JP6026290B2 - X-ray computed tomography system - Google Patents

Description

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

  One scanning method using an X-ray computed tomography apparatus is a helical shuttle scan method. The helical shuttle scan method is a method in which the top plate is reciprocated several times between both ends of the scan range. The helical shuttle scan method is used for dynamic inspection in a wide scan range, for example, CT perfusion. In CT perfusion, a differential image of two reconstructed images relating to the same position is generated, and the temporal change of the blood flow volume of the contrasted cerebral blood vessel is calculated using the differential image, and the presence or absence of ischemia is analyzed. In general, a difference image is generated based on a reconstructed image between forward paths or a reconstructed image between return paths. If the travel distance of the top board in each forward path and return path is not the same, artifacts may be generated in the difference image, which may not be used clinically. Thus, in the helical shuttle scan method, the reproducibility of the position of the top plate is important.

  The top plate position reproducibility is mainly influenced by the degree of coincidence of the stop position (folding position) during reciprocation, and the position reproducibility deteriorates as the stop position varies. One of the factors that cause the stop position to vary is backlash. The backlash occurs with the reversal of the rotation direction of the motor for changing the direction of the top plate, and causes an error between the target stop position and the actual stop position. In order to reduce the error of the movement distance due to the backlash, the movement command amount is corrected according to the amount of loss expected when the motor is reversed. However, the amount of loss due to backlash differs depending on various factors such as the weight of the subject, the amount of movement of the couch, the stop position, and aging deterioration.In the method of correcting the movement command amount, the amount of loss due to backlash is completely reduced. It cannot be removed.

  FIG. 7 is a diagram showing temporal changes in the position of the top plate in the helical shuttle scan according to the conventional example. As shown in FIG. 7, it is assumed that the target stop position A is set to 0.0 mm and the target stop position B is set to 80.0 mm. It is assumed that the target stop position A is set as the scan start position and the target stop position B is set as the return position. Assume that the path from the target stop position A to the target stop position B is the forward path, and conversely, the path from the target stop position B to the target stop position A is the return path.

  The top plate is moved by the rotation of the motor. The rotation of the motor is automatically controlled by a motor control device including a servo amplifier. The motor control device automatically controls the rotation of the motor so that the top board moves by a movement distance corresponding to the movement command amount. Prior to the start of the helical shuttle scan, the top plate is moved from an initial position (not shown) to a target stop position A (scan start position) according to control by the motor control device. Then, the top board is reciprocated between the target stop position A and the target stop position B according to control by the motor control device. However, backlash occurs as the direction of movement of the top plate changes, that is, as the rotation direction of the motor is reversed. Due to the backlash, the top plate stops before the target stop position.

  As shown in FIG. 7, even when the helical shuttle scan starts, even if it stops exactly at the scan start position, the travel distance of the first forward path becomes longer than the travel distance of each path after the first forward path. . Therefore, even if the scanning is accurately stopped at the target stop position at the start of scanning, the reproducibility of the position of the top plate cannot be improved.

  FIG. 8 is a diagram showing temporal changes in the position of the top plate in a helical shuttle scan according to another conventional example. As shown in FIG. 8, when the top plate is arranged at the scan start position (target stop position A) by the user's local operation (operation by the operation panel), the scan starts compared to the case of automatic control by the motor control device. The positioning accuracy of the top plate to the position deteriorates. Therefore, the deviation between the movement distance of the first forward path and the movement distance of each path after the first forward path becomes larger than in the case of automatic motor control. Therefore, the reproducibility of the position of the top plate cannot be improved even when the top plate is arranged at the scan start position by local operation.

  Thus, when the movement distance of each path | route of a top plate differs, an edge-shaped artifact will arise in a difference image.

  An object of the embodiment is to realize an improvement in the reproducibility of the position of the top plate in an X-ray computed tomography apparatus that performs a helical shuttle scan that collects data while reciprocating the top plate.

  An X-ray computed tomography apparatus according to this embodiment includes an X-ray tube that generates X-rays, an X-ray detector that detects X-rays generated from the X-ray tube and transmitted through a subject, and the X-ray tube A rotation support mechanism that rotates the X-ray detector around a rotation axis, a top plate for the subject, a top plate support mechanism that reciprocally supports the top plate along a long axis, An X-ray computed tomography apparatus comprising: a drive unit that generates power for moving a top plate; and a control unit that controls the drive unit to reciprocate the top plate along the long axis. The control unit, when moving the top plate from the initial position to the scan start position before the X-ray exposure by the X-ray tube, folds the top plate from the initial position at a folding position of the scan range, and The drive to move to the scan start position To control.

