JP7224880B2 - X-ray equipment - Google Patents

Description

An embodiment of the present invention relates to an X-ray imaging apparatus.

X-ray imaging devices such as X-ray CT (Computed Tomography) devices and tomosynthesis imaging devices measure the intensity of X-rays that irradiate the subject from the 2π direction after passing through the subject at various angles, acquire projection data, and measure the By reconstructing the obtained data, the linear attenuation coefficient distribution, that is, the internal morphological image of the subject can be obtained.
At this time, if there is no subject in the X-ray propagation path from the X-ray tube to the detector, the X-rays do not attenuate and overflow beyond the X-ray measurement upper limit of the detector. Or, it may result in unnecessary radiation exposure to the operator.

U.S. Patent Application Publication No. 2017/0209105 U.S. Patent Application Publication No. 2018/0063386 U.S. Patent Application Publication No. 2017/0319166

The problem to be solved by the present invention is to reduce unnecessary exposure while reducing artifacts.

An X-ray imaging apparatus according to this embodiment includes an acquisition unit, a prediction unit, and a control unit. An acquisition unit acquires a first detector output in a first view. A predictor predicts a second detector output in a second view after the first view based on the first detector output. A controller controls the dose of X-rays to be irradiated based on the predicted output of the second detector.

FIG. 1 is a block diagram showing an X-ray CT apparatus according to this embodiment. FIG. 2 is a diagram showing a medical information system regarding generation of a trained model according to this embodiment. FIG. 3 is a diagram showing the concept of learning a trained model according to this embodiment. FIG. 4 is a diagram showing the concept of using a trained model according to this embodiment. FIG. 5 is a diagram showing positions of views according to the present embodiment. FIG. 6 is a diagram showing an example of detector output in each view shown in FIG. FIG. 7 is a flowchart showing dose control processing of the X-ray CT apparatus 1 according to this embodiment. FIG. 8 is a diagram showing the concept of dose control processing based on the flowchart of FIG. FIG. 9 is a diagram showing the concept of using both dose control processing and variable pitch helical scanning.

An X-ray CT (Computed Tomography) apparatus will be described below as an example of an X-ray imaging apparatus according to the present embodiment with reference to the drawings, but the present invention can be similarly applied to a tomosynthesis imaging apparatus.
In the following embodiments, it is assumed that parts denoted by the same reference numerals perform the same operations, and overlapping descriptions will be omitted as appropriate. An embodiment will be described below with reference to the drawings.

An X-ray CT apparatus according to this embodiment will be described below with reference to the block diagram of FIG. The X-ray CT apparatus 1 shown in FIG. 1 has a gantry device 10, a bed device 30, and a console device 40 that realizes processing of the X-ray CT device. In FIG. 1, a plurality of gantry devices 10 are depicted for convenience of explanation.

In this embodiment, the rotation axis of the rotating frame 13 in the non-tilt state or the longitudinal direction of the top plate 33 of the bed apparatus 30 is the Z-axis direction, and the axial direction perpendicular to the Z-axis direction and horizontal to the floor surface is are defined as the X-axis direction, the axis direction perpendicular to the Z-axis direction, and the Y-axis direction as the axis direction perpendicular to the floor surface.

For example, the gantry device 10 and the bed device 30 are installed in a CT examination room, and the console device 40 is installed in a control room adjacent to the CT examination room. Note that the console device 40 does not necessarily have to be installed in the control room. For example, the console device 40 may be installed in the same room together with the gantry device 10 and the bed device 30 . In any case, the gantry device 10, the bed device 30, and the console device 40 are connected by wire or wirelessly so as to be able to communicate with each other.

The gantry device 10 is a scanning device having a configuration for X-ray CT imaging of the subject P. As shown in FIG. The gantry 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a data acquisition device 18 (hereinafter , DAS (Data Acquisition System) 18).

The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermal electrons from a cathode (filament) to an anode (target) by applying a high voltage and supplying a filament current from an X-ray high voltage device 14. is. Specifically, X-rays are generated by thermal electrons colliding with a target. For example, the X-ray tube 11 is a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermal electrons. The X-rays generated by the X-ray tube 11 are shaped into a cone beam through, for example, a collimator 17 and irradiated onto the subject P. FIG.

