JP2018202157A - X-ray ct apparatus and photographing condition calculation method - Google Patents

Abstract

To provide an X-ray CT apparatus and a photographing condition calculation method which can reduce radiation exposure dose of an analyte in scanography performed for positioning for real scan and setting of photographing condition before the real scan.SOLUTION: An X-ray CT apparatus comprises: a discrete image acquisition unit acquiring discrete images in multiple discrete position in a body axis direction of an analyte; and a photographing condition calculation unit calculating a photographing condition corresponding to a scan range of real scan on the basis of the multiple discrete images.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to an X-ray CT apparatus and an imaging condition calculation method.

  When a subject is imaged by an X-ray CT (Computed Tomography) apparatus, a scanogram may be obtained in advance by performing scanography before the main scan. By using the scanogram, positioning for the main scan (setting of a range (scan range) for obtaining a tomographic image) and setting of imaging conditions can be performed more accurately.

  However, in scano imaging performed for positioning for main scanning and setting of imaging conditions before main scanning, imaging is often performed while irradiating X-rays continuously in time. In this case, the scan imaging has a lower tube current than the main scan, but the imaging tends to take a long time, so the exposure dose of the subject increases.

JP 2002-263097 A

  The problem to be solved by the present invention is to reduce the exposure dose of the subject in scanography performed for positioning and setting of imaging conditions for the main scan before the main scan.

  The X-ray CT apparatus according to the embodiment includes a discrete image acquisition unit that acquires discrete images at a plurality of discrete positions in the body axis direction of the subject, and a scan range of the main scan based on the plurality of discrete images. An imaging condition calculation unit that calculates the corresponding imaging condition.

1 is a block diagram showing an example of an X-ray CT apparatus according to an embodiment of the present invention. The schematic block diagram which shows the example of an implementation | achievement function by the processor of a processing circuit. The figure for demonstrating the reference | standard image image | photographed before this scan. (A) is explanatory drawing which shows an example of a mode which collated the standard image of a reference image, and the standard image image | photographed before the main scan, (b) is the reference image and the standard image image | photographed before the main scan. Explanatory drawing which shows an example of a mode that image alignment was carried out. (A) is explanatory drawing which shows an example of a scan point, (b) is explanatory drawing which shows an example of a mode that a tube current value is calculated | required from the scan data of a scan point. Explanatory drawing which shows an example of the pulse scan image acquired only in the position corresponding to a scan point. Explanatory drawing which shows an example of the tube current value of AP direction set for every scan point, and the tube current value of RL direction. 9 is a flowchart showing an example of a procedure for reducing the exposure dose of a subject in scanography performed by the processor of the processing circuit for positioning and setting of imaging conditions for the main scan before the main scan. The flowchart which shows an example of the procedure of the determination process of the availability of the past image performed by the reference | standard position image acquisition function by FIG.8 S1.

  Embodiments of an X-ray CT apparatus and an imaging condition calculation method according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an example of an X-ray CT apparatus 1 according to an embodiment of the present invention. In the present embodiment, the axis of rotation of the rotating frame 13 in the non-tilt state or the longitudinal direction of the top plate 33 of the bed apparatus 30 is orthogonal to the z-axis direction and the z-axis direction and is horizontal to the floor surface. Are defined as an y-axis direction and an axial direction perpendicular to the x-axis direction and z-axis direction and perpendicular to the floor surface, respectively (see FIG. 1).

  The X-ray CT apparatus 1 includes a gantry device 10, a bed device 30, and a console device 40.

  Note that the X-ray CT apparatus and the imaging condition calculation method according to an embodiment of the present invention provide imaging with tube current modulation (hereinafter referred to as tube current modulation imaging) or imaging with tube voltage modulation (hereinafter referred to as tube) in the main scan. (Voltage modulation imaging) can be performed, and a scanogram can be obtained by performing scanogram imaging in advance before the main scan.

  The X-ray CT apparatus 1 includes a Rotate / Rotate-Type (third generation CT) in which an X-ray tube and a detector are integrally rotated around a subject, and a large number of X-ray detection elements arrayed in a ring shape. 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. In the following description, an example in which a third generation Rotate / Rotate-Type is employed as the X-ray CT apparatus 1 according to the present embodiment will be described.