The figure which shows the structure of the X-ray computed tomography apparatus which concerns on this embodiment. The figure which shows typically the external appearance of the X-ray computed tomography apparatus of FIG. The figure which shows an example of typical operation | movement of the mount frame 10 and the bed 30 in the helical shuttle scan performed under control of the mount frame / bed control part of FIG. The figure which shows the time change of the position of the top plate in the helical shuttle scan which concerns on Example 1 of this embodiment. The figure which shows the time change of the position of the top plate in the helical shuttle scan which concerns on Example 2 of this embodiment. The figure which shows the time change of the position of the top plate in the helical shuttle scan which concerns on Example 3 of this embodiment. The figure which shows the time change of the position of the top plate in the helical shuttle scan which concerns on a prior art example. The figure which shows the time change of the position of the top plate in the helical shuttle scan which concerns on another prior art example.

  The X-ray computed tomography apparatus according to this embodiment will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an X-ray computed tomography apparatus according to the present embodiment. FIG. 2 is a diagram schematically showing the appearance of the X-ray computed tomography apparatus according to the present embodiment.

  As shown in FIGS. 1 and 2, the X-ray computed tomography apparatus according to this embodiment includes a gantry 10, a bed 30, and a console 60. The gantry 10 and the bed 30 are installed, for example, in a CT imaging room. The console 60 is installed in, for example, a control room adjacent to the CT imaging room.

  As shown in FIGS. 1 and 2, the gantry 10 includes a gantry housing 11 in which an opening 11 a having a substantially cylindrical shape is formed. A rotating ring 12 having a substantially cylindrical shape is mounted inside the gantry housing 11. The gantry casing 11 supports the rotary ring 12 so as to be rotatable about the rotation axis Z. An X-ray tube 13 and an X-ray detector 14 are attached to the rotating ring 12 so as to face each other with the rotation axis Z in between. The partial space region of the opening 11a is set to FOV (field of view). The top plate 31 is inserted into the opening 11a. The rotating ring 12 is rotated by the frame rotating mechanism 15. The frame rotating mechanism 15 rotates the rotating frame 12 around the rotation axis Z at a constant angular velocity according to the control from the gantry / bed control unit 16.

  The X-ray tube 13 generates X-rays in response to application of a high voltage from the high voltage generator 17 and supply of filament current. The high voltage generator 17 applies a high voltage according to the control signal from the gantry / bed control unit 16 to the X-ray tube 13 and supplies a filament current to the X-ray tube 13 according to the control signal from the gantry / bed control unit 16. .

  The X-ray detector 14 detects X-rays generated from the X-ray tube 13. The X-ray detector 14 includes a plurality of detection elements arranged in a two-dimensional manner. Each detection element detects X-rays from the X-ray tube 13 and generates an electrical signal corresponding to the detected X-ray energy. The generated electrical signal is supplied to a data acquisition unit (DAS) 18. The data collection unit 18 collects electrical signals for each view via the X-ray detector 14 under the control of the gantry / bed control unit 16. The data collection unit 18 converts the collected analog electrical signals into digital data. Digital data is called raw data. The raw data is supplied to the console 60.

  As shown in FIGS. 1 and 2, a bed 30 is installed in the vicinity of the gantry 10. The bed 30 includes a top plate 31 for the subject P. The top plate 31 is supported by a top plate support mechanism 32 so as to be able to reciprocate along the long axis A <b> 1 of the top plate 31. The top plate 31 is positioned so that the body axis of the subject P placed on the top plate 31 coincides with the rotation axis Z of the rotary ring 12. The bed 30 and the gantry 10 are installed so that the long axis A1 and the rotation axis Z are parallel to each other.

  The top plate support mechanism 32 supports the top plate 31 so as to reciprocate along the long axis A1. The top plate support mechanism 32 receives the power from the top plate moving mechanism 33 and moves the top plate 31. The top board moving mechanism 33 reciprocates the top board 31 along the long axis A1 according to a control signal from the gantry / bed control section 16. As shown in FIG. 1, the top board moving mechanism 33 includes a bed driving unit 34, a position detector 35, and a bed control unit 36. The bed driving unit 34 converts the driving pulse from the bed control unit 36 into power for operating the table support mechanism 32. This power is transmitted to the top plate support mechanism 32. Specifically, the bed driving unit 34 includes a servo motor. The position detector 35 repeatedly detects the amount of movement of the top plate 31, that is, the position of the top plate 31. The position detector 35 is realized by an encoder, for example. The position detector 35 is attached to the rotation shaft of the servo motor, and generates a pulse every time the servo motor rotates by a certain angle. The generated pulse is supplied to the bed control unit 36. Hereinafter, the pulse generated by the position detector 35 is referred to as a feedback pulse. The bed control unit 36 controls the bed driving unit 34 in accordance with a control signal from the gantry / bed control unit 16. More specifically, the bed control unit 36 controls the bed driving unit 34 to reciprocate the top plate 31 along the long axis A1. Further, the couch controller 36 controls the couch driving unit 34 to move the couchtop 31 at a speed corresponding to the current position of the couchtop 31 using the feedback pulse from the position detector 35. Thus, the top board moving mechanism 36 has a feedback control system that uses the pulses from the position detector 34 as feedback. Details of the top plate moving mechanism 36 will be described later.

