JP2018161472A - X-ray CT apparatus and scan planning apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an X-ray emitted to a region spread out of an imaging range of helical scanning.SOLUTION: An X-ray CT apparatus performs helical scanning to a subject placed on a top plate, and performs reconfiguration processing based on acquired projection data. The X-ray CT apparatus includes an X-ray generation part, an X-ray detection part, and a setting part. The X-ray generation part generates an X-ray to be irradiated to the subject. The X-ray detection part detects the X-ray passing through the subject, and acquires the projection data. The setting part sets a first imaging range of an imaging range of the helical scanning, and sets at least one of a start end range and a finish end range in the first imaging range as a border range. The setting part sets a first view number used for reconfiguration processing of a non-border range other than the border range in the first imaging range, and sets a view number used for reconfiguration processing of the border range so as to be smaller than the first view number.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an X-ray CT apparatus and a scan planning apparatus.

  An X-ray CT (Computed Tomography) apparatus is a type of medical image diagnostic apparatus that scans a subject using X-rays and processes the collected data by a computer, thereby imaging the inside of the subject.

  Some X-ray CT apparatuses have an ECG-synchronized scan function. In the electrocardiogram synchronous scan, for example, projection data is collected at regular intervals by intermittent exposure according to the period of the electrocardiogram waveform. This data collection is repeated in order to align projection data having different projection directions in a certain cardiac time phase by, for example, 360 ° by collecting projection data every time the same cardiac time phase is reached. Using this aligned projection data, a tomographic image free from artifacts due to heart beat is reconstructed. An electrocardiogram synchronous scan is a scan technique used when, for example, the flow of a contrast agent administered to a subject is observed.

  Further, VHP (Variable Helical Pitch) scanning is known as one of methods for scanning a subject in an X-ray CT apparatus. In the VHP scan, the X-ray tube that generates X-rays and the X-ray detector scan continuously along the longitudinal direction of the bed while rotating around the bed (top plate) on which the subject is placed. Perform a helical scan. In the VHP scan, the scan can be performed while modulating the scan pitch of the helical scan. Here, the scan pitch is equal to the distance of the bed that moves during one scan. Modulation basically refers to changing the scan pitch according to the moving speed of the bed on which the subject is placed, for example. However, the modulation is not limited to this, and may mean changing the scan pitch in accordance with the rotational speeds of the X-ray tube and the X-ray detector.

  An ECG synchronization scan may be executed together with the VHP scan. The number of projection data used for reconstruction of one CT image, that is, the number of views, differs between the VHP scan and the electrocardiogram synchronization scan. Specifically, in ECG-synchronized scanning, it is desired to capture a still image of the heart, so that the number of views used for reconstruction is small in order to shorten the time resolution (for example, X-ray tubes and X-ray detectors). (The number of views is half of the number of times data is collected during one rotation). On the other hand, in the VHP scan, since all the scanned views are desired to be used, the CT image is reconstructed using a larger number of views than in the electrocardiogram synchronous scan. Here, in the VHP scan, when attention is paid to the boundary between the first scan performed outside the execution period of the electrocardiogram-synchronized scan and the second scan executing the electrocardiogram-synchronized scan, the number of views at the first scan is More than the number of views during 2 scans.

  For this reason, the scan area of the first scan protrudes from the imaging range (reconstruction range) of the first scan and overlaps the scan area of the second scan, resulting in an area unnecessary for image reconstruction of the electrocardiogram-synchronized scan. Until then, the X-rays of the first scan are exposed. For this reason, it is impossible to shift to the intermittent exposure of the second scan until the first scan is completed, and the time until the X-ray of the second scan is first turned off becomes long.

  A similar situation exists even when a normal helical scan of only the first scan is executed without the second scan. In this case, as described above, when the scan region protrudes from the imaging range of the first scan, X-rays are exposed to the protruded region.

JP 2000-51208 A JP 2007-275551 A

  The problem to be solved by the invention is to reduce the X-rays that are exposed to the region that protrudes from the imaging range of the helical scan.

  The X-ray CT apparatus according to the embodiment executes a helical scan on the subject placed on the top board and executes a reconstruction process based on the obtained projection data. The X-ray CT apparatus includes an X-ray generation unit, an X-ray detection unit, and a setting unit.

  The X-ray generation unit generates X-rays that are irradiated onto the subject.

  The X-ray detection unit detects X-rays that have passed through the subject and obtains the projection data.

  The setting unit sets a first imaging range among the imaging ranges of the helical scan, and sets at least one of a start end range and an end range in the first imaging range as a boundary range. The setting unit sets a first number of views used for reconstruction processing of a non-boundary range other than the boundary range in the first imaging range, and sets the number of views used for reconstruction processing of the boundary range. Set to be smaller than the number of views.

FIG. 1 is a block diagram showing a schematic configuration of the X-ray CT apparatus according to the first embodiment. FIG. 2 is a schematic diagram illustrating an example of the electrocardiographic waveform data and the X-ray control method during the electrocardiographic synchronization scan according to the first embodiment. FIG. 3 is a schematic diagram showing a relationship between a reconstruction range and a margin during a general helical scan. FIG. 4 is a schematic diagram illustrating an outline of the helical pitch, the number of views, and the X-ray exposure timing of the first scan and the second scan according to the comparative example of the embodiment. FIG. 5 is a schematic diagram showing the relationship between the number of views when combining the first scan and the second scan according to the comparative example. FIG. 6 is a schematic diagram illustrating an example of the relationship between the number of views at the time of transition from the first scan to the second scan according to the first embodiment. FIG. 7 is a schematic diagram illustrating another example of the relationship of the number of views at the time of transition from the first scan to the second scan according to the first embodiment. FIG. 8 is a flowchart illustrating an example of processing according to the first embodiment. FIG. 9 is a schematic diagram illustrating the relationship between the number of views when the first scan and the second scan are combined according to the second embodiment. FIG. 10 is a flowchart illustrating an example of processing according to the second embodiment. FIG. 11 is a schematic diagram illustrating an example of the relationship between the number of views in the first scan according to the third embodiment. FIG. 12 is a schematic diagram illustrating another example of the view number relationship in the first scan according to the third embodiment. FIG. 13 is a flowchart illustrating an example of processing according to the third embodiment. FIG. 14 is a block diagram showing a schematic configuration of an X-ray CT system according to the fourth embodiment. FIG. 15 is a block diagram illustrating a schematic configuration of a scan planning apparatus according to the fourth embodiment.

Hereinafter, embodiments of the X-ray CT apparatus and the scan planning apparatus will be described with reference to the drawings. Rotate / Rotate-Type (3rd generation CT) in which the X-ray tube and detector rotate as a single unit, and a large number of X-ray detection elements arranged in a ring shape are fixed to the X-ray CT apparatus There are various types such as Stationary / Rotate-Type (fourth generation CT) in which only the X-ray tube rotates around the subject, and any type is applicable to the present embodiment. The following description will be described by taking the third generation CT as an example.
(First embodiment)
First, the configuration of the X-ray CT apparatus 100 according to the first embodiment will be described with reference to FIGS. 1 to 7. FIG. 1 is a block diagram showing a schematic configuration of an X-ray CT apparatus 100 according to the first embodiment. The X-ray CT apparatus 100 in FIG. 1 includes a gantry device 10 and a console device 30.
[Mounting device]
The gantry device 10 is a device that irradiates the subject P with X-rays and collects X-ray detection data that has passed through the subject. The gantry device 10, the X-ray detector 12, and the rotating frame 13 are collected. A high voltage generator 15, a DAS 16, and a gantry drive device 19. The gantry device 10 is an example of a gantry unit.

  The X-ray generator 11 includes an X-ray tube that generates X-rays (for example, a vacuum tube that generates a cone-shaped or pyramid-shaped X-ray beam). The X-ray tube is a vacuum tube that generates X-rays by irradiating thermoelectrons from a cathode (filament) to an anode (target) when a high voltage is applied from the high-voltage generator 15. X-rays generated by the X-ray generator 11 are emitted toward the subject P placed on the couch top 17 of the bed. The X-ray generator 11 according to the present embodiment switches X-rays ON / OFF according to the electrocardiographic waveform of the subject P when executing an electrocardiogram-synchronized scan in accordance with control from a scan control function 34d described later. The X-ray generator 11 is an example of an X-ray generator.

