JP6021692B2 - Radiographic imaging apparatus, radiographic imaging method and program - Google Patents

Description

  The present invention relates to a radiographic image capturing apparatus, a radiographic image capturing method, and a program, and more particularly to a radiographic image capturing apparatus, a radiographic image capturing method, and a program for capturing a diagnostic radiographic image indicated by radiation transmitted through a subject.

  2. Description of the Related Art Conventionally, radiation image capturing apparatuses that capture medical images for the purpose of medical diagnosis are known. An example of this type of imaging apparatus is a mammography apparatus (mammography apparatus) that performs X-ray imaging of a patient's breast for the purpose of early detection of breast cancer.

  In a radiographic imaging apparatus including a mammography apparatus, in order to acquire a high-quality radiographic image, it is necessary to perform imaging by irradiating an appropriate dose of radiation according to the imaging target region of the subject. In particular, when the region to be imaged is the breast, the radiation transmittance changes depending on the thickness of the breast and the density of the mammary gland. Therefore, it is important to set the radiation dose according to the thickness of the breast and the density of the mammary gland.

  For example, in Patent Document 1, the pre-irradiation required dose is calculated using the breast thickness as a parameter, the pre-irradiation time is controlled, the pre-irradiation is performed, and the pre-irradiation is based on the radiation dose detected by the dose detection sensor. A radiographic imaging apparatus that captures a radiographic image of a breast by calculating a main irradiation necessary dose and controlling the irradiation time to perform main irradiation is described.

  Here, FIG. 1A and FIG. 1B are diagrams illustrating the photographing method described in Patent Document 1 described above. For example, when the measured breast thickness is smaller than the reference value, as shown in FIG. 1A, the tube current value I1 at the time of pre-irradiation is set to the breast thickness so that the pre-irradiation required dose is obtained. The tube current value I2 (I1> I2) is set according to the pre-irradiation, the main irradiation necessary dose is calculated, and the tube current value at the main irradiation is set so that the main irradiation necessary dose is obtained. Irradiate. On the other hand, when the measured breast thickness is larger than the reference value, as shown in FIG. 1B, the tube current value I1 at the time of pre-irradiation is changed to the tube current value I3 (I3>) according to the breast thickness. The main irradiation required dose is calculated by performing pre-irradiation with setting to I1), and the main current irradiation is performed by setting the tube current value at the main irradiation so as to obtain the main irradiation required dose.

JP 2009-22536 A

  As in the apparatus described in Patent Document 1, the radiation dose (tube current value and irradiation time) required during the main irradiation is calculated based on the radiation dose detected by the dose detection sensor during the pre-irradiation (hereinafter referred to as the following). This calculation is also referred to as AEC (Automatic Exposure Control) calculation. After the AEC calculation is completed, the main irradiation is started by changing the setting from the tube current value during pre-irradiation to the tube current value during main irradiation. There is a problem that a series of shooting time from the end of the main irradiation to the end of the main irradiation becomes long. That is, in the apparatus described in Patent Document 1, the main irradiation is started after a lapse of at least the sum of the AEC calculation time and the tube current value setting change time after the pre-irradiation. Here, the setting change of the tube current value is performed by increasing or decreasing the current flowing through the filament constituting the cathode of the radiation source (hereinafter also referred to as filament current). Since it is difficult to increase or decrease the filament current instantaneously, it takes some time to change the setting of the tube current value. In particular, since mammography apparatus compresses the breast from pre-irradiation, the burden on the patient increases when a series of imaging time from the start of pre-irradiation to the end of main irradiation becomes longer.

  The present invention has been made in view of the above points, and a radiographic image capturing apparatus and a radiographic image capturing method capable of shortening a series of imaging time from the start of pre-irradiation to the end of main irradiation as compared with the prior art. And to provide a program.

In order to achieve the above object, a radiographic imaging device according to the present invention includes a radiation source that irradiates a dose of radiation according to a set tube current value and an irradiation time, and an object irradiated from the radiation source. A dose detector for detecting a dose of transmitted radiation, a tube current value acquisition unit for acquiring a first tube current value and a second tube current value set for the radiation source, and the radiation source in advance. Based on the dose of the radiation detected by the dose detector and the predetermined second tube current value when the radiation is irradiated for the first tube current value and the irradiation time determined, the radiation An irradiation time deriving unit for deriving an irradiation time when the source irradiates radiation at the second tube current value; and from the start of radiation irradiation based on the first tube current value and the irradiation time, the second Tube current value and before In a series of shooting time by the irradiation time which is derived by the irradiation time derivation unit until the end of irradiation of radiation, the setting of tube current value for the radiation source prior to the irradiation time is derived by the irradiation time deriving section The tube current value switching unit for switching from the first tube current value to the second tube current value and the irradiation time derived by the second tube current value and the irradiation time deriving unit are irradiated from the radiation source. An image generation unit that detects radiation transmitted through the subject and generates a radiation image of the subject.

  The radiation source may include a pair of electrodes and a filament provided on one of the pair of electrodes, and the tube current value may be determined by the magnitude of the filament current flowing through the filament. In this case, the filament current is derived from the irradiation time deriving unit by the irradiation time deriving unit in response to switching from the first tube current value to the second tube current value by the tube current value switching unit. In parallel, the current value corresponding to the first tube current value may be shifted to the current value corresponding to the second tube current value.

  The radiographic image capturing apparatus according to the present invention includes a thickness detection unit that detects the thickness of the subject, and the first and second based on the thickness of the subject detected by the thickness detection unit. And a tube current value acquisition unit for acquiring the tube current value of the above.

  The tube current value acquisition unit may include a table in which the thickness of the subject and the first and second tube current values are stored in association with each other. In this case, the tube current value acquisition unit may acquire the first and second tube current values according to the thickness of the subject detected by the thickness detection unit based on the table. .

Further, a series of imaging from the start of radiation irradiation by the first tube current value and the irradiation time to the end of radiation irradiation by the irradiation time derived by the second tube current value and the irradiation time deriving unit. In time, the first tube current value in the table is such that the filament current reaches a current value corresponding to the second tube current value before the irradiation time is derived by the irradiation time deriving unit. The first and second tube current values may be set so that a difference from the second tube current value is equal to or less than a predetermined value.

  Further, the radiographic imaging device according to the present invention provides a tube that acquires a tube voltage value set for the radiation source when the radiation source emits radiation at the first and second tube current values. When the irradiation time derived by the voltage value acquisition unit and the irradiation time deriving unit is larger than a predetermined upper limit value, a tube voltage value larger than the tube voltage value acquired by the tube voltage value acquisition unit is set to the radiation source. The tube voltage value smaller than the tube voltage value acquired by the tube voltage value acquisition unit when the irradiation time derived by the irradiation time deriving unit is smaller than a predetermined lower limit value. The tube voltage value acquired by the tube voltage value acquisition unit when the irradiation time derived by the irradiation time deriving unit is within a predetermined range between the upper limit value and the lower limit value. Radiation Further may include a tube voltage value setting unit that sets against. In this case, the radiation source may irradiate radiation with a tube voltage value set by the tube voltage value setting unit.

  In addition, the radiographic imaging device according to the present invention may further include a thickness detection unit that detects the thickness of the subject. In this case, the tube voltage value acquisition unit may acquire the tube voltage value based on the thickness of the subject detected by the thickness detection unit.

  In addition, the tube voltage value setting unit, when the irradiation time derived by the irradiation time deriving unit is larger or smaller than the predetermined range, the irradiation time derived by the irradiation time deriving unit and the upper limit value or You may set the tube voltage value of the magnitude | size according to the difference with the said lower limit with respect to the said radiation source.

In order to achieve the above object, a radiographic imaging method according to the present invention includes a first tube predetermined from a radiation source that irradiates a dose of radiation according to a set tube current value and an irradiation time. Based on the dose detection step for detecting the dose of radiation irradiated at the current value and the irradiation time and transmitted through the subject, and the radiation dose detected in the dose detection step and a predetermined second tube current value From the irradiation time deriving step for deriving the irradiation time when the radiation source irradiates the radiation with the second tube current value, and from the start of radiation irradiation with the first tube current value and the irradiation time, the first in a series of shooting time to the end of the irradiation of the radiation by the derived irradiation time in the second tube current value and the irradiation time derivation step, you the irradiation time derivation step A tube current value switching step for switching the tube current value setting for the radiation source from the first tube current value to the second tube current value before the irradiation time is derived, and the second tube current And an image generation step of generating a radiation image of the subject by detecting the radiation irradiated from the radiation source at the irradiation time derived in the value and the irradiation time deriving step and transmitted through the subject.