  The console 60 includes a preprocessing unit 61, a reconstruction unit 62, an image processing unit 63, a scan condition determination unit 64, a display unit 65, an operation unit 66, a storage unit 67, and a system control unit 68.

  The preprocessing unit 61 performs preprocessing on the raw data from the data collection unit 18 and generates projection data to be used for reconstruction processing. Examples of the preprocessing include logarithmic conversion, gain correction, nonuniformity correction, and offset correction. The projection data is stored in the storage unit 67 in view units.

  The reconstruction unit 62 generates a reconstruction image related to the subject P based on the projection data. For example, the reconstruction unit 62 generates a reconstruction image for each forward path based on the projection data collected for each forward path, or generates a reconstruction image for each backward path based on the projection data collected for each backward path. Or

  The image processing unit 63 performs various image processing on the reconstructed image. For example, the image processing unit 63 generates a difference image based on two reconstructed images related to the same position.

  The scan condition determination unit 64 determines various scan conditions in accordance with instructions from the user via the operation unit 66. Examples of the scan condition include a scan start position, a scan range, and a folding position of the top board.

  The display unit 65 displays a reconstructed image, a difference image, a scan condition setting screen, and the like on a display device. As the display device, for example, a CRT display, a liquid crystal display, an organic EL display, a plasma display, or the like can be used as appropriate.

  The operation unit 66 receives various commands and information input from the user via the input device. As an input device, a keyboard, a mouse, a switch, or the like can be used.

  The storage unit 67 stores projection data, reconstructed image data, and difference image data. The storage unit 76 stores a control program for the X-ray computed tomography apparatus according to the present embodiment. This control program is for causing the system control unit 68 to execute a control function for performing the helical shuttle scan according to the present embodiment.

  The system control unit 68 functions as the center of the X-ray computed tomography apparatus according to this embodiment. Specifically, the system control unit 68 reads out the control program stored in the storage unit 65 and develops it on the memory, and controls each unit in the X-ray computed tomography apparatus according to the developed control program.

  Next, an operation example of the X-ray computed tomography apparatus according to this embodiment will be described.

  First, typical operations of the gantry 10 and the bed 30 during the helical shuttle scan will be described. FIG. 3 is a diagram illustrating an example of typical operations of the gantry 10 and the bed 30 in the helical shuttle scan. As shown in FIG. 3, the scan range is set between the target stop position A and the target stop position B. The top 31 reciprocates between the target stop position A and the target stop position B according to the control by the bed control unit 36. The rotating frame 12 of the gantry 10 is repeatedly rotated by the frame rotating mechanism 15 during the helical shuttle scan. It is assumed that a path from the target stop position A to the target stop position B is an outward path, and a path from the target stop position B to the target stop position A is a return path. The top plate 31 is inserted into the opening 11a of the gantry housing 11 in the forward path, and is pulled out from the opening 11a in the return path. The reciprocating top plate movement direction may be reversed.

  Here, the reciprocation of the top plate performed under the control of the bed control unit 36 will be described in detail. The end of the scan range with respect to the Z axis is set to the acceleration / deceleration region, and the region other than the acceleration / deceleration region of the scan range is set to the constant speed region. The acceleration / deceleration area on the target stop position A side is called an acceleration / deceleration area A, and the acceleration / deceleration area on the target stop position B side is called an acceleration / deceleration area B. The distance of the acceleration / deceleration area is set to a distance required to accelerate the top plate 31 from the stopped state to the set speed, or to decelerate from the set speed to the stopped state. It is assumed that the top plate is placed at the target stop position A at the start of the helical shuttle scan.

  The bed controller 36 reciprocates between the target stop position A and the target stop position B without burdening the subject P by controlling the moving direction, moving speed, moving amount, and the like of the table 31. Let During the helical shuttle scan, the couch controller 36 calculates a movement command amount according to the distance between the target stop position A and the target stop position B. Then, the bed controller 36 repeatedly generates drive pulses for the number of pulses according to the calculated movement command amount. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 rotates by a certain angle every time the driving pulse is supplied. The couch controller 36 uses the feedback pulse from the position detector 35 to change the pulse frequency of the drive pulse according to the current position of the top board 31. The moving speed of the top plate 31 increases as the pulse frequency increases. The bed controller 36 gradually increases the pulse frequency to increase the moving speed of the top 31 to the set speed while passing through the acceleration / deceleration area A from the movement start position (for example, the target stop position A). The couch controller 36 keeps the pulse frequency constant when the top 31 reaches the constant speed region. Then, the bed control unit 36 gradually lowers the pulse frequency so that the top 31 stops at the target stop position B when the acceleration / deceleration area B is reached from the constant speed area. When the top 31 stops, the bed control unit 36 moves the top 31 toward the target stop position A by the same method. The moving direction of the top 31 is changed by reversing the rotation direction around the rotation axis of the bed driving unit 35 (servo motor). The rotation direction of the servo motor is associated with, for example, a phase difference of drive pulses. The couch controller 36 controls the moving direction of the top 31 by supplying the couch drive unit 34 with drive pulses having different phase differences between the forward path and the return path. In this way, the bed control unit 36 reciprocates the top 31 between the target stop position A and the target stop position B.

