JP6238575B2 - X-ray CT system - Google Patents

Description

  Embodiments described herein relate generally to an X-ray CT apparatus.

  Conventionally, in an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus, CT; Computed Tomography), CT fluoroscopy capable of displaying an X-ray CT image in substantially real time has been performed. In CT fluoroscopy, the real-time property of X-ray CT image generation and display is realized by adjusting the projection data collection rate, reconstruction conditions, and the like to shorten the time required for image reconstruction processing.

  For example, in CT fluoroscopy, X-ray CT images are continuously generated and displayed by continuous scanning in which an X-ray tube and an X-ray detector are continuously rotated around the body axis of the subject. In the continuous scan, X-rays are continuously emitted from the X-ray tube.

JP 2000-350724 A

  The problem to be solved by the present invention is to provide an X-ray CT apparatus capable of reducing the exposure dose in CT fluoroscopy by continuous scanning.

The X-ray CT apparatus of the embodiment includes an X-ray tube, an X-ray detector, and a control unit. The X-ray tube emits X-rays. The X-ray detector detects X-rays emitted from the X-ray tube and transmitted through the subject. When the X-ray CT image data is continuously collected by continuously rotating the X-ray tube and the X-ray detector around the subject, the control unit sets the X-ray tube to a preset start position. X-ray exposure is started from the point of arrival. The control unit sets the start position in accordance with the position of the exposure reduction target portion of the subject existing in the imaging space.

FIG. 1 is a diagram illustrating a configuration example of an X-ray CT apparatus according to the first embodiment. FIG. 2 is a diagram (1) for explaining the control unit according to the first embodiment. FIG. 3 is a diagram (2) for explaining the control unit according to the first embodiment. FIG. 4 is a flowchart for explaining an example of the X-ray exposure control process of the X-ray CT apparatus according to the first embodiment. FIG. 5 is a diagram (1) for explaining the control unit according to the second embodiment. FIG. 6 is a diagram (2) for explaining the control unit according to the second embodiment. FIG. 7 is a diagram (1) for explaining the control unit according to the third embodiment. FIG. 8 is a diagram (2) for explaining the control unit according to the third embodiment. FIG. 9 is a flowchart for explaining an example of the X-ray exposure control process of the X-ray CT apparatus according to the third embodiment. FIG. 10 is a diagram for explaining a control unit according to the fourth embodiment.

  Hereinafter, an embodiment of an X-ray CT (Computed Tomography) apparatus will be described in detail with reference to the accompanying drawings.

(First embodiment)
First, the configuration of the X-ray CT apparatus according to the first embodiment will be described. FIG. 1 is a diagram illustrating a configuration example of an X-ray CT apparatus according to the first embodiment. As shown in FIG. 1, the X-ray CT apparatus according to the first embodiment includes a gantry device 10, a couch device 20, and a console device 30.

  The gantry device 10 is a device that irradiates the subject P with X-rays and collects data obtained by detecting X-rays transmitted through the subject P, and includes an X-ray irradiation control unit 11, an X-ray generation device 12, The line detector 13, the collecting unit 14, the rotating frame 15, and the gantry driving unit 16 are included.

  The rotating frame 15 supports the X-ray generator 12 and the X-ray detector 13 opposite to each other with the subject P interposed therebetween, and rotates at a high speed in a circular orbit around the subject P by a gantry driving unit 16 described later. An annular frame.

  The X-ray generator 12 is an apparatus that generates X-rays and irradiates the subject P with the generated X-rays, and includes an X-ray tube 12a, a wedge 12b, and a collimator 12c.

  The X-ray tube 12a emits X-rays. Specifically, the X-ray tube 12a is a vacuum tube that generates an X-ray beam on the subject P by a high voltage supplied by an X-ray irradiation control unit 11 described later. The X-ray tube 12 a exposes the X-ray beam to the subject P as the rotating frame 15 rotates. The X-ray tube 12a generates an X-ray beam that spreads with a fan angle and a cone angle.

  The wedge 12b is an X-ray filter for adjusting the X-ray dose of X-rays emitted from the X-ray tube 12a. The collimator 12c is a slit for narrowing the X-ray irradiation range in which the X-ray dose is adjusted by the wedge 12b under the control of the X-ray irradiation control unit 11 described later.