  In the radiographic imaging method according to the present invention, a tube for acquiring a tube voltage value set for the radiation source when the radiation source emits radiation at the first and second tube current values. When the irradiation time derived in the voltage value acquisition step and the irradiation time deriving step is larger than a predetermined upper limit value, a tube voltage value larger than the tube voltage value acquired in the tube voltage value acquisition step is set to the radiation source. The tube voltage value smaller than the tube voltage value acquired in the tube voltage value acquisition step when the irradiation time derived in the irradiation time derivation step is smaller than a predetermined lower limit value is set to the radiation source. The tube voltage value acquisition step is performed when the irradiation time derived in the irradiation time deriving step is within a predetermined range between the upper limit value and the lower limit value. The has been tube voltage value acquired in-flop may further include and a tube voltage value setting step of setting with respect to the radiation source. In this case, the radiation source may irradiate the radiation with the tube voltage value set in the tube voltage value setting step when irradiating the radiation with the second tube current value.

In order to achieve the above object, a program according to the present invention is a program that causes a computer to transmit radiation that has passed through a subject when the radiation source is irradiated with radiation at a predetermined first tube current value and irradiation time. An irradiation time deriving unit for deriving an irradiation time when the radiation source emits radiation at the second tube current value based on the dose of the first tube current value and the predetermined second tube current value ; The irradiation time in a series of imaging time from the start of radiation irradiation by the tube current value and the irradiation time to the end of radiation irradiation by the irradiation time derived by the second tube current value and the irradiation time deriving unit A tube current value switching unit that switches the setting of the tube current value for the radiation source from the first tube current value to the second tube current value before the irradiation time is derived in the deriving unit; And it is configured as a program to be to function.

  The program according to the present invention further acquires a tube voltage value set for the radiation source when the radiation source emits radiation at the first and second tube current values. And a tube voltage value greater than the tube voltage value acquired by the tube voltage value acquisition unit when the irradiation time derived by the irradiation time deriving unit is greater than a predetermined upper limit value. The tube voltage value set for the radiation source and smaller than the tube voltage value acquired by the tube voltage value acquisition unit when the irradiation time derived by the irradiation time deriving unit is smaller than a predetermined lower limit value. A tube voltage set by the tube voltage value acquisition unit when set for a radiation source and the irradiation time derived by the irradiation time deriving unit is within a predetermined range between the upper limit value and the lower limit value A tube voltage value setting unit for setting to said radiation source, may be configured as a program for functioning as a.

  According to the radiographic image capturing apparatus, radiographic image capturing method, and program according to the present invention, it is possible to shorten a series of imaging time from the start of pre-irradiation to the end of main irradiation as compared with the prior art.

(A) And (b) is a figure which shows the conventional radiographic imaging method. It is a perspective view which shows the structure of the radiographic imaging apparatus which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the radiographic imaging apparatus which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the radiation source which concerns on embodiment of this invention. (A) And (b) is a front view which shows the operation state of a movable arm part. It is a schematic diagram for demonstrating the tomosynthesis imaging | photography function in the radiographic imaging apparatus which concerns on embodiment of this invention. It is a block diagram which shows the electric constitution of the radiographic imaging apparatus which concerns on embodiment of this invention. It is a flowchart which shows the flow of a process in the imaging | photography process program performed by CPU of the imaging device control part which concerns on embodiment of this invention. It is a flowchart which shows the flow of a process in the imaging | photography process program performed by CPU of the imaging device control part which concerns on embodiment of this invention. It is a figure which shows the structure of the table for acquiring 1st tube current value I1 and 2nd tube current value I2 which concern on embodiment of this invention. 4 is a time chart of tube current, tube voltage, and filament current during radiographic imaging processing according to an embodiment of the present invention. It is a time chart of tube current, tube voltage, and filament current concerning a comparative example. It is a flowchart in the case of performing 2D imaging | photography in the radiographic imaging apparatus which concerns on embodiment of this invention. It is a time chart in the case of performing 2D imaging | photography in the radiographic imaging apparatus which concerns on embodiment of this invention. It is a flowchart which shows the flow of a process in the imaging | photography process program performed by CPU of the imaging device control part which concerns on other embodiment of this invention. It is a flowchart which shows the flow of a process in the imaging | photography process program performed by CPU of the imaging device control part which concerns on other embodiment of this invention. It is a figure which shows the structure of the table for acquiring the 1st tube current value I1, the 2nd tube current value I2, and the tube voltage value Vm in the radiographic imaging process which concerns on other embodiment of this invention.

  Hereinafter, a radiographic imaging apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a case where the radiographic imaging device is configured as a mammography device having a tomosynthesis imaging function will be described as an example.

[First Embodiment]
FIG. 2 is a perspective view showing an example of the configuration of the radiographic image capturing apparatus 10 according to the embodiment of the present invention. FIG. 3 is a cross-sectional view taken along the center line in the left-right direction of the radiographic image capturing apparatus 10 according to the embodiment of the present invention. In addition, the up-down direction, the left-right direction, and the front-back direction are directions seen from the patient who is the subject P. A radiographic image capturing apparatus 10 (hereinafter also referred to as an image capturing apparatus 10) includes a base portion 12, a rotary shaft 14 provided so as to be movable along a guide portion 13 provided on the base portion 12, and a rotary shaft. 14 and a movable arm portion 16 attached to 14. The movable arm portion 16 is configured to be movable in the vertical direction by the movement of the rotating shaft 14, and is configured to be able to rotate counterclockwise and clockwise by the rotation of the rotating shaft 14.

  The movable arm portion 16 includes a first rotating portion 18 that is fixed to the rotating shaft 14 and a second rotating portion 20 that is detachably connected to the rotating shaft 14. The second rotating unit 20 is disposed closer to the subject P than the first rotating unit 18. The rotation shaft 14 is fixed to the rotation center of the first rotation unit 18 and is connected to the rotation center of the second rotation unit 20. The rotating shaft 14 and the second rotating portion 20 are provided with gears on both sides, for example, and the second rotating portion 20 is connected to the rotating shaft 14 in a state where the gear is engaged, and in a state where the gear is not engaged. It is separated from the rotating shaft 14.

  One end of an L-shaped support portion 24 is fixed to the first rotating portion 18. At the other end of the support part 24, a radiation irradiation part 28 for irradiating the breast M of the subject P with radiation is provided. The radiation irradiating unit 28 irradiates the radiation source 26 including an X-ray tube and radiation at a tube voltage value, a tube current value, and an irradiation time based on an instruction from the imaging apparatus control unit 50 described later. A radiation source driving unit 27 (see FIG. 7). The radiation source 26 rotates around the rotation axis 14 together with the first rotation unit 18 by the rotation of the rotation axis 14.

  A first holding unit 34 that holds the imaging table 32 is attached to the second rotating unit 20. Further, a handle 46 is provided in the first holding part 34. The imaging table 32 has an imaging surface 32A that comes into contact with the breast M of the subject P. A radiation detector 36 that detects radiation emitted from the radiation source 26 and transmitted through the breast M of the subject P is housed inside the imaging table 32.

  The radiation detector 36 detects radiation emitted from the radiation source 26 and transmitted through the breast M, generates and records image data of a radiation image, and outputs the recorded image data. The radiation detector 36 has, for example, a radiation-sensitive layer and a TFT substrate, and reads out the charges generated in the radiation-sensitive layer by the radiation irradiation and accumulated in the accumulation unit using the TFT, and displays a digital image indicating a radiation image. It is configured as a flat panel detector (FPD) that converts to image data and outputs it.

  Further, a second holding unit 38 that holds the compression plate 40 is attached to the second rotating unit 20. The compression plate 40 is supported by a support mechanism 42 attached to the second holding portion 38 so as to be movable in the vertical direction. By lowering the compression plate 40, the breast M of the subject P is compressed and fixed between the imaging surface 32A and the compression plate 40.

  The radiation detector 36 accommodated in the imaging table 32 is rotated around the rotation shaft 14 together with the second rotation portion 20 by the rotation of the rotation shaft 14 in a state where the rotation shaft 14 and the second rotation portion 20 are connected. Rotate. On the other hand, in a state where the rotary shaft 14 and the second rotary unit 20 are separated, even if the rotary shaft 14 rotates, the second rotary unit 20 does not rotate, and the imaging table 32 and the radiation detector 36 do not rotate. . That is, the radiation irradiation unit 28 and the radiation source 26, the imaging table 32, and the radiation detector 36 can be moved independently of each other.

  The imaging apparatus 10 includes a thickness detection unit 53 (see FIG. 7) that detects the thickness of the breast M in the irradiation direction of the breast M in a state where the breast M of the subject P is pressed by the compression plate 40. The thickness detection unit 53 detects the thickness of the breast M in the radiation direction based on the distance between the contact surface of the compression plate 40 with the breast M and the imaging surface 32A of the imaging table 32.

  In addition, the photographing apparatus 10 includes an operation panel 48 through which various operation instructions for the photographing apparatus 10 are input (see FIG. 7). Note that the operation panel 48 may be provided as a part of the photographing apparatus 10 or may be provided so as to be communicable with the photographing apparatus 10 in a separate console from the photographing apparatus 10.

