JP7140566B2 - X-ray CT device and imaging planning device - Google Patents

Description

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

When capturing a positioning image (also referred to as a scanogram or a scout image), an operator such as a technician determines an imaging start position and an imaging end position. The operator sets a certain range to a fixed dose and performs imaging. The operator arbitrarily operates the irradiation of X-rays from the imaging start position to the imaging end position, and presses the interrupt button to end the imaging.

A positioning image is an image taken for determining the imaging range or calculating the dose of a scan for a main examination (also referred to as a main scan). Therefore, the scouting image is rarely used for diagnosis, and capturing the scouting image leads to unnecessary radiation exposure.
In addition, even though there are images of the same range taken by an X-ray device or X-ray CT (Computed Tomography) device in the past, images taken in the past are usually taken again before the main scan, so the images taken in the past are not effectively utilized.

JP 2006-167346 A JP 2010-279532 A JP 2016-119976 A

A problem to be solved by the present invention is to reduce radiation exposure during positioning image capturing.

The X-ray CT apparatus according to this embodiment includes a setting section. The setting unit selects the present image based on the past image of the subject and the positioning image of the subject photographed by modulating the dose of X-ray irradiation or the positioning image of the subject photographed by switching on/off of X-ray irradiation. Set scan conditions for scanning.

FIG. 1 is a block diagram showing the configuration of an X-ray CT apparatus according to this embodiment. FIG. 2 is a flow chart showing the operation of the X-ray CT apparatus according to this embodiment. FIG. 3 is a flow chart showing scanning condition determination processing according to the present embodiment. FIG. 4 is a diagram showing an example of a past image of a subject according to this embodiment. FIG. 5 is a graph showing changes in body thickness based on past images according to this embodiment. FIG. 6 is a diagram showing an example of a thinned image of a subject according to this embodiment. FIG. 7 is a graph showing changes in body thickness based on thinned images according to this embodiment. FIG. 8 is a diagram showing an example of a superimposed image after image alignment according to this embodiment. FIG. 9 is a graph of ratios calculated from superimposed images according to this embodiment. FIG. 10 is a graph showing an example of the current body thickness estimation result according to the present embodiment. FIG. 11 is a diagram showing an example of a display when a modulation plan for main scanning is performed. FIG. 12 is a diagram showing another example of display when modulation planning is performed during the main scan. FIG. 13 is a diagram showing an example of control of irradiation X-ray dose in low-dose imaging according to a modified example of this embodiment. FIG. 14 is a diagram showing an example of control of irradiation X-ray dose in low-dose imaging according to a modification of this embodiment. FIG. 15 is a block diagram showing the imaging planning device according to this embodiment.

An X-ray CT apparatus and an imaging planning apparatus according to this embodiment will be described below with reference to the drawings. 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.
FIG. 1 is a block diagram showing the configuration of an X-ray CT apparatus according to one embodiment. The X-ray CT apparatus 1 shown in FIG. 1 has a gantry device 10 , a bed device 30 and a console device 40 . For convenience of explanation, FIG. 1 shows that a plurality of gantry devices 10 are drawn. 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 device 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 (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. 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 scintillator array has a plurality of scintillators. The scintillator has a scintillator crystal that outputs light with an amount of photons corresponding to the amount 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 X-ray detector 12 may be a direct conversion type detector having a semiconductor element that converts incident X-rays into electrical signals.

The rotating frame 13 supports the X-ray generator and the X-ray detector 12 so as to be rotatable around 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 substantially matches the field of view (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 . Instead of storing the program in the memory, the control device 15 may be configured to directly incorporate the program into the circuit of the processor. In this case, the processor implements the above control by reading and executing the 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 reads electrical signals from the X-ray detector 12 and generates digital data (hereinafter also referred to as raw data) regarding the dose of X-rays detected by the X-ray detector 12 based on the read electrical signals. The raw 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. The DAS 18 is implemented by, for example, an ASIC (Application Specific Integrated Circuit) equipped with circuit elements capable of generating raw data. Raw data is transferred to the console device 40 .