  As described above, in order to switch the moving direction of the top plate 31 at the folding position of the top plate 31, the rotation direction of the rotating shaft of the bed driving unit 35 (servo motor) is reversed. Backlash occurs with the reversal of the rotation direction of the servo motor, and an error occurs between the actual stop position of the next top plate 31 and the target stop position due to the backlash. Therefore, as described with reference to FIGS. 7 and 8, the moving distance of the first forward path is different from the moving distance of each path after the first forward path, and the reproducibility of the position of the top plate is deteriorated.

  When the top plate operating conditions such as the weight of the subject, the target stop position, and the use of the top plate 21 are the same, the error between the actual stop position and the target stop position is the distance from the movement start position to the target stop position. Depends on. Therefore, the inventor of the present application has the following movement start position (that is, scan start position) for the first outbound path and the travel distance of each path after the first outbound path to be substantially equal to each other. It has been found that both the first condition and the second condition are satisfied. The first condition is to reverse the rotation direction of the servo motor when the top plate 31 is moved at the movement start position of the first forward path. The second condition is that the movement start position for the first forward path and the movement start positions for the second and subsequent paths are spatially substantially at the same position.

  The X-ray computed tomography apparatus according to the present embodiment executes a preliminary operation before executing the helical shuttle scan in order to satisfy both the first condition and the second condition described above. As a preliminary operation, the couch controller 36 does not move the top 31 directly from the initial position to the scan start position (for example, the target stop position A), but instead returns from the initial position to the return position (for example, the target stop position B). ) To the scan start position.

  Hereinafter, the preliminary operation performed before the execution of the helical shuttle scan will be described separately for the first embodiment, the second embodiment, and the third embodiment.

Example 1
FIG. 4 is a diagram illustrating temporal changes in the position of the top 31 in the helical shuttle scan according to the first embodiment. The horizontal axis of FIG. 4 is defined by the position of the top plate 31 along the Z axis. In FIG. 4, the top plate position is indicated by the relative top plate position and the encoder count when one target stop position is 0.0 mm. The top plate position is detected at intervals of 0.5 mm, and is increased or decreased by 0.5 mm every time the encoder counts 32 times. The vertical axis in FIG. 4 is defined by time. In the present embodiment, it is assumed that the target stop position A (control center) is set to 0.0 mm and the target stop position B (control center) is set to 80.0 mm. Further, it is assumed that the target stop position A is set as the scan start position. Assume that the path from the target stop position A to the target stop position B is the forward path, and conversely, the path from the target stop position B to the target stop position A is the return path.

  First, the scan condition determination unit 64 determines various scan conditions in accordance with instructions from the user via the operation unit 66. Examples of the scan condition include a scan range, a scan start position, and a return position. The scan range and the scan start position are determined according to an instruction from the user via the operation unit 66. The scan start position is set at one end of the scan range. In FIG. 4, the scan start position is set to the target stop position A as described above. The return position is automatically determined based on the scan start position and the scan range. Specifically, the return position is calculated by adding the scan range to the scan start position. In FIG. 4, the return position is set to the target stop position B as described above. Note that the top 31 is turned back at the target stop position A after the second forward pass. Data relating to the scanning conditions is supplied to the gantry / bed control section 16. Data relating to the scan range, scan start position, and folding position is supplied from the gantry / bed control unit 16 to the bed control unit 36.

  When various scan conditions are determined by the scan condition determination unit 64, the user presses a scan condition setting button in order to determine the determined scan condition. When the scan condition setting button is pressed, the scan condition determined by the scan condition determination unit 64 is set in the console 60. Further, the gantry / bed control unit 16 controls the frame rotation mechanism 15 to rotate the rotating frame 12 when the scan condition button is pressed. At this stage, X-ray exposure and data collection are not yet started.

  When the subject P is placed on the top board 31 and the preparation for the helical shuttle scan is completed, the user inputs a top board placement instruction via the operation unit 66. For example, the user presses the top plate position set button as the top plate placement instruction. When the top position setting button is pressed, the gantry / bed control unit 16 causes the bed control unit 36 to perform a preset operation. In the preset operation, the couch controller 16 controls the couch driver 34 so as to move the top 31 from the initial position PI to the scan start position (target stop position A) via the turn-back position (target stop position B). . Hereinafter, the preset operation will be described in detail. The initial position PI is specifically the position of the top board 31 at the time when the top board position set button is pressed. In the following description, the description of the speed of the top plate 31 is omitted for the sake of simplicity.

