. Then, in the breast image from which the pectoral muscle region has been removed, a pixel in which the amount of transmission of the radiation R is equal to or less than a threshold value is detected as the mammary gland tissue region pixel. 
     For example, the configuration of the mammography apparatus  10  in a case in which the mammary gland region is derived may be the same as that illustrated in  FIG. 10 . In this case, the acquisition unit  82  acquires the size of the mammary gland region from the radiographic image captured by the radiation detector  30  and outputs information indicating the size of the mammary gland region to the compression control unit  80 . The compression control unit  80  determines whether the size of the mammary gland region is greater than the threshold value on the basis of the input information indicating the size of the mammary gland region. The size of the mammary gland region may be derived from the radiographic image by, for example, the radiation detector  30  or the acquisition unit  82 . For example, the threshold value used for the determination by the compression control unit  80  may be experimentally obtained in advance. For example, the threshold value may vary depending on the thickness of the breast. 
     Modification Example 9 
     As the aspect in which the compression control unit  80  determines whether to change the compression force of the compression plate  34  on the basis of the size of the mammary gland region of the breast as the object, the following aspect may be used: in a case in which the size of the mammary gland region of the breast is equal to or less than the threshold value contrary to Modification Example 8, the compression control unit  80  determines to change the compression force of the compression plate  34 . 
     As described in Modification Example 7, as the size of the mammary gland region becomes larger, the time required to capture an ultrasound image is likely to become longer. Therefore, in a case in which the size of the mammary gland region is equal to or less than the threshold value, the compression control unit  80  may determine to change the compression force of the compression plate  34 . 
     The configuration and the method described in Modification Example 8 may be applied as the configuration of the mammography apparatus  10  and a method for deriving the amount of mammary gland in this modification example. 
     Modification Example 8 and this modification example are opposite aspects. Therefore, for example, Modification Example 8 may be applied in a case in which importance is attached to the development of the mammary gland and Modification Example 9 may be applied in a case in which importance is attached to the pain of the subject. In addition, for example, any one of Modification Example 8 or Modification Example 9 may be applied according to the thickness of the breast compressed by the compression plate  34 . The threshold value used in Modification Example 8 and the threshold value used in Modification Example 9 may be different values or the same value. 
     In this embodiment, in the capture of an ultrasound image, the user moves the ultrasound probe  65  on the upper surface  34 A of the compression plate  34 , which results in a change in the compression force applied to the compression plate  34 . Therefore, the compression control unit  80  may perform feedback control in order to maintain the second compression force or the first compression force on the basis of the change in the compression force detected by the compression force detection sensor  33 . 
     Second Embodiment 
     Next, a second embodiment will be described in detail. In the first embodiment, the aspect in which the compression force against the entire breast is an example of the force of compressing the breast according to the present disclosure has been described. However, in this embodiment, an aspect in which compression pressure that is a compression force per unit area is an example of the force of compressing the breast according to the present disclosure will be described. In each of the above-described embodiments, the compression control unit  80  controls the compression force of the compression plate  34  against the breast. However, in this embodiment, the compression control unit  80  controls the compression pressure of the compression plate  34  against the breast. 
     Even in a case in which the breast is compressed with the same compression force, the pain of the subject with a large breast tends to be less than that of the subject with a small breast since the compression force is dispersed. For this reason, it is preferable to finely control the movement of the compression plate  34  according to the size of the breast. Therefore, the mammography apparatus  10  according to this embodiment controls the compression of the breast by the compression plate  34  on the basis of the compression pressure that is the compression force per unit area, instead of the compression force of the compression plate  34  against the entire breast. 
     Since the overall configuration (see  FIG. 1 ) of a medical imaging system  1  according to this embodiment is the same as that in the first embodiment, the description thereof will not be repeated. In this embodiment, since the configuration of the mammography apparatus  10  is partially different from the configuration of the mammography apparatus  10  according to the first embodiment, the different configuration will be described. 