For example, DAS 18 includes a preamplifier, variable amplifier, integrator circuit and A/D converter for each detector pixel. The preamplifier amplifies the electric signal from the X-ray detection element of the connection source 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 X-ray dose value detected by the X-ray 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 raw 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 projection data and reconstructed image data, for example. 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 projection 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, a preprocessing function 442, a reconstruction processing function 443, a setting function 444 (setting unit), a scan control function 445, and a body thickness estimation function by a processor that executes programs developed in memory. 446 (estimator) is executed. Note that each function (system control function 441, preprocessing function 442, reconstruction processing function 443, setting function 444, scan control function 445, and body thickness estimation function 446) is not limited to being realized by a single processing circuit. . 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 .

A preprocessing function 442 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 443 performs reconstruction processing on the projection data generated by the preprocessing function 442 using a filtered back projection (FBP) method, an iterative reconstruction method, or the like. to generate CT image data.

The setting function 444 is used to set a past image and a positioning image of the subject P captured by modulating the irradiation X-ray dose, which is the X-ray dose irradiated to the subject P, or the subject P captured by switching on/off of X-ray irradiation. , the scanning conditions for the main scan are set based on the positioning image. A positioning image is also called a scanogram or a scout image.

The scan control function 445 controls 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.

The body thickness estimation function 446 estimates the body thickness of the entire positioning image of the subject P using the body thickness calculated based on the positioning image of the subject P and the body thickness information calculated based on the previous image.

The processing circuit 44 also performs the following image processing and display control processing.
In the image processing, the CT image data generated by the reconstruction processing function 443 is transformed into tomographic image data or three-dimensional image data of an arbitrary cross section by a known method based on the input operation received from the operator via the input interface 43. This is the process of converting to
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 detection 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 preprocessing function 442 and the reconstruction processing function 443 may be distributed over a plurality of consoles.

Next, the operation of the X-ray CT apparatus 1 according to this embodiment will be described with reference to the flowchart of FIG.
In step S201, the imaging region of the subject P is determined. Specifically, for example, the processing circuit 44 acquires the ID of the subject P and information about the inspection target site of the subject P from the inspection order or the like, and determines the imaging site from the acquired information.

In step S202, processing circuitry 44 determines whether a past image exists. As the past image, a past positioning image captured by the same X-ray CT apparatus 1 may be used. Specifically, by executing the system control function 441, the processing circuit 44 refers to the incidental information associated with the image, etc., and retrieves the past positioning image having the same ID of the subject P and the imaging region, for example, Search from a PACS (Picture Archiving and Communication System) server. If the past positioning image is found, the processing circuit 44 determines that the past image exists. Even when no past positioning image is found, a CT image (tomographic image) captured in a past main scan by the same X-ray CT apparatus 1 may be used as a past image.

The past image is not limited to the same X-ray CT apparatus 1, and may be a CT image taken using the same series of X-ray CT apparatus of the same manufacturer, or an X-ray CT apparatus of another manufacturer. It may be a CT image that has been processed. Alternatively, an image captured using another medical image diagnostic apparatus such as a magnetic resonance imaging (MRI) may be used. At this time, a higher priority may be set for a CT image captured by an X-ray CT apparatus of the same series so that it is more likely to be adopted as a past image than an image captured using another medical image diagnostic apparatus.
Also, the past image may be generated by combining different parts extracted from different images. For example, by combining an image obtained by imaging only the abdomen and an image obtained by imaging only the lungs, the combined image can be used as a past image obtained by imaging the chest and abdomen.
If the past image exists, the process proceeds to step S204, and if the past image does not exist, the process proceeds to step S203.

In step S203, the X-ray CT apparatus 1 performs normal positioning imaging (scanography). The photographing conditions are set from a normal positioning image that has been photographed. After that, the process proceeds to step S210 to execute the main scan.
At step S204, the processing circuit 44 reads the past image obtained at step S202.
In step S205, the subject P is positioned based on the past image so that the subject P is positioned at the same position as the past image. For example, a projector (not shown) capable of projecting an image projects the past image onto the top board 33 . After that, an operator such as a technician refers to the projected past image and moves the subject P to the same position as the past image. Thus, the positioning of the subject P is completed.

