JP2020000449A - X-ray ct apparatus and photographing planning device - Google Patents

Abstract

To provide an X-ray CT apparatus and a photographing planning device capable of reducing the degree of exposure when photographing a positioning image.SOLUTION: An X-ray CT apparatus of the embodiment includes a setting part. The setting part sets a scanning condition according to a past image of the photographing subject, and a positioning image of the photographing subject which is taken by modulating the irradiation X-ray dose or a positioning image of the photographing subject which is taken by switching on or off of the X-ray irradiation.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to an X-ray CT apparatus and an imaging planning apparatus.

  When capturing a positioning image (also called a scano image or a scout image), an operator such as a technician determines a capturing start position and a capturing end position. An operator performs imaging by setting a fixed range to a fixed dose. The operator arbitrarily operates the X-ray irradiation from the imaging start position to the imaging end position, and presses the stop button to end the imaging.

The positioning image is an image that is taken for determining the imaging range or for calculating the dose of a scan for main inspection (also referred to as main scan). Therefore, the positioning image is rarely used for diagnosis, and photographing the positioning image leads to unnecessary exposure.
In addition, although there is an image of a similar range captured by an X-ray apparatus or an X-ray CT (Computed Tomography) apparatus in the past, the positioning image is usually captured again before the main scan. Has not been used effectively.

JP 2006-167346 A JP 2010-279532 A JP-A-2006-119776

  The problem to be solved by the present invention is to reduce the exposure at the time of capturing a positioning image.

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

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

  Hereinafter, an X-ray CT apparatus and an imaging planning apparatus according to the present embodiment will be described with reference to the drawings. In the following embodiments, portions denoted by the same reference numerals perform the same operation, and redundant description will be omitted as appropriate.

Hereinafter, an embodiment will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of an X-ray CT apparatus according to one embodiment. The X-ray CT apparatus 1 illustrated in FIG. 1 includes a gantry device 10, a bed device 30, and a console device 40. FIG. 1 shows that a plurality of gantry devices 10 are drawn for convenience of explanation. In this embodiment, the longitudinal direction of the rotation axis of the rotating frame 13 or the top plate 33 of the bed device 30 in the non-tilted state is perpendicular to the Z-axis direction and the Z-axis direction, and is an axial direction that is horizontal to the floor surface. Are defined orthogonal to the X-axis direction and the Z-axis direction, and the axis direction perpendicular to the floor surface is defined as the Y-axis direction.

  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 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 communicably connected by wire or wirelessly.

  The gantry device 10 is a scanning device having a configuration for performing X-ray CT imaging of the subject P. 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 collection device 18 (DAS (Data Acquisition System) 18).

  The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermoelectrons from a cathode (filament) to an anode (target) by applying a high voltage from an X-ray high voltage device 14 and supplying a filament current. It is. Specifically, X-rays are generated by the collision of the thermal electrons with the target. The X-rays generated by the X-ray tube 11 are formed into a cone beam shape via, for example, a collimator 17 and are irradiated on the subject P.

  The X-ray detector 12 detects X-rays emitted from the X-ray tube 11 and passed through the subject P, and outputs an electric 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 rows in which a plurality of X-ray detection elements are arranged in a channel direction along one arc around 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 in which a plurality of X-ray detection elements are arranged in a channel direction are arranged in a slice direction (row direction, row direction).

  Specifically, the X-ray detector 12 is, for example, an indirect conversion type detector including a grid, a scintillator array, and an optical sensor array.

  The scintillator array has a plurality of scintillators. The scintillator has a scintillator crystal that outputs light having a photon amount corresponding to the incident X-ray dose.

  The grid has an X-ray shielding plate which is arranged on the surface of the scintillator array on the X-ray incident side and has a function of absorbing scattered X-rays. The grid may be called a collimator (one-dimensional collimator or two-dimensional collimator).