The X-ray detector 12 detects X-rays emitted from the X-ray tube 11 and passing through the subject P, and outputs an electrical signal corresponding to the X-ray dose to the DAS 18 . The X-ray detector 12 has, for example, a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction along one circular arc centering on the focal point of the X-ray tube 11 . The X-ray detector 12 has, for example, a row structure in which a plurality of X-ray detection element rows each having a plurality of X-ray detection elements arranged in the channel direction are arranged in the slice direction (row direction).

Specifically, the X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array, and a photosensor array. The X-ray detector 12 is an example of a detection section.

The scintillator array has a plurality of scintillators. The scintillator has a scintillator crystal that outputs a photon amount of light corresponding to the intensity of incident X-rays.
The grid has an X-ray shielding plate arranged on the surface of the scintillator array on the X-ray incident side and having a function of absorbing scattered X-rays. Note that the grid may also be called a collimator (one-dimensional collimator or two-dimensional collimator).
The photosensor array has a function of amplifying the light received from the scintillator and converting it into an electric signal, and has photosensors such as photomultiplier tubes (PMTs), for example.

The rotating frame 13 supports the X-ray generator (including the X-ray tube 11, the wedge 16 and the collimator 17) and the X-ray detector 12 so as to be rotatable about the rotation axis. Specifically, the rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 so as to face each other and rotates the X-ray tube 11 and the X-ray detector 12 by means of a control device 15, which will be described later. is. The rotating frame 13 is rotatably supported by a fixed frame (not shown) made of metal such as aluminum. Specifically, the rotating frame 13 is connected to the edges of the stationary frame via bearings. The rotating frame 13 receives power from the drive mechanism of the control device 15 and rotates around the rotation axis Z at a constant angular velocity.

In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 further includes an X-ray high-voltage device 14 and a DAS 18 to support them. Such a rotating frame 13 is accommodated in a substantially cylindrical housing in which an opening (bore) 19 forming an imaging space is formed. The aperture approximately matches the FOV. The central axis of the opening coincides with the rotational axis Z of the rotating frame 13 . The detection data generated by the DAS 18 is provided in a non-rotating portion (for example, a fixed frame, not shown in FIG. 1) of the gantry device by optical communication from a transmitter having a light emitting diode (LED), It is transmitted to a receiver (not shown) having a photodiode and forwarded to the console device 40 . The method of transmitting the detected data from the rotating frame to the non-rotating portion of the gantry is not limited to the optical communication described above, and any method of non-contact data transmission may be adopted.

The X-ray high voltage device 14 has electric circuits such as a transformer and a rectifier, and has a function of generating a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11. It has a generating device and an X-ray control device for controlling the output voltage according to the X-rays emitted by the X-ray tube 11 . The high voltage generator may be of a transformer type or an inverter type. Note that the X-ray high-voltage device 14 may be provided on a rotating frame 13 to be described later, or may be provided on a fixed frame (not shown) side of the gantry device 10 .

The control device 15 has a processing circuit having a CPU (Central Processing Unit) and the like, and drive mechanisms such as motors and actuators. The processing circuit has, as hardware resources, a processor such as a CPU or an MPU (Micro Processing Unit) and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). In addition, the control device 15 includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and other complex programmable logic devices (Complex Programmable Logic Device: CPLD ), which may be implemented by a Simple Programmable Logic Device (SPLD). The control device 15 controls the X-ray high-voltage device 14, the DAS 18, etc. according to commands from the console device 40. FIG. The processor implements the control by reading and implementing the program stored in the memory.

The control device 15 also has a function of receiving an input signal from an input interface 43 (described later) attached to the console device 40 or the gantry device 10 and controlling the operations of the gantry device 10 and the bed device 30 . For example, the control device 15 receives an input signal and performs control to rotate the rotating frame 13 , control to tilt the gantry device 10 , and control to operate the bed device 30 and the tabletop 33 . The control for tilting the gantry device 10 is performed by the control device 15 rotating the frame about an axis parallel to the X-axis direction based on inclination angle (tilt angle) information input by the input interface 43 attached to the gantry device 10 . It is realized by rotating 13. Also, the control device 15 may be provided in the gantry device 10 or may be provided in the console device 40 . It should be noted that the control device 15 may be configured so as to directly incorporate the program into the circuit of the processor instead of storing the program in the memory. In this case, the processor implements the above control by reading and executing a program incorporated in the circuit.