In step S206, the processing circuit 44 refers to the past image and determines the start position of positioning imaging. It should be noted that the operator may determine the start position of positioning imaging by visual inspection.
In step S<b>207 , the processing circuit 44 determines a non-imaging region along the body axis direction of the subject P by executing the setting function 444 . As the non-imaging region, for example, a region with high radiosensitivity such as the reproductive organs and lens, or a region such as the abdomen in the case of imaging a pregnant woman that should be least exposed to radiation may be determined as the non-imaging region. Also, in order to reduce radiation exposure, a region such as the lungs, which has a high proportion of air, may be set as an imaging region, and regions other than the imaging region may be set as a non-imaging region. In order to clarify the imaging range of the image, it is desirable that the start position and the end position of positioning imaging are not set as non-imaging areas.

Specifically, a method for determining the non-imaging area includes, for example, preparing in advance a table that associates the imaging part with layout information indicating the non-imaging area as described above for each imaging part. By executing the setting function 444, the processing circuit 44 may acquire the layout information corresponding to the imaging part described in the table and set the non-imaging region.

It should be noted that if the imaging area is determined, the portion other than the imaging area can be determined as the non-imaging area, so the processing circuit 44 may set the imaging area. For example, when performing so-called follow-up diagnosis, there is a demand for capturing a CT image with good image quality in order to accurately grasp changes in the body. Therefore, the processing circuit 44 may determine the determined inspection site of the subject P as the imaging area, and determine the area other than the inspection site as the non-imaging area.

Also, by executing the setting function 444, the processing circuit 44 refers to the landmark information of the subject P when the past image was captured from the PACS server. The landmark information is information that can be grasped from the body or body surface of the subject P, for example, information that there is a pacemaker, a drain, or a metal implant such as a bolt or stent. The processing circuit 44 that executes the setting function 444 may set the site including the landmark information as the imaging region.

In step S208, by executing the scan control function 445, the processing circuit 44 controls the control device 15 to perform positioning imaging (also referred to as thinning imaging) of the thinned subject P having non-imaging regions. . A thinned image is generated by executing the thinned photographing.
In thinning imaging, the X-ray tube 11 is fixed above the subject P (in the +y-axis direction), and the X-ray irradiation is controlled by switching on and off while the tabletop 33 on which the subject P is placed is inserted into the gantry. It is done by being done. Specifically, for example, by executing the scan control function 445, the processing circuit 44 turns off X-ray irradiation so that the subject P is not irradiated with X-rays in the non-imaging region, and X-rays are not emitted in the imaging region. A control signal for turning on X-ray irradiation so that the subject P is irradiated is transmitted to the control device 15 . The control device 15 may perform thinning-out imaging by controlling the X-ray high-voltage device 14, the bed device 30, and the like according to the control signal. Although the fixed angle of the X-ray tube 11 in thinning imaging is above the subject P (typically 0°), it is not limited to this. The fixed angle of the X-ray tube 11 may be below the subject P (typically 180°) or laterally (typically 90° or 270°).
It should be noted that thinning imaging may be performed by the operator operating the input interface to manually perform irradiation control to switch X-ray irradiation ON/OFF so as not to visually photograph non-imaging regions.

In addition, by placing an X-ray shield in the irradiation field while the X-ray irradiation is on and blocking the X-ray irradiation to the subject P, the same effect as turning off the X-ray irradiation to the subject P is obtained. can be obtained. Therefore, thinning-out imaging may be performed not only by switching X-ray irradiation on and off, but also by moving an X-ray shielding object into and out of the X-ray irradiation field.

Further, when helical scanning is performed as positioning imaging, it may be determined whether or not to turn off the X-ray irradiation, that is, whether or not to thin out the X-rays for each rotation. Alternatively, it may be determined whether or not to thin out X-ray irradiation in several views in one rotation.
Furthermore, thinned scanning may be applied in three-dimensional scanning. In this case, it is sufficient to interpolate the scan portion thinned out by the three-dimensional reconstruction processing based on the three-dimensional image captured in the past.