  As the first stage of the preset operation, the bed control unit 36 controls the bed driving unit 34 so as to move the top 31 from the initial position PI to the target stop position B. Specifically, the bed control unit 36 calculates a movement command amount according to the distance from the initial position PI to the target stop position B. Then, the bed controller 36 repeatedly generates drive pulses for the number of pulses according to the calculated movement command amount. At this time, the couch controller 36 generates a drive pulse having a phase difference (phase difference for the forward path) corresponding to the moving direction from the target stop position A toward the target stop position B. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the driving pulse supplied from the bed control unit 36 and rotates the servo motor in the forward direction to move the table 31 toward the target stop position B. In the first stage of the preset operation, the top 31 stops at a position PP substantially equal to the target stop position B.

  When the top 31 stops, the second stage of the preset operation is started. In the second stage of the preset operation, the bed control unit 36 repeatedly generates drive pulses for the number of pulses corresponding to the movement command amount corresponding to the distance from the target stop position B to the scan start position (target stop position A). . At this time, since the bed control unit 36 reverses the moving direction of the top 31 from the moving direction of the first stage, a phase difference (phase difference for the return path) different from the sign of the driving pulse of the first stage is generated. Generate drive pulses. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the drive pulse from the bed control unit 36 and rotates the servo motor in the reverse direction to move the table 31 toward the scan start position (target stop position A). Backlash occurs as the servo motor rotates in the reverse direction. Therefore, the top plate 31 stops at a position PO1 before the target stop position A by the amount of loss due to backlash.

  When the top 31 is stopped, the user inputs a scan start instruction via the operation unit 66. For example, the user presses a scan start button as a scan start instruction. When the scan start button is pressed, the gantry / bed control unit 16 executes a helical shuttle scan according to the scan sequence. That is, the gantry / bed control unit 16 causes the bed control unit 36 to start reciprocating movement of the top plate 31, causes the high voltage generation unit 17 to start X-ray exposure by the X-ray tube 13, and causes the data collection unit 18 to Start collecting raw data. The gantry / bed control section 16 continues to rotate the rotating frame 12 by controlling the frame rotating mechanism 15.

  During the helical shuttle scan, the bed control unit 36 controls the bed driving unit 34 so that the top 31 reciprocates between the target stop position A and the target stop position B. In the first forward path of the helical shuttle scan, the bed control unit 36 repeatedly generates drive pulses for the number of pulses corresponding to the movement command amount corresponding to the distance from the target stop position A to the target stop position B. At this time, the bed control unit 36 generates a driving pulse having a phase difference for the forward path in order to reverse the movement direction of the top board 31 from the movement direction of the preset second stage. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the driving pulse supplied from the bed control unit 36 and rotates the servo motor in the forward direction to move the table 31 toward the target stop position B. Backlash occurs as the servo motor rotates in the reverse direction. Accordingly, in the first forward path, the top 31 stops at a position PH1 before the target stop position B by the amount of loss due to backlash.

  In the first return pass of the helical shuttle scan, the bed control unit 36 repeatedly generates drive pulses for the number of pulses corresponding to the movement command amount corresponding to the distance from the target stop position B to the target stop position A. At this time, the bed control unit 36 generates a driving pulse having a phase difference for the backward path in order to reverse the moving direction of the top board 31 from the forward path direction. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the supply of the driving pulse from the bed control unit 36 and rotates the servo motor in the reverse direction to move the table 31 toward the target stop position A. Backlash occurs as the servo motor rotates in the reverse direction. Accordingly, in the first return pass, the top plate 31 stops at a position PO2 before the target stop position A by the amount of loss due to backlash.

  In this way, the couch controller 36 controls the couch driving unit 34 so that the top 31 reciprocates between the target stop position A and the target stop position B. That is, the top board 31 stops at the position PH2 in the second outward path, the top board 31 stops at the position PO3 in the second backward path, the top board 31 stops at the position PH3 in the third outward path, and the top board in the third backward path. 31 stops at the position PO4, the top 31 stops at the position PH4 in the fourth forward path, and the top 31 stops at the position PO5 in the fourth backward path.

  According to the above description, the bed control unit 36 moves the top 31 in a movement direction (that is, the backward direction) that is different from the initial movement direction (that is, the forward direction) of the helical shuttle scan, and the scan start position ( Since it is arranged at the target stop position A), backlash occurs at the start of the first forward movement. Further, when the couch controller 36 arranges the top 31 at the scan start position (target stop position A), the couch 31 is moved from substantially the same position PP as the target stop position B to the scan start position (target stop position A). It is moved. The movement distance from the position PP to the scan start position is substantially equal to the movement distance of each path after the first forward path. For this reason, the top plate operating conditions for the first forward pass and the top plate operating conditions for the first forward pass and thereafter are substantially the same. That is, the actual stop position PO1 of the first forward path is shifted from the target stop position A by substantially the same distance as the actual stop positions PO2, PO3, and PO4 of the second and subsequent forward paths. Since backlash occurs as in the following, the movement distance on the first forward path is approximately equal to the movement distance on and after the first forward path.