  The gantry device 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13 having an opening 19 in which an imaging region is inherent, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and data collection A circuit (DAS: Data Acquisition System) 18 is provided.

  The X-ray tube 11 is a vacuum tube that irradiates thermionic electrons from a cathode (filament) to an anode (target) when a high voltage is applied from the X-ray high voltage device 14.

  In this embodiment, both a single-tube X-ray CT apparatus and a so-called multi-tube X-ray CT apparatus in which a plurality of pairs of X-ray tubes and detectors are mounted on a rotating ring. Applicable. Further, hardware for generating X-rays is not limited to the X-ray tube 11. For example, instead of the X-ray tube 11, a focus coil that focuses an electron beam generated from an electron gun, a deflection coil that electromagnetically deflects, and an electron beam that surrounds the half circumference of the subject P collide with each other to collide X-rays. X-rays may be generated using a fifth generation method including a target ring to be generated.

  The X-ray detector 12 detects X-rays irradiated from the X-ray tube 11 and passed through the subject P, and outputs an electrical signal corresponding to the X-ray dose to the DAS 18. The X-ray detector 12 includes, for example, a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction along one arc around the focal point of the X-ray tube 11. The X-ray detector 12 has, for example, a structure in which a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arrayed in the channel direction are arrayed in the slice direction (column direction, row 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 has an X-ray shielding plate that is disposed on the surface of the scintillator array on the X-ray incident side and has a function of absorbing scattered X-rays. The optical sensor array has a function of converting into an electrical signal corresponding to the amount of light from the scintillator, 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 electrical signals.

  The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 opposite to each other and rotates the X-ray tube 11 and the X-ray detector 12 by a control device 15 described later. In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 further includes and supports an X-ray high voltage device 14 and a DAS 18. Note that the detection data generated by the DAS 18 is a photo provided on a non-rotating portion of the gantry device 10 such as a fixed frame (not shown) by optical communication from a transmitter having a light emitting diode (LED) provided on the rotating frame 13. It is transmitted to a receiver having a diode and transferred to the console device 40. 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. A fixed frame (not shown) is a frame that rotatably supports the rotating frame 13.

  The X-ray high voltage device 14 has an electrical circuit such as a transformer and a rectifier, and the X-ray tube 11 irradiates a high voltage generator having a function of generating a high voltage to be applied to the X-ray tube 11. And an X-ray control device that controls the output voltage in accordance with the X-rays. The high voltage generator may be a transformer system or an inverter system. The X-ray high voltage device 14 may be provided on the rotating frame 13 or on the fixed frame side of the gantry device 10.

  The control device 15 includes a processor and a storage circuit, and drive mechanisms such as a motor and an actuator. The control device 15 has a function of receiving an input signal from an input interface attached to the console device 40 or the gantry device 10 and performing operation control of the gantry device 10 and the couch device 30. For example, the control device 15 performs control for receiving the input signal to rotate the rotating frame 13, control for tilting the gantry device 10, and control for operating the bed device 30 and the top plate 33. The tilt control of the gantry device 10 is controlled by the control device 15 about the axis parallel to the X-axis direction based on the tilt angle (tilt angle) information input by the input interface attached to the gantry device 10. It is realized by rotating. The control device 15 may be provided in the gantry device 10 or may be provided in the console device 40.

  The wedge 16 is a filter for adjusting the X-ray dose irradiated from the X-ray tube 11. Specifically, the wedge 16 transmits and attenuates the X-rays irradiated from the X-ray tube 11 so that the X-rays irradiated from the X-ray tube 11 to the subject P have a predetermined distribution. It is a filter. For example, the wedge 16 (wedge filter, bow-tie filter) is a filter obtained 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 X-rays transmitted through the wedge 16, and forms a slit by a combination of a plurality of lead plates or the like.

  The DAS 18 (Data Acquisition System) includes an amplifier that performs amplification processing on an electric signal output from each X-ray detection element of the X-ray detector 12 and an A / D converter that converts the electric signal into a digital signal. And generate detection data. The detection data generated by the DAS 18 is transferred to the console device 40.