  The X-ray irradiation control unit 11 is a device that supplies a high voltage to the X-ray tube 12 a as a high voltage generation unit. The X-ray tube 12 a uses the high voltage supplied from the X-ray irradiation control unit 11 to perform X Generate a line. The X-ray irradiation control unit 11 adjusts the X-ray dose irradiated to the subject P by adjusting the tube voltage and tube current supplied to the X-ray tube 12a. The X-ray irradiation control unit 11 adjusts the X-ray irradiation range (fan angle and cone angle) by adjusting the aperture of the collimator 12c.

  The gantry driving unit 16 rotates the rotary frame 15 to rotate the X-ray generator 12 and the X-ray detector 13 on a circular orbit around the subject P.

  The X-ray detector 13 detects X-rays that are exposed from the X-ray tube 12a and transmitted through the subject P. For example, the X-ray detector 13 is a two-dimensional array type detector (surface detector) that detects X-ray intensity distribution data indicating the intensity distribution of X-rays irradiated from the X-ray generator 12 and transmitted through the subject P. is there. The X-ray detector 13 includes a plurality of X-ray detection elements (detection element arrays) arranged in the channel direction (Y-axis direction shown in FIG. 1), in the body axis direction of the subject P (Z-axis shown in FIG. 1). A plurality of rows are arranged along (direction).

  The acquisition unit 14 is a data acquisition system (DAS), and generates X-ray detection data by performing amplification processing, A / D conversion processing, and the like on the X-ray intensity distribution data detected by the X-ray detector 13. Then, the generated X-ray detection data is transmitted to the console device 30 described later.

  The couch device 20 is a device on which the subject P is placed, and includes a couchtop 22 and a couch driving device 21. The top plate 22 is a plate on which the subject P is placed. The bed driving device 21 moves the subject P in the rotating frame 15 (in the imaging space) by moving the top plate 22 in the Z-axis direction under the control of a scan control unit 33 described later.

  For example, the gantry device 10 performs a helical scan that rotates the rotating frame 15 while moving the top plate 22 to scan the subject P in a spiral shape. Alternatively, the gantry device 10 performs a conventional scan in which the subject P is scanned in a circular orbit by rotating the rotating frame 15 while moving the top plate 22 while the position of the subject P is fixed. Alternatively, the gantry device 10 executes a step-and-shoot method in which a conventional scan is performed in a plurality of scan areas by moving the position of the top plate 22 at regular intervals. Note that the X-ray CT apparatus has a control device (not shown) for controlling the bed driving device 21 in the vicinity of the bed device 20 in addition to the scan control unit 33 described later. The operator can move the top plate 22 by operating such a control device before or during shooting.

  The console device 30 is a device that accepts the operation of the X-ray CT apparatus by the operator and reconstructs X-ray CT image data from the X-ray detection data collected by the gantry device 10, and includes an input device 31 and a display device. 32, a scan control unit 33, a preprocessing unit 34, a projection data storage unit 35, an image reconstruction unit 36, an image storage unit 37, and a control unit 38.

  The input device 31 includes a mouse, a keyboard, buttons, foot switches, and the like that are used by an operator of the X-ray CT apparatus to input various instructions and various settings. The control unit 38 receives instructions and setting information received from the operator. Forward to. For example, the input device 31 includes a button (exposure button) and a foot switch (exposure foot switch) for accepting the start of X-ray exposure for CT fluoroscopic imaging.

  The display device 32 is a monitor that is referred to by the operator, displays X-ray CT image data to the operator under the control of the control unit 38, and provides various instructions and various settings from the operator via the input device 31. For example, a GUI (Graphical User Interface) for accepting and the like is displayed. For example, the operator uses the input device 31 to input examination information such as the body position at the time of imaging of the subject P placed on the top 22 into the examination information registration GUI.

  The scan control unit 33 controls the operations of the X-ray irradiation control unit 11, the gantry driving unit 16, the collection unit 14, and the bed driving device 21 under the control of the control unit 38 described later, so that the X in the gantry device 10 is controlled. Controls the line detection data collection process.

  The preprocessing unit 34 performs logarithmic conversion processing and correction processing such as offset correction, sensitivity correction, and beam hardening correction on the X-ray detection data generated by the collection unit 14 to generate projection data. .

  The projection data storage unit 35 stores the projection data generated by the preprocessing unit 34. The image reconstruction unit 36 reconstructs X-ray CT image data using the projection data stored in the projection data storage unit 35. As the reconstruction method, there are various methods, for example, back projection processing. Further, as the back projection process, for example, a back projection process by an FBP (Filtered Back Projection) method can be cited. Alternatively, the image reconstruction unit 36 may reconstruct X-ray CT image data using a successive approximation method.