The optical sensor array has a function of amplifying light received from the scintillator and converting the light into an electric signal, and includes, for example, an optical sensor such as a photomultiplier tube (photomultiplier: PMT).
Note that the X-ray detector 12 may be a direct conversion type detector having a semiconductor element that converts incident X-rays into an electric signal.

  The rotating frame 13 supports the X-ray generation unit and the X-ray detector 12 so as to be rotatable around a rotation axis. Specifically, the rotating frame 13 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 a control device 15 described later. It 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 an edge of the fixed frame via a bearing. The rotary 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.

  The rotating frame 13 further includes and supports an X-ray high-voltage device 14 and a DAS 18 in addition to the X-ray tube 11 and the X-ray detector 12. Such a rotating frame 13 is housed in a substantially cylindrical housing in which an opening (bore) 19 forming an imaging space is formed. The aperture substantially corresponds to the field of view (FOV). The center axis of the opening coincides with the rotation axis Z of the rotation frame 13. The detection data generated by the DAS 18 is provided on 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). The data is transmitted to a receiver (not shown) having a photodiode, and is transmitted to the console device 40. The transmission method of the detection data from the rotating frame to the non-rotating portion of the gantry is not limited to the above-described optical communication, and any method may be adopted as long as it is a non-contact type data transmission.

  The X-ray high voltage device 14 has an electric circuit such as a transformer (transformer) and a rectifier, and has a high voltage having a function of generating a high voltage applied to the X-ray tube 11 and a filament current supplied to the X-ray tube 11. It has a generator and an X-ray controller that controls 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. The X-ray high-voltage device 14 may be provided on a rotating frame 13 described later, or may be provided on a fixed frame (not shown) of the gantry device 10.

  The control device 15 has a processing circuit having a CPU (Central Processing Unit) and the like, and a driving mechanism such as a motor and an actuator. The processing circuit has, as hardware resources, a processor such as a CPU and an MPU (Micro Processing Unit) and a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory). Further, the control device 15 includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and other complex programmable logic devices (CPLDs). ), May be realized by a simple programmable logic device (SPLD). The control device 15 controls the X-ray high-voltage device 14, the DAS 18, and the like in accordance with a command from the console device 40. The processor implements the above control by reading and implementing the program stored in the memory.

  Further, the control device 15 has a function of receiving an input signal from an input interface 43, which will be described later, attached to the console device 40 or the gantry device 10, and controlling the operation of the gantry device 10 and the couch device 30. For example, the control device 15 performs control to rotate the rotating frame 13 in response to the input signal, control to tilt the gantry device 10, and control to operate the bed device 30 and the top board 33. The control for tilting the gantry device 10 is performed by the control device 15 based on the tilt angle (tilt angle) information input by the input interface 43 attached to the gantry device 10 so that the control device 15 rotates the rotation frame about an axis parallel to the X-axis direction. 13 is rotated. Further, the control device 15 may be provided on the gantry device 10 or on the console device 40. Note that, 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 realizes the above control by reading and executing a program incorporated in the circuit.

  The wedge 16 is a filter for adjusting the amount of X-ray emitted from the X-ray tube 11. Specifically, the wedge 16 transmits and attenuates the X-rays radiated from the X-ray tube 11 so that the X-rays radiated to the subject P from the X-ray tube 11 have a predetermined distribution. Filter. For example, the wedge 16 (wedge filter, bow-tie filter) is a filter formed by processing aluminum so as to have a predetermined target angle and a predetermined thickness.

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

  The DAS 18 reads an electric signal from the X-ray detector 12 and generates digital data (hereinafter, also referred to as raw data) related to the dose of the X-ray detected by the X-ray detector 12 based on the read electric signal. The raw data is a set of data indicating a channel number, a column number, a view number indicating a collected view (also referred to as a projection angle) of the source X-ray detecting element, and an integrated value of a detected X-ray dose. is there. The DAS 18 is realized by, for example, an ASIC (Application Specific Integrated Circuit) equipped with a circuit element capable of generating raw data. The raw data is transferred to the console device 40.

