JP2014226475A - X-ray computed tomography apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the total amount of raw data collected during dynamic scan from deviating depending on the real spatial position of data collection.SOLUTION: A pedestal control unit 21 controls a high-voltage generator 25 and a rotation drive unit 19 such that a subject is repeatedly scanned by X rays as an X-ray tube 13 and an X-ray detector 15 are repeatedly rotated about a rotation shaft R. In a scan method which rotates the X-ray tube 13 and the X-ray detector 15 a plurality of turns about the rotation shaft R, the pedestal control unit 21 switches between the exposure and termination of the X rays according to the rotation angle of the X-ray tube 13 such that the total amount of the raw data collected over the plurality of turns at each of the real spatial positions become nearly uniform irrespective of the real spatial position.

Description

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

  In X-ray CT (computed tomography), a method is known in which scanning is repeatedly performed while rotating an X-ray tube and an X-ray detector over a plurality of turns. This scanning method is called dynamic scanning. The X-ray computed tomography apparatus is equipped with a rotating frame in which an X-ray tube and an X-ray detector are arranged to face each other. The X-ray detector is equipped with a plurality of X-ray detection elements arranged two-dimensionally. Each X-ray detection element detects X-rays from the X-ray tube and generates an electrical signal corresponding to the detected X-ray intensity. The generated electrical signal is converted into digital data (raw data) by a data collection unit connected to the X-ray detector.

  FIG. 9 is a diagram schematically showing the total amount of data for each real space position of the raw data in one round scan in which the rotation angle is 0 degree and the exposure start angle, divided into four scan stages. 9A shows the start of one round scan (X-ray tube rotation angle 0 degree), FIG. 9B shows the middle of one round scan (rotation angle 45 degrees), and FIG. (C) in the middle of one-round scanning (rotation angle of 135 degrees) and (d) in FIG. 9 indicate that one-round scanning is stopped (rotation angle of 225 degrees). The one-round scan is a scan for collecting raw data necessary for reconstructing volume data for one volume. The exposure angle range of one round scan according to FIG. 9 is defined from 0 degrees to 225 degrees. A circle in FIG. 9 corresponds to a position in real space (real space position) through which the X-ray detection element passes. The numbers in ○ represent the total amount of digital data. Each time an X-ray is detected by an X-ray detection element arranged at a real space position corresponding to ◯, 1 is added to the number in the ◯. For each X-ray detection element, the amount of digital data collected in one sampling period is “1”.

  FIG. 10 is a diagram showing a graph of the total data amount of the raw data collected in the one round scan of FIG. The vertical axis in FIG. 10 is defined by the data amount, and the horizontal axis is defined by the real space position. As shown in FIG. 10, the amount of data for each real space position collected in one round scan varies depending on the real space position. Therefore, when the X-ray irradiation start angles related to the respective round scans are set to the same angle, the bias corresponding to the real space position of the total data amount over the entire dynamic scan is accumulated. In the above description, for the sake of convenience, the case where the exposure angle range of one round scan is 240 degrees is taken as an example. However, even in other angle ranges such as 360 degrees, it depends on the real space position. The total amount of data will be biased.

  An object is to realize an X-ray computed tomography apparatus that performs scanning while rotating an X-ray tube a plurality of times to prevent a deviation in the total amount of data for each real space position of digital data collected at the time of scanning. .

  The X-ray computed tomography apparatus according to the present embodiment includes an X-ray tube that generates X-rays and a high voltage that generates a high voltage applied to the X-ray tube to generate X-rays from the X-ray tube. A generator, an X-ray detector equipped with a plurality of detection elements for detecting X-rays from the X-ray tube, and a support for rotatably supporting the X-ray tube and the X-ray detector around a rotation axis A mechanism, a rotation driving unit that generates power for rotating the X-ray tube and the X-ray detector around the rotation axis, and an electric signal read from each of the detection elements to express attenuation of the X-ray A high voltage generator and a rotation drive unit for scanning a subject with X-rays while rotating a collection unit for collecting digital data, the X-ray tube and the X-ray detector around the rotation axis repeatedly. X-ray computer comprising a gantry control unit for controlling In the scanning method in which the X-ray tube and the X-ray detector are rotated around the rotation axis over a plurality of turns, the gantry controller is collected over the plurality of turns. Switching between X-ray exposure and stop according to the rotation angle of the X-ray tube so that the total amount of digital data for each real space position becomes substantially uniform regardless of the real space position. And