  In the first embodiment, a preset operation mode is provided before the scan sequence, and the preliminary operation according to the present embodiment is executed in the preset operation mode. In other words, the scan sequence according to the first embodiment is the same as the helical shuttle scan sequence according to the conventional example. Therefore, in the first embodiment, it is not necessary to incorporate the preliminary operation into the scan sequence, and therefore it is possible to reduce the trouble of mounting the preliminary operation.

(Example 2)
It is assumed that the preliminary operation according to the second embodiment is incorporated in the scan sequence. Hereinafter, an X-ray computed tomography apparatus according to Embodiment 2 will be described. In the following description, components having substantially the same functions as those in the first embodiment are denoted by the same reference numerals, and redundant description is provided only when necessary.

  FIG. 5 is a diagram illustrating a temporal change in the position of the top plate 31 in the helical shuttle scan according to the second embodiment.

  As illustrated in FIG. 5, when the top position setting button is pressed, the gantry / bed control unit 16 causes the bed control unit 36 to perform a preset operation. In the preset operation according to the second embodiment, the bed control unit 36 controls the bed driving unit 34 so as to move the top 31 directly from the initial position PI to the target stop position A. The target stop position A is set as the scan start position. In the preset operation, the bed control unit 36 repeatedly generates drive pulses for the number of pulses corresponding to the movement command amount corresponding to the distance from the initial position PI to the target stop position A. At this time, the bed control unit 36 generates a driving pulse having a phase difference for the return path. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the drive pulse supplied from the bed control unit 36 and rotates the servo motor to move the top 31 toward the target stop position A. In the preset operation, the top plate 31 is assumed to have stopped at the position PP1.

  When the top plate 31 is stopped, the user presses a scan start instruction button via the operation unit 66. When the scan start button is pressed, the gantry / bed control unit 16 executes the scan sequence according to the second embodiment. The helical shuttle scan according to the second embodiment includes a sequence related to the preliminary reciprocating operation and a sequence related to the helical shuttle scan. First, the sequence related to the preliminary reciprocating operation is executed prior to the sequence related to the helical shuttle scan.

  In the preliminary reciprocating operation, the gantry / bed control unit 16 causes the bed control unit 36 to start reciprocating movement of the top 31. X-ray exposure and raw data collection have not yet started in the preliminary reciprocation. In the preliminary reciprocating operation, the gantry / bed control unit 16 continues to rotate the rotating frame 12 by controlling the frame rotating mechanism 15.

  In the preliminary reciprocating operation, the bed control unit 36 controls the bed driving unit 34 so that the top 31 reciprocates between the target stop position A and the target stop position B. In the preliminary reciprocating operation, the bed control unit 36 repeatedly generates drive pulses by the number of pulses corresponding to the movement command amount corresponding to the distance from the target stop position A to the target stop position B. At this time, the bed control unit 36 generates a driving pulse having a phase difference for the forward path in order to reverse the moving direction of the top 31 from the moving direction of the preset operation. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the driving pulse supplied from the bed control unit 36 and rotates the servo motor in the forward direction to move the table 31 toward the target stop position B. Backlash occurs as the servo motor rotates in the reverse direction. Accordingly, the top plate 31 stops at the position PP2 before the target stop position B by the amount of loss due to backlash in the forward path of the preliminary reciprocating operation.

  In the return path of the preliminary reciprocating operation, the bed control unit 36 repeatedly generates drive pulses by the number of pulses corresponding to the movement command amount corresponding to the distance from the target stop position B to the target stop position A. At this time, the bed control unit 36 generates a drive pulse having a sign for the backward path in order to reverse the moving direction of the top 31 from the forward direction. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the supply of the driving pulse from the bed control unit 36 and rotates the servo motor in the reverse direction to move the table 31 toward the target stop position A. Backlash occurs as the servo motor rotates in the reverse direction. Therefore, on the return path, the top plate 31 stops at a position PO1 before the target stop position A by the amount of loss due to backlash.

  When the top 31 completes one reciprocation after the preset operation, the preliminary reciprocation operation ends. When the preliminary reciprocating operation ends, the gantry / bed control unit 16 automatically executes a helical shuttle scan. That is, the gantry / bed control unit 16 causes the bed control unit 36 to start reciprocating movement of the top plate 31, causes the high voltage generation unit 17 to start X-ray exposure by the X-ray tube 13, and causes the data collection unit 18 to Start collecting raw data. The gantry / bed control section 16 continues to rotate the rotating frame 12 by controlling the frame rotating mechanism 15.

  During the helical shuttle scan, the bed control unit 36 controls the bed driving unit 34 so that the top 31 reciprocates between the target stop position A and the target stop position B. Note that the control by the bed driving unit 34 in the helical shuttle scan is the same as that in the first embodiment, and a description thereof will be omitted.