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

  The base 31 is a housing that supports the support frame 34 so as to be movable in the vertical direction (y direction). The couch driving device 32 is a motor or actuator that moves the top plate 33 on which the subject P is placed in the long axis direction (z direction) of the top plate 33. 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 long axis direction (z direction) of the top plate 33 in addition to the top plate 33. Further, the bed driving device 32 may be moved together with the base 31 of the bed device 30. When the present invention can be applied to standing CT, a method of moving a patient moving mechanism corresponding to the top board 33 may be used. In addition, the imaging system of the gantry 10 and the top plate 33, such as helical scanning and scano imaging for setting a range (scan range) for obtaining a tomographic image in the main scan (hereinafter referred to as positioning for the main scan as appropriate), etc. In the case of performing photographing with a relative change in the positional relationship, the relative change in the positional relationship may be performed by driving the top plate 33 or by running the fixed frame of the gantry device 10. Or may be performed by a combination thereof.

  The console device 40 includes a memory 41, a display 42, an input interface 43, a network connection circuit 44, and a processing circuit 45. In addition, although the console apparatus 40 demonstrates below as what performs all the functions by a single console, these functions may be performed by several consoles.

  The memory 41 includes a recording medium that can be read by a processor, such as a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk, and an optical disk. The memory 41 stores, for example, projection data and reconstructed image data. The projection data and reconstructed image data generated by the X-ray CT apparatus 1 may be stored in the memory 41, or other electronic devices such as a cloud server that can be connected to the X-ray CT apparatus 1 via a network. May store projection data and reconstructed image data in response to a storage request from the X-ray CT apparatus 1. Similarly, some or all of the programs and data in the recording medium of the memory 41 may be downloaded by communication via a network, or may be given to the memory 41 via a portable storage medium such as an optical disk. Good.

  The memory 41 may store in advance a past image obtained by photographing the subject P in the past with a modality or an optical camera. The past image may be acquired from the image server or the like via the network by the processing circuit 45 and stored in the memory 41.

  Here, the past image is one type of reference image used for positioning (setting of a scan range) for a main scan described later. The reference image according to the present embodiment includes at least an image of a predetermined reference position of the subject P (hereinafter referred to as a reference image) used for positioning for the main scan. In addition to the X-ray CT apparatus 1, various modalities such as a magnetic resonance imaging apparatus and an ultrasonic diagnostic apparatus can be used as modalities for capturing past images. For example, when the modality for capturing a past image is the X-ray CT apparatus 1, the past image may be a scano image generated by, for example, scano imaging.

  The display 42 displays various information. For example, the display 42 outputs a medical image (CT image) generated by the processing circuit 45, a GUI (Graphical User Interface) for receiving various operations from the user, and the like. For example, the display 42 is a liquid crystal display, a CRT (Cathode Ray Tube) display, an OLED (Organic Light Emitting Diode) display, or the like.

  The input interface 43 receives various input operations from the user, converts the received input operations into electrical signals, and outputs them to the processing circuit 45. For example, the input interface 43 receives from the user collection conditions when collecting projection data, reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-process image from a CT image, and the like. For example, the input interface 43 is realized by a mouse, a keyboard, a trackball, a switch, a button, a joystick, or the like.

  The network connection circuit 44 implements various information communication protocols according to the network form. The network connection circuit 44 connects the X-ray CT apparatus 1 and other devices such as an image server according to these various protocols. For this connection, an electrical connection via an electronic network can be applied. Here, the electronic network means an entire information communication network using telecommunications technology. In addition to a wireless / wired hospital backbone local area network (LAN) and the Internet network, a telephone communication network, an optical fiber communication network, a cable. Includes communication networks and satellite communication networks.

  The processing circuit 45 reads out and executes a program stored in the memory 41, thereby performing scan imaging in which positioning for the main scan (setting of the scan range) and setting of imaging conditions are performed before the main scan. It is a processor that executes processing for reducing the exposure dose of the subject P. The processing circuit 45 also controls the overall operation of the X-ray CT apparatus 1.

  FIG. 2 is a schematic block diagram showing an example of functions realized by the processor of the processing circuit 45. As shown in FIG. 2, the processor of the processing circuit 45 realizes a reference position image acquisition function 51, an imaging function 52, a positional relationship calculation function 53, a discrete image acquisition function 54, and an imaging condition calculation function 55. Each of these functions is stored in the memory 41 in the form of a program.