The figure which shows the structure of the X-ray computed tomography apparatus which concerns on this embodiment. The figure which shows the total data amount for every real space position of the raw data in 1 round scan which makes the rotation angle 180 degree | times an exposure start angle divided into 4 scan steps, and is simulated. The figure which shows the graph of the total data amount of the raw data collected in the 1 round scan of FIG. The total amount of raw data collected in the round scan when the exposure start angle is 0 degrees as shown in FIG. 10 and the round data when the exposure start angle is 180 degrees as shown in FIG. The figure which shows the graph of the sum total with the total data amount of raw data to be performed. FIG. 2 is a diagram showing an X-ray exposure period and a stop period in a dynamic scan for each orbital scan, and clearly shows an exposure start angle determined according to a first determination rule by a scan condition determination unit in FIG. 1. FIG. 2 is a diagram illustrating an X-ray exposure period and a stop period in a dynamic scan for each orbital scan, and is a diagram in which an exposure start angle determined according to a second determination rule by a scan condition determination unit in FIG. It is a figure which shows the exposure period and stop period of the X-ray in a dynamic scan for every round scan, and specified the exposure start angle determined according to the modification of the 2nd determination rule by the scanning condition determination part of FIG. Figure. The figure which shows the typical flow of the dynamic scan performed under control of the mount control part of FIG. The figure which shows the total data amount for every real space position of the raw data in 1 round scan which makes rotation angle 0 degree | times an exposure start angle divided into 4 scan steps, and is simulated. The figure which shows the graph of the total data amount of the raw data collected in the 1 round scan of FIG.

  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 1 according to the present embodiment. As shown in FIG. 1, the X-ray computed tomography apparatus 1 includes a gantry 10 and a console 50.

  The gantry 10 is equipped with a rotating frame 11. The rotating frame 11 is mounted with an X-ray tube 13 and an X-ray detector 15 that are arranged to face each other. An FOV (field of view) is set inside the opening of the rotating frame 11. The top plate 17 is positioned so that the imaging region of the subject (patient) P is included in the FOV. The rotating frame 11 is connected to the rotation driving unit 19. The rotation drive unit 19 rotates the rotating frame 11 around the rotation axis R at a constant angular velocity according to control by the gantry control unit 21. The rotation drive unit 19 includes, for example, a motor that generates power for rotating the rotating frame 11. An angle detector 23 such as a rotary encoder is attached to the rotation drive unit 19. The angle detector 23 repeatedly generates an electric pulse signal (hereinafter referred to as an angle signal) every time the rotating frame 11 rotates by a certain angle. The angle signal is supplied to the gantry control unit 21.

  Regarding the rotation angle of the rotary frame 11 around the rotation axis, the rotation angle is 0 degree when the X-ray tube 13 is positioned at the uppermost position, and the rotation angle is 180 degrees when the X-ray tube 13 is positioned at the lowermost position.

  The X-ray tube 13 generates X-rays in response to application of a high voltage from the high voltage generator 25 and supply of a filament current. Specifically, the X-ray tube is equipped with an anode and a cathode. A high voltage is applied by a high voltage generator 25 between the anode and the cathode. A filament current from the high voltage generator 25 is supplied to the cathode. Electrons (thermoelectrons) are emitted from the cathode heated by the supply of the filament current. The thermoelectrons fly toward the anode and collide with the anode by a high voltage applied between the anode and the cathode. X-rays are generated by this collision. A bias electrode is provided between the anode and the cathode. The high voltage generator 25 applies a bias voltage to the bias electrode in order to prevent the thermal electrons emitted from the cathode from colliding with the anode. The number of thermionic electrons that collide with the anode changes by adjusting the potential with respect to the cathode potential by the bias voltage. That is, the high voltage generator 25 can be switched between ON (exposure) and OFF (stop of exposure) of X-rays from the X-ray tube by alternately switching two voltage values of the bias voltage. .