  According to the above description, the bed control unit 36 reciprocates the top board 31 once and arranges it at the scan start position (target stop position A). Therefore, backlash occurs at the start of movement of the first forward pass of the helical shuttle scan. The movement distance from the position PP2 to the scan start position is substantially equal to the movement distance of each path after the first forward path. For this reason, the top plate operating conditions for the first forward pass and the top plate operating conditions for the first forward pass and thereafter are substantially the same. That is, the actual stop position PO1 of the first forward path is shifted from the target stop position A by substantially the same distance as the actual stop positions PO2, PO3, and PO4 of the second and subsequent forward paths. Since backlash occurs as in the following, the movement distance on the first forward path is approximately equal to the movement distance on and after the first forward path.

  In the second embodiment, a preliminary operation is incorporated in the scan sequence. Therefore, the preset operation according to the modification 2 is the same as the conventional example. Therefore, in the second embodiment, the user can issue a scan start instruction with the same feeling as before.

(Example 3)
The third embodiment is a modification of the second embodiment. In the third embodiment, the top plate movement in one direction is executed instead of the preliminary reciprocating operation. Hereinafter, an X-ray computed tomography apparatus according to Embodiment 3 will be described. In the following description, components having substantially the same functions as those in the first embodiment and the second embodiment are denoted by the same reference numerals, and redundant description is provided only when necessary.

  FIG. 6 is a diagram illustrating temporal changes in the position of the top 31 in the helical shuttle scan according to the third embodiment.

  As shown in FIG. 6, when the top position setting button is pressed, the gantry / bed control unit 16 causes the bed control unit 36 to perform a preset operation. Since the preset operation according to the third embodiment is the same as the preset operation according to the second embodiment, the description thereof is omitted.

  When the preset operation is performed and the top plate 31 is stopped, the user presses the scan start instruction button via the operation unit 66. When the scan start button is pressed, the gantry / bed control unit 16 executes the scan sequence according to the third embodiment. The helical shuttle scan according to the third embodiment includes a sequence related to the preliminary movement operation and a sequence related to the helical shuttle scan. First, the sequence related to the preliminary movement operation is executed prior to the sequence related to the helical shuttle scan.

  In the preliminary movement operation, the gantry / bed control unit 16 causes the bed control unit 36 to start moving the table 31 in one direction. X-ray exposure and raw data collection have not yet started in the preliminary movement operation. In the preliminary movement operation, the gantry / bed control unit 16 continues to rotate the rotating frame 12 by controlling the frame rotating mechanism 15.

  In the preliminary movement operation, the bed control unit 36 controls the bed driving unit 34 so that the top 31 reciprocates between the target stop position A and the target stop position B. In the preliminary movement operation, the bed control unit 36 repeatedly generates drive pulses for the number of pulses corresponding to the movement command amount corresponding to the distance from the target stop position A to the target stop position B. At this time, the bed control unit 36 generates a driving pulse having a phase difference for the forward path in order to reverse the moving direction of the top 31 from the moving direction of the preset operation. The generated drive pulse is supplied to the bed driving unit 34. The bed driving unit 34 receives the driving pulse supplied from the bed control unit 36 and rotates the servo motor in the forward direction to move the table 31 toward the target stop position B. Backlash occurs as the servo motor rotates in the reverse direction. Accordingly, in the preliminary movement operation, the top plate 31 stops at the position PH1 before the target stop position B by the amount of loss due to backlash.

  When the top 31 finishes moving in one direction after the preset operation, the preliminary movement operation ends. When the preliminary movement operation ends, the gantry / bed control unit 16 automatically executes a helical shuttle scan. That is, the gantry / bed control unit 16 causes the bed control unit 36 to start reciprocating movement of the top plate 31, causes the high voltage generation unit 17 to start X-ray exposure by the X-ray tube 13, and causes the data collection unit 18 to Start collecting raw data. The gantry / bed control section 16 continues to rotate the rotating frame 12 by controlling the frame rotating mechanism 15.

  During the helical shuttle scan, the bed control unit 36 controls the bed driving unit 34 so that the top 31 reciprocates between the target stop position B and the target stop position A. In the third embodiment, the relationship between the forward path and the return path is opposite to that in the first and second embodiments. That is, the path from the target stop position B to the target stop position A is the forward path, and the path from the target stop position A to the target stop position B is the return path. Note that the control by the bed driving unit 34 in the helical shuttle scan is the same as in the first and second embodiments, and thus the description thereof is omitted.

  According to the above description, the bed control unit 36 reciprocates the top plate 31 by combining the preset operation and the top plate moving operation, and arranges it at the scan start position (target stop position B). Therefore, backlash occurs at the start of movement of the first forward pass of the helical shuttle scan. The movement distance from the position PP1 to the scan start position is substantially equal to the movement distance of each path after the first forward path. For this reason, the top plate operating conditions for the first forward pass and the top plate operating conditions for the first forward pass and thereafter are substantially the same. That is, the actual stop position PH1 of the first forward path is shifted from the target stop position B by substantially the same distance as the actual stop positions PH2, PH3, and PH4 of the second and subsequent forward paths. Since backlash occurs as in the following, the movement distance on the first forward path is approximately equal to the movement distance on and after the first forward path.