  The image reconstruction unit 36 can generate various image data by performing various image processing on the X-ray CT image data. The image reconstruction unit 36 stores the reconstructed X-ray CT image data and image data generated by various image processes in the image storage unit 37.

  The control unit 38 performs overall control of the X-ray CT apparatus by controlling operations of the gantry device 10, the couch device 20, and the console device 30. Specifically, the control unit 38 controls the CT scanning performed by the gantry device 10 by controlling the scan control unit 33. The control unit 38 also controls the image reconstruction process and the image generation process in the console device 30 by controlling the preprocessing unit 34 and the image reconstruction unit 36. The control unit 38 controls the display device 32 to display various image data stored in the image storage unit 37.

  The overall configuration of the X-ray CT apparatus according to the first embodiment has been described above. Under such a configuration, the X-ray CT apparatus according to the first embodiment performs CT fluoroscopic imaging. In CT fluoroscopy, when X-ray CT image data is continuously collected by continuously rotating the X-ray tube 12a and the X-ray detector 13 around the subject P, the projection data collection rate, reconstruction conditions, and the like are adjusted. Then, X-ray CT image data reconstruction processing and display processing are performed in substantially real time. For example, in CT fluoroscopy, correction processing such as offset correction, sensitivity correction, and beam hardening correction in the preprocessing unit 34, adjustment processing of an image reconstruction function, and the like are omitted or simplified. In CT fluoroscopy, not only continuous acquisition of X-ray CT image data of one cross section, but also X-ray detector 13 is a surface detector, so that continuous acquisition of multi-section X-ray CT image data is performed. There is.

  CT fluoroscopy, for example, is performed as preliminary imaging for positioning in order to perform main imaging at an imaging site of the subject P. Further, CT fluoroscopy is performed as preliminary imaging for determining whether or not the contrast agent administered to the subject P has reached the imaging region of the subject P when performing contrast imaging (main imaging), for example. Is called. Further, CT fluoroscopy is performed, for example, in order to capture in real time a puncture needle inserted into the subject P and a puncture target site of the subject P when performing a biopsy or treatment using the puncture needle. .

  In conventional CT fluoroscopy, a continuous scan is usually performed. In the continuous scan, for example, continuous X-ray exposure is started from the time when the exposure button is pressed. On the other hand, in CT fluoroscopy, a method is also known in which X-ray exposure is performed on the back of the subject P in the X-ray exposure range (180 degrees + fan angle) in which half reconstruction is possible, and imaging for one frame is performed. It has been. However, even when performing continuous scanning, a skilled operator can obtain sufficient information from the first one frame of X-ray CT image data.

  The control unit 38 of the X-ray CT apparatus according to the first embodiment performs the following control in order to reduce the exposure dose in CT fluoroscopy by continuous scanning. That is, the control unit 38 according to the first embodiment controls the scan control unit 33 to continuously rotate the X-ray tube 12a and the X-ray detector 13 around the subject P to obtain X-ray CT image data. When performing continuous acquisition, X-ray exposure is started when the X-ray tube 12a reaches a preset start position.

  2 and 3 are diagrams for explaining the first embodiment. For example, as shown in FIG. 2, the control unit 38 has an X-ray exposure range (180 degrees + fan angle) in which half reconstruction is possible on the side opposite to the side on which the subject P is placed on the top plate 22. Is calculated (see the arc-shaped arrow in the figure). Then, as shown in FIG. 2, the control unit 38 sets the start position S according to the X-ray exposure range in which half reconstruction is possible. When receiving the CT fluoroscopic start request, the control unit 38 controls the scan control unit 33 to start the rotation of the rotating frame 15.

  Then, the control unit 38 controls the scan control unit 33 to start the X-ray exposure from the time when the X-ray tube 12a reaches the start position S as illustrated in FIG. The line is continuously exposed. Thereby, projection data for half reconstruction is first collected, the image reconstruction unit 36 reconstructs X-ray CT image data of the first frame by half reconstruction, and the display device 32 performs the first frame. X-ray CT image data is displayed. In the second and subsequent frames, the image reconstruction unit 36 performs half reconstruction or full reconstruction from projection data collected by continuous X-ray exposure, so that X-ray CT image data is continuously displayed. . In the second and subsequent frames, a part of the projection data group used for the reconstruction of the X-ray CT image data of the nth frame may be used for the reconstruction of the X-ray CT image data of the (n + 1) th frame. The first embodiment may be a case where the start position S is set using a range in which half reconstruction is possible, and the X-ray CT image data of the first frame is reconstructed by full reconstruction.