In step S209, by executing the setting function 444 and the body thickness estimation function 446, the processing circuit 44 calculates the body thickness of the subject P calculated based on the past images and the body thickness of the subject P calculated based on the thinned images. The scan conditions for the main scan are determined based on the thickness. Scan conditions are, for example, tube current, tube voltage, filter thickness, filter type, and irradiation time.

In step S210, by executing the scan control function 445, the processing circuit 44 controls the control device 15 to perform the main scan according to the determined scan conditions. This completes the operation of the X-ray CT apparatus 1 according to this embodiment.

Next, the details of the scan condition determination process shown in step S209 will be described with reference to the flowchart of FIG.
In step S301, the processing circuit 44 calculates the body thickness of the subject P based on the past images by executing the body thickness estimation function 446. FIG. The calculation of body thickness may be based on geometry information such as spectra and optics, for example. Specifically, for example, the processing circuit 44 that realizes the body thickness estimation function 446 calculates the X-ray absorption amount based on the pixel value of each pixel of the positioning image, and converts the calculated X-ray absorption amount into a predetermined conversion formula. It can be obtained by converting to water equivalent thickness according to The water-equivalent thickness is the water-equivalent thickness with respect to the photographing direction of the past image.
By executing the body thickness estimation function 446, the processing circuit 44 determines the statistical value of the water equivalent thickness for a plurality of pixels included in the pixel column in the body width direction as the body thickness at the position of the pixel column. By performing the above calculation along the body axis direction (z-axis direction), the body thickness of the entire past image can be calculated. In the present embodiment, the statistical value is assumed to be the average value or median value of the equivalent water thickness, but any value obtained by other statistical processing may be used.

In step S302, the processing circuit 44 calculates the body thickness of the subject P based on the thinned image by executing the body thickness estimation function 446. FIG. The body thickness can be calculated in the same manner as in step S301.
In step S303, if there is a difference in body shape or positioning between the past image and the thinned image of the subject P, the body thickness estimation function 446 is executed so that the processing circuit 44 aligns the past image and the thinned image. (registration). At least one of enlargement processing, reduction processing, rotation processing, and morphing processing may be used as the alignment method. Note that, when landmark information exists, alignment accuracy can be improved by performing alignment with reference to the landmark information. In addition, even when the inspection site is determined in advance, the inspection site is imaged as the imaging site in the thinning-out imaging, so the alignment accuracy can be improved.

In step S304, by executing the body thickness estimation function 446, the processing circuit 44 calculates the ratio of the overlapping portion between the past image and the thinned image. Specifically, the processing circuit 44 may divide the body thickness based on the thinned image by the body thickness based on the past image, and calculate the ratio for the overlapping portion of the past image and the thinned image.
In step S305, by executing the body thickness estimation function 446, the processing circuit 44 performs interpolation processing on the ratio of the thinned region in the thinned image. Although linear interpolation is assumed as interpolation processing, any method such as logarithmic interpolation may be used as long as it can interpolate the ratio.
In step S306, the processing circuitry 44 multiplies the past image by the calculated ratio by executing the body thickness estimation function 446 to obtain an estimate of the current body thickness. This makes it possible to estimate the body thickness of the subject over the entire thinned image from the thinned image.

In step S307, by executing the scan control function 445, the processing circuitry 44 determines scan conditions for the main scan based on the estimated body thickness. Specifically, the scanning conditions may be determined according to the estimated body thickness so as to obtain the target X-ray dose by referring to the scanning conditions when the past images were taken. Scanning conditions include the tube voltage and tube current of the X-ray tube, the type and thickness of the filter, the distance between the subject P and the tube, and the exposure time. With this, the scanning condition determination processing is completed.

Next, a specific example of estimating the current body thickness will be described with reference to FIGS. 4 to 10. FIG.
FIG. 4 shows an example of a past image of the subject P. FIG. In the example of FIG. 4, it is a positioning image of the subject P captured by the X-ray CT apparatus 1 in the past. As shown in FIG. 4, the past image is a general positioning image obtained by imaging the entire imaging region along the body axis direction (+Z-axis direction) of the subject P. As shown in FIG.