  In the present embodiment, an example in which each function 51-55 is realized by the processing circuit 45 of the console device 40 will be described. However, a part or all of these functions 51-55 of the processing circuit 45 are networked. It may be realized by an external device having at least a processor and a storage circuit, which is independent from the X-ray CT apparatus 1, such as a hospital server, a cloud console, and a workstation connected to the computer.

  The reference position image acquisition function 51 acquires a reference image including a predetermined reference position of the subject P when a positioning image for the main scan is necessary. The reference image is an image including at least a standard image (an image at a predetermined standard position of the subject P) in the image. For example, even when a main scan with tube current modulation is performed, there is a case where strict positioning using a scanogram is not performed in a health checkup or the like. In this case, there is no need to acquire a positioning image for the main scan.

  The imaging function 52 images the subject P by a main scan with tube current modulation, a main scan with tube voltage modulation, or a main scan in which tube current modulation and tube voltage modulation are combined. The imaging function 52 captures the reference image 71 by scanning the predetermined reference position of the subject P before the main scan. The reference image 71 is a scano image having a predetermined width including a predetermined reference position of the subject P, and includes an image of the predetermined reference position of the subject P.

  The reference image 71 is taken before the main scan, and is preferably taken on the same day as the main scan, more preferably immediately before the main scan. For example, the imaging of the reference image 71 may be included in the same scan protocol as the pulse scan imaging described later. In this case, since the reference image 71 is captured during execution of the same scan protocol as the pulse scan imaging, the reference image 71 is captured immediately before the main scan in the same manner as a plurality of discrete images obtained by the pulse scan imaging. In this case, the state of the subject P at the time of capturing the reference image 71 and a plurality of discrete images can be considered to be substantially the same as that at the time of capturing the main scan.

  FIG. 3 is a diagram for explaining the reference image 71 photographed before the main scan. FIG. 4A is an explanatory diagram showing an example of a state in which the reference image 171 of the reference image and the reference image 71 photographed before the main scan are collated, and FIG. 4B is the reference image 171 of the reference image and the main image 71. It is explanatory drawing which shows an example of a mode that image alignment was carried out with the reference | standard image 71 image | photographed before the scan.

  The reference image 71 photographed before the main scan is used for image alignment. The predetermined reference position to be included in the reference image 71 photographed before the main scan may be a part in the human body where it is difficult for the absorbed dose to change with time. A plurality of reference positions may be set. For example, when a past image is used as a reference image and the height of the subject P is greatly different between the time when the past image was taken and the present, use two or more different locations in the body axis direction as reference positions. Thus, it can be easily understood that the height of the subject P has changed. Further, the reference position may be, for example, an end portion of the scan range of the main scan included in the imaging condition of the main scan, and in this case, both ends may be used as the reference position (see FIG. 3).

  When performing positioning for the main scan, the positional relationship calculation function 53 collates the standard image 171 included in the reference image with the standard image 71 photographed before the main scan (see FIG. 4A). Next, the positional relationship calculation function 53 aligns the reference image standard image 171 and the standard image 71 photographed before the main scan (see FIG. 4B). At this time, a difference amount (see Xmm in FIGS. 4A and 4B) between the reference image 171 of the reference image and the reference image 71 taken before the main scan is obtained. After image alignment, positioning for the main scan (setting of the scan range) is performed using the reference image, and the scan start position is determined. Further, when the reference image is a past image taken with a modality in the past, and the top plate position information is attached to the past image, the positional relationship calculation function 53 displays the top plate position information attached to the past image. First, the subject P is placed at the start position of the main scan by adjusting the relative positions of the top plate 33 on which the subject P is placed and the imaging system including the X-ray tube 11 and the X-ray detector 12. Can be moved.

  For this reason, the positional relationship calculation function 53 can perform positioning for the main scan using only the reference image 71 photographed before the main scan. Therefore, as compared with the case where the positioning for the main scan is performed using the scan image taken on the whole body (whole body), only a very small part of the subject P needs to be scanned (see FIG. 3). In addition, the exposure amount of the subject P can be reduced.