  FIG. 4 is a cross-sectional view showing the configuration of the radiation source 26. The radiation source 26 includes a vacuum vessel 260, a filament 261 constituting a cathode provided in the vacuum vessel 260, and a target 262 constituting an anode. By passing a current (filament current) through the filament 261, the filament 261 is heated, and thermoelectrons are emitted from the filament 261. At this time, when a voltage (tube voltage) of about several tens of kV is applied between the filament 261 and the target 262, the high electrons accelerate the thermoelectrons in the direction of the target 262. When the thermal electrons collide with the target 262, X-rays are emitted from the target 262. The energy spectrum of the generated X-ray is a mixture of a continuous spectrum by bremsstrahlung with the acceleration energy of electrons as the maximum energy and a line spectrum (also called characteristic X-ray) whose energy is determined by the atomic structure of the target metal. Become. The target material is mainly tungsten when using the continuous spectrum, and the X-ray to be used from metal elements such as copper, molybdenum, cobalt, chromium, iron and silver when using the line spectrum. It is selected according to energy.

  Next, the operation of the movable arm unit 16 of the photographing apparatus 10 will be described. As described above, the imaging apparatus 10 according to the present embodiment includes the movable arm unit 16 that can move the radiation irradiation unit 28 and the radiation source 26, the imaging table 32, and the radiation detector 36 independently of each other. Therefore, it is possible to shoot in various shooting modes including CC shooting (shooting in the head-to-tail direction), MLO shooting (shooting in the inside / outside oblique direction), and tomosynthesis shooting.

  FIG. 5A and FIG. 5B are front views showing an operation state of the movable arm portion 16 of the photographing apparatus 10 according to the present embodiment.

  For example, at the time of CC shooting in a standing position where the subject P is standing, as shown by a solid line in FIG. 5A, the shooting surface 32A of the shooting table 32 is set to face upward so as to face the shooting surface 32A. The radiation irradiation unit 28 is disposed above the imaging surface 32A. The radiation irradiated from the radiation source 26 is irradiated from the upper side to the lower side with respect to the breast M of the subject P in the standing position. Thereby, CC imaging | photography is performed.

  Further, during MLO photographing in a sitting position where the subject P is sitting on a chair or the like, the movable arm unit 16 is moved downward and rotated around the rotation axis 14 as shown by a dotted line in FIG. Tilt to. Specifically, the imaging table 32 is tilted until the imaging surface 32A faces obliquely upward, and the radiation irradiation unit 28 is disposed diagonally above the imaging surface 32A so as to face the imaging surface 32A. The radiation irradiated from the radiation source 26 is irradiated obliquely from above the breast M of the subject P in the sitting position. Thereby, MLO imaging is performed.

  Next, the tomosynthesis imaging function of the imaging device 10 will be described. FIG. 6 is a schematic diagram for explaining a tomosynthesis photographing function in the photographing apparatus 10. According to tomosynthesis imaging, a stereoscopic image can be generated using a plurality of projection radiation images obtained by irradiating radiation from a plurality of directions toward the breast M of the subject P.

  At the time of tomosynthesis photographing with the subject P standing, as shown in FIG. 5 (b), the photographing surface 32 A of the photographing stand 32 is fixed so that the photographing arm 32 faces upward, and the movable arm portion 16 is rotated around the rotation shaft 14. By rotating, radiation is emitted from the radiation source 26 at each of the plurality of angular positions. Thereby, radiation is irradiated to the breast M of the subject P from a plurality of directions.

  As the movable arm portion 16 rotates around the rotation axis 14, the radiation source 26 moves in a circular arc above the radiation detector 36 as shown in FIG. For example, in the case of rotation in the positive direction, the radiation source 26 rotates clockwise from the angle −X ° to the angle + X ° at intervals of the angle θ °. In tomosynthesis imaging, the angular position of the radiation source 26 is moved with respect to the radiation detector 36 by rotating the movable arm 16 while the breast M is being compressed, and a plurality of different directions with respect to the breast M are obtained. A radiation image is acquired by irradiating with radiation. Thereby, a 3D (three-dimensional) tomographic image can be reconstructed.

  FIG. 7 is a block diagram showing an electrical configuration of the radiation image capturing apparatus 10. As described above, the imaging apparatus 10 includes the radiation irradiation unit 28 including the radiation source 26 and the radiation source driving unit 27, the radiation detector 36, the operation panel 48, and the thickness detection unit 53. In addition, the imaging apparatus 10 includes an imaging apparatus control unit 50 that comprehensively controls the operation of the entire apparatus, and a movable unit driving mechanism 52 that drives movable units such as the rotary shaft 14, the movable arm unit 16, and the compression plate 40 during imaging. And a communication interface unit 54 that is connected to a network such as a LAN (Local Area Network) and transmits / receives various information to / from other devices connected to the network.

  The imaging device control unit 50 includes a nonvolatile external storage device 50D such as a CPU (Central Processing Unit) 50A, a ROM (Read Only Memory) 50B, a RAM (Random Access Memory) 50C, and an HDD (Hard Disk Drive). . The imaging device control unit 50 is connected to each of the radiation irradiation unit 28, the radiation detector 36, the operation panel 48, the movable unit driving mechanism 52, the thickness detection unit 53, and the communication interface unit 54. The external storage device 50D or the ROM 50B stores programs executed by the CPU 50A, various data, and the like.

  Each of the radiation source driving unit 27 and the movable unit driving mechanism 52 is driven and controlled by the imaging device control unit 50. Thickness data indicating the thickness of the breast M generated by the thickness detector 53 and image data indicating the radiographic image generated by the radiation detector 36 are supplied to the imaging apparatus controller 50. The operation panel 48 notifies the photographing apparatus control unit 50 of information indicating the photographing mode selected according to the user's input operation.

  Below, the operation | movement at the time of the radiographic imaging in the radiographic imaging apparatus 10 which concerns on embodiment of this invention is demonstrated. Below, the case where the imaging device 10 performs tomosynthesis imaging will be described.

  FIG. 8 and FIG. 9 are flowcharts showing a flow of processing in the photographing processing program executed by the CPU 50A of the photographing device control unit 50 of the photographing device 10. The photographing processing program is stored in the ROM 50B of the photographing device control unit 50. This imaging processing program is executed, for example, when the user performs a predetermined input operation for starting radiographic image capturing on the operation panel 48.

  In step S11, the CPU 50A waits for reception of a shooting mode selection instruction. For example, when the user selects either the normal 2D (two-dimensional) shooting in which shooting is performed from only one direction or the tomosynthesis shooting in which shooting is performed from a plurality of directions with respect to the operation panel 48, an affirmative result is obtained in step S11. The determination is made and the process proceeds to step S12. Here, it is assumed that tomosynthesis imaging is selected by the user.

  In step S <b> 12, the CPU 50 </ b> A transmits an instruction to set the rotation angle position of the movable arm unit 16 to the initial position to the movable unit driving mechanism 52. The movable part drive mechanism 52 that has received such an instruction, for example, moves the movable arm part 16 to the rotation angle position (position −X ° shown in FIG. 6) having the greatest inclination.

  Thereafter, the positioning of the breast M with respect to the imaging table 32 is performed, and when the notification input to the effect that the positioning of the breast M is completed is performed on the operation panel 48, the process proceeds to step S13.

  In step S <b> 13, the CPU 50 </ b> A moves the compression plate 40 in the direction of the imaging table 32 to the movable part driving mechanism 52 and transmits an instruction to compress the breast M. The movable part drive mechanism 52 that has received such an instruction moves the compression plate 40 toward the imaging table 32 and brings it into contact with the breast M. Then, when the pressing force of the compression plate 40 reaches the set pressing force, the movable part drive mechanism 52 stops the movement of the compression plate 40. When the movement of the compression plate 40 stops, the thickness detection unit 53 determines the radiation of the breast M based on the distance between the contact surface of the compression plate 40 with the breast M and the imaging surface 32A of the imaging table 32. The thickness in the irradiation direction is detected, and thickness data indicating the detected thickness of the breast M is transmitted to the CPU 50A.

  In step S <b> 14, the CPU 50 </ b> A waits to receive thickness data from the thickness detection unit 53. When the CPU 50A receives the thickness data from the thickness detector 53, the received thickness data is stored in the RAM 50C, and the process proceeds to step S15.

  In step S15, the CPU 50A acquires the pre-irradiation tube current value I1 and the main irradiation tube current value I2 set in the radiation source 26 based on the thickness data received in the previous step S14. . In the present embodiment, the CPU 50A acquires the tube current values I1 and I2 with reference to a table (see FIG. 10) stored in advance in the ROM 50B. Here, the pre-irradiation is performed for the purpose of estimating an appropriate tube current time product (dose) Q of the radiation irradiated from the radiation source 26 at the time of the main irradiation so that a radiation image having an appropriate contrast can be obtained. This refers to irradiation. The main irradiation refers to irradiation of radiation performed for the purpose of acquiring a diagnostic radiation image.