  The X-ray detector 15 detects X-rays generated from the X-ray tube 13. The X-ray detector 15 is equipped with a plurality of X-ray detection elements arranged in a two-dimensional shape. For example, the plurality of X-ray detection elements are arranged along an arc centered on the rotation axis R of the rotating frame 11. The arrangement direction of the X-ray detection elements along the arc is called a channel direction. A plurality of X-ray detection elements arranged along the channel direction is called an X-ray detection element array. The plurality of X-ray detection element rows are arranged along the row direction along the rotation axis R. Each X-ray detection element detects X-rays generated from the X-ray tube 13 and generates an electric signal corresponding to the detected X-ray intensity. The generated electrical signal is supplied to a data collection unit (DAS) 27.

  The data collection unit 27 collects electrical signals for each view via the X-ray detector 15 according to control by the gantry control unit 21. The view corresponds to the rotation angle of the rotation frame 11 around the rotation axis R. In terms of signal processing, the view corresponds to a data sampling point when the rotating frame 11 is rotated. The data collection unit 27 converts the collected analog electrical signals into digital data. Digital data is data representing the attenuation of X-rays by the subject. Digital data is called raw data. The raw data is supplied to the console 50 for each predetermined view by the transmission unit 29.

  The gantry control unit 21 has a control board that supervises the control of various devices mounted on the gantry 10 in accordance with instructions from the system control unit 63 in the console 50. The gantry control unit 21 controls the rotation drive unit 19, the high voltage generator 25, and the data collection unit 27. Specifically, the rotation driving unit 19 is controlled so that the rotating frame 11 rotates at a predetermined angular velocity. The gantry control unit 21 controls the high voltage generator 25 so that X-rays corresponding to predetermined X-ray conditions are generated from the X-ray tube 13. The gantry control unit 21 controls the data collection unit 27 so as to collect raw data for each view. Further, the gantry control unit 21 calculates the rotation angle of the rotating frame 11, that is, the rotation angle of the X-ray tube 13 based on the angle signal from the angle detector 23. In the dynamic scan method, the gantry control unit 21 switches the exposure and stop of the X-rays from the X-ray tube 13 in synchronization with the X-ray tube 13 reaching a predetermined rotation angle. 25 is controlled.

  The console 50 includes a preprocessing unit 51, a reconstruction unit 53, a display unit 55, an operation unit 57, a storage unit 59, a scan condition determination unit 61, and a system control unit 63. The preprocessing unit 51 performs preprocessing such as logarithmic conversion and sensitivity correction on the raw data transmitted from the transmission unit 29. The raw data that has been preprocessed is called projection data. The reconstruction unit 53 reconstructs image data related to the subject based on the projection data. The display unit 55 displays the image data generated by the reconstruction unit 53 on a display device. The operation unit 57 receives various commands and information input from the user by the input device. The storage unit 59 stores raw data, projection data, and image data. The storage unit 59 stores a control program. The scan condition determining unit 61 determines a scan condition related to the dynamic scan method. The system control unit 63 reads out the control program stored in the storage unit 59 and expands it on the memory, and controls each unit according to the expanded control program.

  Hereinafter, a dynamic scan method of the X-ray computed tomography apparatus according to the present embodiment will be described.

  First, an overview of dynamic scanning according to the present embodiment will be described with reference to FIGS. 2, 3, 9, and 10. FIG. 2 is a diagram schematically showing the total data amount for each real space position of the raw data in one round scan with the rotation angle of 180 degrees as the exposure start angle divided into four scan stages. The angle range of one round scan according to FIG. 2 is defined from 180 degrees to 405 degrees (45 degrees). 2A shows the start of exposure (rotation angle 180 degrees), FIG. 2B shows the middle of scanning (rotation angle 270 degrees), and FIG. 2C shows the middle of scanning. (Rotation angle 315 degrees) is shown, and (d) in FIG. 2 shows the end of scanning (rotation angle 45 degrees). FIG. 3 is a diagram showing a graph of the total data amount of raw data collected in the one round scan of FIG. The vertical axis in FIG. 3 is defined by the data amount, and the horizontal axis is defined by the real space position. In addition, the real space position in FIG. 3 and the real space position in the figure are spatially identical. 2 corresponds to the position (real space position) in the real space through which the X-ray detection element passes, as in FIG. 9, and the number in the circle represents the total amount of digital data. ing. As shown in FIGS. 2 and 3, the raw data amount related to the position B and the position C is smaller than the raw data amount related to the position A and the position D. On the other hand, when the exposure start angle is 0 degree, as shown in FIGS. 9 and 10, the raw data amount related to the position A and the position D is smaller than the raw data amount related to the position B and the position C. Many. As can be seen from the comparison between the case where the exposure start angle is 0 degrees and the case where the exposure start angle is 180 degrees, the real space position where the amount of raw data is small differs depending on the exposure start angle.