Wedge 16 is a filter for adjusting the dose of X-rays emitted from X-ray tube 11 . Specifically, the wedge 16 transmits and attenuates the X-rays irradiated from the X-ray tube 11 so that the X-rays irradiated from the X-ray tube 11 to the subject P have a predetermined distribution. It is a filter that For example, the wedge 16 (wedge filter, bow-tie filter) is a filter processed from aluminum to have a predetermined target angle and a predetermined thickness.

The collimator 17 is a lead plate or the like for narrowing down the irradiation range of the X-rays transmitted through the wedge 16, and a slit is formed by combining a plurality of lead plates or the like. Note that the collimator 17 may also be called an X-ray diaphragm.

The DAS 18 is implemented by, for example, an ASIC (Application Specific Integrated Circuit) equipped with circuit elements capable of generating detection data. DAS 18 and X-ray detector 12 constitute a detector unit.
The DAS 18 reads the electrical signal from the X-ray detector 12 and generates detection data, which is digital data regarding the dose of X-rays detected by the X-ray detector 12, based on the read electrical signal. The detection data is a set of data indicating the channel number and row number of the X-ray detection element from which it was generated, the view number indicating the acquired view (also called projection angle), and the integral value of the detected X-ray dose. be.

For example, DAS 18 includes preamplifiers, variable amplifiers, integrators, and A/D converters for each sensing element. The preamplifier amplifies the electrical signal from the connected detection element with a predetermined gain. A variable amplifier amplifies the electrical signal from the preamplifier with a variable gain. An integrator circuit integrates the electrical signal from the preamplifier over one view period to generate an integrated signal. The crest value of the integral signal corresponds to the dose value of the X-rays detected by the detection element of the connection source over one view period. The A/D converter analog-to-digital converts the integration signal from the integration circuit to generate detection data.

The bed device 30 is a device for placing and moving a subject P to be scanned, and includes a base 31 , a bed driving device 32 , a top board 33 and a support frame 34 .

The base 31 is a housing that supports the support frame 34 so as to be vertically movable.
The bed driving device 32 is a motor or actuator that moves the table 33 on which the subject P is placed in the longitudinal direction of the table 33 . The bed driving device 32 moves the tabletop 33 under the control of the console device 40 or the control device 15 . For example, the bed driving device 32 moves the top plate 33 in a direction orthogonal to the subject P so that the body axis of the subject P placed on the top plate 33 coincides with the central axis of the opening of the rotating frame 13 . do. Further, the bed driving device 32 may move the top board 33 along the body axis direction of the subject P according to the X-ray CT imaging performed using the gantry device 10 . The bed drive device 32 generates power by driving at a rotational speed according to the duty ratio of the drive signal from the control device 15 and the like. The bed driving device 32 is realized by a motor such as a direct drive motor or a servo motor, for example.
A top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. Note that the bed driving device 32 may move the support frame 34 in the longitudinal direction of the top plate 33 in addition to the top plate 33 .

The console device 40 has a memory 41 , a display 42 , an input interface 43 and a processing circuit 44 . Data communication between the memory 41, the display 42, the input interface 43, and the processing circuit 44 is performed via a bus (BUS). Note that the console device 40 is described as being separate from the gantry device 10 , but the console device 40 or a part of each component of the console device 40 may be included in the gantry device 10 .

The memory 41 is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. The memory 41 stores, for example, detection data and reconstructed image data. The memory 41 can be connected to portable storage media such as CDs (Compact Discs), DVDs (Digital Versatile Discs), flash memories, semiconductor memory devices such as RAMs (Random Access Memory), etc., in addition to HDDs and SSDs. It may also be a driving device that reads and writes various information with. Also, the storage area of the memory 41 may be in the X-ray CT apparatus 1 or in an external storage device connected via a network. For example, the memory 41 stores data of CT images and display images. The memory 41 also stores a control program according to this embodiment.

The display 42 displays various information. For example, the display 42 outputs a medical image (CT image) generated by the processing circuit 44, a GUI (Graphical User Interface) for accepting various operations from the operator, and the like. For example, the display 42 may be, for example, a liquid crystal display (LCD: Liquid Crystal Display), a CRT (Cathode Ray Tube) display, an organic EL display (OELD: Organic Electro Luminescence Display), a plasma display, or any other arbitrary display. , is enabled. Also, the display 42 may be provided on the gantry device 10 . The display 42 may be of a desktop type, or may be configured by a tablet terminal capable of wireless communication with the main body of the console device 40, or the like.