  FIG. 10 is a diagram schematically illustrating a form of the table 100 used by the CPU 50A to acquire the tube current values I1 and I2 based on the thickness data of the breast M. As shown in FIG. 10, for example, the table 100 is configured by associating a pair of a tube current value I1 at the time of pre-irradiation and a tube current value I2 at the time of main irradiation for each thickness range of the breast M. ing. Here, the greater the thickness of the breast M, the greater the attenuation of the radiation that passes through the breast M. Therefore, the dose required to obtain a radiation image with an appropriate contrast increases. Therefore, in this embodiment, the table 100 is configured such that the tube current values I1 and I2 increase as the thickness of the breast M increases. Further, in tomosynthesis imaging, the imaging time at each angular position is limited, so it is preferable that the radiation irradiation time at each angular position is somewhat short. In order to obtain a radiographic image having an appropriate contrast in a short irradiation time, it is preferable to set the tube current value I2 to be somewhat large so that an appropriate dose can be obtained. In view of the above circumstances, the table 100 may be configured so that I2> I1 always holds in the paired tube current values I1 and I2. When the CPU 50A receives the thickness data of the breast M, the CPU 50A refers to the table 100 and obtains a pair of pre-irradiation tube current value I1 and main irradiation tube current value I2 corresponding to the thickness data. .

  In step S <b> 16, the CPU 50 </ b> A transmits an instruction to perform pre-irradiation to the radiation source driving unit 27 with the tube current value I <b> 1 acquired in step S <b> 15. The radiation source driving unit 27 that has received the instruction passes a filament current having a current value i1 corresponding to the tube current value I1 to the filament 261 so as to perform radiation irradiation at the tube current value I1. The radiation source driving unit 27 applies a predetermined tube voltage between the filament 261 (cathode) and the target 262 (anode). Thereby, radiation is irradiated from the radiation source 26 and pre-irradiation is performed on the breast M. The radiation that has passed through the breast M is applied to the radiation detector 36. The radiation detector 36 generates a radiation image corresponding to the dose distribution of radiation irradiated through the breast M and transmits image data indicating the radiation image to the imaging apparatus control unit 50.

  In step S <b> 17, the CPU 50 </ b> A transmits an instruction to set the tube current value in the radiation source 26 to the tube current value I <b> 2 at the time of main irradiation acquired in step S <b> 15 to the radiation source driving unit 27. The radiation source driving unit 27 that has received such an instruction shifts the filament current from the current value i1 corresponding to the tube current value I1 during pre-irradiation to the current value i2 corresponding to the tube current value I2 during main irradiation. As a result, the filament current gradually changes from the current value i1 toward the current value i2.

  In step S18, the CPU 50A waits for reception of image data based on pre-irradiation from the radiation detector 36. When image data is received from the radiation detector 36, the process proceeds to step S18. In step S19, the CPU 50A stores the acquired image data in the external storage device 50D.

  In step S20, the CPU 50A calculates the irradiation time of radiation during the main irradiation based on the image data based on the pre-irradiation acquired in the previous step S18 while the filament current is shifting from the current value i1 to i2. . That is, the CPU 50A analyzes the acquired image data and derives an appropriate tube current time product (dose) Q [mAs] of radiation at the time of main irradiation by calculation. Such an operation is referred to as an AEC operation in the technical field. Then, the CPU 50A divides the derived appropriate tube current time product (dose) Q by the tube current value I2 at the time of main irradiation acquired at the previous step S15, thereby giving the irradiation time T ( = Q / I2) is calculated. As described above, in the radiographic image capturing apparatus 10 according to the present embodiment, the transition of the filament current from the current value i1 to i2 and the calculation of the radiation irradiation time T during the main irradiation (AEC calculation) are performed in parallel. .

  In step S <b> 21, the CPU 50 </ b> A transmits an instruction to perform the main irradiation to the radiation source driving unit 27 at the irradiation time T calculated in the previous step S <b> 20. The radiation source driving unit 27 that has received such an instruction drives the radiation source 26 to perform radiation irradiation at the tube current value I2 and the irradiation time T. As a result, radiation is irradiated from the radiation source 26 and main irradiation is performed on the breast M. The radiation that has passed through the breast M is applied to the radiation detector 36. The radiation detector 36 generates a radiation image corresponding to the dose distribution of radiation irradiated through the breast M and transmits image data indicating the radiation image to the imaging apparatus control unit 50.

  In step S22, the CPU 50A waits for reception of image data based on the main irradiation from the radiation detector 36. When the image data is received from the radiation detector 36, the process proceeds to step S23. In step S23, the CPU 50A stores the acquired image data in the external storage device 50D.

  In step S24, the CPU 50A determines whether or not the rotational angle position of the movable arm portion 16 is at the final position (in this embodiment, the position of + X °). If not, the process proceeds to step S25. To do.

  In step S <b> 25, the CPU 50 </ b> A transmits an instruction to move the rotational angle position of the movable arm unit 16 in the positive direction by one step to the movable unit driving mechanism 52. The movable part drive mechanism 52 that has received such an instruction moves the rotational angle position of the movable arm part 16 in the forward direction by one step. When the movement of the movable arm unit 16 is completed, the CPU 50A repeatedly executes the processing from step S21 to step S24. Thus, the main irradiation is performed every time the movable arm portion 16 moves by θ ° from −X ° to + X °, image data is acquired for each angular position, and each of the acquired image data is stored in the external storage device. Stored in 50D.

  When the CPU 50A determines in step S24 that the rotational angle position of the movable arm portion 16 is at the final position, this routine is terminated.

FIG. 11 is a time chart of tube current, tube voltage, and filament current in the radiation source 26 when tomosynthesis imaging is performed according to the above processing flow. When CPU50 at time t ₁ sends an instruction to be carried out pre-irradiation with a tube current value I1 to the radiation source driving unit 27, the radiation source driver 27, the current value i1 corresponding filament current to the tube current value I1 Set. The filament current gradually increases toward the current value i1. When the filament current reaches the current value i1, the radiation source driving unit 27 applies a predetermined tube voltage between the filament 261 (cathode) and the target 262 (anode). As a result, pre-irradiation is performed from the radiation source 26 at the tube current value I1.

At time t ₂ after the pre-irradiation, the CPU50 sends a command to be set in the tube current value I2 in the radiation source driving unit 27, the radiation source driver 27, current corresponding settings filament current to the tube current value I2 Change to value i2. As a result, the filament current gradually changes from the current value i1 toward the current value i2. Further, CPU 50 may calculate the irradiation time T of the radiation at the irradiating (AEC operation) is started based from time t ₂ to the image data obtained by the pre-irradiation. That is, the calculation (AEC calculation) processing of the irradiation time T and the transition of the filament current from the current value i1 to i2 are performed in parallel.

Filament current reaches the current value i2, in and AEC time t ₃ after the completion of the operation, CPU 50 transmits an instruction to conduct the irradiation in the irradiation time T calculated in AEC operation in the radiation source driving unit 27 . The radiation source driving unit 27 that has received the instruction applies a predetermined tube voltage between the filament 261 (cathode) and the target 262 (anode). As a result, the first main irradiation is performed from the radiation source 26 at the tube current value I2 and the irradiation time T, and image data is acquired. CPU50 transmits at time t ₄ after the movement of the movable arm portion 16 is completed, the instruction to be performed a second time the radiation to the radiation source driver 27. Thereby, the second main irradiation is performed at the tube current value I2 and the irradiation time T, and image data is acquired. Thereafter, the movement of the movable arm unit 16 and the main irradiation are repeated, and image data is acquired for each angular position of the movable arm unit 16. As described above, in the imaging apparatus 10 according to the present embodiment, the tube at the time of main irradiation is obtained. The current value I2 is acquired before the AEC calculation is executed, and the setting of the tube current value is changed from I1 to I2 after the pre-irradiation and before the AEC calculation is completed, whereby the filament current is changed from the current value i1. AEC calculation is performed while the current value i2 is shifted. That is, in the photographing apparatus 10 according to the present embodiment, the transition period in which the filament current shifts from the current value i1 to i2 overlaps the AEC calculation period.

FIG. 12 is a time chart according to a comparative example in which both the tube current value I2 and the irradiation time T at the time of main irradiation are calculated by AEC calculation. In this comparative example, at time t ₂₁ after the completion pre irradiation, AEC operation is started. In this AEC calculation, both the tube current value I2 and the irradiation time T during the main irradiation are calculated based on the image data acquired by the pre-irradiation. In this comparative example, switching to the time t ₂₂ in the AEC operation the irradiation time of the tube current value I2 calculated by the AEC operation is completed is started. The filament current gradually changes from the current value i1 toward the current value i2. Then, the filament current at time t ₃ after reaching the current value i2 is the first of the radiation is performed. In the procedure according to this comparative example, since the tube current value I2 at the time of the main irradiation is calculated by the AEC calculation, the filament current setting change is performed after waiting for the result of the AEC calculation. That is, in the procedure of this comparative example, since the AEC calculation processing and the transition from the filament current value i1 to i2 are not performed in parallel, the time from the completion of pre-irradiation to the first main irradiation start time It becomes longer than the case where the procedure which concerns on embodiment of this invention is used.