  4 shows the total amount of raw data collected in the round scan when the exposure start angle is 0 degree as shown in FIG. 10 and the case where the exposure start angle is 180 degrees as shown in FIG. It is a figure which shows the graph of the sum total with the total data amount of the raw data collected in a round scan. As shown in FIG. 4, the total of the total data amount is uniform regardless of the real space position. The gantry controller 21 changes the exposure start angle for each predetermined number of round scans in a dynamic scan that repeats round scans over a plurality of rounds, thereby changing the real space position of the raw data collected during the dynamic scan. To prevent bias in the total amount of data.

  First, determination of scan conditions by the scan condition determination unit 61 will be described. The scan conditions are, for example, an exposure start angle, an exposure angle range, and the number of round scans. In the exposure angle range, the exposure start angle is determined for each round scan. A method for determining the exposure start angle will be described later in detail. This is an angle range of one round scan, that is, an angle range from the start angle to the stop angle of X-ray exposure in one round scan. For example, the scan condition determination unit 61 determines the exposure angle range in accordance with an instruction from the user via the operation unit 57. The number of round scans is the total number of round scans included in the dynamic scan. The scan condition determination unit 61 may determine automatically based on scan conditions such as the scan time of dynamic scan, or may determine according to an instruction via the operation unit 57 by the user. The determined scan condition is stored in the storage unit 59.

  The determination of the exposure start angle by the scan condition determination unit 61 will be described. The scan condition determination unit 61 determines the exposure start angle of a plurality of round scans so as to reduce the bias of the total data amount for each real space position of the raw data collected during the dynamic scan. More specifically, the scan condition determination unit 61 determines the exposure start angle in each round scan according to the number of round scans. There are roughly two types of rules for determining the exposure start angle.

  The first determination rule is to determine the exposure start angles of a plurality of orbital scans so that the exposure start angles are distributed at equal intervals within an angular range of 0 to 360 degrees in each orbital scan. In other words, the exposure start angle is set to a value obtained by equally dividing 360 degrees by the number of round scans. For example, when the number of circular scans is m, the scan condition determining unit 61 determines the exposure start angle θm, n related to the nth circular scan according to the following equation (1). However, m is an integer greater than or equal to 1, and n is an integer which satisfy | fills 1 <= n <= m. Θm, 1 is the exposure start angle of the first scan. The angle θm, 1 is preferably specified individually by the user via the operation unit 57. The angle θm, 1 may be set in advance as a preset.

θm, n = (360 ° / m) · (n−1) + m, 1 (1)
FIG. 5 is a diagram showing an X-ray exposure period and a stop period in the dynamic scan for each round scan, and is a diagram clearly showing the exposure start angle determined by the scan condition determination unit 61 according to the first determination rule. It is. In FIG. 5, it is assumed that the dynamic scan includes four round scans, the exposure angle range is 360 degrees, and the exposure start angle θ4,1 of the first round scan is 0 degrees. In this case, the exposure start angle θ4,2 of the second round scan is 90 degrees, the exposure start angle θ4,3 of the third round scan is 180 degrees, and the exposure start of the fourth round scan is started. The angle θ4,4 is 270 degrees.