  For example, DAS 18 includes a preamplifier, a variable amplifier, an integrator, and an A / D converter for each detector pixel. The preamplifier amplifies an electric signal from the connection source X-ray detection element with a predetermined gain. The variable amplifier amplifies the electric signal from the preamplifier with a variable gain. The integrating circuit integrates the electric signal from the preamplifier over one view period to generate an integrated signal. The peak value of the integration signal corresponds to the X-ray dose value detected by the connection source X-ray detection element over one view period. The A / D converter converts the integration signal from the integration circuit from analog to digital to generate raw data.

The couch device 30 is a device on which the subject P to be scanned is placed and moved, and includes a base 31, a couch driving device 32, a top plate 33, and a support frame.
The base 31 is a housing that supports the support frame 34 movably in the vertical direction.

  The couch driving device 32 is a motor or an actuator that moves the table 33 on which the subject P is placed in the longitudinal direction of the table 33. The couch driving device 32 moves the couchtop 33 according to control by the console device 40 or control by the control device 15. For example, the couch driving device 32 moves the table 33 in a direction perpendicular to the object P so that the body axis of the object P placed on the table 33 coincides with the center axis of the opening of the rotating frame 13. I do. Further, the couch driving device 32 may move the couchtop 33 along the body axis direction of the subject P in accordance with X-ray CT imaging performed using the gantry device 10. The couch driving device 32 generates power by being driven at a rotation speed according to a duty ratio of a driving signal from the control device 15 or the like. The couch driving device 32 is realized by, for example, a motor such as a direct drive motor or a servo motor.

  The top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. The couch 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 among the memory 41, the display 42, the input interface 43, and the processing circuit 44 is performed via a bus (BUS). Although the console device 40 is described as being separate from the gantry device 10, the gantry device 10 may include the console device 40 or some of the components of the console device 40.

  The memory 41 is a storage device such as a hard disk drive (HDD), a solid state drive (SSD), or an integrated circuit storage device for storing various information. The memory 41 stores, for example, projection data and reconstructed image data. The memory 41 is connected to a portable storage medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), a flash memory, and a semiconductor memory element such as a RAM (Random Access Memory) in addition to the HDD and the SSD. It may be a driving device for reading and writing various information. 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 a CT image and a display image. The memory 41 stores a control program according to the present 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 receiving various operations from the operator, and the like. For example, as the display 42, 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 display is appropriately used. , Has become available. The display 42 may be provided on the gantry device 10. Further, the display 42 may be a desktop type, or may be configured by a tablet terminal or the like that can wirelessly communicate with the console device 40 main body.

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

  The processing circuit 44 controls the entire operation of the X-ray CT apparatus 1 in accordance with the input operation electric signal output from the input interface 43. For example, the processing circuit 44 has, as hardware resources, a processor such as a CPU, an MPU, and a GPU (Graphics Processing Unit) and a memory such as a ROM and a RAM. The processing circuit 44 includes a system control function 441, a pre-processing function 442, a reconstruction processing function 443, a setting function 444 (setting unit), a scan control function 445, and a body thickness estimating function by a processor that executes a program developed in the memory. 446 (estimating unit) is executed. 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 processor may execute a program to realize each function.

  The system control function 441 controls each function of the processing circuit 44 based on an input operation received from the operator via the input interface 43. Specifically, the system control function 441 reads the control program stored in the memory 41, expands it on the memory in the processing circuit 44, and controls each unit of the X-ray CT apparatus 1 according to the expanded 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.

  The preprocessing function 442 generates data obtained by performing preprocessing such as logarithmic conversion processing, offset correction processing, sensitivity correction processing between channels, and beam hardening correction on the detection data output from the DAS 18. Note that raw data (detection data) before preprocessing and data after preprocessing are sometimes collectively referred to as projection data.