  In the above example, X-ray exposure for half reconstruction is performed around the opposite side of the side on which the subject P is placed, so that the subject P mainly passes through the top plate 22. Since X-rays are irradiated, the amount of X-ray exposure to the subject P can be reduced.

  Next, an X-ray exposure control process of the X-ray CT apparatus according to the first embodiment will be described with reference to FIG. FIG. 4 is a flowchart for explaining an example of the X-ray exposure control process of the X-ray CT apparatus according to the first embodiment.

  As illustrated in FIG. 4, the control unit 38 of the X-ray CT apparatus according to the first embodiment determines whether a CT fluoroscopic start request has been received from the operator (step S <b> 101). Here, when the CT fluoroscopy start request is not received (No at Step S101), the control unit 38 waits until the start request is received.

  On the other hand, when a CT fluoroscopic start request is received (Yes at Step S101), the control unit 38 sets a start position (Step S102). For example, the control unit 38 according to the first embodiment sets the start position according to the position of the top plate 22. Then, under the control of the control unit 38 via the scan control unit 33, the rotating frame 15 starts rotating (step S103). Then, the control unit 38 determines whether or not the X-ray tube 12a has reached the start position (step S104). If the X-ray tube 12a has not reached the start position (No at Step S104), the control unit 38 waits until the X-ray tube 12a reaches the start position.

  On the other hand, when the X-ray tube 12a reaches the start position (Yes at Step S104), the X-ray tube 12a starts X-ray exposure under the control of the control unit 38 via the scan control unit 33 (Step S105). ). Then, the control unit 38 determines whether or not a CT fluoroscopic end request has been received from the operator (step S106). Here, when the CT fluoroscopy end request is not accepted (No at Step S106), the X-ray tube 12a continues the X-ray exposure under the control of the control unit 38 via the scan control unit 33 (Step S108). . And the control part 38 performs determination of step S106 again.

  On the other hand, when an end request for CT fluoroscopy is received (Yes at Step S106), the X-ray tube 12a stops the X-ray exposure under the control of the control unit 38 via the scan control unit 33 (Step S107). The process ends.

  As described above, in the first embodiment, control is performed so that X-ray exposure is not performed from the initial position to the start position of the X-ray tube 12a in CT fluoroscopy by continuous scanning. In the first embodiment, for example, the control unit 38 can reconstruct the X-ray CT image data of the first frame by half reconstruction, and most of the X-rays irradiated to the subject P are celestial. The position to be X-rays after passing through the plate 22 is set as the X-ray exposure start position. Therefore, in the first embodiment, the exposure dose in CT fluoroscopy by continuous scanning can be reduced.

  Further, as described above, even in continuous scanning, a skilled operator can obtain sufficient information from the first frame of X-ray CT image data. That is, even when the exposure control described in the first embodiment is performed, a skilled operator refers to the X-ray CT image data of the first frame and X-ray CT image data of several frames. By doing so, CT fluoroscopy can be terminated. Therefore, in the first embodiment, when CT fluoroscopy by continuous scanning is performed by a skilled operator, the exposure dose can be further reduced. In the above description, the case where the start position is set according to the X-ray exposure range in which half reconstruction is possible has been described. However, in the first embodiment, if the exposure dose of the subject P is reduced, the start position can be set to an arbitrary position.

(Second Embodiment)
In the second embodiment, a case where the start position is changed and set according to various conditions will be described with reference to FIGS. 5 and 6. 5 and 6 are diagrams for explaining a control unit according to the second embodiment.

  The X-ray CT apparatus according to the second embodiment is configured similarly to the X-ray CT apparatus according to the first embodiment described with reference to FIG. However, the control unit 38 according to the second embodiment performs the following control. That is, the control unit 38 sets the start position according to the position of the exposure reduction target part of the subject P existing in the imaging space. In other words, the control unit 38 sets the X-ray exposure start position so that X-rays are not exposed as much as possible to the exposure reduction target part in the first rotation. The exposure reduction target part is a part determined by the position of a human being present in the imaging space. Here, the human being in the imaging space refers to the subject P and the subject P with reference to the X-ray CT image data collected by CT fluoroscopy (for example, biopsy puncture). It is a surgeon who performs the operation.