  Further, in the third embodiment, compared with the second embodiment, the moving distance of the top plate 31 before the helical shuttle scan is shorter by one route. Therefore, the X-ray computed tomography apparatus according to the third embodiment realizes a shorter inspection time than the second embodiment.

[effect]
As described above, the X-ray computed tomography apparatus according to this embodiment includes the top plate support mechanism 32, the bed driving unit 34, and the bed control unit 36. The top plate support mechanism 32 supports the top plate 31 so as to reciprocate along the long axis A1. The bed driving unit 34 generates power for moving the top board 31. The bed control unit 36 controls the bed driving unit 23 to perform a preliminary operation when the table 31 is moved from the initial position to the scan start position before X-ray exposure by the X-ray tube 13. In the preliminary operation, the couch controller 36 controls the couch driving unit 34 so that the couchtop 31 is turned from the initial position at the turn-back position of the scan range and moved to the scan start position.

  According to the above configuration, the X-ray computed tomography apparatus according to the present embodiment performs the preliminary operation to improve the reproducibility of the position of the top plate 31, that is, the first outbound path. When the top plate 31 is moved at the movement start position, the rotation direction of the servo motor is reversed (first condition), and the movement start position of the first forward path and the movement start positions of the second forward path and the subsequent are substantially spatially approximate. Both of being in the same position (second condition) can be satisfied. Therefore, regardless of the presence or absence of backlash, the travel distance of the first forward path and the travel distance of each path after the first forward path can be made substantially equal. Since the movement distance of the first forward path and the movement distances of the other paths are substantially equal, the difference in movement distance included in the difference image between the reconstructed image related to the first forward path and the reconstructed image related to the other path. Derived artifacts are reduced.

  Thus, according to the present embodiment, it is possible to improve the reproducibility of the position of the top board in the X-ray computed tomography apparatus that performs the helical shuttle scan that collects data while reciprocating the top board.

  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 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 10 ... Mount, 11 ... Mount housing, 11a ... Opening, 12 ... Rotating frame, 13 ... X-ray tube, 14 ... X-ray detector, 15 ... Frame moving mechanism, 16 ... Mount / bed control part, 17 ... High Voltage generating unit, 18 ... data collecting unit, 30 ... couch, 31 ... couch, 32 ... couch support mechanism, 33 ... couch moving mechanism, 34 ... couch driving unit, 35 ... position detector, 36 ... couch controller , 60 ... console, 61 ... pre-processing unit, 62 ... reconstruction unit, 63 ... image processing unit, 64 ... scanning condition determination unit, 65 ... display unit, 66 ... operation unit, 67 ... storage unit, 68 ... system control unit

Claims (6)

An X-ray tube that generates X-rays, an X-ray detector that detects X-rays generated from the X-ray tube and transmitted through the subject,
A rotation support mechanism for rotating the X-ray tube and the X-ray detector around a rotation axis;
A top plate for the subject;
A top plate support mechanism for reciprocally supporting the top plate along the long axis;
A drive unit for generating power for moving the top plate;
A control unit for controlling the driving unit to reciprocate the top plate along the long axis;
An X-ray computed tomography apparatus comprising:
When the controller moves the top plate from an initial position to a scan start position before X-ray exposure by the X-ray tube, the controller folds the top plate from the initial position at a return position in a scan range. Controlling the drive to move to a starting position;
X-ray computed tomography apparatus.   The control unit moves the top plate from the initial position to the scan start position via the folding position in accordance with a top plate placement instruction from the user, and from the X-ray tube in accordance with a scan start instruction from the user. The X-ray computed tomography apparatus according to claim 1, wherein X-ray exposure is started and the top plate is reciprocated between the scan start position and the folding position.   The control unit moves the top plate directly from the initial position to the scan start position in accordance with a top plate placement instruction from the user, and moves the top plate to the scan start position in accordance with a scan start instruction from the user. The X-ray tube starts to reciprocate once, and the top plate reciprocates once to reach the scan start position. The X-ray computed tomography apparatus according to claim 1, wherein the X-ray computed tomography apparatus is reciprocated between a scan start position and the folding position.   The control unit moves the top plate directly from the initial position to the folding position according to a top plate placement instruction from a user, and moves the top plate from the folding position according to a scan start instruction from the user. It moves linearly to a start position, starts exposure of X-rays from the X-ray tube when the top plate reaches the scan start position, and moves the top plate to the scan start position and the folding position. The X-ray computed tomography apparatus according to claim 1, wherein the X-ray computed tomography apparatus is reciprocally moved between the X-ray computer and the X-ray computed tomography apparatus.   The X-ray computed tomography apparatus according to claim 1, further comprising a determination unit that determines the return position based on the scan range and the scan start position. The drive unit has a motor that can rotate in a forward direction and a reverse direction around a rotation axis,
The control unit causes the top plate to be folded by switching between the forward direction and the reverse direction.
The X-ray computed tomography apparatus according to claim 1.

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