  The X-ray detector 12 includes 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 arc centered on the focal point of the X-ray tube. X-rays that pass through are detected, and an electrical signal corresponding to the X-ray dose is output to the DAS 16. As the X-ray detector 12, for example, an X-ray detector (surface detector) in which a plurality of X-ray detection elements are arranged in two directions (slice direction and channel direction) orthogonal to each other is used. A plurality of X-ray detection element arrays are provided, for example, 320 along the slice direction. The slice direction corresponds to the rotation axis direction of the rotary frame 13, and the channel direction corresponds to the rotation direction of the X-ray generator 11. In this embodiment, the rotational axis direction of the rotating frame 13 or the longitudinal direction of the top plate 17 in the non-tilt state is the Z-axis direction, the axial direction orthogonal to the Z-axis direction and horizontal to the floor surface is the X-axis direction, An axial direction orthogonal to the Z-axis direction and perpendicular to the floor surface is defined as a Y-axis direction.

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

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

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

  The optical sensor array has a function of converting into an electric signal corresponding to the amount of light from the scintillator, and includes 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 electrical signals. The X-ray detector 12 and the DAS 16 are examples of the X-ray detection unit.

  The rotary frame 13 supports the X-ray generator 11 and the X-ray detector 12 so as to face each other with the subject P interposed therebetween, and the X-ray generator 11 and the X-ray detector 12 are scanned when the subject P is scanned. An annular frame that rotates around and supports a subject. The rotating frame 13 has an opening region 14 penetrating in the slice direction. In addition to the X-ray generator 11 and the X-ray detector 12, the rotating frame 13 further includes and supports a high voltage generator 15 and a DAS 16. The detection data generated by the DAS 16 is a non-rotating portion of the gantry device 10 (for example, a fixed frame. The illustration in FIG. 1 is omitted) by optical communication from a transmitter having a light emitting diode (LED) provided on the rotating frame 13. And is transmitted to the console device 30. The detection data transmission method from the rotating frame 13 to the non-rotating portion of the gantry device 10 is not limited to the optical communication described above, and any method may be adopted as long as it is a non-contact type data transmission. The rotating frame 13 is an example of a rotating unit.

  The high voltage generation device 15 is a voltage generation circuit that applies a high voltage to the X-ray generation device 11 (hereinafter, “voltage” means a voltage between an anode and a cathode in the X-ray tube). The X-ray generator 11 generates X-rays with the high voltage from the high voltage generator 15. The high voltage generator 15 is an example of a high voltage generator.

  The DAS 16 (Data Acquisition System) is an electrical circuit that collects electrical signals (received data) obtained from the X-ray detection elements of the X-ray detector 12 and collects detection data. Specifically, the DAS 16 includes an amplifier that performs amplification processing on an electric signal output from each X-ray detection element, and an A / D converter that converts the electric signal into a digital signal. The detection data corresponding to each X-ray irradiation direction from is generated. The X-ray irradiation direction is also referred to as a view. Then, the DAS 16 outputs the generated detection data for each view to the processing circuit 34 of the console device 30. For example, the DAS 16 outputs data (sinogram data) obtained by mapping detection data indicating the X-ray detection amount for each X-ray detection element for each X-ray irradiation direction to the processing circuit 34 of the console device 30. The number of detection data for each view included in the single sinogram data is referred to as a view number. In the present embodiment, the DAS 16 outputs sinogram data having different numbers of views during a first scan and a second scan described later. Note that the first scan refers to a scan that is performed outside the execution period of the ECG-synchronized scan in the VHP scan, and the second scan refers to an ECG-synchronized scan in the VHP scan. The DAS 16 is an example of a data collection unit.

The gantry driving device 19 has a function of rotating the rotating frame 13 and driving the bed and the top plate 17 and is configured by, for example, a motor or an actuator. The gantry driving device 19 according to the present embodiment moves the bed along the rotation axis direction of the rotary frame 13 when the first scan is executed and the second scan is executed under the control of the scan control function 34d described later. At this time, the gantry driving device 19 performs control so that the moving speed of the top plate 17 is slower in the second scan than in the first scan. The rotational axis direction of the rotary frame 13 may be called the longitudinal direction of the top plate 17 or the body axis direction of the subject P. The moving method of the top plate 17 may be a method of moving only the top plate 17 or a method of moving the top plate 17 together with a support frame (not shown). In addition, as a method of changing the relative positional relationship between the top board 17 and the gantry device 10 during the helical scan, a method of moving the top board 17 or a method of moving the gantry apparatus 10 may be used. A method that combines the above may be used. However, in each of the following embodiments, a method of moving the top board 17 will be described as an example. The gantry driving device 19 is an example of a driving unit.
[Console device]
The console device 30 is a device used for operation input to the X-ray CT apparatus 100. The console device 30 also has a function of reconstructing CT image data (tomographic image data and volume data) indicating the internal form of the subject P from sinogram data collected by the DAS 16 of the gantry device 10. The console device 30 includes a memory 31, a display 32, an input interface 33, and a processing circuit 34. Although the console device 30 is described as a separate body from the gantry device 10, the gantry device 10 may include the console device 30 or a part of each component of the console device 30. In addition, the console device 30 is not limited to a configuration in which a plurality of functions are executed by a single console, and a configuration in which a plurality of functions are executed by separate consoles may be employed. For example, the functions of the processing circuit 34 such as the preprocessing function 34b and the reconstruction processing function 34c may be distributed. The console device 30 is an example of a console unit.

  The memory 31 is realized by, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. The memory 31 stores detection data, projection data obtained by performing preprocessing described later on the detection data, CT image data after reconstruction processing, and the like. The storage of projection data and reconstructed image data is not limited to being executed by the memory 31, but may be executed by a cloud server that can be connected to the X-ray CT apparatus 100 via a communication network such as the Internet. For example, the cloud server may store projection data and reconstructed image data by receiving a storage request from the X-ray CT apparatus 100. In addition, the memory 31 in the present embodiment, as shown in FIGS. 2 to 7, includes an electrocardiographic waveform of the subject P output from the electrocardiograph 18 to be described later and each reconstruction range of the first scan and the second scan. The shooting range, boundary range, number of views, helical pitch, FOV (Field Of View), etc. corresponding to are stored. However, although the first view number in the boundary range shown in FIGS. 4 and 5 can be set, it is the number of views used in the comparative example and is not used in the present embodiment. Detailed description regarding FIGS. 2 to 7 will be described later. The memory 31 is an example of a storage unit.

  The display 32 displays various information. For example, the display 32 outputs a medical image (CT image) generated by the processing circuit 34, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. For example, the display 32 is an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube) display. For example, the display 32 displays CT images after reconstruction processing acquired by the first scan and the second scan. The display may be called a display device. The display 32 is an example of a display unit. The display 32 may be provided in the gantry device 10. Further, the display 32 may be a desktop type or may be configured by a tablet terminal or the like that can wirelessly communicate with the console device 30 main body.

  The input interface 33 receives various input operations from the operator, converts the received input operations into electrical signals, and outputs them to the processing circuit 34. For example, the input interface 33 receives from the operator collection conditions when collecting projection data, reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-processed image from a CT image, and the like. . In addition, the input interface 33 is configured to set an imaging range, a boundary range, the number of views, a helical pitch corresponding to the reconstruction range at the time of the first scan and the second scan, as shown in FIGS. The setting is accepted from the operator. However, although the first view number in the boundary range shown in FIGS. 4 and 5 can be set, it is the number of views used in the comparative example and is not used in the present embodiment. Such an input interface 33 is realized by, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, or the like. Further, a GUI (Graphical User Interface) can be used as a part of the input interface 33. The input interface 33 is an example of an input unit. Further, the input interface 33 may be provided in the gantry device 10. Further, the input interface 33 may be configured by a tablet terminal or the like capable of wireless communication with the console device 30 main body.