       FIG. 11  is a block diagram illustrating an example of the configuration of the mammography apparatus  10  and the console  12  according to this embodiment. As illustrated in  FIG. 11 , the mammography apparatus  10  according to this embodiment differs from the mammography apparatus  10  according to the first embodiment in that it comprises a pressure sensor  35  instead of the compression force detection sensor  33 . 
     As illustrated in  FIG. 12 , n ( 50  in this embodiment) pressure sensors  35  are two-dimensionally arranged on the imaging surface  40 A of the imaging table  40  and each pressure sensor  35  detects the pressure applied to the imaging table  40  in a case in which the breast is compressed by the compression plate  34 . The size of a region in which each pressure sensor  35  according to this embodiment detects pressure (the area of the imaging surface  40 A; hereinafter, referred to as a “pressure detection area”) is predetermined. 
     It is preferable that the pressure sensor  35  is made of a material which transmits the radiation R. In a case in which the pressure sensor  35  is made of a material which absorbs a portion of the radiation R, the image data of the acquired radiographic image is corrected according to the radiation transmittance of the pressure sensor  35 . 
     An example of the functional configuration of the mammography apparatus  10  according to this embodiment is the same as that of the mammography apparatus  10  (see  FIG. 6 ) according to the first embodiment except the operation of the compression control unit  80 . 
       FIG. 13  is a functional block diagram illustrating an example of the configuration of the mammography apparatus  10  according to this embodiment. As illustrated in  FIG. 13 , the mammography apparatus  10  according to this embodiment comprises the compression control unit  80  similarly to the mammography apparatus  10  (see  FIG. 6 ) according to the first embodiment. 
     Information indicating the pressure which is the detection result of the pressure sensor  35  is input to the compression control unit  80  according to this embodiment. The compression control unit  80  outputs a command related to the movement of the compression plate  34  to the compression plate driving unit  32 . 
     In a case in which the continuous imaging that captures a radiographic image of the breast compressed by the compression plate  34  and then captures an ultrasound image of the breast in the compressed state is performed, the compression control unit  80  performs control to set the compression pressure of the compression member against the breast to a first compression pressure in the capture of the radiographic image and to change the compression pressure of the compression plate  34  against the breast from the first compression pressure to a second compression pressure lower than the first compression pressure in the capture of the ultrasound image. 
     The compression control unit  80  according to this embodiment derives the compression pressure on the basis of the detection results acquired from each pressure sensor  35 . A method for deriving the compression pressure is not particularly limited. For example, the compression control unit  80  may select the maximum value from the detection results of the n pressure sensors  35  and may derive the compression pressure on the basis of the selected maximum value and the pressure detection area. For example, the compression control unit  80  may select a predetermined number of detection results in descending order from the detection results of the n pressure sensors  35  and may derive the compression pressure on the basis of the average value of the selected detection results and the pressure detection area. For example, since the detection results of the pressure sensors  35  provided in a portion of the imaging surface  40 A with which the breast does not come into contact change little from 0 N/mm 2 , the compression control unit  80  may derive the compression pressure on the basis of the pressure detection area and the average value of the detection results except 0 N/mm 2  or the detection results in a predetermined range from 0 N/mm 2  in consideration of errors. As such, it is preferable to derive the compression pressure on the basis of the detection results of the pressure sensors  35  provided in a portion of the imaging surface  40 A with which the breast comes into contact. 
     The compression control unit  80  according to this embodiment repeatedly acquires the detection results of the pressure sensors  35  at a predetermined interval (0.1 seconds in this embodiment) and directs the compression plate driving unit  32  to move the compression plate  34  in the compression direction or the decompression direction until the compression pressure derived on the basis of the detection results of the pressure sensors  35  reaches the first compression pressure or the second compression pressure. 
     A compression control process of the compression control unit  80  in the mammography apparatus  10  according to this embodiment may be performed by changing the compression force in the compression control process (see  FIG. 9 ) of the compression control unit  80  according to the first embodiment to the compression pressure. Since the overall flow of the compression control process according to this embodiment and processes in each step are the same as those in the first embodiment, the description thereof will not be repeated. 