The input interface 43 receives various input operations from the operator, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuit 44 . For example, the input interface 43 receives acquisition conditions for acquiring detection data, reconstruction conditions for reconstructing CT images, image processing conditions for generating post-processed images from CT images, and the like from the operator. . As the input interface 43, for example, a mouse, keyboard, trackball, switch, button, joystick, touch pad, touch panel display, etc. can be used as appropriate. In addition, in the present embodiment, the input interface 43 is not limited to physical operation components such as a mouse, keyboard, trackball, switch, button, joystick, touch pad, and touch panel display. For example, the input interface 43 includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs the electrical signal to the processing circuit 44. . The input interface 43 may be provided on the gantry device 10 . Also, the input interface 43 may be composed of a tablet terminal or the like capable of wireless communication with the main body of the console device 40 .

The processing circuit 44 controls the operation of the entire X-ray CT apparatus 1 according to the electric signal of the input operation output from the input interface 43 . For example, the processing circuit 44 has, as hardware resources, processors such as a CPU, MPU, and GPU (Graphics Processing Unit), and memories such as a ROM and a RAM. The processing circuit 44 performs a system control function 441 , an acquisition function 442 , a prediction function 443 , a dose control function 444 , a collimator control function 445 , a preprocessing function 446 and a reconstruction processing function 447 by a processor that executes programs developed in memory. to run. Note that each function (system control function 441, acquisition function 442, prediction function 443, dose control function 444, collimator control function 445, preprocessing function 446, and reconstruction processing function 447) is realized by a single processing circuit. is not limited to A processing circuit may be configured by combining a plurality of independent processors, and each function may be realized by each processor executing a program.

The system control function 441 controls each function of the processing circuit 44 based on input operations received from the operator via the input interface 43 . Specifically, the system control function 441 reads the control program stored in the memory 41, develops it on the memory in the processing circuit 44, and controls each part of the X-ray CT apparatus 1 according to the developed control program. . For example, the processing circuit 44 controls each function of the processing circuit 44 based on an input operation received from the operator via the input interface 43 . For example, the system control function 441 acquires a two-dimensional positioning image of the subject P for determining the scan range, imaging conditions, and the like. A positioning image is also called a scanogram or a scout image.

Acquisition function 442 acquires a first detector output (detection data) of X-ray detector 12 in a first view.

The prediction function 443 predicts, based on the first detector output, the x-ray detector in a second view after the first view, in other words, a second view acquired after the first view. Predict 12 second detector outputs. A prediction function 443 generates a second detector output from the first detector output according to a trained model described below. Note that the second detector output may be generated according to a rule-based learned model, not limited to a model that has been learned by machine learning, which will be described later.

A dose control function 444 controls the delivered X-ray dose based on the predicted second detector output. Specifically, the dose of X-rays irradiated toward the subject P is controlled by controlling the imaging conditions such as the magnitude of the tube current (mA).
The collimator control function 445 controls the X-ray dose irradiated toward the subject P by controlling the collimator 17 based on the predicted second detector output.

A preprocessing function 446 generates data by performing preprocessing such as logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, and beam hardening correction on the detection data output from the DAS 18 . Raw data (detection data) before preprocessing and data after preprocessing may be collectively referred to as projection data.

A reconstruction processing function 447 performs reconstruction processing on the projection data generated by the preprocessing function 446 using a filtered back projection method (FBP method), an iterative reconstruction method, or the like. to generate CT image data.

The processing circuit 44 also performs scan control processing, image processing, and display control processing.
The scan control process is a process of controlling various operations related to X-ray scanning, such as causing the X-ray high-voltage device 14 to supply a high voltage and causing the X-ray tube 11 to emit X-rays.
Image processing converts CT image data generated by the reconstruction processing function 447 into tomographic image data or three-dimensional image data of an arbitrary cross section based on input operations received from the operator via the input interface 43. is. Note that the generation of the three-dimensional image data may be directly performed by the reconstruction processing function 447 .
The display control process is a process of controlling the display 42 so as to display information during processing or processing results in each function or processing of the processing circuit 44 .

The processing circuit 44 is not limited to being included in the console device 40, and may be included in an integrated server that collectively processes data acquired by a plurality of medical image diagnostic apparatuses.
Although the console device 40 has been described as executing a plurality of functions with a single console, the plurality of functions may be executed by separate consoles. For example, the functions of the processing circuit 44 such as the acquisition function 442 and the prediction function 443 may be distributed.