  An example of the exposure reduction target part is a part of the subject P that is highly influenced by the X-ray exposure. The part having a high influence degree due to the X-ray exposure is, for example, the abdomen of the subject P. Therefore, the control unit 38 sets the start position according to the posture of the subject P at the time of imaging.

  An example of the exposure reduction target part is a position where an operator's hand or the like is present, that is, a position where an operation is performed on the subject P. Therefore, the control unit 38 sets the start position according to the position where the operation is performed on the subject P.

  First, a case where the start position is set according to the posture of the subject P at the time of imaging will be described. In such a case, for example, the control unit 38 acquires the posture of the subject P included in the examination information input by the operator before imaging. And the control part 38 sets a start position according to the position of the back surface of the subject P determined by the acquired body posture. For example, the control unit 38 reconstructs the X-ray CT image data of the first frame from the projection data for the half reconstruction collected mainly by the X-rays being exposed to the back surface of the subject P. Set the start position to

  FIG. 5A illustrates the start position S1 that is set when the subject P is in the supine position. FIG. 5B illustrates the start position S2 that is set when the subject P is in the right-side position. FIG. 5C illustrates the start position S3 that is set when the subject P is in the prone position. FIG. 5D illustrates the start position S4 that is set when the subject P is in the left-side position.

  Next, a case where the start position is set according to the position where the operation is performed on the subject P will be described. In such a case, for example, the operator uses the input device 31 to input in which range of the tube phase the treatment is performed. And the control part 38 sets a start position according to the phase range which the operator input before imaging | photography. For example, the control unit 38 obtains the X-ray CT image data of the first frame from the projection data for the half reconstruction acquired by exposing the X-rays outside the phase range input by the operator before imaging. Set the starting position to be reconfigured.

  FIG. 6A illustrates the start position S5 that is set when the treatment is performed in a phase range centered on the tube phase “0 degrees”. FIG. 6B illustrates the start position S6 that is set when the treatment is performed in a phase range centered on the tube phase “30 degrees”.

  Note that the contents described in the first embodiment can be applied to the second embodiment except that the start position is set according to the exposure reduction target site. Further, the X-ray exposure control process of the X-ray CT apparatus according to the second embodiment is that the start position setting process of step S102 described using FIG. 4 is performed according to the exposure reduction target part, Since it is the same as that of 1st Embodiment, description is abbreviate | omitted. Note that the control unit 38 according to the second embodiment may set the start position according to both the posture of the subject P at the time of imaging and the position where the operation is performed on the subject P.

  As described above, in the second embodiment, in CT fluoroscopy by continuous scanning, control is performed so that X-ray exposure is started avoiding the exposure reduction target site. Therefore, in the first embodiment, the influence of exposure on the subject P and the operator can be reduced.

(Third embodiment)
In the third embodiment, the CT fluoroscopy based on the continuous scan described in the first or second embodiment is changed to CT fluoroscopy (single scan) for one frame according to the operation of the operator. Such a case will be described with reference to FIGS. 7 and 8 are diagrams for explaining a control unit according to the third embodiment.

  The X-ray CT apparatus according to the third embodiment is configured similarly to the X-ray CT apparatus according to the first embodiment described with reference to FIG. However, the control unit 38 according to the third embodiment performs the following control. Here, as described above, the input device 31 includes a button (exposure button) and a foot switch (exposure foot switch) for receiving an instruction to start CT fluoroscopy by an operator's operation. In the third embodiment, the control unit 38 switches the CT fluoroscopic imaging from the continuous scan to the single scan according to the operation time for the input device 31.

  First, the control unit 38 determines whether or not the operator's operation on the input device 31 is finished before the predetermined period elapses. Then, when the operation of the operator with respect to the input device 31 is finished before the predetermined period elapses, the control unit starts X-ray exposure from the start position, When the X-ray tube 12a reaches the “end position” determined by the radiation exposure range, the X-ray exposure is terminated.

  Here, the predetermined period refers to the time when the X-ray tube 12a reaches the start position, and the X-ray tube 12a reaches the “end position determined by the start position and the X-ray exposure range where half reconstruction is possible”. This is the period until the time. Hereinafter, this period is referred to as a “half period”.

  For example, the control unit 38 determines whether or not the time point when the operator turns off the exposure button after turning it on is before the half period elapses. Then, the control unit 38 switches to single scanning when the time when the operator turns off after turning on the exposure button is before the half period elapses, and performs CT fluoroscopy when the half period elapses. finish. In such a case, one frame of X-ray CT image data reconstructed by half reconstruction is displayed, and CT fluoroscopy ends.