  The reconstruction processing function 443 performs a reconstruction process on the projection data generated by the preprocessing function 442 using a filtered back projection method (FBP method), a successive approximation reconstruction method, or the like. To generate CT image data.

  The setting function 444 is a positioning image of the subject P obtained by modulating the past image and the irradiation X-ray amount, which is the X-ray amount irradiated to the subject P, or the subject P imaged by switching the X-ray irradiation on and off. The scan conditions for the main scan are set based on the positioning image. The positioning image is also called a scano image or a scout image.

  The scan control function 445 controls various operations related to X-ray scanning, such as supplying a high voltage to the X-ray high-voltage device 14 and irradiating the X-ray tube 11 with X-rays.

  The body thickness estimating 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 past image.

The processing circuit 44 also performs the following image processing and display control processing.
The image processing is based on an input operation received from the operator via the input interface 43, and converts CT image data generated by the reconstruction processing function 443 into tomographic image data or three-dimensional image data of an arbitrary cross section by a known method. This is the process of converting to.
The display control process is a process of controlling the display 42 so as to display information on a process or processing result in each function or process of the processing circuit 44.

  The processing circuit 44 is not limited to the case where the processing circuit 44 is included in the console device 40, and may be included in an integrated server that collectively performs processing on 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 to a plurality of consoles.

Next, the operation of the X-ray CT apparatus 1 according to the present embodiment will be described with reference to the flowchart in FIG.
In step S201, the imaging region of the subject P is determined. More specifically, for example, the processing circuit 44 may acquire the ID of the subject P and information on the region to be examined of the subject P from an examination order or the like, and determine the imaging region from the acquired information.

  In step S202, the processing circuit 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 incidental information associated with the image and the like, and determines a past positioning image in which the ID of the subject P and the imaging region are the same, for example, Search from PACS (Picture Archiving and Communication System) server. If the past positioning image is found, the processing circuit 44 determines that a past image exists. Even when a past positioning image cannot be found, a CT image (tomographic image) captured by a past main scan in 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, but may be a CT image taken using an X-ray CT apparatus of the same manufacturer and of the same series, or set up using an X-ray CT apparatus of another manufacturer. May be a CT image. Alternatively, an image captured using another medical image diagnostic apparatus such as a magnetic resonance tomography apparatus (MRI: Magnetic Resonance Imaging) may be used. At this time, the priority of a CT image captured by an X-ray CT apparatus of the same series may be set higher so that the image is more likely to be used as a past image than an image captured using another medical image diagnostic apparatus.
The past image may be generated by combining different parts extracted from different images. For example, by combining an image of only the abdomen and an image of only the lungs, the image can be used as a past image of the chest and abdomen.
If a past image exists, the process proceeds to step S204. If a past image does not exist, the process proceeds to step S203.

In step S203, the X-ray CT apparatus 1 performs normal positioning imaging (scano imaging). The photographing conditions are set from the photographed normal positioning images. Thereafter, the process proceeds to step S210 to execute the main scan.
In step S204, the processing circuit 44 reads the past image acquired in step S202.
In step S205, the subject P is positioned based on the past image so that the position of the subject P is the same as the past image. For example, a projector (not shown) capable of projecting an image projects a past image on the top plate 33. Then, 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 determines the start position of the positioning imaging with reference to the past image. Note that the operator may visually determine the start position of the positioning imaging.
In step S207, by executing the setting function 444, the processing circuit 44 determines a non-imaging area along the body axis direction of the subject P. As the non-imaging region, for example, a region that is not exposed as much as possible, such as a region with high radiation sensitivity such as a genital organ or a lens, or an abdomen when imaging a pregnant woman, may be determined as the non-imaging region. Further, in order to reduce exposure, an area such as a lung having a high air content may be set as an imaging area, and an area other than the imaging area may be set as a non-imaging area. In addition, in order to clarify the photographing range of the image, it is desirable that the photographing is performed without setting the start position and the end position of the positioning photographing as non-imaging regions.