Next, an example of a medical information processing system that generates a trained model to be used by the prediction function 443 will be described with reference to the block diagram of FIG.
The medical information processing system shown in FIG. 2 includes an X-ray imaging apparatus (an X-ray CT apparatus 1 as an example), a learning data storage device 20 and a model learning device 22 .

The learning data storage device 20 stores learning data including multiple learning samples. For example, the learning data storage device 20 is a computer with a built-in mass storage device. The learning data storage device 20 may also be a mass storage device communicatively connected to a computer via a cable or communication network. As the storage device, an HDD, an SSD, an integrated circuit storage device, or the like can be used as appropriate.

The model learning device 22 generates a trained model 411 by causing the model to perform machine learning according to a model learning program (algorithm) based on the learning data stored in the learning data storage device 20 . In the present embodiment, machine learning algorithms include neural networks, deep learning, recurrent neural networks (RNN), LSTM (Long Short-Term Memory), etc., which are particularly superior in handling time-series data. It is envisioned, but not limited to, other machine learning algorithms such as Hidden Markov Models (HMM). RNNs have loops in internal intermediate layers, called hidden layers, that allow information to persist until processing at a later time. Also, LSTM is a network that can learn long-term information dependencies better than RNN. The model learning device 22 is a computer such as a workstation having a processor such as CPU and GPU.

The model learning device 22 and the learning data storage device 20 may be communicably connected via a cable or a communication network. Also, the learning data storage device 20 may be installed in the model learning device 22 . In these cases, learning data is supplied from the learning data storage device 20 to the model learning device 22 . Note that the model learning device 22 and the learning data storage device 20 do not have to be communicably connected. In this case, the learning data is supplied from the learning data storage device 20 to the model learning device 22 via the portable storage medium storing the learning data.

The X-ray CT apparatus 1 and the model learning apparatus 22 may be communicably connected via a cable or a communication network. A trained model 411 generated by the model learning device 22 is supplied to the X-ray CT apparatus 1 and the trained model 411 is stored in the memory 41 . Note that the X-ray CT apparatus 1 and the model learning apparatus 22 do not necessarily have to be communicably connected. In this case, the trained model 411 is supplied from the model learning device 22 to the X-ray CT apparatus 1 via a portable storage medium or the like in which the trained model 411 is stored.

Note that the trained model 411 can also be said to be a parameterized synthetic function obtained by synthesizing a plurality of functions. A parameterized composite function is defined by a combination of multiple adjustable functions and parameters. A trained model can be any parameterized composite function that meets the above requirements.

The trained model 411 according to the present embodiment is generated by performing machine learning on a multi-layered network (simply referred to as a model) before machine learning using an algorithm that handles time-series data such as RNN or LSTM. Not limited to RNN and LSTM, the trained model 411 may be generated by learning a model using the machine learning algorithm described above.

Next, the concept of learning the trained model 411 according to this embodiment will be described with reference to FIG.
At the time of model learning, for example, at the time of shipment from the factory, the model learning device 22 performs machine learning on the multi-layered network 410 using learning data.
The learning data used here includes the detector output 61 of the X-ray detector 12 in each of a plurality of views (view A, view B, and view C) in which the subject P was actually imaged, and information on the imaging target (hereinafter referred to as , also referred to as imaging target information) and imaging conditions 63 as input data, and the detector output of the X-ray detector 12 regarding a view (view D, hereinafter also referred to as a predicted view) after the view used as input data. is learning data with correct data (output data). The model learning device 22 trains the multi-layered network 410 using the learning data, and generates a trained model 411 that has learned the trend of change in the detector output.

A plurality of views used as input data may be continuous views, or intermittent views skipping one or more views such as every other view or every third view. In other words, the permutation of views or the number of views that can recognize changes in the detector output over time may be used. Here, view A, view B, and view C use three consecutive views as input data. In addition, it is assumed that the detector output changes in a predetermined manner according to the view. Therefore, in such a case, if a change in the detector output in subsequent views can be recognized from the imaging target site, view number, and detector output, the view number and detection for one view can be performed without inputting a plurality of views. The device output may be used as input data.