  Each of line segment a to line segment f illustrated in FIG. 7 exemplifies a period from when the operator turns on the exposure button to when it is turned off. Line segment a to line segment f illustrated in FIG. 7 exemplify that the operator has turned off the exposure button before the half period that starts when the X-ray tube 12a reaches the start position elapses. ing. When an operation as indicated by line segment a to line segment f is performed, the control unit 38 switches the CT fluoroscopy to the single scan as illustrated in FIG.

  On the other hand, when the operation of the operator with respect to the input device 31 is continued even after a predetermined period (half period) has elapsed, the control unit 38 causes the following two modes to be continuously scanned. For example, when the operator continues to press the exposure button even after the half period has elapsed (see the line segment g and the line segment h in FIG. 7), the control unit 38 is illustrated in the left diagram of FIG. The first mode is continuously scanned. In the first mode, the control unit 38 continues the X-ray exposure after the time when the X-ray tube 12a reaches the end position. The first mode is the same continuous scan as the continuous scan described with reference to FIG. 3 in the first embodiment. That is, in the first mode, projection data for half reconstruction is collected in the first rotation, and projection data that can be fully reconstructed is continuously collected in the second and subsequent rotations.

  Alternatively, for example, when the operator continues to press the exposure button even after the half period has elapsed (see line segment g and line segment h in FIG. 7), the control unit 38 displays the right diagram in FIG. The continuous scan in the second mode illustrated is executed. In the second mode, the control unit 38 repeatedly performs X-ray exposure from the start position to the end position. In the second mode, every time the rotation frame 15 makes one rotation, projection data for half reconstruction is collected. That is, in the second mode, every time the rotating frame 15 makes one rotation, X-ray CT image data of one frame is reconstructed and displayed by half reconstruction. Compared to the first mode, the time resolution is slightly reduced in the second mode, but it is an effective imaging method from the viewpoint of reducing the exposure dose in CT fluoroscopy.

  Whether to execute the first mode or the second mode can be changed and set by the operator. In the present embodiment, the input device 31 may include a first foot switch for executing the first mode and a second foot switch for executing the second mode. In such a case, the operator can set the continuous scan mode by stepping on the first foot switch or the second foot switch while keeping pressing the exposure button.

  In such a case, the operator can switch the continuous scan to the second mode by stepping on the second foot switch while the continuous scan of the first mode is being executed. Alternatively, the operator can switch the continuous scan to the first mode by stepping on the first foot switch while executing the continuous scan in the second mode.

  In the above description, the case of switching to the single scan according to the operation period of the exposure button has been described. However, the third embodiment is a case of switching to the single scan according to the operation period of the exposure foot switch. May be. The contents described in the first and second embodiments can also be applied to the third embodiment except that the CT fluoroscopy is switched from the continuous scan to the single scan according to the operation period.

  Next, an X-ray exposure control process of the X-ray CT apparatus according to the third embodiment will be described with reference to FIG. FIG. 9 is a flowchart for explaining an example of the X-ray exposure control process of the X-ray CT apparatus according to the third embodiment.

  As illustrated in FIG. 9, the control unit 38 of the X-ray CT apparatus according to the third embodiment determines whether or not a button (an exposure button) has been pressed (step S201). If the button has not been pressed (No at Step S201), the control unit 38 waits until the button is pressed.

  On the other hand, when the button is pressed (Yes at Step S201), the control unit 38 sets a start position (Step S202). Then, under the control of the control unit 38 via the scan control unit 33, the rotating frame 15 starts to rotate (step S203). Then, the control unit 38 determines whether or not the X-ray tube 12a has reached the start position (step S204). If the X-ray tube 12a has not reached the start position (No at Step S204), the control unit 38 waits until the X-ray tube 12a reaches the start position.

  On the other hand, when the X-ray tube 12a reaches the start position (Yes at Step S204), the X-ray tube 12a starts X-ray exposure under the control of the control unit 38 via the scan control unit 33 (Step S205). ). Then, the control unit 38 determines whether or not the button is turned off before the half period has elapsed (step S206). Here, when the button is turned off before the half period has elapsed (Yes at Step S206), the X-ray tube 12a reaches the end position under the control of the control unit 38 via the scan control unit 33. X-ray exposure is stopped (step S207), and the process is terminated. On the other hand, when the button is continuously pressed even after the half period has elapsed (No at Step S206), the X-ray tube 12a controls the X-ray in the setting mode under the control of the control unit 38 via the scan control unit 33. Exposure is continued (step S208).