  In the above embodiment, the case where the movable arm unit 16 is moved stepwise from −X ° to + X ° by the angle θ ° is exemplified. However, the movable arm unit 16 is operated in the following manner to perform tomosynthesis. Shooting may be performed. That is, pre-irradiation is performed in a state where the movable arm portion 16 is stopped at, for example, a position of −X °, and then the movable arm portion 16 starts moving toward an angular position of + X °. The movable arm portion 16 moves at a low speed without stopping from -X ° to + X °. While the movable arm portion 16 moves from −X ° to + X °, a predetermined number of main irradiations are performed, and thereby radiographic images at a plurality of angular positions are taken.

  Note that the imaging apparatus 10 according to the present embodiment can perform 2D imaging in which imaging is performed from only one direction in addition to tomosynthesis imaging. FIG. 13 is a flowchart showing the flow of processing in a shooting processing program executed by the CPU 50A when performing 2D shooting. Note that the processing from steps S11 to S19 shown in FIG. 8 is the same as the flow at the time of tomosynthesis imaging, and therefore the processing after step S19 will be described.

  In step S <b> 30, the CPU 50 </ b> A calculates the irradiation time of radiation during the main irradiation based on the image data acquired by performing the pre-irradiation while the filament current is shifted from the current value i <b> 1 to i <b> 2. That is, the CPU 50A analyzes the acquired image data and derives an appropriate tube current time product (dose) Q [mAs] of radiation at the time of main irradiation by calculation. Then, the CPU 50A divides the derived appropriate tube current time product (dose) Q by the tube current value I2 at the time of main irradiation acquired at the previous step S15, thereby giving the irradiation time T ( = Q / I2) is calculated. That is, even when performing 2D imaging, the transition of the filament current from the current value i1 to i2 and the calculation of the irradiation time T of radiation at the time of main irradiation (AEC calculation) are performed in parallel.

  In step S <b> 31, the CPU 50 </ b> A transmits an instruction to perform the main irradiation to the radiation source driving unit 27 at the irradiation time T calculated in the previous step S <b> 30. The radiation source driving unit 27 that has received such an instruction drives the radiation source 26 to perform radiation irradiation at the tube current value I2 and the irradiation time T. As a result, radiation is irradiated from the radiation source 26 and main irradiation is performed on the breast M. The radiation that has passed through the breast M is applied to the radiation detector 36. The radiation detector 36 generates a radiation image corresponding to the dose of radiation that has been transmitted through the breast M, and transmits image data indicating the radiation image to the imaging apparatus control unit 50.

  In step S32, the CPU 50A waits for reception of image data based on the main irradiation from the radiation detector 36. When the image data is received from the radiation detector 36, the process proceeds to step S33. In step S33, the CPU 50A stores the acquired image data in the external storage device 50D, and this routine ends. In 2D imaging, CC imaging in which imaging is performed without tilting the movable arm 16 is preferable, but imaging may be performed at any angular position.

FIG. 14 is a time chart of tube current, tube voltage, and filament current in the radiation source 26 when 2D imaging is performed according to the above processing flow. When CPU50 at time t ₁ sends an instruction to be carried out pre-irradiation with a tube current value I1 to the radiation source driving unit 27, the radiation source driver 27, the current value i1 corresponding filament current to the tube current value I1 Set. The filament current gradually increases toward the current value i1. When the filament current reaches the current value i1, the radiation source driving unit 27 applies a predetermined tube voltage between the filament 261 (cathode) and the target 262 (anode). Thereby, radiation is irradiated from the radiation source 26 with the tube current I1, and pre-irradiation is performed.

At time t ₂ after the pre-irradiation, the CPU50 sends a command to be set in the tube current value I2 in the radiation source driving unit 27, the radiation source driver 27, current corresponding settings filament current to the tube current value I2 Change to value i2. The filament current gradually changes from the current value i1 toward the current value i2. Further, CPU 50 may calculate the irradiation time T of the radiation at the irradiating (AEC operation) is started based from time t ₂ to the image data obtained by the pre-irradiation. That is, the calculation (AEC calculation) processing of the irradiation time T and the transition of the filament current from the current value i1 to i2 are performed in parallel.

Filament current reaches the current value i2, in and AEC time t ₃ after the completion of the operation, CPU 50 transmits an instruction to conduct the irradiation in the irradiation time T calculated in AEC operation in the radiation source driving unit 27 . The radiation source driving unit 27 that has received the instruction applies a predetermined tube voltage between the filament 261 (cathode) and the target 262 (anode). As a result, radiation is irradiated from the radiation source 26 at the tube current I2 and the irradiation time T, and main irradiation for 2D imaging is performed to acquire image data. Note that, when the tube current values I1 and I2 are acquired from the thickness of the breast M of the subject P, a 2D imaging table different from the tomosynthesis imaging table may be used. That is, the imaging apparatus 10 has a table in which a pair of the tube current value I1 at the time of pre-irradiation and the tube current value I2 at the time of main irradiation is associated with each thickness range of the breast M for each imaging mode. Also good. In 2D imaging, since main irradiation is performed only once, the tube current value I2 at the time of main irradiation may be set smaller than when performing tomosynthesis imaging, while the irradiation time may be set longer than when performing tomosynthesis imaging. . Therefore, in the table for 2D imaging, the table may be configured so that I1> I2 in the paired tube current values I1 and I2.

  In the radiographic imaging apparatus 10 according to the present embodiment, when tomosynthesis imaging is performed, image data generated by pre-irradiation can be used for AEC calculation and also used as a diagnostic image (2D image). As described above, the image data can be generated. In this case, when an instruction to move the movable arm unit 16 to the initial position is issued from the CPU 50A in step S12 of the flowchart shown in FIG. 8, the movable unit drive mechanism 52 moves the movable arm unit 16 to the angular position where the tilt is zero. It may be moved. In this case, the movable arm portion 16 is positioned so that the radiation direction is substantially perpendicular to the imaging surface 32A. In step S16 of the flowchart shown in FIG. 8, when an instruction to start pre-irradiation with the tube current value I1 is issued from the CPU 50A, the radiation source driving unit 27 performs the tube current value I1, the predetermined tube voltage, and the irradiation. The radiation source 26 is driven so that radiation is emitted in time. At this time, the tube current value I1, the tube voltage, and the irradiation time set for the radiation source 26 may be set to values different from the case where the image generated by the pre-irradiation is used only for the AEC calculation. .

  The radiation detector 36 generates a radiation image corresponding to the dose of radiation that has been transmitted through the breast M, and transmits image data indicating the radiation image to the imaging apparatus control unit 50. Then, in step S17 of the flowchart shown in FIG. 8, the CPU 50A waits for reception of image data based on the pre-irradiation from the radiation detector 36. When the image data is received from the radiation detector 36, the process proceeds to step S18. . In step S18, the CPU 50A stores the acquired image data in the external storage device 50D. Such image data is used for calculation of the irradiation time of radiation at the time of main irradiation and is used as a diagnostic image. After the pre-irradiation is completed, the movable arm unit 16 moves from the position of zero tilt to, for example, the angle position of −X ° having the largest tilt. Thereafter, every time the movable arm unit 16 moves by θ ° from −X ° to + X °, main irradiation is performed, image data is acquired for each angular position, and each of the acquired image data is stored in the external storage device 50D. Is remembered.

  As is clear from the above description, according to the radiographic imaging device 10 according to the embodiment of the present invention, the thickness of the breast M is detected and detected when the breast M of the subject P is compressed with the compression plate 40. Based on the thickness of the breast M, the tube current value I1 during pre-irradiation and the tube current value I2 during main irradiation are acquired. Then, after pre-irradiation is performed at the tube current value I1, the setting of the tube current value is changed from I1 to I2 without waiting for the result of the AEC calculation. That is, according to the radiographic imaging apparatus 10 according to the present embodiment, the AEC calculation for calculating the radiation irradiation time T at the time of the main irradiation is performed by using the tube current from the current value i1 corresponding to the tube current value I1 of the filament current. It is performed simultaneously with the period changing toward the current value i2 corresponding to the value I2. Therefore, the tube current value I2 at the time of the main irradiation is calculated by the AEC calculation, and compared with the case where the setting of the tube current value is changed after the AEC calculation (see FIG. 12), from the start of the pre-irradiation to the end of the main irradiation. A series of imaging time can be shortened, and the burden on the patient can be reduced.