Moreover, the predicted view used for the output data is preferably a view after the timing when the X-ray dose can be controlled from the view of the input data. This is because even if the detector output for the view immediately after the input data is obtained, there is a possibility that the subsequent X-ray dosage control processing will not be completed in time. Therefore, the number of views after the view used as input data to be set as the predicted view depends on the view after which dose control processing can be performed for the predicted view generated based on the last view used as input data. view. For example, if it takes time to photograph 100 views for X-ray modulation, view D used for output data may be a view 100 views later than view C for input data.

The imaging target information includes information such as the subject P's sex, age, and body type. The imaging conditions include the imaging target site of the subject P, the helical pitch, and the X-ray conditions.
For the imaging target region, for example, information on a region specified by a user instruction may be acquired, or a table in which an image and information on the imaging target region are associated in advance based on a positioning image acquired by positioning imaging. By referring to , you may acquire the information of the part.

The helical pitch is determined by the moving speed of the bed (for example, the tabletop 33), the rotational speed of the rotating frame 13, and the number of views. Therefore, the imaging conditions may include information on the movement speed, rotation speed, and number of views of the bed together with or instead of the information on the helical pitch.
X-ray conditions include, for example, tube voltage (kV), tube current (mA), view rate, filter information, collimator information, and the like. Note that the learned model 411 may be updated when the X-ray CT apparatus 1 is repaired or software is updated.

Note that the learned model 411 may be prepared according to the shooting target information and the shooting conditions. In this case, the prediction function 443 allows the processing circuit 44 to select and use the learned model 411 corresponding to the shooting target information and shooting conditions at the time of shooting.

As the subject P, a phantom, a deceased patient, a living animal, or a dead animal may be used in addition to a patient or healthy subject. When imaging the subject P and collecting input data, materials (air, water, elements) and thickness are taken into consideration as transmission conditions. In particular, when the subject P is a phantom, it is desirable to use a phantom such as an elliptical cylinder in which the thickness of the subject through which the X-ray path passes varies as the rotating frame 13 rotates.

In addition, in whole-body imaging, the head, particularly the neck, of the subject is narrower than the torso, so overflow is likely to occur when imaging the vicinity of the head. Therefore, a detector output that causes an overflow in advance may be used as the correct data. In other words, the information of the imaging target site where overflow is likely to occur is used as input data, and the overflowed detector output in the X-ray propagation path (so-called air path) in which the X-rays reach the detector without passing through the subject and the subject. The model may be learned using learning data in which the imaging target region of the specimen is the correct data.

Next, the concept of using the trained model 411 according to this embodiment will be described with reference to FIG.
As shown in FIG. 4, when the learned model 411 is used, the detector outputs 61 of a plurality of views (view A, view B, and view C), and the shooting target information and shooting conditions 63 at the time of shooting are combined into the learned model 411. 411 to output the detector output of the later predicted view (view D) than the input view.

Next, the concept of views and detector outputs according to this embodiment will be described with reference to FIGS. 5 and 6. FIG.

FIG. 5 is a diagram showing the position of the X-ray tube 11 with respect to the subject P, that is, the view position. Detector output for each view from the X-ray detector 12 (not shown) facing the X-ray tube 11 in FIG. is obtained. Here, as the output of the trained model 411, the detector output for the prediction view D indicated by the dashed line is predicted from the detector outputs for the three views.

FIG. 6 shows the detector output for each view in FIG. 5, where the horizontal axis indicates the channel direction and the vertical axis indicates the magnitude of the detector output. Detector output of view A, detector output of view B, and detector output of view C are shown in order from the top. Also, the detector output for the predicted view D is shown by the dashed line.

As shown in FIG. 6, the irradiation position on the subject P changes as the view changes, so the shape (profile) of the detector output also changes. In FIG. 6, since the subject P is imaged from the front view A, the view B, and the view C toward the side of the subject P, the detector output is the body thickness of the subject P. The portion where the detector output is increasing becomes smaller, and the portion where the detector output is smaller moves to the end in the channel direction. As shown in FIG. 6, it is possible to predict what kind of detector output will be by a trained model 411 that has learned changes in the shape of the detector output according to the transition of the view.

Next, dose control processing of the X-ray CT apparatus 1 according to this embodiment using the learned model 411 will be described with reference to the flowchart of FIG.

In step S701, the acquisition function 442 causes the processing circuitry 44 to acquire detector outputs of multiple views as input data.
In step S702, the prediction function 443 causes the processing circuitry 44 to input the detector outputs of the multiple views acquired in step S701 to the trained model 411 and generate the detector output of the predicted view later than the input data.