  Then, the control unit 38 determines whether a CT fluoroscopy end request has been received from the operator (step S209). If the CT fluoroscopic end request is not accepted (No at Step S209), the X-ray tube 12a continues the X-ray exposure in the setting mode in Step S208.

  On the other hand, when an end request for CT fluoroscopy is received (Yes at Step S209), the X-ray tube 12a stops the X-ray exposure under the control of the control unit 38 via the scan control unit 33 (Step S210). The process ends.

  As described above, in the third embodiment, CT fluoroscopy can be switched from continuous scan to single scan by a simple input operation of adjusting the time for which the operator presses the button, for example. Therefore, in the third embodiment, the exposure dose in CT fluoroscopy can be greatly reduced according to the operator's request.

  In the third embodiment, CT fluoroscopy by continuous scanning can be set to continuous scanning in the second mode limited to a half period from the start position to the end position in response to an operator's request. When the second mode is performed, the exposure dose in CT fluoroscopy by continuous scanning can be greatly reduced.

(Fourth embodiment)
In the fourth embodiment, a case where tube current modulation is performed in the CT fluoroscopic imaging described in the first to third embodiments will be described with reference to FIG. FIG. 10 is a diagram for explaining a control unit according to the fourth embodiment.

  The X-ray CT apparatus according to the fourth embodiment is configured similarly to the X-ray CT apparatus according to the first embodiment described with reference to FIG. However, the control unit 38 according to the fourth embodiment performs the following control. That is, the control unit 38 according to the fourth embodiment responds to the thickness at which the X-rays emitted from the X-ray tube 12a pass through the subject P during the period in which the X-ray tube 12a performs X-ray exposure. The tube current supplied to the X-ray tube 12a is adjusted.

  The control unit 38 increases the tube current when the X-ray transmission range is thick, and executes tube current modulation that decreases the tube current when the X-ray transmission range is thin. The thickness at which the X-rays pass through the subject P varies depending on the position of the X-ray tube 12a. The tube current is adjusted according to the position of the X-ray tube 12a and the posture of the subject P at the time of imaging.

  10A and 10B, when the X-ray tube 12a is positioned at the tube phase “0 degree”, X-rays are exposed toward the front of the abdomen of the subject P, and the X-ray tube 12a is When the tube phase is “180 degrees”, the case where X-rays are exposed toward the front of the back of the subject P is illustrated. In FIGS. 10A and 10B, when the X-ray tube 12a is positioned at the tube phase “90 degrees”, X-rays are exposed toward the right side of the subject P, and the X-ray tube 12a. Shows a case where X-rays are exposed toward the left side of the subject P when the tube phase is located at the tube phase “270 degrees”. Usually, the thickness in the left-right direction is larger than the thickness in the dorsoventral direction.

  FIG. 10A illustrates a case where the magnitude of the tube current modulated in the scan section (XY plane) is set as an ellipse. The ellipse illustrated in FIG. 10A has a major axis in the left-right direction and a minor axis in the dorsoventral direction. In FIG. 10A, the distance from the ellipse center “O” to the ellipse corresponds to the magnitude of the tube current. In the setting example of FIG. 10A, the tube current supplied to the X-ray tube 12a when the X-ray is irradiated from a position of 0 degrees (abdominal side) or 180 degrees (back side) is 90 degrees ( When X-rays are irradiated from a position on the right side) or 270 degrees (left side), it is adjusted so as to be smaller than the tube current supplied to the X-ray tube 12a.

  When executing the continuous scan or the single scan, the control unit 38 causes the scan control unit 33 to adjust the tube current based on the ellipse shown in FIG. For example, when a single scan is performed, the X-ray tube 12a performs X-ray exposure from the start position S illustrated in FIG. 10A to the end position E while rotating clockwise. In such a case, the control unit 38 adjusts the tube current supplied to the X-ray tube 12a in the exposure period from the start position S to the end position E based on the ellipse shown in FIG. Thereby, the influence of the exposure with respect to the subject P in CT fluoroscopic imaging can be reduced. Note that, in the case of continuous scanning in the first mode, the control unit 38 determines that X is based on the ellipse shown in FIG. 10A even during the period of “end position E to 0 degrees to start position S”. The tube current supplied to the tube 12a is adjusted.