  The processing circuit 34 controls the overall operation of the X-ray CT apparatus 100. For example, the processing circuit 34 performs various processes on the detection data transmitted from the DAS 16. The processing circuit 34 includes a system control function 34a, a preprocessing function 34b, a reconstruction processing function 34c, a scan control function 34d, and a heart rate detection function 34e. The processing circuit 34 is an example of a processing unit.

  The system control function 34 a controls various functions of the processing circuit 34 based on an input operation received from the operator via the input interface 33.

  Further, the system control function 34 a sets a scan plan including an imaging range, a boundary range, and the number of views according to the operation of the input interface 33. For example, the system control function 34a sets the first imaging range in the helical scan imaging range, sets at least one of the start end range and the end range in the first imaging range as the boundary range, and sets the boundary in the first imaging range. The first number of views used for reconstruction processing for non-boundary ranges other than the range is set, and the number of views used for reconstruction processing for boundary ranges is set to be smaller than the first number of views. Here, the setting of the boundary range may be executed, for example, by designating a terminal range having a predetermined length as the boundary range. Note that the value of “predetermined length” may be determined by presetting the parameter file in the memory 31, for example. For example, as illustrated in FIG. 6, the system control function 34 a may be set to reduce the number of views used for boundary range reconstruction processing at a time. Further, for example, as shown in FIG. 7, the system control function 34a may be set so that the number of views used for boundary range reconstruction processing is reduced stepwise. As a method of reducing the size stepwise, an arbitrary method such as a method of uniformly reducing the size or a method of rapidly reducing the size near the end can be used as appropriate.

  Further, the system control function 34a sets a second shooting range adjacent to the boundary range on the side opposite to the non-boundary range, and sets the second view number used for the reconstruction process of the second shooting range as the first view number. The minimum value of the number of views used for boundary range reconstruction processing may be set to the same value as the second view number. As the second view number, any value can be used as long as it is a value less than the first view number and a value greater than or equal to the view number of the half-scan reconstruction method. Here, as described above, the system control function 34a may set the number of views used for boundary range reconstruction processing to be small at a time or may be set to be small in steps. When the number of views used for the boundary range reconstruction process is set to be small at a time, the number of views and the second view number used for the boundary range reconstruction process may be set to the same value.

  Further, the system control function 34a uses the first helical pitch in the non-boundary range, uses the second helical pitch narrower than the first helical pitch in the second imaging range, and uses the first helical pitch in the boundary range. The scan condition may be set so that a helical pitch modulated between the pitch and the second helical pitch is used. This scan condition is included in the scan plan. Note that a scan control function 34d, which will be described later, may control the gantry driving device 19 based on this scanning condition.

  The system control function 34a performs overall control of the X-ray CT apparatus 100 by controlling operations of the gantry device 10, the console device 30, and a couch device (not shown). The system control function 34a is an example of a system control unit. In the system control function 34a, a function for setting a scan plan is an example of a setting unit. The system control unit may include a setting unit or may not include a setting unit.

  The pre-processing function 34b performs pre-processing such as logarithmic conversion processing, offset correction, sensitivity correction, and beam hardening correction on the detected data output from the DAS 16 or sinogram data generated from the detected data, and outputs projection data. create. Note that pre-processing data (detection data, sinogram data) and pre-processing data may be collectively referred to as projection data. The preprocessing function 34b is an example of a preprocessing unit.

  The reconstruction processing function 34c creates CT image data (tomographic image data and volume data) by performing reconstruction processing on the projection data created by the preprocessing function 34b. To reconstruct a CT image, the full scan reconstruction method requires 360 degrees of projection data around the subject P. Even in the half-scan reconstruction method, projection data for 180 ° + fan angle is required. The present embodiment can be applied to any reconfiguration method. For example, the first view number may be used as the view number in the full scan reconstruction method, and the second view number may be used as the view number in the half scan reconstruction method. The tomographic image data is image data of a specific tomographic plane of the subject P, and the volume data is three-dimensional image data of the subject P constructed by an aggregate of tomographic image data. For reconstruction of tomographic image data, any method such as a two-dimensional Fourier transform method, a convolution / back projection method, a successive approximation reconstruction method, or the like can be employed. Volume data is created by interpolating a plurality of reconstructed tomographic image data. For the reconstruction of volume data, for example, any method such as a cone beam reconstruction method, a multi-slice reconstruction method, an enlargement reconstruction method, or the like can be adopted. The reconstruction processing function 34c is an example of a reconstruction processing unit.

  The scan control function 34d controls various operations related to X-ray scanning. For example, the scan control function 34d applies a high voltage to the X-ray generator 11 and controls the high voltage generator 15 to generate X-rays. The scan control function 34d controls to rotate the rotating frame 13 during scanning. The scan control function 34d in the present embodiment controls the gantry driving device 19 so that the moving speed of the top plate 17 is slower in the second scan than in the first scan. The scan control function 34d acquires electrocardiographic waveform data of the subject P from a heart rate detection function 34e described later, and controls the X-ray ON / OFF timing in the second scan. The scan control function 34d is an example of a scan control unit.

  The heart rate detection function 34e identifies, for example, a period of a P wave, which will be described later, from the electrocardiographic waveform data acquired by the external electrocardiograph 18 connected to the X-ray CT apparatus 100, and is subjected to detection based on the period. It has a function of measuring the heart rate of the specimen P. The heart rate detection function 34e outputs the electrocardiographic waveform data acquired from the electrocardiograph 18 to the scan control function 34d. The heart rate detection function 34e is an example of a detection unit.

  The electrocardiograph 18 is a sensor that detects a weak current generated by the heart beat of the subject P, which is provided separately from the X-ray CT apparatus 100, and the time change of the detected current as an electrocardiogram. Output. A scan control function 34d of the processing circuit 34, which will be described later, controls the X-ray irradiation by the X-ray generator 11 (electrocardiographic synchronization function) using the electrocardiographic waveform shown in the electrocardiograph.

  FIG. 2 is a schematic diagram showing an example of the electrocardiographic waveform data acquired by the electrocardiograph 18 and an X-ray control method at the time of the electrocardiogram synchronization scan. As shown in FIG. 2, characteristic waveforms such as P wave, Q wave, S wave, and T wave appear in the heartbeat cycle in the electrocardiographic waveform data. One heartbeat of the heart movement is divided into a systole, a relaxation period, and an equal relaxation period. The systole during which the heart contracts comes about a certain time after the R wave having the most characteristic and high peak. This systole is followed by a relaxation period in which the heart expands. These contraction period and relaxation period are periods in which the size of the heart fluctuates drastically. The period from immediately after the relaxation period to just before the contraction period of the next heartbeat cycle is a period in which the variation in the size of the heart, called the equivalent relaxation period, is relatively gentle.

  In the ECG-synchronized scan, the X-ray is turned on during the equivalent relaxation period, in which the heart size fluctuation is relatively mild, and the heart time phase has a large heart size fluctuation. The exposure dose can be reduced by turning off X-rays during the systole and the relaxation period. Note that turning on X-rays corresponds to turning on an X-ray control signal, generating X-rays, or irradiating X-rays. Turning off the X-ray corresponds to turning off the X-ray control signal or stopping the X-ray.

  Therefore, the heart rate detection function 34e specifies the period of the equal relaxation period from the electrocardiographic waveform data of the subject P acquired from the electrocardiograph 18, and outputs the period information of the equal relaxation period to the scan control function 34d. To do. The scan control function 34d can irradiate the subject P with X-rays during the equal relaxation period, thereby performing a scan of the heart of the subject P at a timing when the fluctuation of the heart size is gentle. .

  Here, the description returns to the processing circuit 34 of FIG.

  The view number adjustment function 34f has a function of adjusting the number of views during the first scan and the second scan. For example, the view number adjustment function 34f reads the number of views in the first scan and the second scan from the memory 31 and sets the number of views according to the scan condition. The view number adjustment function 34f will be described in detail with reference to FIG. The view number adjustment function 34f is an example of a view number adjustment unit. In addition, the region of the subject P that is scanned during the first scan is an example of a first imaging region, and the region of the subject P that is scanned during the second scan is an example of a second imaging region.