Next, FIG. 5 shows a graph showing changes in body thickness along the body axis direction calculated based on the past images shown in FIG. The vertical axis indicates the body thickness, and the horizontal axis indicates the position with respect to the body axis direction. The body thickness is calculated by the process of step S301 described above.

Next, FIG. 6 shows an example of a thinned image obtained by performing thinning imaging of the subject P. In FIG.
The notation “ON” shown in FIG. 6 indicates the case where the subject P is irradiated with X-rays. On the other hand, the notation "OFF" indicates that the subject P is not irradiated with X-rays. That is, the portion not irradiated with X-rays is the non-imaging region.

Next, FIG. 7 shows a graph showing changes in body thickness along the body axis direction calculated based on the thinned images shown in FIG. The vertical and horizontal axes are the same as in FIG.
The body thickness of the thinned image may be calculated in the same manner as in step S302 described above. The body thickness is calculated for the imaging region, but the body thickness is not calculated for the non-imaging region, resulting in a graph with discrete values.

Next, FIG. 8 shows an example of a superimposed image after image alignment between the past image and the thinned image.
A superimposed image 800 is generated by the process of step S303. A dashed line 801 indicates the contour of the body shape in the thinned image, and a solid line 802 indicates the contour of the body shape in the previous image. To facilitate understanding of the superimposed state, only the outline of the past image is shown. As shown in FIG. 8, it can be understood from the superimposed image that there is a difference in body thickness between the past image and the thinned image.

Next, a graph of ratios calculated from superimposed image 800 is shown in FIG.
The vertical axis indicates the ratio, and the horizontal axis indicates the position in the body axis direction. A solid line 901 indicates the ratio of the portion of the thinned image where the image exists. Interpolation processing is performed on the thinned portion of the thinned image because the ratio to the past image cannot be calculated. A dashed line 902 indicates the result of linear interpolation here.

Next, FIG. 10 shows a graph showing changes in the current body thickness, which is the estimation result of the body thickness.
As shown in FIG. 10, the body thickness can be estimated based on the thinned image having portions where no data exists. In the example of FIG. 10, an increase in body thickness can be confirmed at the position of region 1001 as compared with the body thickness of the past image. As described above, body thickness can be estimated even when thinning imaging is performed without positioning imaging for the entire imaging range, so that mA modulation is possible for the entire imaging range.

It should be noted that, during thinning-out imaging, past images may be referred to so that it is possible to grasp which region of the subject P is being irradiated with X-rays. For example, by executing the system control function 441 , the processing circuit 44 causes the display 42 to display the acquired past image and the real-time thinned-out image being captured in parallel. The processing circuit 44 receives, for example from the control device 15, coordinate information regarding the imaging area of the subject P being imaged. The processing circuit 44 displays the shooting area on the past image corresponding to the coordinate information on the display 42 with, for example, a marker. This allows the operator to control the imaging range.

A camera (not shown) may also be used, and the current body surface information of the subject P photographed by the camera and real-time thinned-out images being photographed may be displayed side by side on the display 42 . As in the case of displaying the past image on the display 42, the operator can control the photographing range even when the camera is also used.

Next, an example of a display when a modulation plan for the main scan is performed will be described with reference to FIG.
FIG. 11 is a display example in which the past image 60 is displayed on the left side of the display 42 and the modulation graph 62 is displayed on the right side of the display 42 . In the modulation graph 62, the vertical axis indicates the position in the body axis direction, and the horizontal axis indicates the irradiation X-ray dose. In the modulation graph 62, two irradiation X-ray doses are displayed. A solid line 621 indicates the irradiation X-ray dose calculated from the body thickness calculated based on the past image 60, and a dashed line 622 indicates the irradiation X-ray dose calculated from the estimated current body thickness.
By doing so, the operator can make a modulation plan for the main scan while comparing the past irradiation X-ray dose and the current irradiation X-ray dose.