  Here, the scan imaging for setting the tube current value in the main scan with tube current modulation will be described.

  Conventionally, when performing a main scan with tube current modulation, scan imaging for setting a tube current value is performed before the main scan. Scano imaging is performed in a range including the scan range of the main scan. For example, when the main scan has a scan range from the cervix to the pelvis, conventionally, scan image data from the cervix to the pelvis is acquired before the main scan, and a tube for tube current control is based on the scan image data. A current change pattern is determined.

  However, in order to set the tube current value, scan image data at each of a plurality of discrete positions (hereinafter referred to as scan points) along the body axis direction of the subject P within the scan range of the main scan is obtained. If there is enough. For this reason, in the conventional method, the subject P receives useless exposure by scano imaging other than the scan point.

  FIG. 5A is an explanatory diagram illustrating an example of the scan point 62, and FIG. 5B is an explanatory diagram illustrating an example of how the tube current value is obtained from the scan data of the scan point 62.

  For example, when the main scan is a helical scan, the scan point 62 corresponds to the AP direction (vertical direction, see FIG. 5A) or RL direction of the subject P in the locus 61 of the X-ray tube 11 in the helical scan (see FIG. 5A). The left and right direction) should be projected.

  If there is scano image data in the AP direction (or RL direction), the area when converted to an elliptical water phantom and the length of the short axis (or long axis length) at the water equivalent thickness are determined. The major axis length (or minor axis length) can be calculated. For this reason, the water equivalent thickness converted into an elliptical water phantom at each scan point 62 is obtained only from the scan image data in the AP direction (or RL direction). Therefore, the tube current value to be set at each scan point 62 can be obtained from the scanogram data at each scan point 62 (see FIG. 5B).

  Thus, by performing pulse scan imaging for acquiring a discrete image only at a plurality of discrete positions (scan points 62) along the body axis direction of the subject P, the main scan among the imaging conditions of the main scan is performed. At least one of the tube current value and tube voltage value corresponding to the scan range of the scan can be set, and the exposure dose of the subject P is greatly increased compared to the case of scanning from the neck to the pelvis before the main scan. Can be reduced.

  Therefore, the processing circuit 45 according to the present embodiment performs scanning in scanography for setting at least one of the tube current value and the tube voltage value corresponding to the scan range of the main scan among the imaging conditions performed before the main scan. Pulse scan imaging is performed only at the point 62 (a plurality of discrete positions along the body axis direction of the subject P).

  In order to obtain the position of the scan point 62 more accurately, the positional relationship calculation function 53 first determines the position of the scan point 62 and the scan range of the main scan based on the reference image and the reference image 71 taken before the main scan. Find the positional relationship with. More specifically, the positional relationship calculation function 53 performs positioning for the main scan (setting of the scan range) based on the reference image and the reference image 71 photographed before the main scan, and then performs tube current modulation or Based on the rotational speed of the imaging system included in the imaging conditions of the main scan with tube voltage modulation, the relative speed between the top 33 and the imaging system, and information on the set scan range, the position of the scan point 62 and the main scan The positional relationship with the scan range is obtained. By performing positioning for the main scan before the pulse scan imaging, the positional relationship calculation function 53 is able to more accurately determine the position of the scan point within the scan range of the main scan than when positioning for the main scan is not performed. It can be determined easily and accurately.

  FIG. 6 is an explanatory diagram showing an example of a discrete image acquired only at a position 72 corresponding to the scan point 62.

  The imaging function 52 scan points 62 obtained by the positional relationship calculation function 53 in order to set the tube current value in the main scan with tube current modulation or in order to set the tube voltage value in the main scan with tube voltage modulation. A plurality of discrete images (hereinafter referred to as pulse scan images) are obtained by performing pulse scan imaging (intermittent scan imaging) of the subject P only at a plurality of discrete positions 72 corresponding to. At this time, scano imaging is not performed at the non-irradiation position 73 excluding the position 72 corresponding to the scan point 62. That is, a plurality of discrete images are acquired by repeating ON / OFF of X-ray irradiation at a plurality of discrete positions (scan points 62) in the body axis direction of the subject P.

  For this reason, in the scan imaging for setting at least one of the tube current value and the tube voltage value corresponding to the scan range, the exposure amount of the subject P is greatly increased as compared with the case of scan imaging in the entire scan range of the main scan. Can be reduced.