  Here, it is preferable that the transition of the filament current from the current value i1 to i2 is completed by the end of the AEC calculation. In other words, it is preferable that the transition period of the filament current from the current value i1 to i2 falls within the AEC calculation period. As a result, the main irradiation can be performed immediately after the completion of the AEC calculation, so that the time from the pre-irradiation to the main irradiation can be minimized. Since the change rate of the filament current and the AEC calculation period are substantially constant, the greater the difference between the current values i1 and i2 (that is, the greater the difference between the tube current values I1 and I2), the more the filament current transitions. It takes a lot of time. Therefore, the table 100 may be constructed by limiting the difference ΔI between the tube current values I1 and I2 so that the transition period of the filament current from the current value i1 to i2 falls within the AEC calculation period.

[Second Embodiment]
A radiographic imaging apparatus according to the second embodiment of the present invention will be described below. In tomosynthesis imaging, as described above, radiographic images are captured while the radiation direction of the breast M is sequentially moved by moving the rotational angle position of the movable arm 16. In tomosynthesis imaging, the period from imaging at a certain angular position to imaging at the next angular position (that is, the imaging cycle) is substantially constant, for example, about 0.5 seconds. Since it is necessary to complete imaging, reading of image data from the radiation detector 36, and movement of the movable arm portion 16 within this imaging cycle, an upper limit value of the radiation irradiation time T in the main irradiation is determined. Moreover, since the precision will deteriorate if the irradiation time of radiation becomes extremely short, the lower limit of irradiation time T is also defined.

  In the radiographic image capturing apparatus according to the second embodiment of the present invention, the tube current value I2 at the time of main irradiation is acquired and the AEC calculation is performed before the AEC calculation is performed, as in the first embodiment. And filament current transfer in parallel. Here, the irradiation time T calculated by the AEC calculation may exceed a predetermined upper limit value or be lower than a predetermined lower limit value. The case where the upper limit value is exceeded is, for example, a case where the density of the mammary gland is higher than expected, and the case where the density falls below the lower limit value is, for example, a case where the density of the mammary gland is lower than expected. In the radiographic imaging device according to the second embodiment, when the radiation irradiation time T calculated by the AEC calculation is not within a predetermined upper and lower limit range, the magnitude of the tube voltage is changed from the initial set value. By changing, a radiographic image having an appropriate contrast is generated.

  The operation at the time of radiographic image capturing in the radiographic image capturing apparatus according to the second embodiment of the present invention will be described below. In the following description, a case where the radiographic imaging apparatus performs tomosynthesis imaging will be described. Note that the hardware configuration of the radiographic imaging apparatus according to the second embodiment is the same as that of the radiographic imaging apparatus 10 according to the first embodiment described above.

  FIGS. 15 and 16 are flowcharts showing the flow of processing in the photographing processing program executed by the CPU 50A of the photographing device control unit 50 according to the second embodiment. The photographing processing program is stored in the ROM 50B of the photographing device control unit 50. This imaging processing program is executed, for example, when the user performs a predetermined input operation for starting radiographic image capturing on the operation panel 48.

  In step S41, the CPU 50A waits for reception of a shooting mode selection instruction. For example, when the user selects either the normal 2D shooting for shooting from one direction or the tomosynthesis shooting for shooting from a plurality of directions on the operation panel 48, an affirmative determination is made in step S41. The process proceeds to step S42. Here, it is assumed that tomosynthesis imaging is selected by the user.

  In step S <b> 42, the CPU 50 </ b> A transmits an instruction to set the rotation angle position of the movable arm unit 16 to the initial position to the movable unit driving mechanism 52. The movable part drive mechanism 52 that has received such an instruction, for example, moves the movable arm part 16 to the rotation angle position (position −X ° shown in FIG. 6) having the greatest inclination.

  Thereafter, the positioning of the breast M with respect to the imaging table 32 is performed, and when the user inputs a notification indicating that the positioning of the breast M is completed to the operation panel 48, the process proceeds to step S43.

  In step S <b> 43, the CPU 50 </ b> A moves the compression plate 40 toward the imaging table 32 toward the movable unit driving mechanism 52 and transmits an instruction to compress the breast M. The movable part drive mechanism 52 that has received such an instruction moves the compression plate 40 toward the imaging table 32 and brings it into contact with the breast M. Then, when the pressing force of the compression plate 40 reaches the set pressing force, the movable part drive mechanism 52 stops the movement of the compression plate 40. When the movement of the compression plate 40 stops, the thickness detection unit 53 irradiates the radiation of the breast M based on the distance between the contact surface of the compression plate 40 with the breast M and the imaging surface 32A of the imaging table 32. The thickness in the direction is detected, and thickness data indicating the detected thickness of the breast M is transmitted to the CPU 50A.

  In step S <b> 44, the CPU 50 </ b> A waits to receive thickness data from the thickness detection unit 53. When the CPU 50A receives the thickness data from the thickness detector 53, the received thickness data is stored in the RAM 50C, and the process proceeds to step S45.

  In step S45, the CPU 50A determines the pre-irradiation tube current value I1 set in the radiation source 26 and the main irradiation tube current based on the thickness data indicating the thickness of the breast M received in the previous step S44. The value I2 and the tube voltage value Vm during pre-irradiation and main irradiation are acquired. In the present embodiment, the CPU 50A obtains the tube current values I1 and I2 and the tube voltage value Vm with reference to a table (see FIG. 17) stored in advance in the ROM 50B.

  FIG. 17 is a diagram illustrating a form of the table 110 used by the CPU 50A to acquire the tube current values I1 and I2 and the tube voltage value Vm based on the thickness data of the breast M. 17, for example, for each thickness range of the breast M, the tube current value I1 during pre-irradiation, the tube current value I2 during main irradiation, and the tube voltage values during pre-irradiation and main irradiation are shown in FIG. A set of Vm is associated with each other. The greater the thickness of the breast M, the greater the attenuation of radiation that passes through the breast M, and the greater the dose required to obtain a proper radiographic image. Therefore, in this embodiment, the table 110 is configured such that the tube current values I1 and I2 and the tube voltage value Vm increase as the thickness of the breast M increases. When the CPU 50A receives the thickness data of the breast M, the CPU 50A refers to the table 110 to obtain the tube voltage value Vm, the pre-irradiation tube current value I1, and the main irradiation tube current I2 corresponding to the thickness data. get.

  In step S46, the CPU 50A transmits to the radiation source driving unit 27 an instruction to perform pre-irradiation with the tube current value I1 and the tube voltage value Vm acquired in step S45. The radiation source driving unit 27 that has received the instruction causes the filament 261 to pass a filament current having a current value i1 having a magnitude corresponding to the tube current value I1 in order to perform radiation irradiation with the tube current value I1. The radiation source driving unit 27 applies a tube voltage having a voltage value Vm between the filament 261 (cathode) and the target 262 (anode). Thereby, radiation is irradiated from the radiation source 26 and pre-irradiation is performed on the breast M. The radiation that has passed through the breast M is applied to the radiation detector 36. The radiation detector 36 generates a radiation image corresponding to the dose distribution of radiation irradiated through the breast M and transmits image data indicating the radiation image to the imaging apparatus control unit 50.

  In step S47, the CPU 50A transmits an instruction to set the tube current value in the radiation source 26 to the tube current value I2 at the time of main irradiation acquired in the previous step S45 to the radiation source driving unit 27. The radiation source driving unit 27 that has received such an instruction shifts the filament current from the current value i1 corresponding to the tube current value I1 during pre-irradiation to the current value i2 corresponding to the tube current value I2 during main irradiation. As a result, the filament current gradually changes from the current value i1 toward the current body i2.

  In step S48, the CPU 50A waits for reception of image data based on the pre-irradiation from the radiation detector 36. When the image data is received from the radiation detector 36, the process proceeds to step S49. In step S49, the CPU 50A stores the acquired image data in the external storage device 50D.

  In step S50, the CPU 50A determines the radiation irradiation time during the main irradiation based on the image data based on the pre-irradiation acquired in the previous step S48 while the filament current is shifting from the current value i1 to the current value i2. calculate. That is, the CPU 50A analyzes the acquired image data and derives an appropriate tube current time product (dose) Q [mAs] of radiation at the time of main irradiation by calculation (AEC calculation). Then, the CPU 50A divides the derived appropriate tube current time product (dose) Q by the tube current value I2 at the time of main irradiation acquired at the previous step S46, thereby giving the irradiation time T ( = Q / I2) is calculated. Thus, in the radiographic imaging device according to the present embodiment, the transition of the filament current from the current value i1 to i2 and the calculation of the radiation irradiation time T during the main irradiation (AEC calculation) are performed in parallel.

  In step S51, the CPU 50A determines whether or not the irradiation time T calculated in the previous step S50 is longer than a predetermined upper limit value Tmax. The upper limit value Tmax is a value defined based on, for example, the imaging cycle at each angular position when tomosynthesis imaging is performed. When the CPU 50A determines that the shooting time T calculated by the AEC calculation is smaller than the upper limit value Tmax (negative determination), the CPU 50A moves the process to step S52, and the shooting time T calculated by the AEC calculation is the predetermined upper limit. If it is determined that the value is greater than the value (positive determination), the process proceeds to step S53.