In step S703, processing circuitry 44, through prediction function 443 or dose control function 444, determines whether the detector output for the predicted view is greater than or equal to the threshold for overflow. If the detector output is greater than or equal to the threshold, proceed to step S705; if the detector output is less than the threshold, proceed to step S704. For example, the detector output of each channel is compared with a uniform threshold, and if the number of channels whose detector output exceeds the threshold exceeds a predetermined number, the detector output is determined to be greater than or equal to the threshold, and the process proceeds to step S705. . The predetermined number may be 1, or 2 or more.
In step S704, the dose control function 444 causes the processing circuitry 44 to either maintain the x-ray condition because the detector output is not overflowing, or to x-ray if the expected counts are low and there is a risk of low count artifacts. Radiation conditions may be increased to increase x-ray dose (intensity or energy). X-ray condition parameters for adjusting the X-ray dose include tube current (mA) and tube voltage (kV). For example, the tube current and tube voltage may be increased in order to increase the X-ray dose.

In step S705, the dose control function 444 causes the processing circuit 44 to control the dose control function 444 to reduce the X-ray dose, for example, the tube current, when actually performing imaging in the predictive view because the detector output is overflowing. For example, processing circuitry 44 determines a target value for tube current such that the measured detector output in the predicted view is equal to or less than a threshold. The processing circuit 44 controls the X-ray high voltage device 14 so that the actual value of the tube current in the predicted view becomes the target value.
In step S706, the control function causes the processing circuit 44 to determine whether the scan is finished. If the scan has ended, the process ends, and if the scan has not ended, the process returns to step S701 to continue the dose control process. In other words, the dose control process according to the present embodiment is repeated each time the detector output in the view is obtained, including the case where the predicted view is actually captured as the scan progresses, until the main scan is completed.

In the dose control process shown in FIG. 7, collimator control may be performed during scanning to control unnecessary exposure by changing the shape of the irradiation field by controlling the collimator according to the position of the view. The specific collimator control is, for example, an actuator that opens and closes the collimator 17 so that the processing circuit 44 by the collimator control function 445 does not irradiate X-rays in the region assumed to be the air path in the detector output of the predicted view. is driven to close the collimator 17 .

Next, the concept of dose control processing based on the flowchart of FIG. 7 will be described with reference to FIG.
FIG. 8 shows the detector output in each view of FIG. 5 which is the same as FIG. Here, attention is paid to the contour portion 70 corresponding to the edge of the subject P in the detector output. Here, contour portion 70 of detector output 81 for predicted view D exceeds overflow threshold 83 . Therefore, the dose control function 444 causes the processing circuit 44 to decrease the tube current, for example, as the dose control processing in step S705. As a result, the actually obtained detector output becomes the detector output 85, so that the detector output can be obtained without overflow. As a result, unnecessary radiation exposure can be reduced.

In addition to the control to reduce the X-ray dose, X-rays that do not pass through the subject P can be blocked by controlling the collimator based on the detector output of the predicted view. As a result, the actually obtained detector output becomes the detector output 87, so unnecessary exposure can be further reduced.

Also, the dose control processing according to the present embodiment may be used in combination with so-called variable pitch helical scanning, in which a region of interest (ROI) and a portion other than the ROI are scanned with different helical pitches.
The concept of using the dose control process according to this embodiment and the variable pitch helical scan together will be described with reference to FIG. 9 .

FIG. 9 shows a scanogram 91 of the subject P and a setting example of the helical pitch for the imaging range of the subject P in the scanogram 91 . In addition, a conceptual diagram 97 when the size of the helical pitch is changed is also displayed.
In the example of FIG. 9, when the ROI 93 is the heart, the ROI 93 is imaged in detail by narrowing the helical pitch (decreasing the value of the helical pitch). On the other hand, in a range 95 other than the ROI 93, the helical pitch is widened (the value of the helical pitch is increased) and normal imaging is performed.

When the variable pitch helical scan and the dose control process according to the present embodiment are used together in this way, when learning the trained model 411, the detector output, the imaging target information, and the imaging conditions in a plurality of views actually measured. In addition, the scan range of the subject P, the target region to be the ROI in the scan range, the helical pitch when imaging the target region, and the helical pitch when imaging regions other than the target region are learned as input data. All you have to do is Note that the correct data is the detector output in the prediction view as in the above case.