  For example, the main scan is a helical scan in which imaging is performed while rotating the imaging system while changing the relative position between the top board 33 and the imaging system at a predetermined constant relative speed, and the rotational speed of the imaging system is 0.5. Consider the case of seconds / rotation. In this case, the imaging function 52 acquires the imaging conditions of the main scan including information such as the rotation speed from the memory 41 or from a cloud server or the like via the network, and the top board 33 and the imaging system are moved at the same speed as the main scanning. By scanning the scanogram intermittently every 0.5 seconds while changing the relative position, a pulse scan image of only the position 72 corresponding to the scan point 62 can be shot.

  The discrete image acquisition function 54 is a pulse scan image (photographed at a plurality of discrete positions in the body axis direction of the subject P) that was photographed by the gantry 10 under the control of the photographing function 52 or photographed by an external imaging device. Obtained a plurality of discrete images).

  Note that the positional relationship calculation function 53 may improve the accuracy of the scan range by adjusting the scan range using a pulse scan image. In this case, since the positioning for the main scan can be performed using only the reference image 71 and the pulse scano image captured before the main scan, the positioning for the main scan using the scan image captured for the whole body (whole body). Compared with the case where the exposure is performed, the non-irradiation position 73 can greatly reduce the exposure amount of the subject P.

  In the above example, the case where the scano imaging in one direction such as the AP direction (or the RL direction) is set to the pulse scano imaging is described, but the scano imaging may be performed in two directions such as both the AP direction and the RL direction. Good. In this case, by setting the scan imaging in at least one direction to pulse scan imaging, the exposure amount of the subject P can be significantly reduced as compared with the case where the entire scan range is scanned in both directions.

  Further, the positional relationship calculation function 53 displays a past image obtained by photographing the subject P with a modality or an optical camera in advance on the display 42, and a position designated by the user via the input interface 43 while checking the past image. Based on this, the position 72 for performing pulse scan imaging may be specified.

  It should be noted that the pulse scan imaging for setting the tube current value is preferably performed again for each main scan even if the tube current value setting for the same subject P was performed most recently such as the previous day. This is because even if the subject P is the same, the absorbed dose may vary depending on the state of the subject P.

  Further, as described above, the imaging of the reference image 71 and the pulse scan imaging for setting the tube current value may be included in the same scan protocol.

  FIG. 7 is an explanatory diagram showing an example of the tube current value 65 AP in the AP direction and the tube current value 65 RL in the RL direction set for each scan point 62.

  The imaging condition calculation function 55 obtains imaging conditions corresponding to the scan range of the main scan based on the pulse scan image for each position 72 corresponding to the scan point 62. For example, when the main scan is tube current modulation imaging, the imaging condition calculation function 55 calculates a tube current value for each scan point 62, and the scan range of the main scan based on the tube current value for each scan point 62. Is obtained (see FIG. 7).

  Next, an example of the operation of the X-ray CT apparatus 1 according to this embodiment will be described. In the following description, an example of performing a main scan with tube current modulation is shown.

  FIG. 8 shows an example of a procedure for reducing the exposure dose of the subject P in scanography performed by the processor of the processing circuit 45 for positioning and setting of imaging conditions for the main scan before the main scan. It is a flowchart to show. In FIG. 8, reference numerals with numbers added to S indicate steps in the flowchart.

  This procedure is started when information of a past image including a predetermined reference position of the subject P is acquired from the memory 41 or from an image server or the like via a network.

  First, in step 1, the reference position image acquisition function 51 determines whether or not the past image can be used as a positioning reference image for the main scan.

  FIG. 9 is a flowchart illustrating an example of a procedure for determining whether or not the past image can be used, which is executed by the reference position image acquisition function 51 in step S1 of FIG.

  The reference position image acquisition function 51 determines whether or not the past image can be used as a positioning reference image for the main scan, based on a change in the shape of the subject P between when the past image is captured and the present. . For this reason, for example, the reference position image acquisition function 51 first determines the age range to which the subject P belongs (steps S101 to 103).