  The operation of the gantry control unit 21 related to the dynamic scan in FIG. 5 will be briefly described. The gantry control unit 21 rotates the rotating frame 11 and controls the high voltage generator 25 and the data collection unit 27 when the X-ray tube 13 reaches θ4,1 = 0 degrees, and the first round Scanning is started (a in FIG. 5). Scanning is performed only for the exposure angle range determined by the scanning condition determination unit 61. When the X-ray tube 13 is rotated by the exposure angle range (in the case of FIG. 5, when the X-ray tube 13 reaches 0 degree), the gantry control unit 21 receives the high voltage generator 25. And the data collection unit 27 are controlled, the X-ray exposure is stopped, and the raw data collection is stopped (b in FIG. 5). Then, when the X-ray tube 13 has reached the exposure start angle θ4,2 = 90 degrees of the second round scan, the gantry controller 21 starts the second round scan (c in FIG. 5). When the X-ray tube 13 is rotated by the exposure angle range (in the case of FIG. 5, when the X-ray tube 13 reaches 90 degrees), the gantry control unit 21 receives the high voltage generator 25. And the data collection unit 27 are controlled, the X-ray exposure is stopped, and the raw data collection is stopped (d in FIG. 5). Then, when the X-ray tube 13 reaches the exposure start angle θ4,3 = 180 degrees of the third round scan, the gantry controller 21 starts the third round scan (e in FIG. 5). When the X-ray tube 13 is rotated by the exposure angle range (in the case of FIG. 5, when the X-ray tube 13 reaches 180 degrees), the gantry control unit 21 receives the high voltage generator 25. And the data collection unit 27 are controlled, the X-ray exposure is stopped, and the raw data collection is stopped (f in FIG. 5). Then, when the X-ray tube 13 reaches the exposure start angle θ4,4 = 270 degrees of the fourth round scan, the gantry controller 21 starts the fourth round scan (c in FIG. 5). When the X-ray tube 13 is rotated by the exposure angle range (in the case of FIG. 5, when the X-ray tube 13 reaches 270 degrees), the gantry control unit 21 The high voltage generator 25 and the data collection unit 27 are controlled to end the dynamic scan.

  The second determination rule is a method in which a plurality of exposure start angles determined according to the number of round scans are repeatedly used in order for each predetermined round. The total number of these exposure start angles is a divisor other than 1 for the number of round scans. First, the scan condition determination unit 61 determines a divisor of the number of round scans based on the number of round scans. When there are a plurality of divisors, the scan condition determining unit 61 determines any one of the plurality of divisors according to a predetermined rule. The predetermined rule is to determine the largest divisor or the smallest divisor among a plurality of divisors. Further, the scan condition determining unit 61 may determine an arbitrary divisor specified by the user via the operation unit 57. The scan condition determination unit 61 determines the X-ray exposure angle in each round scan by equally dividing 360 degrees by the determined divisor. In other words, the divisor is an equal fraction. Specifically, when the determined divisor is D, the scan condition determination unit 61 determines the exposure start angle θD, n related to the nth round scan according to the following equation (2). However, n is an integer satisfying 1 ≦ n ≦ D.

θD, n = (360 ° / D) · (n−1) + θD, 1 (2)
FIG. 6 is a diagram showing an X-ray exposure period and a stop period in a dynamic scan for each round scan, and is a diagram clearly showing an exposure start angle determined by the scan condition determination unit 61 according to the second determination rule. It is. In FIG. 6, the dynamic scan is composed of four round scans, the exposure angle range is 360 degrees, the divisor D is 2, and the exposure start angle θ2,1 of the first scan is 0 degrees. It shall be. In this case, the exposure start angle θ2,2 of the second round scan is 180 degrees, the exposure start angle θ2,3 of the third round scan is 360 degrees (0 degree), and the fourth round scan The exposure start angle θ2,4 is 540 degrees (180 degrees). The operation of the gantry control unit 21 in the dynamic scan illustrated in FIG. 6 is different from the operation of the gantry control unit 21 in the dynamic scan illustrated in FIG.

  In the second determination rule, the scan condition determination unit 61 determines the order of a plurality of exposure start angles so that the exposure start angles are switched in order for each round scan. However, this embodiment is not limited to this. In a modification of the second determination rule, the scan condition determination unit 61 may determine the order of the plurality of exposure start angles so that the round scans with the same X-ray irradiation start angle are continuously performed.