  Each process performed by the system control function 34a, the preprocessing function 34b, the reconstruction processing function 34c, the scan control function 34d, the heart rate detection function 34e, and the view number adjustment function 34f, which are components of the processing circuit 34. The functions are recorded in the memory 31 in the form of a program that can be executed by a computer. The processing circuit 34 is a processor that implements a function corresponding to each program by reading the program from the memory 31 and executing the program. In other words, the processing circuit 34 in a state where each program is read has each function shown in the processing circuit 34 of FIG. In FIG. 1, a single processing circuit 34 performs a system control function 34a, a preprocessing function 34b, a reconstruction processing function 34c, a scan control function 34d, a heart rate detection function 34e, and a view number adjustment function 34f. However, the processing circuit 34 may be configured by combining a plurality of independent processors, and the functions may be realized by each processor executing a program.

  FIG. 3 is a schematic diagram showing a relationship between a reconstruction range and a margin during a general helical scan. For example, FIG. 3 shows a case where the helical scan is performed in the positive direction of the Z axis. The reconstruction range R here corresponds to the imaging range set by the operator. When the reconstruction range R is helically scanned, the scan is performed in a range obtained by adding the margin N to the set reconstruction range R. Therefore, during the helical scan, the scan range A wider than the set reconstruction range R. Will be irradiated with X-rays. Here, the margin N corresponds to an area where the X-rays are exposed outside the imaging range. In each of the following embodiments, the range of at least one margin N is narrowed to reduce the X-rays exposed to the region protruding from the imaging range of the helical scan. The term “scan range” corresponds to “scan area”.

  FIG. 4 shows a size corresponding to one pitch of the helical scan (hereinafter referred to as a helical pitch) when the first scan and the second scan according to the comparative example (comparison target) of the first embodiment are executed in combination. It is a schematic diagram which shows the outline of the number of views and the X-ray exposure timing. Here, the helical pitch is equal to the distance of the bed that moves while the X-ray generator 11 and the X-ray detector 12 make one rotation in the helical scan. In the case of the fourth generation CT, the description is rewritten so that only the X-ray generator 11 rotates. The upper part of FIG. 4 shows the scan range in the subject P. The middle part of FIG. 4 is a graph for showing the change of the helical pitch when the first scan and the second scan are executed in combination. The vertical axis is the helical pitch and the horizontal axis is the Z-direction distance. The lower part of FIG. 4 is a graph showing the X-ray irradiation timing when the first scan is executed in combination with the second scan, the vertical axis indicates the X-ray irradiation amount, and the horizontal axis indicates time. Note that the lengths of the arrows shown together in the lower part of FIG. 4 correspond to the number of views in each scan, and are long during the first scan and short during the second scan.

  As shown in FIG. 4, when scanning is performed by combining the first scan and the second scan, the helical pitch is modulated in the scan range 40 including the heart and the other scan ranges, and the scan is executed. Here, the modulation of the helical pitch basically refers to changing the helical pitch by changing the moving speed of the bed, for example. However, the modulation of the helical pitch is not limited to this, and may refer to changing the helical pitch by changing the rotational speeds of the X-ray generator 11 and the X-ray detector 12. In the case of the fourth generation CT, the description will be replaced as described above. In the comparative example shown in FIG. 4, for example, the helical pitch in the scan range from the head of the subject P to the scan range 40 including the heart is set large, and the helical pitch in the heart region is set small. When the helical scan is executed, the helical pitch gradually decreases as approaching the heart region as shown in FIG. At this time, the number of views at the time of executing the helical scan is constant because the image noise is not reduced if the number exceeds a certain number. However, at the time of the second scan, the number of views used for reconstruction of the heart region is exceptional. To improve the time resolution. This is because the time resolution decreases when reconstruction is performed during the second scan with the same number of views as during the first scan. For this reason, at the time of the second scan, for example, the time resolution is improved by performing the reconstruction with the number of views of the half scan. For this reason, the number of views in the second scan is smaller than the number of views in the first scan. However, when attention is paid to the moment when the second scan area is reached during data collection of the first scan, the number of views during the first scan is larger than the number of views during the second scan, so the second scan is started. It takes time until the X-ray is turned off at the time of shifting, and it takes time to shift to the second scan.

  More specifically, the switching from the first scan to the second scan is executed immediately at time t1 shown in FIG. 4, and it is ideal to switch from the time t1 to the ECG-synchronized view number. However, since the number of views during the first scan is larger than the number of views during the second scan, it takes time to turn off the X-rays during the second scan, as shown in FIG. The time for switching off the X-ray is delayed to t2. That is, since the number of views in the first scan is large, it takes time to complete the first scan, and the time until the X-ray in the second scan shifts to OFF is delayed. Therefore, in the first and second embodiments described below, the X-ray OFF timing at the second scan is advanced compared to the comparative example by eliminating the margin from the time t1 to t2 that occurs at the first scan. The purpose is to reduce the exposure dose.

  FIG. 5 is a schematic diagram showing in more detail the relationship of the number of views when switching from the first scan to the second scan in the comparative example described in FIG. Here, the horizontal axis of FIG. 5 indicates time. Note that the length of the arrow in FIG. 5 corresponds to the number of views necessary for each scan and the time range for view acquisition. The vertical bar at the center of the arrow corresponds to the acquisition timing of the slice image within the reconstruction range. If the horizontal axis in FIG. 5 is the coordinate axis in the Z direction, the vertical bar at the center of the arrow corresponds to the Z position of the slice image within the reconstruction range. The explanation regarding these horizontal axes and arrows is the same in the following drawings.

  As shown in FIG. 5, in the comparative example, the first scan is performed up to the boundary t1 between the reconstruction range (first reconstruction range) corresponding to the first scan and the electrocardiogram synchronous reconstruction range (second reconstruction range). In this case, the view acquisition time range at the time of the first scan straddles the ECG synchronization reconstruction range. Therefore, when intermittent X-ray exposure is performed by the second scan, the timing at which the X-ray can be turned off is shifted to time t2 shown in FIG.

  Therefore, in the first embodiment, when shifting from the first scan to the second scan, the time required for the end of the first scan is shortened by performing processing to reduce the number of views on the first scan side, The purpose is to advance the timing of turning off the X-rays in the second scan.

  6 and 7 are schematic diagrams illustrating an example of the relationship between the number of views at the time of the first scan during the transition from the first scan to the second scan according to the first embodiment. In the first embodiment, a case will be described in which the number of views in the first scan is decreased to match the number of views in the second scan. In the first embodiment, the view number adjustment function 34f reads the number of views at the time of the second scan (hereinafter referred to as the second view number) from the memory 31. Further, the view number adjustment function 34f receives timing information related to X-ray ON / OFF during the second scan from the scan control function 34d. The view number adjustment function 34f uses the timing information received from the scan control function 34d to change the number of views (first view number) in the end range of the first reconstruction range as shown in FIG. Adjust so that it decreases with the number.

  6 and 7, the first imaging range corresponding to the first reconstruction range, the boundary range that is the end range in the first imaging range, and the non-boundary range other than the boundary range in the first imaging range are reproduced. The first view number used for the configuration process and the view number used for the boundary range reconstruction process are set by the processing circuit 34, respectively. The number of views used for boundary range reconstruction processing is set to be smaller than the first view number. Further, the first imaging range has a start end range, an intermediate range, and an end range. When the boundary range is a terminal range, the non-boundary ranges other than the boundary range are the start range and the intermediate range.

Also, as shown in FIG. 6, the view number adjustment function 34f may control the number of views for several slices in the boundary range of the first reconstruction range to match the second view number. As shown in FIG. 7, the number of views of the first scan may be decreased step by step. As shown in FIG. 7, by gradually reducing the number of views of the first scan, the change in the image quality of the image acquired by the first scan and the image acquired by the second scan becomes moderate. Of the arrows indicating the number of views shown in FIG. 6 and FIG. 7, the uppermost one indicates the number of views when the number of views is not adjusted among the number of views during the first scan. Yes. Thereby, at the time of switching from the first scan to the second scan, the timing for turning off the X-ray can be made earlier than before, and the exposure dose can be reduced. In addition, the scan (number of slices) that requires adjustment of the number of views at the time of the first scan has a second time range required to acquire the number of views when the number of views of the normal first scan is used, for example. All of the scans that overlap the scan start timing (corresponding to the view base point in FIGS. 6 and 7) may be included.
[Operation]
Next, an example of processing of the X-ray CT apparatus 100 configured as described above will be described with reference to the flowchart of FIG.