  Specifically, for the method of determining the non-imaging area, for example, a table in which the imaging area and the layout information indicating the non-imaging area as described above are prepared in advance for each imaging area. 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 area.

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

  Also, by executing the setting function 444, the processing circuit 44 refers to the landmark information of the subject P at the time of capturing the past image from the PACS server. The landmark information is information that can be grasped from the body or the body surface of the subject P, for example, information that a pacemaker, a drain, or an embedding of a metal such as a bolt or a stent exists. The processing circuit 44 that executes the setting function 444 may set a part including the landmark information as the imaging region.

In step S208, the processing circuit 44 controls the control device 15 by executing the scan control function 445, and performs positioning imaging (also referred to as thinning imaging) of the thinned subject P in which the non-imaging area exists. . By performing the thinning shooting, a thinned image is generated.
The thinning-out imaging is controlled by switching the X-ray irradiation on and off while the X-ray tube 11 is fixed above the subject P (in the + y-axis direction) and the couchtop 33 carrying the subject P 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 the irradiation of the X-ray so that the X-ray is not irradiated to the subject P in the non-imaging region, and the X-ray is not irradiated in the imaging region. A control signal for turning on the X-ray irradiation so as to irradiate the subject P 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 and the bed device 30 according to the control signal. Although the fixed angle of the X-ray tube 11 in the thinned-out imaging is assumed to be above the subject P (typically 0 °), the present invention is not limited to this. The fixed angle of the X-ray tube 11 may be below (typically 180 °) or beside (typically 90 ° or 270 °) the subject P.
Note that the operator may operate the input interface to perform irradiation control for manually switching on / off the X-ray irradiation so that the non-imaging region is not visually imaged, thereby executing the thinning-out imaging.

  The same effect as turning off X-ray irradiation on the subject P by putting the X-ray shield in the irradiation field while keeping the X-ray irradiation on and blocking the X-ray irradiation on the subject P is obtained. Can be obtained. Therefore, in addition to switching on / off of X-ray irradiation, thinning-out imaging may be performed by taking an X-ray shield into and out of an X-ray irradiation field.

When helical scanning is performed as positioning imaging, it may be determined whether or not X-ray irradiation is turned off every rotation, that is, whether or not thinning is performed. Alternatively, it may be determined whether or not to reduce the X-ray irradiation in several views in one rotation.
Further, a thinning scan may be applied in the three-dimensional scan. In this case, it is sufficient to interpolate a scan portion thinned out by the three-dimensional reconstruction processing based on a three-dimensional image captured in the past.

  In step S209, by executing the setting function 444 and the body thickness estimating function 446, the processing circuit 44 causes the body thickness of the subject P calculated based on the past image and the body of the subject P calculated based on the thinned image. 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 execute the main scan according to the determined scan condition. Thus, the operation of the X-ray CT apparatus 1 according to the present embodiment ends.

Next, details of the scan condition determination processing shown in step S209 will be described with reference to the flowchart in FIG.
In step S301, the processing circuit 44 calculates the body thickness of the subject P based on the past image by executing the body thickness estimation function 446. The calculation of the body thickness may be performed based on geometrical arrangement information such as spectra and optics. Specifically, for example, the processing circuit 44 for realizing the body thickness estimating 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. In this case, the water equivalent thickness may be converted to the water equivalent thickness. The water equivalent thickness is a water equivalent thickness in the shooting 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 row in the body width direction as the body thickness at the position of the pixel row. 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 average value or the intermediate value of the water equivalent thickness is assumed as the statistical value, but any value obtained by other statistical processing may be used.