  Next, the reference position image acquisition function 51 includes a weight change threshold value (step S201), a height change threshold value (step S202) set for each age range to which the subject P belongs, and from the time point when the past image was captured to the present time. If the threshold value for the elapsed time (step S203) or the like does not exceed a threshold value that is expected to have greatly changed the shape of the subject P, it is determined that the past image may be used for positioning for the main scan ( Step S31), the process proceeds to Step S2 in FIG. On the other hand, when the threshold value that the predicted shape of the subject P has greatly changed is exceeded, it is determined that the past image should not be used for positioning for the main scan (step S32), and step S3 in FIG. 8 is performed. Proceed to

  If it is determined in step S31 in FIG. 9 that the past image may be used for positioning for the main scan, the process returns to FIG. 8, and in step S2, the reference position image acquisition function 51 is connected via the memory 41 or the network. Then, a past image including a predetermined reference position of the subject P is acquired from an image server or the like.

  On the other hand, if it is determined in step S32 in FIG. 9 that the past image should not be used for positioning for the main scan, the process returns to FIG. 8 and the reference position image acquisition function 51 performs the main scan in step S3. It is determined whether or not an image for positioning is necessary. If a positioning image for the main scan is required, the process proceeds to step S4.

  On the other hand, if the positioning image for the main scan is unnecessary, the process proceeds to step S7. For example, when a tube current modulation scan is performed without performing a precise positioning using a scano image, such as a health checkup, the positioning image for the main scan is not necessary.

  In this embodiment, the example in which step S3 for determining whether or not the positioning image for the main scan is necessary is executed after step S1, but may be executed before step S1. In this case, if it is determined that a positioning image for the main scan is necessary, the process of step S1 is executed, and if it is determined that it is not necessary, the process proceeds to step S7. In this case, positioning for the main scan by the positional relationship calculation function 53 is omitted regardless of whether or not the past image is available.

  When it is determined in step S3 that an image for positioning for the main scan is necessary, the reference position image acquisition function 51 determines the position for positioning for the main scan including the predetermined reference position of the current subject P in step S4. A reference image is acquired, and the process proceeds to step S7. The newly acquired reference image for positioning for the main scan may be an image acquired by the optical camera in step S4, or a scano image taken again in step S4 by the X-ray CT apparatus 1. Note that when a scano image is captured again, it is only necessary to capture a range in which the main scan scan range can be set. Note that the scano image in this case may be taken during execution of the same protocol as the pulse scano scan executed in step S9, for example.

  Next, in step S5, the imaging function 52 images a reference image 71 including a predetermined reference position of the subject P before the main scan (see FIGS. 3 and 4A). In addition, you may image | photograph this imaging | photography during execution of the same protocol as the pulse scan imaging performed by step S9.

  Next, in step S6, the positional relationship calculation function 53 aligns the reference image standard image 171 and the standard image 71 photographed before the main scan (see FIG. 4B).

  Next, in step S7, the positional relationship calculation function 53 performs positioning for the main scan to set the scan range, and the imaging conditions for the main scan with tube current modulation are clouded from the memory 41 or via the network. Obtain from the server.

  Next, in step S8, the positional relationship calculation function 53 determines the position of the scan point 62 and the scan range of the main scan based on the reference image, the standard image 71 shot before the main scan, and the shooting conditions of the main scan. A positional relationship is obtained (see FIG. 5A). If there is no reference image or standard image 71, these positional relationships may be obtained based on the photographing conditions of the main scan.

  Next, in step S <b> 9, the imaging function 52 performs pulse scan imaging of the subject P only at the position 72 corresponding to the scan point 62 specified by the positional relationship calculation function 53. The discrete image acquisition function 54 acquires a plurality of discrete images (pulse scan images) obtained by pulse scan imaging (see FIG. 6).

  Next, in step S10, the imaging condition calculation function 55 obtains a tube current value corresponding to the scan range of the main scan based on the pulse scan image for each position 72 corresponding to the scan point 62 (see FIG. 7).

  Next, in step S11, the imaging function 52 performs a main scan with tube current modulation based on the tube current value in the scan range of the main scan calculated by the imaging condition calculation function 55, and the series of procedures is completed. Become.

  According to at least one embodiment described above, it is possible to reduce the exposure dose of the subject P in scanography performed for positioning and setting of imaging conditions for the main scan before the main scan.