  In step S53, the CPU 50A derives a tube voltage value Vh larger than the tube voltage value Vm acquired in the previous step S45. The tube voltage value Vh may be a value determined to increase as the difference between the irradiation time T calculated by, for example, AEC calculation and the upper limit value Tmax increases. For example, the CPU 50A may derive the tube voltage value Vh by performing a predetermined calculation using the difference between the irradiation time T and the upper limit value Tmax as a parameter. Further, the CPU 50A obtains an increase ΔV with respect to the tube voltage value Vm corresponding to the difference value by referring to a predetermined table using the difference value between the irradiation time T and the upper limit value Tmax as a search key. The value Vh (= Vm + ΔV) may be derived. That is, when the main irradiation is performed at the tube current value I2 and the irradiation time Tmax when the irradiation time T of the radiation calculated by the AEC calculation exceeds the upper limit value Tmax, the irradiation is performed from the radiation source 26 in the main irradiation. The radiation dose is less than the appropriate tube current time product (dose) Q. Therefore, in such a case, by changing the initially set tube voltage value Vm to a tube voltage value Vh larger than this and irradiating with radiation, the shortage with respect to an appropriate tube current time product (dose) Q can be reduced. It is supplemented by the tube voltage, which makes it possible to acquire a radiation image having an appropriate contrast.

  In step S52, the CPU 50A determines whether or not the irradiation time T calculated by the AEC calculation is smaller than a predetermined lower limit value Tmin. This lower limit value Tmin is a value defined based on, for example, the required accuracy of irradiation time. When the CPU 50A determines that the irradiation time T calculated by the AEC calculation is larger than the lower limit value Tmin (negative determination), the CPU 50A moves the process to step S55, and the irradiation time T calculated by the AEC calculation is the predetermined lower limit. If it is determined that the value is smaller than the value (positive determination), the process proceeds to step S54.

  In step S54, the CPU 50A derives a tube voltage value Vl smaller than the tube voltage value Vm acquired in the previous step S45. The tube voltage value Vl may be a value determined so as to decrease as the difference between the irradiation time T calculated by AEC calculation and the lower limit value Tmin increases, for example. For example, the CPU 50A may derive the tube voltage value Vl by performing a predetermined calculation using the difference between the irradiation time T and the lower limit value Tmin as a parameter. Further, the CPU 50A obtains a decrease ΔV with respect to the tube voltage value Vm corresponding to the difference value by referring to a predetermined table using the difference value between the irradiation time T and the lower limit value Tmin as a search key, thereby obtaining the tube voltage. The value Vl (= Vm−ΔV) may be derived. That is, if the main irradiation is performed with the tube current value I2 and the irradiation time Tmin when the irradiation time T of the radiation calculated by the AEC calculation is less than the lower limit value Tmin, the radiation irradiated from the radiation source 26 in the main irradiation. The dose is greater than the appropriate tube current time product (dose) Q. Therefore, in such a case, by changing the initially set tube voltage value Vm to a smaller tube voltage value Vl and irradiating with radiation, an excess amount with respect to an appropriate tube current time product (dose) Q can be obtained. It is possible to acquire a radiographic image having a snowy contrast, which is canceled by the tube voltage. When the irradiation time T calculated by the AEC calculation is within a predetermined range (that is, when the irradiation time T is not less than the lower limit value Tmin and not more than the upper limit value Tmax), the initial tube voltage value Vm is maintained. Is done.

  In step S <b> 55, the CPU 50 </ b> A transmits an instruction to perform main irradiation to the radiation source driving unit 27. At this time, when the tube voltage value is changed to Vh in step S53, the CPU 50A issues an instruction to perform main irradiation with the tube voltage value Vh and the irradiation time Tmax. In addition, when the tube voltage value is changed to Vl in step S54, the CPU 50A issues an instruction to perform main irradiation with the tube voltage value Vl and the irradiation time Tmin. Further, when maintaining the tube voltage value Vm, the CPU 50A issues an instruction to perform the main irradiation with the tube voltage value Vm and the irradiation time T. The radiation source driving unit 27 that has received such an instruction drives the radiation source 26 to perform radiation irradiation under the instructed condition. As a result, radiation is irradiated from the radiation source 26 and main irradiation is performed on the breast M. The radiation that has passed through the breast M is applied to the radiation detector 36. The radiation detector 36 generates a radiation image corresponding to the dose distribution of radiation irradiated through the breast M and transmits image data indicating the radiation image to the imaging apparatus control unit 50.

  In step S56, the CPU 50A waits for reception of image data based on the main irradiation from the radiation detector 36. When image data is received from the radiation detector 36, the process proceeds to step S57. In step S57, the CPU 50A stores the acquired image data in the external storage device 50D.

  In step S58, the CPU 50A determines whether or not the rotational angle position of the movable arm portion 16 is at the final position (in this embodiment, the position of + X °). If not, the process proceeds to step S59. To do.

  In step S <b> 59, the CPU 50 </ b> A transmits an instruction to move the rotational angle position of the movable arm unit 16 in the positive direction by one step to the movable unit driving mechanism 52. The movable part drive mechanism 52 that has received such an instruction moves the rotational angle position of the movable arm part 16 in the forward direction by one step. When the movement of the movable arm unit 16 is completed, the CPU 50A repeatedly executes the processing from step S55 to step S58. Thus, the main irradiation is performed every time the movable arm portion 16 moves by θ ° from −X ° to + X °, image data is acquired for each angular position, and each of the acquired image data is stored in the external storage device. Stored in 50D.

  When the CPU 50A determines in step S58 that the rotational angle position of the movable arm portion 16 is in the final position, this routine ends.

  As described above, in the radiographic imaging device according to the second exemplary embodiment of the present invention, as in the first exemplary embodiment, the tube current value I2 at the time of main irradiation is calculated by the AEC calculation, and the tube current is calculated after the AEC calculation. Compared with the case of changing the value setting (see FIG. 12), the time from the pre-irradiation to the main irradiation can be shortened, and the burden on the patient can be reduced. Further, in the radiographic imaging device according to the second embodiment, when the irradiation time T calculated by the AEC calculation exceeds the predetermined upper limit value Tmax, the radiographic imaging device is set based on the thickness of the breast M of the subject P. The tube voltage value Vm is changed to a tube voltage value Vh larger than this, and the main irradiation is performed with the tube voltage value Vh, the irradiation time Tmax, and the tube current value I2. On the other hand, when the irradiation time T calculated by the AEC calculation is less than the predetermined lower limit value Tmin, the tube voltage value Vm set based on the thickness of the breast M of the subject P is smaller than this. It is changed to Vl, and the main irradiation is performed with the tube voltage value Vl, the irradiation time Tmin, and the tube current value I2. This makes it possible to acquire a radiation image with an appropriate contrast in tomosynthesis imaging in which upper and lower limits are set for the irradiation time of radiation at each angular position.

  In each of the above embodiments, the case where the tube current values I1 and I2 corresponding to the thickness of the breast M of the subject P are obtained by referring to the table 100 or 110 stored in advance is exemplified. It is not limited. For example, a relational expression between the thickness of the breast M and the tube current values I1 and I2 may be stored, and the tube current values I1 and I2 corresponding to the thickness of the breast M may be calculated using this relational expression. .

  In each of the above embodiments, in the table 100 and the table 110, the tube current value I1 at the time of pre-irradiation and the tube current value I2 at the time of main irradiation are stored in association with the thickness of the breast M. The current values i1 and i2 of the filament current may be stored in association with the thickness of the breast M.

  Further, in each of the above embodiments, the case where the thickness of the breast M of the subject P is measured and the tube current values I1 and I2 are acquired based on the measured thickness in the flow of radiographic image capturing processing is illustrated. However, the thickness of the breast M of the subject P may be measured before the radiographic image capturing process is started, and the tube current values I1 and I2 obtained from the result may be input to the radiographic image capturing apparatus. . That is, in this case, the radiographic image capturing apparatus performs pre-irradiation and main irradiation with tube current values I1 and I2 given from the outside.

  In each of the above embodiments, the case where the CPU 50A performs the AEC calculation after instructing the change of the tube current value from I1 to I2 is exemplified. However, the CPU 50A changes the tube current value from the I1 to I2 during the AEC calculation. An instruction may be issued. That is, in this case, the transition of the filament current from the current value i1 to the current value i2 is started during the AEC calculation.

  Further, in each of the above embodiments, the case where the AEC calculation is performed using the image data generated by the radiation detector 36 at the time of pre-irradiation is illustrated. However, for example, the dose of radiation transmitted through the subject P is detected and detected. A dedicated sensor that outputs a detection signal corresponding to the dose received may be provided in the imaging table 32 or the radiation detector 36, and AEC calculation may be performed based on the detection signal of the sensor.