  First, the X-ray CT apparatus 100 receives scan conditions from an operator via the input interface 33. For example, the input interface 33 receives the scan range of the first scan and the second scan. Further, the system control function 34a of the processing circuit 34 sets the first imaging range of the helical scan imaging range, for example, in accordance with the operation of the input interface 33, and at least the start end range and the end range in the first imaging range. One is set as the boundary range. Further, the processing circuit 34 sets a first view number used for reconstruction processing of a non-boundary range other than the boundary range in the first imaging range, and sets the number of views used for boundary range reconstruction processing to the first view number. Set to be smaller. Further, the processing circuit 34 sets a second shooting range adjacent to the boundary range on the side opposite to the non-boundary range, and sets the second view number used for the reconstruction process of the second shooting range from the first view number. Is also set to a small value, and the minimum value of the number of views used for boundary range reconstruction processing is set to the same value as the second view number. Further, the processing circuit 34 uses the first helical pitch in the non-boundary range, uses the second helical pitch that is narrower than the first helical pitch in the second imaging range, and uses the first helical pitch in the boundary range. The scanning condition is set so as to use a helical pitch modulated between the first helical pitch and the second helical pitch. For the setting of these scan plans, for example, scanograms taken before the first scan and the second scan can be used. Further, the subject P is placed on the top board 17 by the operator or the like (step S01).

  Next, the scan control function 34d reads the scan plan including the scan condition received by the input interface 33, and executes the first scan. At this time, the gantry driving device 19 moves the top plate 17 at a speed corresponding to the first scan (first speed). For example, in the first scan, the region of the subject P closer to the head than the heart is scanned (step S02).

  Next, the view number adjustment function 34 f reads the imaging range (second imaging range) of the second scan received via the input interface 33 and reads the second view number from the memory 31. The heart rate detection function 34e reads the electrocardiographic waveform data of the subject P acquired from the electrocardiograph 18. At this time, the scan control function 34d extracts, for example, a period corresponding to the equivalent relaxation period from the electrocardiographic waveform data acquired from the heart rate detection function 34e, and sets it as the X-ray ON period. A period other than is set as an X-ray OFF period (step S03). Note that step S03 may be performed prior to step S02.

  Next, the view number adjustment function 34f calculates the number of views on the first scan side (first view number) during the transition period from the first scan to the second scan (the number of second views). ) To adjust. At this time, the gantry driving device 19 moves the top board 17 at a speed (second speed) corresponding to the second scan. Here, the transition period from the first scan to the second scan indicates a time period during which the helical pitch changes so as to decrease when the transition from the first scan to the second scan is performed. The transition period corresponds to the boundary range period. In the present embodiment, the view number adjustment function 34f adjusts the view number in the boundary range at the time of the first scan to be small so as to coincide with the second view number (step S04).

  Next, the scan control function 34d executes the second scan with the second number of views in the imaging range of the second scan. At this time, since the number of views in the boundary range in the first scan is the same as the second view number in step S04, the X-ray can be immediately controlled to be turned off when the second scan is started. It becomes possible. At this time, the scan control function 34d uses the electrocardiogram waveform data acquired from the heart rate detection function 34e to control the X-ray ON / OFF timing and execute the second scan (step S05).

  The detection data obtained by the first scan and the second scan is converted into sinogram data in the DAS 16, for example, and transmitted to the console device 30. In the console device 30, projection data is generated by pre-processing the sinogram data acquired by the pre-processing function 34b. The generated projection data is subjected to reconstruction processing by the reconstruction processing function 34c, and a CT image is generated. Note that, as described above, the number of views of projection data is different between the execution of the first scan and the second scan. Therefore, the number of views used in the reconstruction process is different, and the number of views in the second scan is set to be small. . For this reason, the CT image obtained by the second scan has a higher time resolution than the CT image obtained by the first scan (step S06).

  Finally, the system control function 34a displays the CT image acquired by the reconstruction processing function 34c on the display 32 (step S07).

  According to the first embodiment described above, it is possible to advance the X-ray OFF timing at the time of the second scan when performing a scan in which the first scan and the second scan are combined. It becomes possible to reduce exposure.

  Specifically, according to the first embodiment, the first imaging range is set out of the helical scan imaging ranges, and at least one of the start end range and the end range in the first imaging range is set as the boundary range. In addition, a first view number used for reconstruction processing of a non-boundary range other than the boundary range in the first imaging range is set, and the number of views used for boundary range reconstruction processing is made smaller than the first view number. Set to. Therefore, in order to narrow the margin that extends beyond the first imaging range with a configuration that sets the number of views used for boundary range reconstruction processing to be small, the area is exposed to an area that protrudes from the imaging range of the helical scan. X-rays can be reduced. This effect can be obtained both in the case of the VHP scan having the first scan and the electrocardiogram synchronization scan and in the case of the normal helical scan having only the first scan.

  Further, according to the first embodiment, the second imaging range that is adjacent to the boundary range on the side opposite to the non-boundary range is set, and the second view number used for the reconstruction processing of the second imaging range is set to the first Is set to a value smaller than the number of views, and the minimum number of views used for boundary range reconstruction processing is set to the same value as the second view number. Therefore, by setting the minimum value of the number of views used for the boundary range reconstruction process to the same value as the second view number, the minimum value of the view number used for the boundary range reconstruction process is set to the second view number. Compared with the case of setting a larger value, the marginal range can be further narrowed, so that the X-rays exposed to the region that protrudes from the imaging range can be further reduced.

  Further, according to the first embodiment, the first helical pitch is used in the non-boundary range, the second helical pitch narrower than the first helical pitch is used in the second imaging range, and the first helical pitch is used in the boundary range. Scan conditions are set so that a helical pitch modulated between one helical pitch and a second helical pitch is used. Therefore, a VHP scan having the above-described effect can be executed.

  In addition, according to the first embodiment, the number of views used for boundary range reconstruction processing may be set to be reduced stepwise. Thereby, the fluctuation | variation of the image quality of a boundary range can be smoothed.

Further, according to the first embodiment, the number of views and the second number of views used for boundary range reconstruction processing may be set to the same value. Thereby, the number of views used for the boundary range reconstruction process can be easily set as compared to the case where the number of views used for the boundary range reconstruction process is set to be reduced stepwise.
(Second Embodiment)
In the first embodiment, when shifting from the first scan to the second scan, the case has been described in which the number of views at the end of the first scan is reduced so as to coincide with the second view number. In the second embodiment, a case will be described in which the presence / absence of adjustment of the number of views at the end of the first scan is switched.

  In the second scan, as shown in FIG. 2, the exposure dose is reduced by turning X-rays on and off in accordance with fluctuations in the size of the heart. Therefore, when shifting from the first scan to the second scan, the timing for turning off the X-rays is not always reached, and there is a case where the X-ray irradiation remains on and the process proceeds to the second scan. In this case, since the X-ray is in the ON state in the time domain of the second scan, it is not necessary to reduce the number of views at the end of the first scan. Therefore, in the second embodiment, when it is necessary to receive an electrocardiogram waveform from the electrocardiograph 18 when shifting from the first scan to the second scan and adjust the number of views at the end of the first scan. If the number of views described in the first embodiment is adjusted and the adjustment of the number of views at the end of the first scan is unnecessary, the first scan including the X-ray ON period in the second scan is included. Increase the number of views to increase the spatial resolution during the first scan.

  FIG. 9 is a schematic diagram illustrating the relationship between the number of views when the first scan and the second scan are combined according to the second embodiment. Specifically, FIG. 9 shows the view at the time of the first scan including the X-ray ON period at the second scan without adjusting the number of views at the first scan according to the second view number. The case of acquiring the number is shown.