  The processing circuit 45 in the present embodiment is an example of a processing circuit in the claims.

  In the above embodiment, the term “processor” is, for example, a dedicated or general-purpose CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC), It shall mean a circuit such as a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and an FPGA). The processor implements various functions by reading and executing a program stored in the storage medium.

  In the above embodiment, an example in which a single processor of a processing circuit realizes each function has been described. However, a processing circuit is configured by combining a plurality of independent processors, and each processor realizes each function. Also good. Further, when a plurality of processors are provided, the storage medium for storing the program may be provided for each processor individually, or one storage medium stores the programs corresponding to the functions of all the processors in a lump. Also good.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope 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.

DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus 33 ... Top plate 45 ... Processing circuit 51 ... Reference position image acquisition function 52 ... Imaging function 53 ... Position relation calculation function 54 ... Discrete image acquisition function 55 ... Imaging condition calculation function 62 ... Scan point 65AP ... Tube Current value 65RL ... tube current value 71 ... standard scano image

Claims (13)

A discrete image acquisition unit that acquires discrete images at a plurality of discrete positions in the body axis direction of the subject;
An imaging condition calculation unit that calculates imaging conditions corresponding to the scan range of the main scan based on the plurality of discrete images;
An X-ray CT apparatus comprising: The discrete image acquired by the discrete image acquisition unit is acquired by repeating ON / OFF of X-ray irradiation at a plurality of discrete positions in the body axis direction of the subject.
The X-ray CT apparatus according to claim 1. The imaging condition calculation unit calculates at least one of a tube current value or a tube voltage value corresponding to a scan range of the main scan;
The X-ray CT apparatus according to claim 1. The shooting condition calculation unit
Based on the plurality of discrete images corresponding to each of the plurality of discrete positions, a tube current value at each of the plurality of discrete positions is obtained, and a tube at each of the obtained plurality of discrete positions is obtained. Find the tube current value corresponding to the scan range of the main scan based on the current value,
The X-ray CT apparatus according to claim 3. An imaging unit that performs the main scan with tube current modulation based on a tube current value corresponding to a scan range of the main scan calculated by the imaging condition calculation unit;
The X-ray CT apparatus according to claim 4, further comprising: A reference position image acquisition unit for acquiring a reference image including a reference position in the subject, and a reference image including the reference position and captured during execution of the same scan protocol as the discrete image;
A positional relationship calculating unit that calculates a positional relationship between the plurality of discrete positions and a scan range of the main scan based on the reference image and the reference image;
Further equipped with,
The X-ray CT apparatus according to any one of claims 1 to 5. The positional relationship calculation unit
Based on the rotation speed of the imaging system in the main scan and the relative speed of the imaging system and the top plate on which the subject is placed, each of the plurality of discrete positions within the scan range of the main scan is determined. Calculate the position,
The X-ray CT apparatus according to claim 6. The reference position image acquisition unit
As the reference image, obtain a past image including the reference position obtained by photographing the subject in the past with a modality or an optical camera.
The X-ray CT apparatus according to claim 6 or 7. The reference position image acquisition unit
As the reference image, a scanogram including the reference position acquired by scanning the subject in the past is acquired.
The X-ray CT apparatus according to claim 6 or 7. The reference position image acquisition unit
Determining whether or not the past image can be used as the reference image based on a change in the shape of the subject between the time when the past image was captured and the current time;
The X-ray CT apparatus according to claim 8 or 9. The reference position image acquisition unit
When it is determined that the past image can be used as the reference image, the past image is acquired as the reference image, and when it is determined that the past image cannot be used, a current image of the subject is acquired as the reference image.
The X-ray CT apparatus according to claim 10. Based on the top position information attached to the reference image and the reference image, the reference image and the reference image are adjusted by adjusting the relative position between the top plate on which the subject is placed and the imaging system. An alignment unit for image alignment,
The X-ray CT apparatus according to any one of claims 6 to 11, further comprising: Obtaining discrete images at a plurality of discrete positions in the body axis direction of the subject;
Calculating imaging conditions corresponding to the scan range of the main scan based on the plurality of discrete images;
An imaging condition calculation method comprising:

Images