     Third Embodiment 
     Next, a third embodiment will be described in detail.  FIG. 14  is a diagram illustrating an example of the overall configuration of a medical imaging system  1  according to this embodiment. As illustrated in  FIG. 14 , the medical imaging system  1  according to this embodiment differs from the medical imaging system  1  (see  FIG. 1 ) according to the first embodiment in that it comprises a medical imaging apparatus  11  instead of the mammography apparatus  10  and the ultrasonography apparatus  16 . 
     The medical imaging apparatus  11  is an apparatus that is configured by combining the mammography apparatus  10  and the ultrasonography apparatus  16  according to the first embodiment, that is, an apparatus that can capture a radiographic image and an ultrasound image of the breast. For example, the medical imaging apparatus  11  according to this embodiment is a mammography apparatus that can automatically capture an ultrasound image. 
       FIG. 15  is a block diagram illustrating an example of the configuration of the medical imaging apparatus  11  and the console  12  according to this embodiment. As illustrated in  FIG. 15 , the medical imaging apparatus  11  according to this embodiment differs from the mammography apparatus  10  according to the first embodiment in that it further comprises an ultrasound probe  65  and a probe moving mechanism  67 . As in an example illustrated in  FIG. 16 , the ultrasound probe  65  and the probe moving mechanism  67  are provided in the compression unit  46 . 
     The ultrasound probe  65  is moved along the upper surface (a surface opposite to the surface on which the breast of the subject is placed)  34 A of the compression plate  34  by the probe moving mechanism  67  and scans the breast with ultrasonic waves to acquire an ultrasound image of the breast. The ultrasound probe  65  is moved by the probe moving mechanism  67 . 
     In a case in which an ultrasound image is captured, the compression control unit  80  controls the ultrasound probe  65  and the probe moving mechanism  67  in a state in which the breast is compressed by the compression plate  34 . The compression control unit  80  checks the position of the ultrasound probe  65  moved by the probe moving mechanism  67  and directs the probe moving mechanism  67  to move the ultrasound probe  65 . The compression control unit  80  transmits and receives ultrasonic waves to capture an ultrasound image while moving the ultrasound probe  65  using the probe moving mechanism  67 . 
     The medical imaging apparatus  11  illustrated in  FIG. 15  is an apparatus that scans the upper surface  34 A of the compression plate  34  using the ultrasound probe  65  to capture an ultrasound image from the side of the radiation source  36 R. However, the medical imaging apparatus  11  may be an imaging apparatus that captures an acoustic image from the opposite side, that is, the side of the imaging table  40 . 
     Since the compression control process performed by the compression control unit  80  of the medical imaging apparatus  11  according to this embodiment is the same as the compression control process (see  FIG. 9 ) performed by the compression control unit  80  according to the first embodiment, the description thereof will not be repeated. In this embodiment, since the medical imaging apparatus  11  captures an ultrasound image, it is possible to check the time required to capture the ultrasound image before the ultrasound image is captured. Therefore, the compression control unit  80  can check the time from the start of the capture of the radiographic image to the end of the capture of the ultrasound image before the ultrasound image is captured. 
     As described above, the mammography apparatus  10  or the medical imaging apparatus  11  according to each of the above-described embodiments comprises the compression control unit  80 . 
     In a case in which the continuous imaging that captures a radiographic image of the breast compressed by the compression plate  34  and then captures an ultrasound image of the breast in the compressed state is performed, the compression control unit  80  performs control to set the compression force of the compression plate  34  against the breast to the first compression force in the capture of the radiographic image and to change the compression force of the compression plate  34  against the breast from the first compression force to the second compression force lower than the first compression force in the capture of the ultrasound image. 
     Alternatively, in a case in which the continuous imaging that captures a radiographic image of the breast compressed by the compression plate  34  and then captures an ultrasound image of the breast in the compressed state is performed, the compression control unit  80  performs control to set the compression pressure of the compression plate  34  against the breast to the first compression pressure in the capture of the radiographic image and to change the compression pressure of the compression plate  34  against the breast from the first compression pressure to the second compression pressure lower than the first compression pressure in the capture of the ultrasound image. 