In step S302, by executing the body thickness estimation function 446, the processing circuit 44 calculates the body thickness of the subject P based on the thinned image. The body thickness may be calculated in the same manner as in step S301.
In step S303, when there is a difference in body type or positioning between the past image of the subject P and the thinned image, the processing circuit 44 executes the body thickness estimation function 446 to adjust the position of the past image and the thinned image. (Registration). As a positioning method, at least one of an enlargement process, a reduction process, a rotation process, and a morphing process may be used. When landmark information is present, by performing alignment with reference to the landmark information, the accuracy of the alignment can be improved. In addition, even when the inspection part is determined in advance, the inspection part is imaged as the imaging part in the thinning-out imaging, so that the accuracy of the alignment 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 calculate the ratio by dividing the body thickness based on the thinned image by the body thickness based on the past image, for the overlapping portion between the past image and the thinned image.
In step S305, by executing the body thickness estimation function 446, the processing circuit 44 performs an interpolation process on the ratio of the thinned region in the thinned image. As the interpolation processing, linear interpolation is assumed, but the present invention is not limited to this, and any method capable of interpolating the ratio, such as logarithmic interpolation, may be used.
In step S306, by executing the body thickness estimating function 446, the processing circuit 44 multiplies the calculated ratio by the past image to obtain a current estimated value of the 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 circuit 44 determines the scan conditions for the main scan based on the estimated body thickness. More specifically, the scan conditions may be determined in accordance with the estimated body thickness so that the target irradiation X-ray dose is obtained with reference to the scan conditions when the past image was taken. The scanning conditions include a tube voltage and a tube current of the X-ray tube, a type and thickness of a filter, a distance between the subject P and the tube, an irradiation time, and the like. This completes the scan condition determination processing.

Next, a specific example of estimating the current body thickness will be described with reference to FIGS.
FIG. 4 shows an example of a past image of the subject P. 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 illustrated in FIG. 4, the past image is a general positioning image in which the entire imaging region is imaged along the body axis direction (+ Z axis direction) of the subject P.

  Next, FIG. 5 is a graph showing a change in body thickness along the body axis direction calculated based on the past image 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 processing in step S301 described above.

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

Next, FIG. 7 is a graph showing a change in body thickness along the body axis direction calculated based on the thinned image 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. Although the body thickness is calculated for the imaging region, the body thickness is not calculated for the non-imaging region, and the graph has discrete values.

Next, FIG. 8 shows an example of a superimposed image after image alignment between the past image and the thinned image.
The superimposed image 800 is generated by the process of step S303. A broken line 801 indicates the contour of the body in the thinned image, and a solid line 802 indicates the contour of the body in the past image. In order to make it easy to understand the superimposed state, the past image shows only the outline. As shown in FIG. 8, it can be understood that there is a difference in body thickness between the past image and the thinned image from the superimposed image.

Next, a graph of the ratio calculated from the 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 a ratio of a portion where an image exists in the thinned image. Since the ratio of the thinned image in the thinned image to the past image cannot be calculated, the interpolation process is performed. The broken line 902 indicates the result of linear interpolation here.

Next, FIG. 10 is a graph showing a change 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 including a portion where no data exists. In the example of FIG. 10, an increase in the body thickness can be confirmed at the position of the region 1001 as compared with the body thickness of the past image. As described above, even when thinning-out imaging is performed without performing positioning imaging in the entire imaging range, the body thickness can be estimated, so that mA modulation can be performed in the entire imaging range.

  At the time of thinning-out imaging, a past image may be referred to so as to be able 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 image being captured in parallel on the display 42. The processing circuit 44 receives, for example, from the control device 15, coordinate information on the imaging region of the subject P being imaged. The processing circuit 44 displays a shooting area on the past image corresponding to the coordinate information on the display 42 with, for example, a marker. Thereby, the operator can control the photographing range.

  In addition, a camera (not shown) may be used in combination, and the body surface information of the current subject P photographed by the camera and the real-time thinned image during the photographing may be displayed on the display 42 in parallel. As in the case where the past image is displayed on the display 42, the operator can control the photographing range also when using the camera together.