Next, another example of the display when the modulation plan for the main scan is performed will be described with reference to FIG.
FIG. 12 is a display example in which the thinned image 64 is displayed on the left side of the display 42 and the modulation graph 66 is displayed on the right side of the display 42. FIG. The modulation graph 66 displays one graph showing the irradiation X-ray dose calculated from the current body thickness estimated from the thinned image 64 . A solid line 661 is the irradiation X-ray dose calculated based on the body thickness actually calculated from the imaging region of the thinned image 64 . On the other hand, a dashed line 662 is the irradiation X-ray dose calculated based on the estimated body thickness in the non-imaging region of the thinned image 64 . By doing so, the operator can easily grasp the portion of the irradiation X-ray dose calculated from the interpolated body thickness.
11 and 12, both the past image 60 and the thinned image 64 may be displayed.

According to the present embodiment described above, an imaging region and a non-imaging region are determined during positioning imaging, and X-rays are irradiated to the subject only in the imaging region to perform thinning imaging. Since the processing circuit estimates the current body thickness based on the past images and the thinned-out images, it is possible to reduce the exposure dose during positioning imaging without repeatedly performing positioning imaging before main scanning. .

(Modification of this embodiment)
In the above-described embodiment, thinning-out imaging is performed in which X-rays are not irradiated in the non-imaging region when the positioning image of the subject P is captured. This modification is different in that the radiography is performed by modulating the irradiation X-ray dose when radiographing the scouting image. Specifically, the portion corresponding to the non-imaging region of the above-described embodiment is positioned and photographed with an X-ray dose (low dose) that is smaller than the irradiation X-ray dose of the portion corresponding to the imaging region of the thinning-out imaging. Low-dose positioning imaging is defined as low-dose imaging below.

An example of control of the irradiation X-ray dose when performing low-dose imaging will be described with reference to FIGS. 13 and 14. FIG.
A graph 70 in the upper part of FIGS. 13 and 14 shows the imaging range of the subject P, and the horizontal direction corresponds to the Z-axis. A lower graph 72 shows the magnitude of the X-ray dose. As shown in FIG. 13, a low-dose imaging region 74 is determined in the imaging range of the subject P, and the low-dose imaging region 74 may be imaged with a lower irradiation X-ray dose than other regions. As a method of setting the irradiation X-ray dose lower than that of other regions, for example, a preset X-ray dose value may be used, or the operator may input the X-ray dose value at the time of imaging.
Specifically, by executing the setting function 444, the processing circuit 44 determines the low-dose imaging region 74 by the same processing as the setting of the non-imaging region in this embodiment. After that, the processing circuit 44 may control the control device 15 to perform low-dose imaging so that the irradiation X-ray dose is low in the low-dose imaging region 74 .
FIG. 14 is another example of the X-ray dose control shown in FIG. As shown in FIG. 14, the X-ray dose may be changed smoothly in the low-dose imaging region.

According to the modified example of the present embodiment described above, since the X-ray dose is smaller than that in normal positioning radiography by performing low-dose radiography, the body thickness can be calculated from the image portion of the low-dose radiography region. Even if you can't, you can shoot the outline of your body shape. As a result, the image registration between the past image and the low-dose image obtained by the low-dose imaging can be performed more easily and accurately than in the case of the thinned-out image. As a result, radiation exposure during positioning imaging can be reduced as in the present embodiment.

In the above-described embodiments and modifications, when the past image is a CT image captured in a standing or sitting position, and the thinned image to be captured in the future is captured in a supine position, or vice versa, Even if the imaging conditions are different, the current body thickness can be estimated by converting the image.
For example, a conversion table relating to correction amounts of organ positions (organ sagging) corresponding to two combinations of standing, sitting and lying positions is created in advance. By executing the setting function 444, the processing circuit 44 may refer to the photographing states of the past image and the thinned image and the conversion table to correct the organ position.

The setting function 444 and the body thickness estimation function 446 in the X-ray CT apparatus 1 may be included in the imaging planning apparatus. FIG. 15 shows a block diagram of an imaging planning apparatus according to this embodiment and the modification.
The imaging planning device 50 includes a setting function 444 and a body thickness estimation function 446 . The imaging planning apparatus 50 and the X-ray CT apparatus 1 are connected by wire or wirelessly.
According to the radiography planning apparatus 50 shown in FIG. 15, the X-ray CT apparatus 1 side does not need to perform body thickness estimation processing and scan condition determination processing, but the radiography planning device 50 side can execute the processing. .