     With the above-mentioned configuration, in a case in which the mammography apparatus  10  and the medical imaging apparatus  11  according to each of the above-described embodiments continuously captures a radiographic image and an ultrasound image in this order, the compression force or the compression pressure of the compression plate  34  against the breast is reduced. Therefore, according to the mammography apparatus  10  and the medical imaging apparatus  11 , it is possible to effectively relieve the pain of the subject. 
     In each of the above-described embodiments, in a case in which the compression force or the compression pressure of the compression plate  34  is changed from the first compression force or the first compression pressure to the second compression force or the second compression pressure, the compression control unit  80  continuously reduces the compression force or the compression pressure, that is, reduces the compression force or the compression pressure without passing through the compression force or the compression pressure lower than the second compression force or the second compression pressure. However, the present disclosure is not limited to each of the above-described embodiments. The overlap of the mammary gland tissues is developed by compressing the breast as described above. Therefore, the compression control unit  80  can change the compression force or the compression pressure to the extent that the overlap of the mammary gland tissues, that is, the development of the mammary gland tissues is not changed or the amount of change is within an allowable range even though the overlap is changed. For example, as the compressed state of the breast for the time from the start of the capture of a radiographic image to the end of the capture of an ultrasound image, the breast may be continuously compressed to the extent that the area of the breast which comes into contact with the imaging surface  40 A of the imaging table  40  is not changed. Therefore, the mammography apparatus  10  may reduce the compression against the breast according to the area of the breast which comes into contact with the imaging surface  40 A after a radiographic image is captured and before an ultrasound image is captured. 
     In each of the above-described embodiments, the mammography apparatus  10  or the medical imaging apparatus  11  comprises the compression control unit  80  and functions as the control device according to the present disclosure. However, the apparatus comprising the compression control unit  80  is not limited to each of the above-described embodiments. For example, another apparatus, such as the console  12 , in the medical imaging system  1  may have the functions of the compression control unit  80  and may function as the control device according to the present disclosure. 
     In each of the above-described embodiments, for example, the following various processors can be used as the hardware structure of processing units performing various processes such as the compression control unit  80  and the acquisition unit  82 . The various processors include, for example, a programmable logic device (PLD), such as a field-programmable gate array (FPGA), that is a processor whose circuit configuration can be changed after manufacture and a dedicated electric circuit, such as an application specific integrated circuit (ASIC), that is a processor having a dedicated circuit configuration designed to perform a specific process, in addition to the CPU that is a general-purpose processor which executes software (program) to function as various processing units as described above. 
     One processing unit may be configured by one of the various processors or a combination of two or more processors of the same type or different types (for example, a combination of a plurality of FPGAs or a combination of a CPU and an FPGA). In addition, a plurality of processing units may be configured by one processor. 
     A first example of the configuration in which a plurality of processing units are configured by one processor is an aspect in which one processor is configured by a combination of one or more CPUs and software and functions as a plurality of processing units. A representative example of this aspect is a client computer or a server computer. A second example of the configuration is an aspect in which a processor that implements the functions of the entire system including a plurality of processing units using one integrated circuit (IC) chip is used. A representative example of this aspect is a system-on-chip (SoC). As such, various processing units are configured by using one or more of the various processors as a hardware structure. 
     In addition, specifically, an electric circuit (circuitry) obtained by combining circuit elements, such as semiconductor elements, can be used as the hardware structure of the various processors. 
     In each of the above-described embodiments, the aspect in which the compression control processing program  21  is stored (installed) in the ROM  20 B in advance has been described. However, the invention is not limited thereto. The compression control processing program  21  may be recorded on a recording medium, such as a compact disk read only memory (CD-ROM), a digital versatile disk read only memory (DVD-ROM), or a universal serial bus (USB) memory, and then provided. In addition, the compression control processing program  21  may be downloaded from an external apparatus through the network. 
     For example, the configurations and operations of the medical imaging system  1 , the radiography system  2 , and the mammography apparatus  10  described in each of the above-described embodiments are illustrative and may be changed according to the situation, without departing from the scope and spirit of the invention. In addition, the above-described embodiments may be appropriately combined with each other. 
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