  FIG. 7 is a diagram showing an X-ray exposure period and a stop period in the dynamic scan for each round scan, and shows the exposure start angle determined by the scan condition determination unit 61 according to the modification of the second determination rule. FIG. In FIG. 7, the dynamic scan is composed of four round scans, the exposure angle range is 360 degrees, the divisor D is 2, and the exposure start angle θ2,1 of the first scan is 0. Suppose that it is a degree. In this case, the exposure start angle θ2,2 of the second round scan is 0 degree, the exposure start angle θ2,3 of the third round scan is 180 degrees, and the exposure start of the fourth round scan is started. The angle θ2,4 is 180 degrees. The operation of the gantry control unit 21 in the dynamic scan illustrated in FIG. 7 is the same as the operation of the gantry control unit 21 in the dynamic scan illustrated in FIG.

  By the modified example of the first determination rule, the second determination rule, or the second determination rule, the scan condition determination unit 61 can calculate the total data for each real space position of the raw data collected during the dynamic scan. The exposure start angle of a plurality of orbital scans is determined so that the amount deviation is reduced. The decision rule can be set by the user via the operation unit 57 from the first decision rule, the second decision rule, or a modification of the second decision rule.

  Next, an example of dynamic scan operation performed under the control of the gantry control unit 21 according to the present embodiment will be described. FIG. 8 is a diagram illustrating a typical flow of dynamic scanning performed under the control of the gantry control unit 21 according to the present embodiment.

  As shown in FIG. 8, the system control unit 63 supplies a dynamic scan start signal to the gantry control unit 21 when a dynamic scan start instruction is given via the operation unit 57 or the like. In addition, the system control unit 63 transmits data related to the scan conditions of the dynamic scan to the gantry control unit 21.

  Upon receiving the start signal, the gantry control unit 21 first controls the rotation drive unit 19 to rotate the rotating frame 11 at a predetermined angular velocity (step S1). The gantry control unit 21 starts calculating the rotation angle of the X-ray tube 13 based on the angle signal from the angle detector (step S2). After step S2, the gantry control unit 21 repeatedly calculates the rotation angle of the X-ray tube 13 based on the angle signal from the angle detector 23. The gantry control unit 21 waits for the X-ray tube 13 to reach the predetermined exposure start angle of the first round scan. The gantry control unit 21 starts the first round scan when the X-ray tube 13 reaches the exposure start angle of the first round scan (step S3). Specifically, the gantry control unit 21 controls the high voltage generator 25 to repeatedly emit X-rays from the X-ray tube 13. X-rays generated from the X-ray tube 13 pass through the subject and are detected by the X-ray detector 15. The gantry control unit 21 controls the data collection unit 27 to collect raw data for each view via the X-ray detector 15.

  When the first round scan is started, the gantry controller 21 determines whether or not to end the first round scan, that is, the predetermined exposure angle range X from the start of the first round scan. It is repeatedly determined whether or not the tube 13 has been rotated (step S4). For example, the gantry controller 21 immediately calculates the current rotation angle of the X-ray tube 13 based on the angle signal from the exposure start angle of the first round scan, and starts the exposure start angle of the first round scan. It is determined whether or not the X-ray tube 13 has reached an angle obtained by adding a predetermined exposure angle range to the above. If it has not reached, it means that the circular scan has not been completed, that is, the X-ray tube 13 has not been rotated by a predetermined exposure angle range. On the other hand, when it arrives, it means that the circular scan is completed, that is, the X-ray tube 13 is rotated by a predetermined exposure angle range. Alternatively, the gantry control unit 21 measures the elapsed time from the start of the first rotation scan, and whether or not the measured elapsed time reaches the time required for the X-ray tube 13 to rotate by the exposure angle range. Determine whether. If it has not reached, it means that the circular scan has not been completed, that is, the X-ray tube 13 has not been rotated by a predetermined exposure angle range. On the other hand, when it arrives, it means that the circular scan is completed, that is, the X-ray tube 13 is rotated by a predetermined exposure angle range.

  When it is determined that the first round scan is to be ended, the gantry control unit 21 ends the first round scan (step S5). In step S5, the gantry control unit 21 specifically controls the high voltage generator 25 to stop the X-ray exposure from the X-ray tube 13, and controls the data collection unit 27 to collect raw data. Stop. Even when the round scan is terminated, the gantry control unit 21 controls the rotation driving unit 19 to rotate the rotating frame 11.