  As shown in FIG. 2, since the X-ray ON / OFF period at the second scan is determined according to the electrocardiogram waveform data, the heart is equal in the switching timing from the first scan to the second scan. When the relaxation period is reached, the X-ray ON timing of the second scan may be just reached. In this case, the timing for turning off the X-ray is delayed by a time corresponding to the first X-ray ON period ΔT of the second scan as shown in FIG.

  For example, the view number adjustment function 34f acquires the electrocardiogram waveform data of the subject P from the external electrocardiograph 18, and adjusts the number of views used for boundary range reconstruction processing based on the electrocardiogram waveform data. Determine no. The view number adjustment function 34f generates the X-rays immediately after the boundary range by using the number of views used for the boundary range reconstruction processing when the second imaging range immediately after the boundary range generates X-rays. Expand based on the period you want.

  Specifically, the view number adjustment function 34f reads the electrocardiogram waveform data of the subject P from the heart rate detection function 34e, and if the X-ray is to be turned on, the view number adjustment function 34f In the case of an electrocardiographic waveform in which the range acquired by the number of views is extended to the range on the second scan side and the X-ray should be turned off, the number of views at the first scan end is set as in the first embodiment. Adjust to fit the second view number.

  Note that the view number adjustment function 34f according to the second embodiment includes information related to the X-ray ON / OFF timing at the time of the second scan received from the scan control function 34d in addition to the functions described in the first embodiment. It is read, and it is determined whether or not it is necessary to adjust the view number of the first scan when shifting from the first scan to the second scan.

  Other configurations are the same as those of the first embodiment.

  Next, an example of processing of the X-ray CT apparatus 100 configured as described above will be described with reference to the flowchart of FIG. Note that the processes according to steps S11 to S13 and steps S17 to S19 are the same as the processes according to steps S01 to S03 and steps S05 to S07 in the flowchart of the first embodiment shown in FIG. Omit.

  The view number adjustment function 34f receives information related to the X-ray ON / OFF timing of the second scan immediately after the transition period for shifting from the first scan to the second scan from the scan control function 34d. As the information, for example, the equivalent relaxation period based on the electrocardiographic waveform data of the subject P acquired from the external electrocardiograph 18 is set as the X-ray ON period, and the period other than the equivalent relaxation period is set as the X-ray OFF. As the period, information indicating the switching timing of each period can be used. The view number adjustment function 34f reads the information and determines whether or not the view number needs to be adjusted during the first scan (step S14). At this time, if the second scan immediately after the transition period (boundary range) is the X-ray ON timing (step S14, NO), it is determined that adjustment of the number of views during the first scan is unnecessary, and the second scan X Data collection is continued at the timing of line ON, and the number of views at the first scan is expanded (step S16). If the second scan immediately after the transition period is the X-ray OFF timing (step S14, YES), it is determined that it is necessary to adjust the number of views during the first scan, and the first scan is performed as in the first embodiment. The number of views at the end during scanning is adjusted so as to become smaller in accordance with the number of views during the second scanning (step S15).

  According to the second embodiment described above, the transition period between the first scan and the second scan is a period in which the X-ray should be turned on depending on whether the X-ray is turned on or off. In this case, it is possible to acquire an image with high spatial resolution at the time of the first scan without reducing the number of views of the first scan, and when the X-ray should be turned off, the number of views at the time of the first scan can be set. By making small adjustments according to the second number of views, it is possible to shorten the period required to turn off the X-rays and to reduce the exposure dose.

  Further, according to the second embodiment, similarly to the first embodiment, the X-rays in the second scan are reduced by reducing the number of views in the boundary range in accordance with the second view number in the second scan. It becomes possible to advance the timing of turning off.

In the first and second embodiments described above, it has been described that the second scan is executed after the first scan. However, when the VHP scan is executed, the object is covered along the longitudinal direction of the top plate 17. In order to scan a wide range including the heart region of the specimen P, the first scan may be executed after the second scan is executed. In this case, at the switching timing between the second scan and the first scan, the view number of the first scan may be adjusted similarly to the switching timing between the first scan and the second scan.
(Third embodiment)
In the first and second embodiments, the case where both the first scan and the second scan are executed has been described. In the third embodiment, a case of a normal helical scan in which only the first scan is executed without executing the second scan (electrocardiogram synchronization scan) will be described. In this case, when setting at least one of the start end range and the end end range in the first imaging range of the first scan as the boundary range, the system control function 34a executes one of the processes (i) to (iii). .

  (I) Processing for setting only the start end range as the boundary range.

  (Ii) Processing for setting only the end range as the boundary range.

  (Iii) Processing for setting both the start end range and the end range as boundary ranges.

  In the following description, the process (iii) will be described as an example. However, the present invention is not limited to this, and the above processing (i) or (ii) is also possible. Further, the helical scan of the present embodiment is not a VHP scan, but may be a VHP scan.

  11 and 12 are schematic diagrams illustrating an example of the relationship between the number of views in the first scan. In the third embodiment, the first imaging range corresponding to the first reconstruction range, the two boundary ranges that are the start range and the end range of the first imaging range, and the non-boundary range other than the boundary range are reproduced. The system control function 34a sets the first view number used for the configuration process and the view number used for the boundary range reconstruction process. The number of views used for boundary range reconstruction processing is set to be smaller than the first view number. Further, the first imaging range has a start end range, an intermediate range, and an end range. When the boundary range is the start range and the end range, the non-boundary range other than the boundary range is an intermediate range.

  Here, the setting of the boundary range may be executed, for example, by designating each of the start end range and the end range having a predetermined length as the boundary range. Note that the value of “predetermined length” may be determined by presetting the parameter file in the memory 31, for example. Also, the scan (number of slices) that requires changing the number of views in the start range is, for example, when the first view number is used, the time range required to acquire the first view number is the first scan number. All of the scans that overlap the start timing (corresponding to the first base point of the view in FIGS. 11 and 12) may be included. Similarly, the scan (number of slices) that requires changing the number of views in the end range is, for example, when the first view number is used, the time range required to acquire the first view number is the first scan. It is only necessary to include all the scans that overlap with the end timing (corresponding to the second base point of the view in FIGS. 11 and 12). For example, as shown in FIG. 11, the system control function 34a may be set to change the number of views used for boundary range reconstruction processing at a time. Further, the system control function 34a may be set to change the number of views used for boundary range reconstruction processing step by step as shown in FIG. 12, for example. In FIG. 11 and FIG. 12, the minimum value of the number of views used for the boundary range reconstruction processing is referred to as a second view number. However, the second view number here does not mean the view number of the second scan, unlike the first and second embodiments. This is because the third embodiment does not have the second scan.

  As a setting method of the first view number and the second view number, a value of the view number may be set, or a percentage value corresponding to the view number may be set. As a percentage value, for example, when the number of first views is the number of views in the full scan reconstruction method, the value corresponding to the number of first views may be 100%. Similarly, when the second view number is the number of views in the half-scan reconstruction method, the value corresponding to the second view number may be 0%.

  Other configurations are the same as those of the first embodiment.

  Next, an example of processing of the X-ray CT apparatus 100 configured as described above will be described using the flowchart of FIG.

  First, the X-ray CT apparatus 100 receives a scan plan from an operator via the input interface 33. For example, the system control function 34a of the processing circuit 34 sets the first imaging range in the helical scan imaging range in accordance with the operation of the input interface 33, and sets both the start end range and the end range in the first imaging range. Set as boundary range. In addition, the processing circuit 34 sets a first view number used for reconstruction processing of an intermediate range other than the boundary range in the first shooting range, and sets the number of views used for boundary range reconstruction processing from the first view number. Also set to be smaller. Further, the processing circuit 34 sets the minimum value of the number of views used for the boundary range reconstruction processing as the second number of views. For the setting of these scan plans, for example, scanograms taken before the first scan and the second scan can be used. Further, the subject P is placed on the top board 17 by the operator or the like (step S21).