  In each of the above embodiments, the radiographic image capturing apparatus that generates a radiographic image by X-ray irradiation is illustrated. However, a radiographic image that generates a radiographic image by irradiation with radiation other than X-rays such as α-rays and γ-rays. The present invention can also be applied to a photographing apparatus.

  Moreover, although the mammography apparatus was illustrated as embodiment of this invention, it is also possible to apply this invention to radiographic imaging apparatuses other than a mammography apparatus.

  The radiation detector 36 corresponds to the dose detection unit and the image generation unit in the present invention. The thickness detector 53 corresponds to the thickness detector in the present invention. Further, the CPU 50A refers to the table 100 or 110 to acquire the tube current values I1 and I2 and the tube voltage value Vm corresponding to the detected thickness of the breast M, so that the tube current value acquisition unit in the present invention and A tube voltage value acquisition unit is realized. Further, the CPU 50A performs the AEC calculation based on the image data based on the pre-irradiation to calculate the radiation irradiation time T at the time of main irradiation, thereby realizing the irradiation time deriving unit in the present invention. Further, the tube voltage value Vm is changed to the tube voltage value Vh or Vl in accordance with the difference between the radiation irradiation time T in the main irradiation calculated by the AEC calculation by the CPU 50A and the upper and lower limits Tmax and Tmin of the predetermined irradiation time. By setting, the tube voltage value setting unit in the present invention is realized.

DESCRIPTION OF SYMBOLS 10 Radiation imaging device 16 Movable arm part 26 Radiation source 28 Radiation irradiation part 32 Imaging stand 32A Imaging surface 36 Radiation detector 40 Compression board 50 Imaging apparatus control part 50A CPU
50B ROM
50C RAM
50D External storage device 53 Thickness detector 261 Filament 262 Target

Claims (12)

A radiation source that emits a dose of radiation according to the set tube current value and irradiation time;
A dose detector for detecting a dose of radiation irradiated from the radiation source and transmitted through the subject;
Based on the second tube current value determined dose of radiation detected and advance the dose detection unit when the radiation source irradiates the radiation in the first tube current value and the irradiation time to a predetermined An irradiation time deriving unit for deriving an irradiation time when the radiation source emits radiation at the second tube current value;
In a series of imaging time from the start of radiation irradiation by the first tube current value and the irradiation time to the end of radiation irradiation by the irradiation time derived by the second tube current value and the irradiation time deriving unit A tube current value switching unit that switches the setting of the tube current value for the radiation source from the first tube current value to the second tube current value before the irradiation time is derived by the irradiation time deriving unit;
An image generation unit that detects radiation that has been irradiated from the radiation source at the second tube current value and the irradiation time derived by the irradiation time deriving unit and transmitted through the subject, and generates a radiation image of the subject; ,
A radiographic imaging apparatus including: The radiation source includes a pair of electrodes and a filament provided on one of the pair of electrodes, and the tube current value is determined by the magnitude of the filament current flowing through the filament,
The filament current is parallel to the derivation of the irradiation time by the irradiation time deriving unit in response to switching from the first tube current value to the second tube current value by the tube current value switching unit. The radiographic image capturing apparatus according to claim 1, wherein a current value corresponding to the first tube current value shifts to a current value corresponding to the second tube current value. A thickness detector for detecting the thickness of the subject;
A tube current value acquisition unit that acquires the first and second tube current values based on the thickness of the subject detected by the thickness detection unit;
The radiographic imaging apparatus according to claim 2, further comprising:   The tube current value acquisition unit includes a table in which the thickness of the subject and the first and second tube current values are stored in association with each other, and the subject detected by the thickness detection unit based on the table The radiographic imaging device according to claim 3, wherein the first and second tube current values corresponding to the thickness of the radiographic image are acquired. In a series of imaging time from the start of radiation irradiation by the first tube current value and the irradiation time to the end of radiation irradiation by the irradiation time derived by the second tube current value and the irradiation time deriving unit the such that the filament current before the irradiation time is derived by the irradiation time derivation unit reaches the current value corresponding to the second tube current value, wherein the first tube current value in said table first The radiographic image capturing apparatus according to claim 4, wherein the first and second tube current values are set such that a difference between the second tube current value and the second tube current value is a predetermined value or less. A tube voltage value acquisition unit that acquires a tube voltage value set for the radiation source when the radiation source emits radiation at the first and second tube current values;
When the irradiation time derived by the irradiation time deriving unit is larger than a predetermined upper limit value, the tube voltage value larger than the tube voltage value acquired by the tube voltage value acquisition unit is set for the radiation source, When the irradiation time derived by the irradiation time deriving unit is smaller than a predetermined lower limit value, a tube voltage value smaller than the tube voltage value acquired by the tube voltage value acquisition unit is set for the radiation source, When the irradiation time derived by the irradiation time deriving unit is within a predetermined range between the upper limit value and the lower limit value, the tube voltage value acquired by the tube voltage value acquisition unit is applied to the radiation source. A tube voltage value setting unit to be set,
The radiation source, the radiation image capturing apparatus according to claim 1 or claim 2 for emitting radiation at the set tube voltage value by said tube voltage setting unit. A thickness detector for detecting the thickness of the subject;
The radiographic imaging apparatus according to claim 6, wherein the tube voltage value acquisition unit acquires the tube voltage value based on a thickness of the subject detected by the thickness detection unit.   The tube voltage value setting unit, when the irradiation time derived by the irradiation time deriving unit is larger or smaller than the predetermined range, the irradiation time derived by the irradiation time deriving unit and the upper limit value or the lower limit The radiographic imaging device according to claim 6 or 7, wherein a tube voltage value having a magnitude corresponding to a difference from the value is set for the radiation source. Dose for detecting a dose of radiation that has been irradiated from a radiation source that emits a dose of radiation according to a set tube current value and irradiation time at a predetermined first tube current value and irradiation time and transmitted through the subject. A detection step;
Irradiation for deriving an irradiation time when the radiation source emits radiation at the second tube current value based on the radiation dose detected in the dose detection step and a predetermined second tube current value A time derivation step;
In a series of imaging time from the start of radiation irradiation by the first tube current value and the irradiation time to the end of radiation irradiation by the irradiation time derived in the second tube current value and the irradiation time deriving step. A tube current value switching step for switching the setting of the tube current value for the radiation source from the first tube current value to the second tube current value before the irradiation time is derived in the irradiation time deriving step;
An image generation step of detecting a radiation irradiated from the radiation source at the second tube current value and the irradiation time derived in the irradiation time deriving step and transmitting the subject to generate a radiation image of the subject; ,
A radiographic imaging method comprising: A tube voltage value acquisition step of acquiring a tube voltage value set for the radiation source when the radiation source emits radiation at the first and second tube current values;
When the irradiation time derived in the irradiation time derivation step is larger than a predetermined upper limit value, a tube voltage value larger than the tube voltage value acquired in the tube voltage value acquisition step is set for the radiation source, When the irradiation time derived in the irradiation time derivation step is smaller than a predetermined lower limit value, a tube voltage value smaller than the tube voltage value acquired in the tube voltage value acquisition step is set for the radiation source, When the irradiation time derived in the irradiation time deriving step is within a predetermined range between the upper limit value and the lower limit value, the tube voltage value acquired in the tube voltage value acquisition step is applied to the radiation source. A tube voltage value setting step for setting,
The radiographic imaging method according to claim 9, wherein the radiation source irradiates the radiation with the tube voltage value set in the tube voltage value setting step when irradiating the radiation with the second tube current value. . Computer
The radiation source is first tube current value and the radiation source based on the second tube current value determined dose and pre-radiation transmitted through an object when irradiated with radiation in the irradiation time is the predetermined An irradiation time deriving unit for deriving an irradiation time when irradiating with radiation at the second tube current value;
In a series of imaging time from the start of radiation irradiation by the first tube current value and the irradiation time to the end of radiation irradiation by the irradiation time derived by the second tube current value and the irradiation time deriving unit A tube current value switching unit that switches the setting of the tube current value for the radiation source from the first tube current value to the second tube current value before the irradiation time is derived in the irradiation time deriving unit;
Program to function as. Computer,
A tube voltage value acquisition unit that acquires a tube voltage value set for the radiation source when the radiation source emits radiation at the first and second tube current values;
When the irradiation time derived by the irradiation time deriving unit is larger than a predetermined upper limit value, the tube voltage value larger than the tube voltage value acquired by the tube voltage value acquisition unit is set for the radiation source, When the irradiation time derived by the irradiation time deriving unit is smaller than a predetermined lower limit value, a tube voltage value smaller than the tube voltage value acquired by the tube voltage value acquisition unit is set for the radiation source, When the irradiation time derived by the irradiation time deriving unit is within a predetermined range between the upper limit value and the lower limit value, the tube voltage value acquired by the tube voltage value acquisition unit is applied to the radiation source. A tube voltage value setting section to be set;
The program of Claim 11 for functioning as.

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