JP2013192750A - X-ray diagnostic apparatus and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray diagnostic apparatus capable of achieving reduction of exposure to radiation while maintaining required image quality, even in performing image pickup in which a relative moving velocity between a top plate and an X-ray tube changes.SOLUTION: An X-ray diagnostic apparatus includes: a top plate 2a enabling a subject P to lie down; an X-ray tube 3c1 for emitting an X-ray toward the subject P on the top plate 2a; an X-ray detector 3e for detecting the X-ray having passed through the subject P on the top plate 2a; a moving drive section 2b for relatively moving the top plate 2a and the X-ray tube 3c1 in the body axis direction of the subject P on the top plate 2a; a velocity detecting section 12 for detecting the relative moving velocity between the top plate 2a and the X-ray tube 3c1; and a tube current adjusting section 13 for adjusting a tube current supplied to the X-ray tube 3c1 so that the minimum X-ray dose may be stable even if the relative movement velocity between the top plate 2a and the X-ray tube 3c1 changes, depending on the relative movement velocity between the top plate 2a and the X-ray tube 3c1 which is detected by the velocity detecting section 12, where the minimum X-ray dose for obtaining the required image quality is the X-ray dose emitted from the X-ray tube 3c1 depending on the body thickness of the subject P.

Description

  Embodiments described herein relate generally to an X-ray diagnostic apparatus and a method for controlling the X-ray diagnostic apparatus.

  The X-ray diagnostic apparatus irradiates a subject such as a patient with X-rays, detects X-rays transmitted through the subject, and collects X-ray transmission data based on the detected X-ray dose by a data collection device. Thereafter, the X-ray diagnostic apparatus performs reconstruction processing on the X-ray transmission data to generate a slice image (tomographic image) of the subject. As this X-ray diagnostic apparatus, for example, an X-ray tube and an X-ray detector are opposed to each other with a subject on a couch top, and imaging is performed while rotating them around the body axis of the subject. A line CT apparatus (X-ray computed tomography apparatus) has been developed.

  In such an X-ray diagnostic apparatus, since a scan range (imaging range) is usually set before imaging, imaging is performed without rotating the X-ray tube and the X-ray detector, and a scanogram (positioning image) is collected. To do. In this X-ray diagnostic apparatus, the thickness of each part of the subject is converted into a water equivalent thickness using the scanogram, and the tube current value (mA) is determined by the designated SD (standard deviation) (AEC). Products with Auto Exposure Control already exist. In this AEC, the X-ray dose that matches the body thickness of each part of the subject, that is, the tube current is automatically calculated from the scan image, and then the tube current is finely controlled for each rotation of the X-ray tube and the X-ray detector. To do. As a result, unnecessary exposure is suppressed while maintaining the required image quality, and exposure reduction is realized.

  In the X-ray diagnostic apparatus, when imaging by helical scanning, the top plate on which the subject lies is positioned in the body axis direction of the subject on the top plate, that is, from the foot to the head or from the head to the foot. While moving in one direction at the same speed, the X-ray tube and the X-ray detector are rotated around the body axis of the subject to perform imaging. The X-ray irradiation control at this time is performed on the assumption that the moving speed of the top board (relative moving speed between the top board and the X-ray tube) is a constant speed (speed within an allowable range). X-ray irradiation control for realizing exposure reduction is realized by AEC based on the above.

JP 7-124152 A

  However, the variable helical pitch scan (vHP) and the shuttle helical scan that is being realized in recent years are not scans in which the relative movement speed between the top plate and the X-ray tube is constant as described above. Due to the change, there is a case where the intended exposure reduction cannot be realized by the modulation of the tube current by the normal AEC. This is because the X-ray dose (X-ray irradiation density) between slices cannot be controlled because the relative movement amount per unit time (slice) is different.

  The problem to be solved by the present invention is an X-ray diagnostic apparatus capable of reducing exposure while maintaining the required image quality even when imaging is performed in which the relative movement speed of the top plate and the X-ray tube changes. And a method for controlling an X-ray diagnostic apparatus.

  The X-ray diagnostic apparatus according to the embodiment detects a top plate on which the subject lies, an X-ray tube that emits X-rays toward the subject on the top plate, and X-rays that have passed through the subject on the top plate Speed detector that detects the relative movement speed between the top plate and the X-ray tube, the X-ray detector that performs the relative movement of the top plate and the X-ray tube in the body axis direction of the subject on the top plate The X-ray dose of X-rays emitted from the X-ray tube is set to the minimum X-ray dose for obtaining the required image quality according to the body thickness of the subject, and the top plate and the X-ray tube detected by the speed detector A tube current adjusting unit that adjusts a tube current supplied to the X-ray tube so that the minimum X-ray dose remains unchanged even if the relative movement speed between the top plate and the X-ray tube changes according to the relative movement speed of Is provided.