The X-ray CT apparatus 1 includes a Rotate/Rotate-Type (third-generation CT) in which an X-ray tube and a detector are rotated around the subject P as a unit, and a large number of X-rays arrayed in a ring. There are various types such as Stationary/Rotate-Type (4th generation CT) in which the detection element is fixed and only the X-ray tube rotates around the subject P, and any type can be applied to this embodiment.

Note that hardware for generating X-rays is not limited to the X-ray tube 11 . For example, in place of the X-ray tube 11, a focus coil for converging the electron beam generated from the electron gun, a deflection coil for electromagnetic deflection, and the deflected electron beam surrounding the half circumference of the subject P collide with each other to emit X-rays. X-rays may be generated using a fifth generation system including a target ring to be generated.
Furthermore, in the present embodiment, both a single-tube type X-ray CT apparatus and a so-called multi-tube type X-ray CT 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 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 method can be stored and distributed in a storage medium such as a magnetic disk (hard disk, etc.), optical disk (CD-ROM, DVD, etc.), semiconductor memory, etc. .

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.

Reference Signs List 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 (DAS)
19 aperture (bore)
30 bed device 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 50 imaging planning device 60 past image 62, 66 modulation graph 64 thinned image 70, 72 graph 74 low Dosimetry area 441 System control function 442 Preprocessing function 443 Reconstruction processing function 444 Setting function 445 Scan control function 446 Body thickness estimation function 621, 661, 802, 901 Solid line 622, 662, 801, 902 Broken line 800 Superimposed image 1001 Region

Claims (11)

A past image of the subject obtained in a past examination, and a localization image of the subject obtained by modulating the irradiation X-ray dose in an examination different from the past examination, or photographing by switching on/off of X-ray irradiation a setting unit that sets scan conditions for the main scan based on the obtained positioning image of the subject;
An X-ray CT apparatus comprising: An estimating unit that estimates the body thickness of the entire positioning image using the body thickness calculated based on the past image and the body thickness calculated based on the positioning image,
2. The X-ray CT apparatus according to claim 1, wherein said setting unit determines said scanning conditions based on the calculated body thickness. 3. The X-ray CT apparatus according to claim 2, wherein the estimating unit estimates the body thickness of the entire positioning image of the subject by calculating the ratio in the overlapping portion of the past image and the positioning image. The past image is a positioning image or a tomographic image captured in the past using the same device that captured the positioning image of the subject, or an image captured by another medical image diagnostic device. 4. The X-ray CT apparatus according to any one of items 3. wherein, when the past image and the positioning image of the subject are superimposed, if there is a difference in body shape or positioning between the positioning image of the subject and the past image, image registration is performed. The X-ray CT apparatus according to any one of claims 1 to 4. 6. The X-ray CT apparatus according to any one of claims 1 to 5, wherein the scouting image is a thinned image having non-imaging regions not irradiated with the X-rays. 6. The positioning image is an image in which a low-dose imaging region imaged with a lower radiation dose than other imaging regions exists along the body axis direction of the subject. The X-ray CT apparatus according to . 8. The X-ray CT apparatus according to any one of claims 1 to 7, wherein the past image is generated by combining different regions extracted from different images. 9. The X-ray CT apparatus according to any one of claims 1 to 8, wherein the setting unit corrects the organ position according to whether the past image was taken in an upright position or in a supine position. A past image of the subject obtained in a past examination, and a localization image of the subject obtained by modulating the irradiation X-ray dose in an examination different from the past examination, or photographing by switching on/off of X-ray irradiation a setting unit that sets scan conditions for the main scan based on the obtained positioning image of the subject;
A photography planning device comprising: 11. The X-ray CT apparatus according to any one of claims 1 to 9, or the imaging plan according to claim 10, wherein said past examination is an examination based on an examination order different from said another examination. Device.

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