Next, an example of a display when performing a modulation plan at the time of the main scan 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-rays are displayed. A solid line 621 indicates the irradiation X-ray amount calculated from the body thickness calculated based on the past image 60, and a broken line 622 indicates the irradiation X-ray amount calculated from the estimated current body thickness.
In this way, the operator can make a modulation plan for the main scan while comparing the past irradiation X-ray dose with the current irradiation X-ray dose.

Next, another example of the display when performing the modulation plan at the time of the main scan 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. In the modulation graph 66, one graph showing the irradiation X-ray dose calculated from the current body thickness estimated from the thinned image 64 is displayed. A solid line 661 is an irradiation X-ray amount calculated based on the body thickness actually calculated from the imaging region of the thinned image 64. On the other hand, a broken line 662 is an irradiation X-ray amount calculated based on the estimated body thickness in the non-imaging region of the thinned image 64. In this manner, the operator can easily grasp the portion of the irradiation X-ray dose calculated from the interpolated body thickness.
In FIGS. 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 at the time of positioning imaging, and thinning imaging is performed by irradiating the subject with X-rays only in the imaging region. Since the processing circuit estimates the current body thickness based on the past image and the thinned image, it is possible to reduce the exposure dose during the positioning imaging without performing the positioning imaging many times before the main scan. .

(Modification of this embodiment)
In the above-described embodiment, the description has been given of performing the thinning-out imaging without irradiating the X-ray in the non-imaging region when the positioning image of the subject P is imaged. The present modified example is different from the first embodiment in that, when a positioning image is taken, the irradiation X-ray dose is modulated and taken. More specifically, the portion corresponding to the non-imaging region in the above-described embodiment is positioned and photographed with an X-ray dose (lower dose) smaller than the irradiation X-ray amount of the portion corresponding to the thinning photographing region. Hereinafter, positioning imaging with a low dose is defined as low-dose imaging.

A control example of the irradiation X-ray dose when performing low-dose imaging will be described with reference to FIGS.
13 and 14 show an imaging range of the subject P, and the horizontal direction corresponds to the Z axis. The 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 than other regions. As a method of setting the irradiation X-ray dose lower than the other regions, for example, a preset X-ray dose value may be used, or the operator may be able to input the X-ray dose value during imaging.
As specific processing, by executing the setting function 444, the processing circuit 44 determines the low-dose imaging area 74 by the same processing as the setting of the non-imaging area in the present embodiment. After that, the processing circuit 44 controls the control device 15 to execute low-dose imaging so that the low-dose imaging region 74 has a low irradiation X-ray dose.
FIG. 14 is another example of the control of the X-ray dose 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, by performing low-dose imaging, since the dose is smaller than the X-ray dose during normal positioning imaging, the calculation of the body thickness from the image portion of the low-dose imaging region is performed. Even if it is not possible, it is possible to photograph the outline of the body shape. This makes it possible to more easily and accurately align the image between the past image and the low-dose image obtained by the low-dose imaging than in the case of the thinned image. As a result, similarly to the present embodiment, exposure during positioning imaging can be reduced.

In the above-described embodiments and modifications, the past image is a CT image captured in a standing position or a sitting position, and a thinned image to be captured in the future is captured in a recumbent position, or when the reverse is the case. Even when the imaging state is different, the current body thickness can be estimated by converting the image.
For example, a conversion table relating to the correction amount of the organ position (organ sag) corresponding to two combinations of the standing position, the sitting position, and the lying position is created in advance. By executing the setting function 444, the processing circuit 44 may correct the organ position with reference to the shooting state of the past image and the thinned image and the conversion table.

Note that 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 is a block diagram of an imaging plan apparatus according to the present embodiment and the modification.
The imaging planning apparatus 50 includes a setting function 444 and a body thickness estimation function 446. The imaging planning device 50 and the X-ray CT device 1 are connected by wire or wirelessly.
According to the imaging planning apparatus 50 shown in FIG. 15, the X-ray CT apparatus 1 can execute the processing on the imaging planning apparatus 50 side without performing the processing for estimating the body thickness and the processing for determining the scanning conditions. .