  FIG. 10B illustrates the case where the magnitude of the tube current modulated in the scan section (XY plane) is set by combining two elliptical arcs having the same major axis but different minor axes. Yes. In FIG. 10B, the distance from the point “O ′” to the elliptical arc corresponds to the magnitude of the tube current. In the setting example of FIG. 10B, the tube current is modulated in the dorsal and lateral directions, and the tube current when exposed on the dorsal side is the tube current when exposed on the ventral side. It is adjusted to be smaller.

  When executing the continuous scan or the single scan, the control unit 38 causes the scan control unit 33 to adjust the tube current based on the graphic shown in FIG. For example, when a single scan is performed, the controller 38 supplies the tube current supplied to the X-ray tube 12a during the exposure period from the start position S to the end position E based on the graphic shown in FIG. Adjust. Note that, in the case of continuous scanning in the first mode, the control unit 38 determines that X is based on the figure shown in FIG. 10B even during the period of “end position E to 0 degrees to start position S”. The tube current supplied to the tube 12a is adjusted. Thereby, the X-ray dose irradiated to the abdomen which is the exposure reduction target part can be reduced, and the influence of the exposure on the subject P in CT fluoroscopic imaging can be further reduced.

  Note that the control unit 38 performs, for example, the adjustment illustrated in FIGS. 10A and 10B from the information on the posture of the subject P at the time of imaging. Alternatively, the control unit 38 exemplifies, for example, (A) and (B) of FIG. 10 according to the body shape of the subject P estimated from the X-ray CT image data of the subject P that is preliminarily imaged. Make adjustments.

  The contents described in the first to third embodiments are also applicable to the fourth embodiment except that the tube current modulation is performed during the X-ray exposure.

  As described above, in the fourth embodiment, the tube current is adjusted according to the thickness at which the X-rays exposed from the X-ray tube 12a pass through the subject P, thereby causing exposure in CT fluoroscopy. The influence can be reduced.

  In the description of the above-described embodiment, each component of each illustrated apparatus is functionally conceptual and does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to the one shown in the figure, and all or a part of the distribution / integration is functionally or physically distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. Further, all or a part of each processing function performed in each device can be realized by a CPU and a program that is analyzed and executed by the CPU, or can be realized as hardware by wired logic.

  As described above, according to the first to fourth embodiments, the exposure dose in CT fluoroscopy by continuous scanning can be reduced.

  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 their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

12a X-ray tube 13 X-ray detector 38 Control unit

Claims (8)

An X-ray tube that emits X-rays;
An X-ray detector for detecting X-rays exposed from the X-ray tube and transmitted through the subject;
When the X-ray tube and the X-ray detector are continuously rotated around the subject to continuously acquire X-ray CT image data, the X-ray tube reaches a preset start position. A control unit for starting X-ray exposure;
Equipped with a,
The X-ray CT apparatus , wherein the control unit sets the start position according to a position of an exposure reduction target portion of the subject existing in an imaging space . The X-ray CT apparatus according to claim 1 , wherein the control unit sets the start position according to a posture of the subject at the time of imaging. Wherein, in response to said position the practitioner to the subject is performed, X-rays CT apparatus according to claim 1 or 2, characterized in that for setting the starting position. Wherein, in response to X-ray irradiation range capable half reconstruction, X-ray CT apparatus according to any one of claims 1-3, characterized in that for setting the starting position. An input unit that receives an instruction to start shooting by an operator's operation;
Further comprising
When the operation of the operator on the input unit is completed before a predetermined period elapses, the control unit can reconfigure the start position and the half after starting X-ray exposure from the start position. The X-ray CT apparatus according to any one of claims 1 to 4 , wherein the X-ray exposure is ended when the X-ray tube reaches an end position determined by an X-ray exposure range. The control unit continues X-ray exposure after the X-ray tube reaches the end position when the operation of the operator on the input unit is continued even after the predetermined period has elapsed. The X-ray CT apparatus according to claim 5 , wherein: The control unit repeatedly performs X-ray irradiation from the start position to the end position when the operation of the operator on the input unit is continued even after the predetermined period has elapsed. The X-ray CT apparatus according to claim 5 . The control unit supplies the X-ray tube to the X-ray tube according to the thickness at which the X-ray irradiated from the X-ray tube passes through the subject during a period in which the X-ray tube is exposed. X-ray CT apparatus according to any one of claims 1-7, characterized in that to adjust the tube current.

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