  Next, the scan control function 34d executes the first scan based on the scan plan received by the input interface 33 (step ST22). At this time, the gantry driving device 19 moves the top plate 17 at a speed corresponding to the first scan. Further, the view number adjustment function 34f adjusts the view number in the start range from the base point of the view of the first scan so as to increase to match the first view number in the intermediate range. Thereafter, the view number adjustment function 34f adjusts the number of views from the base point of the first scan view to the end range to be smaller than the first view number. This completes the first scan.

  The detection data obtained by the first scan is converted into sinogram data in the DAS 16, for example, and transmitted to the console device 30. In the console device 30, projection data is generated by pre-processing the sinogram data acquired by the pre-processing function 34b. The generated projection data is subjected to reconstruction processing by the reconstruction processing function 34c, and a CT image is generated. Since the number of views of the projection data is different between the boundary range and the intermediate range of the first scan, the number of views used in the reconstruction process is different, and the number of views in the boundary range is set to be small. For this reason, the CT image in the boundary range has higher time resolution and lower image quality than the CT image in the intermediate range (step S24).

  Finally, the system control function 34a displays the CT image acquired by the reconstruction processing function 34c on the display 32 (step S25).

  According to the third embodiment described above, the first imaging range of the helical scan imaging range is set, and at least one of the start end range and the end range in the first imaging range is set as the boundary range. In addition, a first view number used for reconstruction processing of a non-boundary range other than the boundary range in the first imaging range is set, and the number of views used for boundary range reconstruction processing is made smaller than the first view number. Set to. Therefore, in the case of a normal helical scan with only the first scan, it is possible to reduce the X-rays exposed to the region that protrudes from the imaging range.

  Further, according to the third embodiment, the number of views used for boundary range reconstruction processing may be set to be changed stepwise. In this case, fluctuations in image quality in the boundary range can be smoothed.

  According to the third embodiment, the number of views used for boundary range reconstruction processing may be set to be changed at a time. In this case, the number of views can be easily set as compared with the case where the number of views is set to be changed stepwise.

(Modification)
Next, a modification of the third embodiment will be described. In this modification, the system control function 34a is modified to set the boundary range based on the examination site. The term “examination site” may be appropriately changed to another term such as “examination site”, “imaging site”, “imaging site”, and the like. Other configurations are the same as those of the third embodiment.

  Specifically, in the case of an examination site where the image quality of either the start end range or the end range may be reduced, the system control function 34a delimits either the start end range or the end range corresponding to the examination site. Set as a range. For example, when the examination site is the lower limb and the end range is the toe of the foot, the system control function 34a sets the end range as the boundary range corresponding to the test site. When the examination site is a lower limb and the starting end range is a toe of a foot, the hospital sets the starting end range as a boundary range corresponding to the examination site. For example, when the examination site is the upper limb and the start end range is the fingertip of the hand, the system control function 34a sets the start end range as a boundary range corresponding to the test site. When the terminal range is the fingertip of the hand, the terminal range is set as the boundary range as described above. Further, for example, when the examination sites are the chest and abdomen, both the start end range and the end range are set as the boundary range corresponding to the test site. Alternatively, for example, when the examination sites are the chest and the abdomen, the boundary range is not set corresponding to the examination site (setting of the boundary range is turned off).

  In such a configuration, for example, information in which an examination site is associated with at least one of a start end range and an end end range is stored in advance, and the system control function 34a sets a boundary range based on the information. Can be easily realized.

According to the above modification, in addition to the effect of the third embodiment, the effort to set the boundary range is reduced by the configuration in which at least one of the start end range and the end range is set as the boundary range based on the examination site. can do.
(Fourth embodiment)
FIG. 14 is a block diagram showing a schematic configuration of an X-ray CT system according to the fourth embodiment. This X-ray CT system includes one or a plurality of X-ray CT apparatuses 100 and a scan planning apparatus 70. One or a plurality of X-ray CT apparatuses 100 and the scan planning apparatus 70 are communicably connected via a network.

  The X-ray CT apparatus 100 performs CT inspection according to the scan plan notified from the scan planning apparatus 70. The X-ray CT apparatus 100 according to the fourth embodiment has a configuration in which a function for setting a scan plan is omitted from the processing circuit 34 shown in FIG.

  The scan planning device 70 is a computer device that sets a scan plan related to a helical scan of a subject and notifies the X-ray CT apparatus 100 of the set scan plan. The terms “scan plan” and “scan plan apparatus” may be replaced with other terms such as “imaging plan” and “imaging plan apparatus”.

  FIG. 15 is a block diagram illustrating a schematic configuration of the scan planning apparatus 70. The scan planning apparatus 70 includes a memory 71, a display 72, an input interface 73, a communication interface 74, and a processing circuit 75. Data communication among the memory 71, the display 72, the input interface 73, the communication interface 74, and the processing circuit 75 is performed via a bus (BUS).

  The memory 71 is a storage device such as an HDD, an SSD, or an integrated circuit storage device that stores various information. The memory 71 may be a drive device that reads and writes various information between a portable storage medium such as a CD, a DVD, and a flash memory, a semiconductor memory element such as a RAM, and the like in addition to an HDD, an SSD, and the like. . The memory 71 stores, for example, an imaging range, boundary range, view number, helical pitch, FOV, control program and table according to the present embodiment corresponding to the reconstruction ranges of the first scan and the second scan. . The memory 71 is an example of a storage unit.

  The display 72 displays various information. For example, the display 72 outputs a scan plan set by the processing circuit 75, a GUI for receiving various operations from the operator, and the like. For example, as the display 72, for example, a liquid crystal display, a CRT display, an organic EL display, a plasma display, or any other display can be used as appropriate. The display 72 is an example of a display unit.

  The input interface 73 receives various input operations from the operator, converts the received input operations into electric signals, and outputs them to the processing circuit 75. As the input interface 73, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, a touch panel display, or the like can be used as appropriate. In the present embodiment, the input interface 73 is not limited to a physical operation component such as a mouse, keyboard, trackball, switch, button, joystick, touch pad, and touch panel display. For example, an example of the input interface 73 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 apparatus and outputs the electric signal to the processing circuit 75. . The input interface 73 is an example of an input unit.

  The communication interface 74 is a communication circuit that performs data communication with the X-ray CT apparatus 50 via wired or wireless (not shown). For example, the communication interface 74 notifies the X-ray CT apparatus 100 of the scan plan set by the setting function 75b. The communication interface 74 is an example of a communication unit. The communication unit may be called a notification unit.

  The processing circuit 75 controls the operation of the entire scan planning apparatus 70 in accordance with the input operation electrical signal output from the input interface 73. For example, the processing circuit 75 includes, as hardware resources, a processor such as a CPU, MPU, or GPU and a memory such as a ROM or RAM. The processing circuit 75 executes a control function 75a, a setting function 75b, a display control function 75c, and the like by a processor that executes a program loaded in the memory. The control function 75a may include a setting function 75b. Each function 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.

  In the control function 75a, the processing circuit 75 controls each function of the processing circuit 75 based on the input operation received from the operator via the input interface 73, as in the first embodiment. The control function 75a is an example of a control unit.

  In the setting function 75b, the processing circuit 75 sets the first imaging range in the helical scan imaging range, sets at least one of the start end range and the end range in the first imaging range as the boundary range, and sets the first imaging range in the first imaging range. By setting the number of first views used for reconstruction processing of non-boundary ranges other than the boundary range, and setting the number of views used for reconstruction processing in the boundary ranges to be smaller than the number of first views, scanning Set up a plan. In this setting function 75b, the processing circuit 75 may set the number of views in the boundary range to be reduced stepwise.

  In this setting function 75b, the processing circuit 75 sets the second shooting range adjacent to the boundary range on the side opposite to the non-boundary range in the scan plan, and sets the second view number used for the reconstruction processing in the second shooting range. The scan plan may be set to be equal to or less than the minimum value of the number of views used for boundary range reconstruction processing. In the setting function 75b, the processing circuit 75 may set the number of views and the second number of views used for boundary range reconstruction processing to the same value.