  Next, the gantry control unit 21 determines whether or not to end the dynamic scan (step S6). In step S <b> 6, the gantry control unit 21 determines whether or not the number of circular scans performed from the start of the dynamic scan has reached a preset number of circular scans. If it has not reached, it means that the dynamic scan is continued, and if it has reached, it means that the dynamic scan is ended.

  If it is determined not to end the dynamic scan (step S6: NO), the gantry control unit 21 determines whether or not to start the next round scan, that is, the rotation angle of the X-ray tube 13 is the exposure of the next round scan. It is determined whether or not the start angle has been reached (step S7). The gantry controller 21 starts the orbital scan again when the X-ray tube 13 reaches the exposure start angle of the next one orbital scan (step S3).

  In this way, the gantry control unit 21 repeats Steps S3 to S7 until it determines that the dynamic scan is to be ended. When it is determined in step S6 that the dynamic scan is to be ended (step S6: YES), when the gantry control unit 21 determines that the dynamic scan is to be ended, the gantry control unit 21 controls the high voltage generator 25 to perform X The X-ray exposure from the X-ray tube 13 is terminated, the data collection unit 27 is controlled to terminate the collection of raw data, and the rotation drive unit 19 is controlled to terminate the rotation of the rotating frame 11.

  Thereby, the dynamic scan according to the present embodiment is completed.

  Thus, according to the present embodiment, in the X-ray computed tomography apparatus 1 that executes a dynamic scan while rotating the X-ray tube 13 a plurality of times, the total data amount for each real space position of the raw data collected during the dynamic scan It is possible to prevent this bias.

  In the above description, the top plate 17 during the dynamic scan is not particularly mentioned. The present embodiment can be applied to the case where the top plate 17 is stationary during the dynamic scan and the case where the top plate 17 moves along the rotation axis R.

  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 1 ... X-ray computed tomography apparatus, 10 ... Mount, 11 ... Rotating frame, 13 ... X-ray tube, 15 ... X-ray detector, 17 ... Top plate, 19 ... Rotation drive part, 21 ... Mount control part, 23 ... Angle detector, 25 ... high voltage generator, 27 ... data collection unit, 29 ... transmission unit, 50 ... console, 51 ... pre-processing unit, 53 ... reconstruction unit, 55 ... display unit, 57 ... operation unit, 59 ... Storage unit, 61 ... scan condition determination unit, 63 ... system control unit

Claims (3)

An X-ray tube that generates X-rays;
A high voltage generator for generating a high voltage applied to the X-ray tube to generate X-rays from the X-ray tube;
An X-ray detector equipped with a plurality of detection elements for detecting X-rays from the X-ray tube;
A support mechanism for supporting the X-ray tube and the X-ray detector so as to be rotatable around a rotation axis;
A rotation drive unit that generates power for rotating the X-ray tube and the X-ray detector around the rotation axis;
A collection unit that reads out an electrical signal from each of the detection elements and collects digital data representing attenuation of X-rays;
A gantry control unit that controls the high voltage generation unit and the rotation drive unit to repeatedly scan the subject with X-rays while repeatedly rotating the X-ray tube and the X-ray detector around the rotation axis; ,
An X-ray computed tomography apparatus comprising:
The gantry control unit is configured to rotate the X-ray tube and the X-ray detector around the rotation axis over a plurality of turns in a real space position of digital data collected over the turns. Switching between X-ray exposure and stop according to the rotation angle of the X-ray tube so that the total amount of data for each is substantially uniform regardless of the real space position,
An X-ray computed tomography apparatus characterized by that.   The gantry control unit controls the high voltage generation unit to irradiate X-rays from the X-ray tube when the X-ray tube has reached a predetermined exposure start angle for each scan, 2. The X-ray exposure from the X-ray tube is stopped by controlling the high-voltage generation unit when the X-ray tube moves by a predetermined angle range from a predetermined exposure start angle. The X-ray computed tomography apparatus described.   The X-ray computed tomography apparatus according to claim 2, further comprising a determination unit that determines a predetermined exposure start angle in each scan according to the total number of scans.

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