Similarly, when using the learned model 411, the scan range of the subject P, the target region to be the ROI in the scan range, the helical pitch when imaging the target region, and the helical pitch when imaging regions other than the target region The pitch is input to the trained model 411 . As a result, even if the helical pitch fluctuates during imaging, it is possible to generate the detector output of the predicted view linked to the variable-pitch helical scan from the learned model 411, and to perform appropriate dose control. can.

According to the present embodiment described above, by predicting the detector output in the prediction view after the input view based on the detector outputs in a plurality of views, the detector output in the prediction view is actually control to lower the X-ray dose so as not to overflow when imaging. Also, X-ray irradiation to unnecessary irradiation fields is blocked by collimator control based on the predicted detector output. As a result, it is possible to always continue optimum collimator opening/closing control and X-ray dosage adjustment. As a result, the overall exposure to both the subject and the operator can be reduced, for example, by reducing the tube current at locations where the subject's body thickness is reduced.

Also in the image reconstruction process, overflow artifacts can be reduced because the detector output does not overflow. Furthermore, since the tube current can be automatically modulated, the operator's operational burden can be reduced.

The X-ray CT apparatus includes a Rotate/Rotate-Type (3rd generation CT) in which the X-ray tube and detector are rotated around the subject P as a unit, and a large number of X-ray detectors arrayed in a ring. There are various types such as Stationary/Rotate-Type (4th generation CT) in which the element is fixed and only the X-ray tube rotates around the subject P, and any type can be applied to this embodiment.
Furthermore, in the present embodiment, both a single-tube type X-ray imaging apparatus and a so-called multi-tube type X-ray imaging apparatus in which a plurality of pairs of X-ray tubes and detectors are mounted on a rotating ring can be used. Applicable.

In addition, each function according to the embodiment can also be realized by installing a program for executing the above processing in a computer such as a workstation and deploying them on the memory. At this time, the program that allows the computer to execute the above method can be distributed by being stored in a storage medium such as a magnetic disk (hard disk, etc.), optical disk (CD-ROM, DVD, etc.), semiconductor memory, or the like. .

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

1 X-ray CT apparatus 10 Mounting device 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimator 18 Data acquisition device 19 Opening 20 Learning data storage device 22 Model learning device 30 Bed Apparatus 31 Base 32 Bed drive device 33 Top plate 34 Support frame 40 Console device 41 Memory 42 Display 43 Input interface 44 Processing circuit 61, 81, 85, 87 Detector output 63 Imaging condition 70 Contour part 83 Overflow threshold 91 Scano image 95 Range 410 Layered network 411 Trained model 441 System control function 442 Acquisition function 443 Prediction function 444 Dose control function 445 Collimator control function 446 Preprocessing function 447 Reconstruction processing function

Claims (7)

an acquisition unit that acquires a first detector output at a plurality of first views;
For a trained model trained using detector outputs in a plurality of views and information about an object to be photographed and photographing conditions as input data, and detector outputs in views subsequent to the plurality of views as correct data, the first a prediction unit that predicts a second detector output in a second view after the first view by inputting the detector output of
a controller that controls the amount of X-rays to be irradiated based on the predicted output of the second detector;
An X-ray imaging device comprising: The X-ray imaging apparatus according to claim 1, wherein said controller controls said X-ray dose by controlling a collimator based on said second detector output. 2. The X-ray imaging apparatus according to claim 1, wherein said control unit controls said X-ray dose by controlling tube current of an X-ray tube based on said second detector output. The learned model is one of a plurality of learned models that are respectively learned according to information about a shooting target and shooting conditions,
2. The X-ray imaging apparatus according to claim 1 , wherein said prediction unit selects and uses, from among said plurality of trained models, a trained model corresponding to information about an imaging target at the time of imaging and imaging conditions. The information about the imaging target includes information about the imaging target site, the sex and body type of the subject,
5. The X-ray imaging apparatus according to claim 4 , wherein said imaging conditions include helical pitch. 6. The X-ray imaging apparatus according to claim 5 , wherein said prediction unit determines said imaging target site based on a positioning image obtained by positioning imaging. When the helical pitch differs between the region of interest and other parts in the imaging range, the learned model inputs the imaging range, the region of interest, the helical pitch for the region of interest, and the helical pitch for the other part as input data. 7. The X-ray imaging apparatus according to any one of claims 4 to 6 , wherein the model is learned as .

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