  In the setting function 75b, the processing circuit 75 uses the first helical pitch in the non-boundary range, uses the second helical pitch narrower than the first helical pitch in the second imaging range, and in the boundary range, The scan plan may be set to use a helical pitch modulated between the first helical pitch and the second helical pitch. The setting function 75b is an example of a setting unit.

  The display control function 75 c causes display data or the like to be displayed on the display 72 in accordance with the processing of the processing circuit 75. For example, the display control function 75c causes the display 72 to display the scan plan set by the setting function 75b. The display control function 75c is an example of a display control unit.

  Other configurations are the same as those of the first to third embodiments and modifications.

  According to the configuration as described above, the setting function 75 b is provided in the scan planning apparatus 70 that is an external apparatus of the X-ray CT apparatus 100. With this configuration, the operational effects of the first to third embodiments can be obtained similarly. In addition to this, the scan plan can be set only by providing the setting function 75b in the processing circuit 75 of the scan planning apparatus 70 without modifying the processing circuit 34 of the X-ray CT apparatus 100. When there are a plurality of X-ray CT apparatuses 100 in the X-ray CT system, it is not necessary to provide the setting function 75b for each X-ray CT apparatus 100, so that the cost can be reduced.

  According to at least one embodiment described above, the first imaging range of the helical scanning imaging range is set, and at least one of the start end range and the end range in the first imaging range is set as the boundary range. In addition, a first view number used for reconstruction processing of a non-boundary range other than the boundary range in the first imaging range is set, and the number of views used for boundary range reconstruction processing is made smaller than the first view number. Set to. Therefore, it is possible to reduce the X-rays that are exposed to the region that protrudes from the imaging range of the helical scan.

  Note that the components described as “units” in each of the above embodiments may be realized by hardware, software, or hardware. It may be realized by a combination with software.

  Although several embodiments of the present invention have been described, these embodiments are 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 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 included in the invention described in the claims and the equivalents thereof.

  The X-ray CT apparatus in the embodiment of Japanese Patent Application No. 2017-61289 which is the basic Japanese application of the present application will be additionally described below.

  [1]: The X-ray CT apparatus of the embodiment includes a top plate, an X-ray generation unit, an X-ray detection unit, a detection unit, an input unit, a scan control unit, and a view number adjustment unit. The top plate moves at least a first speed and a second speed slower than the first speed in a state where the subject is placed. The X-ray generation unit generates X-rays that are irradiated onto the subject placed on the top board. The X-ray detector detects X-rays that have passed through the subject and generates reception data. The detection unit acquires electrocardiographic waveform data of the subject from an external electrocardiograph. The input unit sets scan conditions related to the first scan and the second scan according to the input. In the first scan, the top plate is moved at the first speed in the first imaging region of the subject and reconfigured with the first number of views. In the second scan, the top plate is moved at the second speed in the second imaging region of the subject, and the electrocardiographic waveform data corresponds to a predetermined cardiac time phase. Reconstruct with a small number of second views. The scan control unit changes the moving speed and the number of views of the top board based on the scan condition, and performs X-ray irradiation by the X-ray generation unit and generation of the reception data by the X-ray detection unit. To control. The view number adjustment unit sets a base point for shifting from the first scan to the second scan based on the electrocardiographic waveform data, and includes the first scan performed before shifting to the second scan The number of views used for reconstruction of the first scan in a predetermined transition period is adjusted to be smaller than the first number of views.

  [2]: In the X-ray CT apparatus according to [1], the number-of-views adjustment unit increases the number of views acquired by the first scan in the transition period stepwise according to the number of second views. Make it smaller.

  [3]: In the X-ray CT apparatus according to [1], the view number adjustment unit matches the number of views acquired by the first scan in the transition period with the second view number.

  [4]: In the X-ray CT apparatus according to [1], the view number adjustment unit determines whether adjustment of the number of views acquired by the first scan in the transition period based on the electrocardiographic waveform data. to decide.

  [5]: In the X-ray CT apparatus according to [4], when the second scan immediately after the transition period is a timing at which the X-ray is turned on, The number of views acquired by one scan is expanded based on a period during which the X-ray of the second scan is turned on.

  DESCRIPTION OF SYMBOLS 10 ... Mount apparatus, 11 ... X-ray generator, 12 ... X-ray detector, 16 ... Data acquisition circuit, 18 ... Electrocardiograph, 19 ... Mount drive apparatus, 30 ... Console apparatus, 31, 71 ... Memory, 32, 72 ... Display, 33, 73 ... Input interface, 34, 75 ... Processing circuit, 34a ... System control function, 34b ... Pre-processing function, 34c ... Reconfiguration processing function, 34d ... Scan control function, 34e ... Heart rate detection function, 34f ... view number adjustment function, 70 ... scan planning device, 74 ... communication interface, 75a ... control function, 75b ... setting function, 75c ... display control function.

Claims (10)

In an X-ray CT apparatus that executes a helical scan on a subject placed on a top plate and executes a reconstruction process based on the obtained projection data,
An X-ray generation unit for generating X-rays irradiated to the subject;
An X-ray detector that detects X-rays passing through the subject and obtains the projection data;
A first imaging range of the helical scan imaging range is set, at least one of a start end range and an end range in the first imaging range is set as a boundary range, and a non-boundary range other than the boundary range in the first imaging range is set. A setting unit configured to set a first number of views used for boundary range reconstruction processing and to set a number of views used for boundary range reconstruction processing to be smaller than the first number of views;
An X-ray CT apparatus comprising:   The setting unit sets a second shooting range adjacent to the boundary range on the side opposite to the non-boundary range, and sets a second view number used for reconstruction processing of the second shooting range to the first view. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is set to a value smaller than a number, and a minimum value of the number of views used for the boundary range reconstruction processing is set to the same value as the second view number.   The setting unit uses a first helical pitch in the non-boundary range, uses a second helical pitch narrower than the first helical pitch in the second imaging range, and uses the first helical pitch in the boundary range. The X-ray CT apparatus according to claim 2, wherein a scan condition is set so as to use a helical pitch modulated between the helical pitch of the second helical pitch and the second helical pitch.   The X-ray CT apparatus according to claim 1, wherein the setting unit sets the number of views in the boundary range to be reduced stepwise.   The X-ray CT apparatus according to claim 2, wherein the setting unit sets the number of views used for the reconstruction processing of the boundary range and the second number of views to the same value.   The setting unit acquires electrocardiographic waveform data of the subject from an external electrocardiograph, and determines whether or not it is necessary to adjust the number of views in the boundary range based on the electrocardiographic waveform data. The X-ray CT apparatus described.   When the second imaging range immediately after the boundary range is the timing for generating the X-ray, the setting unit sets the number of views in the boundary range to a period for generating the X-ray immediately after the boundary range. The X-ray CT apparatus according to claim 6, wherein the X-ray CT apparatus is expanded based on the X-ray CT apparatus. In a scan planning apparatus that sets a scan plan of an X-ray CT apparatus that executes a helical scan on a subject placed on a top plate and executes a reconstruction process based on the obtained projection data,
A first imaging range of the helical scan imaging range is set, at least one of a start end range and an end range in the first imaging range is set as a boundary range, and a non-boundary range other than the boundary range in the first imaging range is set. By setting a first view number to be used for boundary range reconstruction processing and setting the number of views to be used for reconstruction processing in the boundary range to be smaller than the first view number, A setting section to be set;
A scan planning apparatus comprising: a notification unit that notifies the X-ray CT apparatus of the set scan plan.   The setting unit sets a second shooting range adjacent to the boundary range on the side opposite to the non-boundary range in the scan plan, and sets a second view number used for reconstruction processing in the second shooting range, The scan planning apparatus according to claim 8, wherein the scan plan is set so as to be equal to or less than a minimum value of the number of views used for the reconstruction process of the boundary range.   The setting unit uses a first helical pitch in the non-boundary range, uses a second helical pitch narrower than the first helical pitch in the second imaging range, and uses the first helical pitch in the boundary range. The scan planning apparatus according to claim 9, wherein the scan plan is set so as to use a helical pitch modulated between a helical pitch of the second helical pitch and the second helical pitch.