  The control method of the X-ray diagnostic apparatus according to the embodiment includes a top plate on which the subject lies, an X-ray tube that emits X-rays toward the subject on the top plate, and X that has passed through the subject on the top plate. An X-ray diagnostic apparatus for controlling an X-ray diagnostic apparatus comprising: an X-ray detector for detecting a line; and a movement drive unit for relatively moving a top plate and an X-ray tube in a body axis direction of a subject on the top plate A control method that detects the relative movement speed of the top plate and the X-ray tube by the speed detection unit, and requires the X-ray dose of X-rays emitted from the X-ray tube according to the body thickness of the subject. The minimum X-ray dose for obtaining a good image quality, and the minimum X-ray dose changes the relative movement speed between the tabletop and the X-ray tube according to the relative movement speed between the tabletop and the X-ray tube. And adjusting the tube current supplied to the X-ray tube so as not to change.

1 is a diagram illustrating a schematic configuration of an X-ray diagnostic apparatus according to an embodiment. It is a figure which shows schematic structure of a control part with the bed and part of an imaging device with which the X-ray diagnostic apparatus which concerns on embodiment is equipped. It is explanatory drawing for demonstrating the movement of the top plate to the Z-axis direction and the Z-axis direction in the shuttle helical scan which concerns on embodiment. It is a graph which shows the time change of the moving speed of the top plate in the shuttle helical scan which concerns on embodiment. It is a graph which shows the time change of X-ray dose by tube current fixed in the shuttle helical scan which concerns on embodiment. It is a graph which shows X dose fixed by tube current adjustment in the shuttle helical scan which concerns on embodiment. It is explanatory drawing for demonstrating the X-axis direction and the Y-axis direction in the shuttle helical scan which concerns on embodiment. It is a graph which shows the time change of the X-ray dose by the XYZ axial direction modulation of the tube current in the shuttle helical scan which concerns on embodiment. It is a graph which shows the time change of the X-ray dose by the synthetic tube electric current in the shuttle helical scan which concerns on embodiment. It is a flowchart which shows the flow of the imaging process which the X-ray diagnostic apparatus which concerns on embodiment performs.

  An embodiment will be described with reference to the drawings.

  As shown in FIG. 1, an X-ray diagnostic apparatus 1 according to the present embodiment includes a bed 2 on which a subject P such as a patient lies, an imaging device 3 that performs imaging on the subject P on the bed 2, and A control device 4 that controls the bed 2 and the imaging device 3 is provided. An example of the X-ray diagnostic apparatus 1 is an X-ray CT apparatus (X-ray computed tomography apparatus).

  The couch 2 includes a rectangular top plate 2a on which the subject P is placed, and a movement drive unit 2b that supports the top plate 2a and moves it in the horizontal direction and the vertical direction (up and down direction). The movement drive unit 2b has a movement mechanism for moving the top board 2a, a drive source for supplying driving force for the movement, and the like. The couch 2 moves the table 2a to a desired height by the movement drive unit 2b, and further moves the table 2a in the horizontal direction to move the subject P on the table 2a to a desired position.

  The imaging device 3 includes a rotating body 3a that is rotatably provided in a gantry A serving as a casing, a rotation driving unit 3b that rotates the rotating body 3a, an X-ray irradiator 3c that emits X-rays, A high voltage generator 3d for supplying a high voltage to the X-ray irradiator 3c, an X-ray detector 3e for detecting X-rays transmitted through the subject P on the top 2a, and the X-ray detector 3e And a data collection unit 3f that collects the X-rays as X-ray transmission data (X dose distribution data).

  The rotating body 3a is an annular rotating frame that supports and rotates the X-ray irradiator 3c, the X-ray detector 3e, and the like. The rotating body 3a is rotatably held by the gantry A. An X-ray irradiator 3c and an X-ray detector 3e are provided on the rotating body 3a so as to face each other. The X-ray irradiator 3c and the X-ray detector 3e sandwich the subject P on the top 2a. Then, the periphery of the subject P is rotated around the body axis of the subject P.

  The rotation driving unit 3 b is provided in the gantry A of the imaging device 3. The rotation driving unit 3 b performs rotation driving of the rotating body 3 a according to control by the control device 4. For example, the rotation drive unit 3b rotates the rotating body 3a in one direction at a predetermined rotation speed based on the control signal transmitted from the control device 4.

  The X-ray irradiator 3c includes an X-ray tube 3c1 that emits X-rays and an X-ray restrictor 3c2 such as a collimator that narrows the X-rays emitted from the X-ray tube 3c1, and is fixed to the rotating body 3a. Has been. The X-ray irradiator 3c emits X-rays by an X-ray tube 3c1, and the X-rays are narrowed by an X-ray restrictor 3c2 to form a fan beam having a cone angle with respect to the subject P on the top 2a. For example, pyramid-shaped X-rays are irradiated.

  Here, as the X-ray diaphragm 3c2, various types of X-ray diaphragms can be used. For example, an X-ray restrictor of a type in which two X-ray blocking plates such as lead are moved toward and away from each other and the size of an opening (gap) formed by these X-ray blocking plates is appropriately changed. It is possible to use. The X-ray irradiation field (irradiation range) can be adjusted by the X-ray diaphragm 3c2.

  The high voltage generator 3 d is provided in the gantry A of the imaging device 3. The high voltage generator 3d is a device that generates a high voltage to be supplied to the X-ray tube 3c1 of the X-ray irradiator 3c. The high voltage generator 3d boosts and rectifies the voltage supplied from the control device 4, and supplies the voltage to the X-ray tube. To 3c1. The control device 4 controls various conditions such as the waveform of the voltage applied to the high voltage generator 3d, that is, the amplitude and the pulse width, in order to generate a desired X-ray by the X-ray tube 3c1.

  The X-ray detector 3e is fixed to the rotating body 3a so as to face the X-ray irradiator 3c. The X-ray detector 3e converts X-rays that have passed through the subject P on the top 2a into electrical signals and transmits them to the data collection unit 3f. As the X-ray detector 3e, a multi-row multi-channel X-ray detector can be used. This multi-row multi-channel X-ray detector is configured by arranging X-ray detection elements for detecting X-rays in a grid pattern. The channel row is a row in which a plurality of (for example, about several hundred to several thousand) X-ray detection elements are arranged in the channel direction (the direction around the body axis of the subject P). A plurality of rows (for example, 16 rows and 64 rows) are arranged along the body axis direction of P.

  The data collection unit 3 f is provided in the gantry A of the imaging device 3. The data collection unit 3f converts the electrical signal transmitted from the X-ray detector 3e into a digital signal, collects X-ray transmission data (X dose distribution data) that is digital data, and controls the X-ray transmission data. Transmit to device 4.

  The control device 4 includes a control unit 4a that controls each unit, an image processing unit 4b that performs various image processing on X-ray transmission data, a storage unit 4c that stores various programs and various data, and a user (user). ), And a display unit 4e for displaying an image. These control unit 4a, image processing unit 4b, storage unit 4c, operation unit 4d and display unit 4e are electrically connected by a bus line 4f.

  The control unit 4a controls each unit such as the movement drive unit 2b of the bed 2, the rotation drive unit 3b of the imaging device 3, and the high voltage generation unit 3d based on various programs and various data stored in the storage unit 4c. In addition, the control unit 4a also controls the X-ray diaphragm 3c2 of the X-ray irradiator 3c, and further displays various images such as slice images (tomographic images) and scanograms (positioning images) on the display unit 4e. Also controls. As the control unit 4a, for example, a CPU (Central Processing Unit) or the like can be used.

  The image processing unit 4b performs pre-processing using the X-ray transmission data transmitted from the data collection unit 3f as projection data, image reconstruction processing for performing image reconstruction on the projection data, and scan information for generating a scan image. Various image processing such as image generation processing is performed. As the image processing unit 4b, for example, an array processor or the like can be used.

  The storage unit 4c is a storage device that stores various programs, various data, and the like, and stores, for example, slice images, scanograms, and the like as various data. As the storage unit 4c, for example, a hard disk (magnetic disk device), a flash memory (semiconductor disk device), or the like can be used in addition to a ROM (Read Only Memory) and a RAM (Random Access Memory).

  The operation unit 4d is an input unit that receives an input operation by a user, and receives various input operations such as an imaging instruction, image display, image switching, and various settings. For example, an input device such as a keyboard, a mouse, or a lever can be used as the operation unit 4d.

  The display unit 4e is a display device that displays various images such as a slice image, a scano image, and an operation screen of the subject P. As the display unit 4e, for example, a liquid crystal display, a CRT (CRT) display, or the like can be used.

  Here, the above-described X-ray diagnostic apparatus 1 has various imaging modes, such as a scano imaging mode for imaging a scanogram and a tomographic imaging mode for imaging a slice image. Examples of the tomographic imaging mode include a normal multi-slice scan mode (normal CT), a helical scan mode (helical CT), a variable helical pitch scan mode, and a shuttle helical scan mode.

  The scano imaging mode is an imaging mode for imaging a scanogram for setting positioning and a scan range (imaging range) prior to imaging in the tomographic imaging mode. For example, in the scan plan, a scano image is captured in advance, the scano image is displayed on the display unit 4e, the operator confirms the scano image, and inputs the operation unit 4d to set the scan range.

  In capturing a scanogram, the X-ray irradiator 3c and the X-ray detector 3e are fixed at a predetermined position, that is, at a predetermined view angle (for example, 0 degrees or 90 degrees), and the top 2a of the bed 2 is fixed to the subject P. The X-ray detector 3e detects X-rays that are irradiated with X-rays by the X-ray irradiator 3c and transmitted through the subject P on the top plate 2a while moving to a predetermined position in the body axis direction of the X-ray. Collect data. Thereafter, the collected X-ray transmission data is processed by the image processing unit 4b to generate a scano image, the generated scano image is stored in the storage unit 4c, and additionally displayed on the display unit 4e.

  The helical scan mode is an imaging mode that captures a slice image while moving the top 2a at a constant speed (speed within an allowable range) in one direction (for example, a direction from the foot to the head) in the body axis direction of the subject P. The imaging mode in which the speed of the top 2a is changed according to the imaging target region at the time of imaging is the variable helical pitch scan mode. Further, the moving direction of the top plate 2a is alternately changed in two directions in the body axis direction of the subject P (for example, two directions from the foot to the head and from the head to the foot), and the top plate 2a is moved. On the other hand, an imaging mode for capturing a slice image is a shuttle helical scan mode. Thus, the X-ray diagnostic apparatus 1 can perform X-ray imaging in various imaging modes.

  In the imaging of the slice image, the rotating body 3a is rotated by the rotation driving unit 3b, and the X-ray irradiator 3c and the X-ray detector 3e are rotated around the body axis of the subject P on the top 2a and further moved. X-rays are irradiated by the X-ray irradiator 3c while the top plate 2a of the bed 2 is moved in the body axis direction of the subject P by the drive unit 2b. Thereafter, X-rays transmitted through the subject P on the top 2a are detected by the X-ray detector 3e, and X-ray transmission data is collected. Further, the collected X-ray transmission data is processed by the image processing unit 4b to generate a slice image, the generated slice image is stored in the storage unit 4c, and additionally displayed on the display unit 4e.

  Next, the aforementioned control unit 4a will be described in detail with reference to FIG.

  As shown in FIG. 2, the control unit 4a detects the positions (positions in the rotation direction) of the X-ray tube 3c1 and the X-ray detector 3e that rotate around the body axis of the subject P on the top 2a. A detection unit 11, a speed detection unit 12 that detects the moving speed of the top plate 2a from position information of the moving top plate 2a, and a tube current adjustment unit 13 that adjusts the tube current supplied to the X-ray tube 3c1 are provided. Yes.

  These rotational position detection unit 11, speed detection unit 12, and tube current adjustment unit 13 may be configured by hardware such as an electric circuit, or may be configured by software such as a program for executing these functions. Also good. Moreover, you may comprise by the combination of both hardware and software.

  In addition, the movement drive part 2b has the position information acquisition part 2b1 which acquires the position information of the top plate 2a which is a moving mobile body. The position information acquisition unit 2b1 outputs the acquired position information of the top board 2a to the speed detection unit 12. As the position information acquisition unit 2b1, for example, an encoder can be used. This encoder is attached to a drive source such as a motor provided in the movement drive unit 2b.

  The rotation drive unit 3b includes a rotation angle information acquisition unit 3b1 that acquires a rotation angle position of the rotating rotator 3a (an angle position indicating how many times the rotation body 3a is rotated from a predetermined reference position). The rotation angle information acquisition unit 3b1 outputs the acquired rotation angle information of the rotating body 3a to the rotation position detection unit 11. For example, an encoder can be used as the rotation angle information acquisition unit 3b1. This encoder is attached to a drive source such as a motor provided in the rotation drive unit 3b.

  The rotation position detector 11 receives the rotation angle information of the rotating body 3a output from the rotation angle information acquisition unit 3b1, and the positions of the X-ray tube 3c1 and the X-ray detector 3e (positions in the rotation direction) from the rotation angle information. And the rotation position information is output to the tube current adjustment unit 13.

  The speed detection unit 12 receives the position information of the top plate 2a output from the position information acquisition unit 2b1, and determines the moving speed of the top plate 2a from the position information of the top plate 2a (relative between the top plate 2a and the X-ray tube 3c1). Deriving the movement speed). That is, the speed detection unit 12 calculates the amount of movement per unit time from the position information continuously obtained according to the moving top plate 2a, obtains the moving speed of the top plate 2a, and the moving speed information is Output to the current adjustment unit 13.

  The tube current adjusting unit 13 determines the body thickness of the subject P and the top plate 2a based on the rotational position information of the X-ray tube 3c1 and the X-ray detector 3e, the elapsed time from the start of rotation, the moving speed information of the top plate 2a, and the like. The tube current supplied to the X-ray tube 3c1 is adjusted in accordance with the moving speed of. More specifically, the tube current adjusting unit 13 obtains a tube current for obtaining a required image quality according to the body thickness of the subject P, and the moving speed of the top 2a detected by the speed detecting unit 12 is obtained from the obtained tube current. And adjusts the voltage to the X-ray tube 3c1 via the high voltage generator 3d.

  When obtaining a tube current to obtain a required image quality according to the body thickness of the subject P, as AEC, Z-axis direction modulation for modulating the tube current in the body axis direction of the subject, XY-axis direction modulation that modulates at the same time, and XYZ-axis direction modulation that modulates the tube current by combining Z-axis direction modulation and XY-axis direction modulation are used. Thereby, since the tube current is finely controlled at the time of imaging, it is possible to suppress excessive exposure.

  Here, as an example, tube current adjustment when the imaging mode is the shuttle helical scan mode and the AEC is XYZ axial direction modulation will be described with reference to FIGS.

  In the shuttle helical scan mode, as shown in FIG. 3, the top 2a is first moved in the forward direction from the foot to the head in the Z-axis direction that is the body axis direction of the subject P on the top 2a. Then, the reciprocating motion of moving in the return direction (return) from the head to the foot is repeated. Thereby, the top plate 2a and the X-ray tube 3c1 move relatively in both directions of reciprocation.

  At this time, as shown in FIG. 4, the moving speed V of the top plate 2a changes with time. The moving speed V of the top plate 2a gradually increases until reaching a constant maximum speed value (predetermined set value) in both the forward path and the return path, and then gradually after a predetermined time has elapsed since reaching the maximum speed value. It will decrease to. In FIG. 4, the reciprocating motion is shown only once, but this is shown in a simplified manner and is actually repeated a predetermined number of times (other FIGS. 5, 6, 8 and 8). The same applies to FIG. 9). The number of reciprocating operations can be arbitrarily set as necessary.

  In this way, in the shuttle helical scan mode, the moving speed of the top 2a changes, and therefore, as shown in FIG. 5, if the tube current A1 supplied to the X-ray tube 3c1 is constant, the body axis direction of the subject P The X-ray dose B1 for each cross section (slice) orthogonal to is not constant according to the movement speed change of the top 2a. Here, in the bar graph of the X-ray dose B1 in FIG. 5, the horizontal width of one bar is a unit time for obtaining one section. Therefore, when the moving speed of the top plate 2a changes, the moving amount per unit time (slice) is different, so that the X-ray dose between the cross sections is not uniform. For example, the X-ray dose increases as the moving speed of the top plate 2a decreases, and conversely, the X-ray dose decreases as the moving speed increases, and the moving speed of the top plate 2a and the X-ray dose are in an inversely proportional relationship.

  Therefore, as shown in FIG. 6, the tube current (first tube current) A2 supplied to the X-ray tube 3c1 depends on the moving speed of the top plate 2a for each cross section orthogonal to the body axis direction of the subject P. The X-ray dose B2, that is, the X-ray dose between the cross sections (between slices) is adjusted to be constant. For example, the tube current A2 supplied to the X-ray tube 3c1 is adjusted so that the X-ray dose of the entire cross section obtained by imaging becomes the X-ray dose at the constant maximum speed described above.

  On the other hand, in XYZ-axis direction modulation (AEC), as shown in FIG. 7, in addition to the Z-axis direction that is the body axis direction of the subject P on the top 2a, they are orthogonal to each other in the cross-section orthogonal to the Z-axis direction. The tube current is modulated in the X-axis direction and the Y-axis direction. The X axis is horizontal to the placement surface of the top plate 2a, and the Y axis is orthogonal to the placement surface of the top plate 2a. The X-ray tube 3c1 stops at a predetermined view angle such as 0 degrees or 90 degrees when capturing a scanogram, and rotates around the body axis of the subject P on the top 2a when capturing a slice image. To do.

  According to this XYZ axial direction modulation, as shown in FIG. 8, the tube current (second tube current) A3 supplied to the X-ray tube 3c1 has a water equivalent thickness from the scan image for each part of the subject P. And automatically determined by the designated SD (standard deviation). At this time, while maintaining the image SD, that is, the required image quality, the minimum tube current at that time is calculated in the XYZ axis directions. Thereby, the X-ray dose B3 for each cross section orthogonal to the body axis direction of the subject P becomes the minimum X-ray dose that can obtain the required image quality for each part of the subject P.

  Thereafter, the tube current A2 modulated according to the moving speed of the top 2a and the tube current A3 modulated according to the body thickness of the subject P are combined, and as shown in FIG. 9, the X-ray tube 3c1 Is obtained. As a result, the X-ray dose B4 for each cross section orthogonal to the body axis direction of the subject P does not vary according to the speed change even when the moving speed of the top 2a changes, and the region of the subject P The minimum X-ray dose that can obtain the required image quality every time.

  The flow of obtaining the tube current A4 by such synthesis is a concept. Actually, first, the tube current A3 corresponding to the body thickness of the subject P is obtained by XYZ axial direction modulation, and the obtained tube current A3 is calculated as the sky. It adjusts according to the moving speed of the board 2a. At this time, the control unit 4a calculates the ratio of the current speed (the moving speed of the top 2a detected by the speed detecting unit 12) to the maximum speed (predetermined set value) at which the moving speed of the top 2a is constant. The tube current A3 is multiplied by the calculated ratio to obtain the tube current supplied to the X-ray tube 3c1. Thereby, the tube current A3 is adjusted in real time according to the moving speed of the top plate 2a, and becomes the tube current A4 which is the aforementioned combined tube current.

  Next, imaging processing (including tube current adjustment processing) performed by the above-described X-ray diagnostic apparatus 1 will be described with reference to FIG. As in the above example, the shuttle helical scan mode is set as the imaging mode, and XYZ-axis direction modulation is set as the AEC.

  As shown in FIG. 10, first, a desired image SD is set in accordance with a user input operation on the operation unit 4d (step S1). In step S1, for example, when the operation unit 4d is operated by the user and a desired image SD (standard deviation) is input, the image SD is set.

  After the process of step S1, a scano image is captured based on a predetermined tube current (step S2). In this step S2, for example, a scanogram is captured at view angle positions of 0 degrees (plane position) and 90 degrees (side position) and stored in the storage unit 4c. At this time, the irradiation field is maximized.

  At the plane position of 0 degrees, X-rays are detected by irradiating the upper surface of the subject P on the top 2a with X-rays and transmitted through the subject P. As a planar image of the subject P, the AP direction ( A scano image in the front-rear direction is captured. In addition, at the side surface position of 90 degrees, X-rays irradiated to the side surface of the subject P on the top 2a and transmitted through the subject P are detected, and as a side image of the subject P, the LR direction ( A scanogram in the left-right direction is captured.

  After the process of step S2, the tube current by XYZ axial direction modulation (AEC) is acquired (step S3), and then the shuttle helical scan is started based on the acquired tube current (step S4). As described above, in the shuttle helical scan, the moving direction of the top 2a is alternately changed in two directions in the body axis direction of the subject P (for example, two directions from the foot to the head and from the head to the foot). In other words, it is a scan for capturing a slice image while moving the top 2a.

  In the above-described step S3, the tube current A3 is automatically determined according to the image SD set in the above-described step S1 by XYZ axis direction modulation (see FIG. 8). At this time, the thickness of each part of the subject P (the body thickness of the subject P) is converted into a water equivalent thickness from the above-described scan image in the AP direction and the LR direction while maintaining the image SD, that is, the required image quality. Thus, the minimum tube current is calculated in the XYZ axis directions. Thereby, the X-ray dose B3 for each cross section orthogonal to the body axis direction of the subject P becomes the minimum X-ray dose that can obtain the necessary image quality for each part of the subject P.

  In step S4, when the shuttle helical scan is started, the rotational positions of the X-ray tube 3c1 and the X-ray detector 3e are detected by the rotational position detector 11 according to the rotation of the rotating body 3a. Is moved by the speed detector 12 (step S5). Thereafter, the tube current is adjusted according to the rotational position of the X-ray tube 3c1 and the X-ray detector 3e, the moving speed of the top plate 2a, and the like, and supplied to the X-ray tube 3c1 (step S6).

  In step S6 described above, the ratio of the current speed of the top plate 2a detected in step S5 to the maximum speed (predetermined set value) at which the moving speed of the top plate 2a is constant is calculated. A tube current A4 supplied to the X-ray tube 3c1 is obtained by multiplying the above-described tube current A3 (see FIG. 9). Since the tube current A3 changes due to XYZ axis modulation, the tube current A3 is determined by the rotational positions of the X-ray tube 3c1 and the X-ray detector 3e, the elapsed time from the start of rotation, and the like. Since the tube current A4 is obtained in this way, the X-ray dose B4 for each cross section orthogonal to the body axis direction of the subject P is necessary for each part of the subject P even when the moving speed of the top 2a changes. The minimum X-ray dose that can achieve image quality.

  After the process of step S6, it is determined whether or not imaging has been completed (step S7). If it is determined that imaging has not been completed (NO in step S7), the process returns to step S5, and after step S5 The process is repeated. On the other hand, if it is determined that imaging has been completed (YES in step S7), the process ends.

  In step S7, the determination as to whether or not imaging has been completed is made by determining whether or not the top 2a has reached a predetermined imaging completion position, for example. When the imaging mode is the shuttle helical scan mode, it is determined whether or not the reciprocation of the predetermined number of times has been completed and the top 2a has reached a predetermined imaging completion position, and the top 2a is at the predetermined imaging completion position. If it is determined that it has arrived, it is determined that imaging has been completed.

  According to such an imaging process, the tube current A3 obtained by XYZ axis direction modulation is adjusted according to the moving speed of the top plate 2a and supplied to the X-ray tube 3c1. As a result, the X-ray dose irradiated to the subject P lying on the top 2a does not change due to the speed change of the top 2a, but only changes by XYZ axial direction modulation (AEC). For this reason, even when imaging with a change in the speed of the top plate 2a is performed, exposure can be reduced while maintaining the required image quality.

  In the shuttle helical scan, the top plate 2a reciprocates. However, it is important to perform imaging even when a speed change occurs such as switching between the reciprocating movements in order to shorten the scan time (imaging time). It is possible to adjust the tube current in response to such a speed change (see FIG. 4). Similarly, in the variable helical pitch scan, the moving speed of the top plate 2a changes stepwise, for example, but the tube current can be adjusted corresponding to the speed change at this time.

  As described above, according to the embodiment, according to the body thickness of the subject P, the celestial detected by the speed detector 12 is further detected so that the X-ray dose becomes the minimum X-ray dose for obtaining the required image quality. In accordance with the relative movement speed between the plate 2a and the X-ray tube 3c1, the X-ray tube is such that the minimum X-ray dose described above does not change even if the relative movement speed between the top plate 2a and the X-ray tube 3c1 changes. The tube current supplied to 3c1 is adjusted by the tube current adjusting unit 13. Thereby, the tube current is controlled in accordance with the moving speed of the top board 2a in addition to the body thickness of the subject P. For this reason, even when imaging is performed in which the relative movement speed of the top 2a and the X-ray tube 3c1 changes, the X-ray dose does not fluctuate according to the speed change, and the necessary image quality for each part of the subject P can be obtained. Since the minimum X-ray dose that can be obtained is obtained, it is possible to reduce exposure while maintaining the required image quality.

  In particular, since a tube current for obtaining a required image quality is obtained according to the body thickness of the subject P, and the obtained tube current is adjusted according to the moving speed of the top plate 2a detected by the speed detector 12, The tube current can be reliably adjusted according to the body thickness of the specimen P and the moving speed of the top plate 2a, and even when imaging is performed in which the relative moving speed of the top plate 2a and the X-ray tube 3c1 changes. The exposure reduction can be realized while maintaining the image quality required for the operation.

  Further, when the top plate 2a and the X-ray tube 3c1 are alternately moved relative to each other in two directions in the body axis direction of the subject P on the top plate 2a as in the shuttle helical scan, the speed change for switching the two directions is performed. Since the tube current supplied to the X-ray tube 3c1 is adjusted in accordance with the body thickness of the subject P and the moving speed of the top 2a during the moving period involving the movement of the subject P, desired imaging can be executed even during the moving. Therefore, the necessary image quality can be maintained and the exposure can be reduced while shortening the scanning time.

  In the above-described embodiment, the moving speed of the top board 2a that moves during imaging is detected and used. However, the present invention is not limited to this, and the relative moving speed between the top board 2a and the X-ray tube 3c1 is determined. What is necessary is just to be able to detect and use. For example, as the X-ray diagnostic apparatus 1, an X-ray diagnostic apparatus that moves the gantry A instead of the top plate 2a by a movement drive unit (for example, having a rail mechanism, a drive source, a position information acquisition unit, etc.) during imaging. Since the gantry A is a moving body including the X-ray irradiator 3c, the X-ray detector 3e, the rotating body 3a, etc., the moving speed of the gantry A is detected and used. .

  In the above-described embodiment, as an example, the case where the imaging mode is the shuttle helical scan mode and the AEC is the XYZ axial direction modulation is described. However, the present invention is not limited to this. The imaging mode may be a variable helical pitch scan mode, and AEC may be Z-axis direction modulation, XY-axis direction modulation, or the like.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 X-ray diagnostic apparatus 2a Top plate 2b Movement drive part 3c1 X-ray tube 3e X-ray detector 12 Speed detection part 13 Tube electric current adjustment part P Subject

Claims (10)

A tabletop on which the subject lies;
An X-ray tube that emits X-rays toward the subject on the top;
An X-ray detector for detecting X-rays transmitted through the subject on the top plate;
A movement drive unit for relatively moving the top plate and the X-ray tube in the body axis direction of the subject on the top plate;
A speed detector for detecting a relative movement speed between the top plate and the X-ray tube;
According to the body thickness of the subject, the X-ray dose of X-rays emitted from the X-ray tube is set to the minimum X-ray dose for obtaining a required image quality, and the top plate and the X-ray detected by the speed detector The tube current supplied to the X-ray tube is adjusted according to the relative movement speed with the tube so that the minimum X-ray dose remains unchanged even if the relative movement speed between the top plate and the X-ray tube changes. A tube current adjusting unit,
An X-ray diagnostic apparatus comprising:   The tube current adjustment unit obtains a minimum tube current for obtaining a required image quality according to the body thickness of the subject, and the top plate and the X-ray detected by the velocity detection unit for the obtained minimum tube current. The X-ray diagnostic apparatus according to claim 1, wherein the X-ray diagnostic apparatus is adjusted according to a relative moving speed with respect to the tube.   The tube current adjusting unit obtains the minimum tube current to obtain a required image quality according to the body thickness of the subject, and the tube current in the X-axis direction and the Y-axis direction orthogonal to the body axis direction of the subject. The X-ray diagnostic apparatus according to claim 2, wherein the X-ray diagnostic apparatus is modulated.   When obtaining the minimum tube current to obtain the required image quality according to the body thickness of the subject, the tube current adjusting unit, in addition to the X axis direction and the Y axis direction orthogonal to the body axis direction of the subject, The X-ray diagnostic apparatus according to claim 3, wherein the tube current is modulated in a Z-axis direction that is a body axis direction of the subject. The movement drive unit relatively moves the top plate and the X-ray tube alternately in two directions in the body axis direction of the subject on the top plate,
The tube current adjusting unit adjusts the body thickness of the subject and the relative moving speed of the top plate and the X-ray tube detected by the speed detecting unit during a moving period accompanied by a speed change for switching the two directions. The X-ray diagnostic apparatus according to claim 1, wherein a tube current supplied to the X-ray tube is adjusted accordingly. A top plate on which the subject lies; an X-ray tube that emits X-rays toward the subject on the top plate; an X-ray detector that detects X-rays transmitted through the subject on the top plate; A control method of an X-ray diagnostic apparatus for controlling an X-ray diagnostic apparatus comprising a movement drive unit that relatively moves a top plate and the X-ray tube in a body axis direction of a subject on the top plate,
Detecting a relative movement speed between the top plate and the X-ray tube by a speed detector;
According to the body thickness of the subject, the X-ray dose of X-rays emitted from the X-ray tube is set to the minimum X-ray dose for obtaining a required image quality, and the top plate and the X-ray detected by the speed detector The tube current supplied to the X-ray tube is adjusted according to the relative movement speed with the tube so that the minimum X-ray dose remains unchanged even if the relative movement speed between the top plate and the X-ray tube changes. And steps to
A control method for an X-ray diagnostic apparatus, comprising:   In the adjusting step, a minimum tube current for obtaining a required image quality is obtained in accordance with the body thickness of the subject, and the calculated top tube current and the X-ray tube detected by the speed detection unit are obtained. The method of controlling an X-ray diagnostic apparatus according to claim 6, wherein the control is performed according to a relative movement speed of the X-ray diagnostic apparatus.   In the adjusting step, when obtaining a minimum tube current for obtaining a required image quality according to the body thickness of the subject, the tube current is set in the X-axis direction and the Y-axis direction orthogonal to the body axis direction of the subject. The method of controlling an X-ray diagnostic apparatus according to claim 7, wherein the modulation is performed.   In the adjusting step, when obtaining a minimum tube current for obtaining a required image quality according to the body thickness of the subject, in addition to the X-axis direction and the Y-axis direction orthogonal to the body axis direction of the subject, the subject 9. The method of controlling an X-ray diagnostic apparatus according to claim 8, wherein the tube current is modulated in a Z-axis direction that is a body axis direction of the specimen.   In the adjusting step, when the top plate and the X-ray tube are moved relative to each other in two directions in the body axis direction of the subject on the top plate alternately by the movement driving unit, a speed change for switching the two directions is performed. The tube current supplied to the X-ray tube is adjusted according to the body thickness of the subject and the relative movement speed of the top plate and the X-ray tube detected by the speed detection unit during the movement period involving The method for controlling an X-ray diagnostic apparatus according to claim 6, wherein:

Images