  The X-ray CT apparatus 1 includes a Rotate / Rotate-Type (third generation CT) in which an X-ray tube and a detector rotate around the subject P integrally, and a large number of X-rays arranged in a ring shape. There are various types such as Stationary / Rotate-Type (fourth 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 the present embodiment.

The hardware that generates X-rays is not limited to the X-ray tube 11. For example, instead of the X-ray tube 11, a focus coil for focusing an electron beam generated from an electron gun, a deflection coil for electromagnetic deflection, and an electron beam that deflects around a half circumference of the subject P and deflects X-rays. X-rays may be generated using a fifth generation method including a target ring to be generated.
Further, in the present embodiment, a so-called multi-tube X-ray CT apparatus in which a plurality of pairs of an X-ray tube and a detector are mounted on a rotating ring, as well as a single-tube X-ray CT apparatus. Applicable.

  In addition, each function according to the embodiment can also be realized by installing a program for executing the processing on a computer such as a workstation and expanding the program on a memory. At this time, a program capable of causing the computer to execute the method can be stored in a storage medium such as a magnetic disk (such as a hard disk), an optical disk (such as a CD-ROM or a DVD), or a semiconductor memory and distributed. .

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

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 10 Mount apparatus 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high-voltage apparatus 15 Controller 16 Wedge 17 Collimator 18 Data acquisition device (DAS)
19 Opening (bore)
REFERENCE SIGNS LIST 30 bed device 31 base 32 bed driving device 33 top plate 34 support frame 40 console device 41 memory 42 display 43 input interface 44 processing circuit 50 shooting planning device 60 past image 62, 66 modulation graph 64 thinned image 70, 72 graph 74 low Dose imaging 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 area

Claims (10)

Scan conditions of the main scan based on a past image of the subject and a positioning image of the subject taken by modulating the irradiation X-ray dose or a positioning image of the subject taken by switching on / off X-ray irradiation. Setting section for setting
X-ray CT apparatus comprising: Using a body thickness calculated based on the past image and a body thickness calculated based on the positioning image, further comprising an estimating unit that estimates a body thickness of the entire positioning image,
The X-ray CT apparatus according to claim 1, wherein the setting unit determines the scan condition based on the calculated body thickness.   The X-ray CT apparatus according to claim 2, wherein the estimating unit estimates a body thickness of the entire positioning image of the subject by calculating a ratio in an overlapping portion between the past image and the positioning image.   The said past image is a positioning image previously imaged using the same apparatus as the apparatus which image | photographed the positioning image of the said test object, a tomographic image, or an image image | photographed by other medical image diagnostic apparatuses. Item 4. The X-ray CT apparatus according to any one of Items 3.   The setting unit, when superimposing the past image and the positioning image of the subject, performs image positioning when there is a difference in body type or positioning between the positioning image of the subject and the past image. The X-ray CT apparatus according to any one of claims 1 to 4.   The X-ray CT apparatus according to any one of claims 1 to 5, wherein the positioning image is a thinned image including a non-imaging region to which the X-ray is not irradiated.   The said positioning image is an image in which the low-dose imaging | photography area | region image | photographed by the lower dose than another imaging | photography area exists along the body axis direction of the said subject. 2. The X-ray CT apparatus according to claim 1.   The X-ray CT apparatus according to any one of claims 1 to 7, wherein the past image is generated by combining different parts extracted from different images.   9. The X-ray CT apparatus according to claim 1, wherein the setting unit corrects an organ position according to whether the past image is a standing image or a recumbent image. 10. Scan conditions of the main scan based on a past image of the subject and a positioning image of the subject taken by modulating the irradiation X-ray dose or a positioning image of the subject taken by switching on / off X-ray irradiation. Setting section for setting
An imaging planning device comprising: