JP2006158690A - Radiation ct apparatus and method for controlling radiation of radiation ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation CT apparatus capable of reducing the exposure according to the condition and characteristics of a subject. <P>SOLUTION: The radiation CT apparatus comprises a scanning gantry with an X-ray tube 20 for applying X-rays to the subject H for rotating the X-ray tube 20 around the body axis of the subject H, a table 4 with a cradle 41 on which the subject H is placed for moving the cradle 41 in the direction of the body axis of the subject H, a body movement detecting part 5 for detecting the periodical movement of the subject H, a rotation position specifying part 30a for specifying the rotation position of the X-ray tube 20 relative to the subject H, a body axis directional position specifying part 30b for specifying the position of the X-ray tube 20 relative to the subject H in the direction of the body axis, and an X-ray tube controller 25 for modulating the tube current of the X-ray tube 20 based on the position specified at least either by the rotation position specifying part 30a or by the body axis directional position specifying part 30b and the phase of the periodical movement detected by the body movement detecting means 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radiation CT apparatus capable of adjusting the intensity of radiation applied to a subject and a radiation control method for the radiation CT apparatus.

  In a radiation CT apparatus such as an X-ray CT apparatus, it is known that the exposure to a subject increases while the image quality is improved by increasing the intensity of radiation. That is, regarding the increase / decrease in the intensity of radiation, there is a trade-off relationship between improvement in image quality and reduction in exposure, and it is desirable to increase / decrease the intensity of radiation according to the required image quality.

  As a technique for solving this problem, an X-ray CT apparatus that increases or decreases the intensity of X-rays in synchronization with a heartbeat is known (for example, Patent Document 1). With this technology, for example, by increasing the intensity of X-rays only in a specific phase where pulsation is stable and collecting projection data, it is possible to obtain a high-quality image of the heart in that phase while reducing exposure. it can.

In addition, since the structure and shape of the tomography of the subject are not uniform and the structure and shape of the tomography vary depending on the position in the body axis direction of the subject, the X-ray irradiation angle and the body of the subject are different. The X-ray absorption rate of the subject varies depending on the position in the axial direction. Therefore, a technique for increasing or decreasing the intensity of X-rays according to the relative angle of the subject and the X-ray source around the body axis direction or the relative position in the body axis direction has also been proposed (for example, Patent Document 2).
Japanese Patent Laid-Open No. 2000-189412 JP 2001-178713 A

  However, the technique of emitting X-rays in synchronization with the heartbeat does not consider the reduction of exposure based on the relative position between the subject and the X-ray source in the body axis direction or the rotation direction around the body axis. Therefore, when obtaining a tomographic image at a specific phase of pulsation, useless exposure occurs depending on the relative position between the subject and the X-ray source. On the other hand, the technique of modulating the tube current based on the relative position between the subject and the X-ray source is generally intended to obtain a tomographic image of the entire slice plane, and the tube is adapted to the movement of a specific part such as the heart. It does not modulate the current. That is, the exposure reduction according to the state of the subject that changes with time and the exposure reduction according to the spatial characteristics such as the structure and shape of the subject are not compatible.

  An object of the present invention is to provide a radiation CT apparatus and a radiation control method for the radiation CT apparatus that can reduce exposure according to the state and characteristics of the subject.

  A radiation CT apparatus according to a first aspect of the present invention includes a radiation source that irradiates a subject with radiation, a scanning gantry that rotates the radiation source around a body axis of the subject, and the subject is placed thereon. A table for moving the cradle in the body axis direction of the subject, body motion detecting means for detecting a periodic motion of the subject, and detecting a rotational position of the radiation source relative to the subject. At least one of a rotational position detecting means, a body axis direction position detecting means for detecting the position of the radiation source in the body axis direction with respect to the subject, the rotational position detecting means, and the body axis direction position detecting means. Modulation means for modulating the tube current of the radiation source on the basis of the position detected by one of them and the phase of the periodic movement detected by the body movement detection means.

  Preferably, the modulation means modulates the tube current so that the tube current of the radiation source increases or decreases in a specific phase of the periodic motion.

  Preferably, the modulation means increases the tube current when the position detected by at least one of the rotational position detection means and the body axis direction position detection means is within a predetermined range. The tube current is modulated so as to decrease.

  Preferably, the modulation means identifies a first target tube current that increases or decreases in accordance with the phase of the periodic motion, and a second target tube current that increases or decreases in response to the change in the detected position. Then, a third target tube current is specified based on the first and second target tube currents, and the tube current is modulated so that the tube current becomes the third target tube current. For example, the third target tube current is obtained by various methods such as arithmetic average, geometric mean, sum, product, logical product, maximum value, minimum value, fitting, etc. of the first target tube current and the second target tube current. May be specified.

  A radiation CT apparatus according to a second aspect of the present invention includes a radiation source that irradiates a subject with radiation, a moving unit that moves the radiation source relative to the subject, and a radiation source that is irradiated by the radiation source. Control means for controlling the intensity, wherein the control means is adapted to the intensity of the radiation according to the passage of time based on a predetermined state of the subject and a change in the relative position of the radiation source with respect to the subject. The intensity of the radiation is controlled so as to change.

  Preferably, the radiation source irradiates a predetermined part of the subject that moves periodically, and the time based on the predetermined state is a phase of the periodic movement.

  Preferably, the moving means includes a rotary moving means for rotating the radiation source relative to the subject around a predetermined axis of the subject, and the radiation source in the direction of the predetermined axis. Linear movement means that moves relative to the subject, and the control means responds to a change in at least one of a rotational position of the radiation source relative to the subject and a relative position in the axial direction. And controlling the intensity of the radiation source so as to change the intensity of the radiation source.

  Preferably, the control means is based on a first target radiation intensity that increases / decreases with the passage of time based on the predetermined state and a second target radiation intensity that increases / decreases with a change in the relative position. The intensity of the radiation is controlled so as to be the third target radiation intensity specified. For example, the third target radiation intensity is obtained by various methods such as arithmetic average, geometric mean, sum, product, logical product, maximum value, minimum value, fitting, and the like of the first target radiation intensity and the second target radiation intensity. May be specified.

  According to the radiation control method of the radiation CT apparatus of the present invention, the radiation source of the radiation CT apparatus that reconstructs an image by collecting projection data of the subject at a plurality of positions while moving the radiation source relative to the subject. A radiation control method for controlling radiation intensity, wherein the radiation intensity is changed in accordance with a lapse of time based on a predetermined state of the subject and a change in a relative position of the radiation source with respect to the subject.

  According to the present invention, exposure can be reduced when obtaining a tomographic image of a subject in a specific state.

  FIG. 1 is a block diagram showing an overall configuration of an X-ray CT apparatus 1 as a radiation CT apparatus according to an embodiment of the present invention. The X-ray CT apparatus 1 is configured as a CT apparatus that collects projection data of a subject from a plurality of view directions by so-called helical scanning and performs image reconstruction based on the projection data. The present invention is also applicable to a non-helical scan X-ray CT apparatus.

  The X-ray CT apparatus 1 includes a scanning gantry 2, an operation console 3, an imaging table 4, and a body motion detection unit (electrocardiograph) 5.

  The scanning gantry 2 detects an X-ray from the X-ray tube 20 as a radiation source, a collimator 22 for shaping the radiation from the X-ray tube 20, and the X-ray from the X-ray tube 20, and an electrical signal corresponding to the detected X-ray dose , An X-ray detector 23 that outputs projection data, a data acquisition unit (DAS) 24 that collects projection data based on the electrical signal output from the X-ray detector 23, and an X-ray tube controller 25 that controls the driving of the X-ray tube 20. And a collimator controller 26 that drives and controls the collimator 22. Further, the scanning gantry 2 includes an X-ray tube 20 and an X-ray detector 23, and includes a rotating unit 27 that rotates integrally therewith, and a rotation controller 28 that drives and controls the rotating unit 27. The scanning gantry 2 includes a bore 29 into which a subject is carried, and an X-ray tube 20 and an X-ray detector 23 are disposed to face each other with the bore (cavity) 29 interposed therebetween. For example, the X-ray tube controller 25 controls the tube current (mA) of the X-ray tube 20 based on a control signal from the central processing unit 30 to adjust the intensity of X-rays irradiated by the X-ray tube 20. The rotation unit 27 is driven and controlled based on a control signal from the central processing unit 30 via the rotation controller 28.

  The operation console 3 includes an input device 31 that receives input from the operator, and an image reconstruction process based on projection data collected by the data collection unit 24 based on signals from various devices such as the input device 31 and the scanning gantry 2. A central processing unit 30 for executing the various processes, a display device 32 for displaying a CT image reconstructed by the central processing unit 30, a program, data, and an X-ray CT image used for processing of the central processing unit 30. And a storage device 7 for storing.

  The imaging table 4 includes a cradle 41 on which a subject is placed and which is taken in and out of the bore 29 of the scanning gantry 2. The cradle 41 is driven by, for example, a servo motor (not shown) built in the imaging table 4, and the servo motor is controlled based on a control signal from the central processing unit 30 via a servo amplifier (not shown).

  The body motion detection means 5 is constituted by an electrocardiograph, for example, and outputs a detection signal corresponding to the pulsation of the subject to the central processing unit 30.

  The central processing unit 30 specifies a rotational position identifying unit 30a that identifies (detects) the rotational position of the X-ray tube 20 relative to the subject, and a body axis that identifies (detects) the position of the X-ray tube 20 relative to the subject in the body axis direction. And a direction position specifying unit 30b.

  The rotational position specifying unit 30 a is configured to be able to specify the rotational position of the rotating unit 27. For example, the rotational position of the rotation unit 27 can be specified (detected) by the control amount of the rotation controller 28 instructed by the central processing unit 30. Alternatively, the X-ray CT apparatus 1 is provided with a detection unit that detects the rotation position of the rotation unit 27 and outputs a detection result to the rotation position specifying unit 30a. If the orientation of the subject on the cradle 41 is specified, the rotational position of the rotating unit 27 and the relative position of the X-ray tube 20 with respect to the subject can be converted to each other. The rotation position specifying unit 30a can specify the rotation position of the X-ray tube 20 with respect to the subject. Therefore, in the following, the rotational position of the rotating unit 27 and the relative position of the X-ray tube 20 with respect to the subject may be described without particular distinction.

  The body axis direction position specifying unit 30b is configured as follows, for example. The body axis direction position specifying unit 30b is configured to be able to acquire information for specifying the relative position between the cradle 41 and the subject. The relative position between the subject and the cradle 41 is specified, for example, by acquiring an image of the subject on the cradle 41 taken from one direction by the X-ray CT apparatus 1, which is called a so-called scout image. The body axis direction position specifying unit 30b is configured to be able to specify the position of the cradle 41. For example, the position of the cradle 41 can be specified (detected) by the control amount of the imaging table 4 instructed by the central processing unit 30. Alternatively, the X-ray CT apparatus 1 is provided with a detection unit that detects the position of the cradle 41 and outputs the detection result to the body axis direction position specifying unit 30b. The body axis direction position specifying unit 30b specifies the relative position between the subject and the X-ray tube 20 from the relative position between the subject and the cradle 41 and the position of the cradle 41. If the relative position between the subject and the cradle 41 is specified, the specification of the position of the cradle 41 is nothing but the specification of the position of the X-ray tube 20 with respect to the subject. In some cases, the relative position of the X-ray tube 20 with respect to the subject is not particularly distinguished.

  In the above configuration, the central processing unit 30 and the X-ray tube controller 25 function as adjustment means or control means, the rotating unit 27 functions as rotational movement means, and the imaging table 10 functions as linear movement means.

  As shown in FIG. 2, the cradle 41 places the subject H and moves in the body axis direction (z-axis direction) of the subject. Thereby, the relative position of the subject H and the X-ray tube 20 in the body axis direction changes. On the other hand, as the subject H and the X-ray tube 20 move relative to each other in the body axis direction, the X-ray tube 20 and the X-ray detector 23 rotate around the body axis. Accordingly, the X-ray tube 20 moves spirally with respect to the subject H, and irradiates the subject with X-rays B at a plurality of positions in the body axis direction and a plurality of view directions around the body axis. The intensity of the X-ray B at each position or each time is adjusted to an appropriate value by controlling the tube current (mA) of the X-ray tube 20 by the central processing unit 30 via the X-ray tube controller 25. Is done.

  FIG. 3 is a conceptual diagram showing a tube current control method by the central processing unit 30 and the X-ray tube controller 25. The central processing unit 30 includes a target tube current mAt based on the heartbeat of the subject H, a target tube current mAz based on the relative position of the subject H and the X-ray tube 20 in the body axis direction, and the subject H and the X-ray tube 20. The target tube current mAθ based on the rotational position (tube angle) around the body axis is specified (steps S1 to S3), and the actual target tube current mAa is specified based on each target tube current (step S4). ). Then, an instruction signal is output to the X-ray tube controller 25 so that the tube current of the X-ray tube 20 becomes the actual target tube current mAa (step S5).

  Below, each step S1-S4 is explained in full detail.

  FIG. 4 shows a method of specifying the target tube current mAt based on the heartbeat of the subject (step S1). FIG. 4A is a diagram showing a correspondence relationship between pulsation and target tube current mAt, the horizontal axis is time, the vertical axis of the upper graph is the signal intensity of the electrocardiograph 5, and the vertical axis of the lower graph. Is the tube current.

  The body motion signal due to the heartbeat motion has a systole and a diastole within one cycle, and FIG. 4 shows body motion signals for four cycles. On the other hand, the target tube current mAt indicated by the solid line is set such that the value increases or decreases in synchronization with the heartbeat motion. For example, the intensity of X-rays is set to be increased in a stable period in which heartbeat movement is relatively stable. In FIG. 4, the target tube current mAt is set to a relatively large value attH for a predetermined time interval Tc after t1 after the signal intensity of the electrocardiograph 5 reaches a peak, and is set to a relatively small value atL at other times. An example is shown.

  FIG. 4B is a diagram showing the timing of the time interval Tc at which the target tube current mAt is set large in FIG. 4A converted into a position in the body axis direction, and the horizontal axis is the position in the body axis direction. The vertical axis is the position in the direction perpendicular to the body axis (y-axis direction in FIG. 2). Hc indicated by an ellipse schematically shows the shape of the heart as a predetermined part that performs periodic exercise. Each position z0 to z3 in FIG. 4B corresponds to an intermediate position of each time interval Tc in FIG.

  As described above, the X-ray CT apparatus 1 is configured by a helical scan CT apparatus, and the X-ray tube 20 moves in the body axis direction with respect to the subject H as time elapses. Therefore, increasing the target tube current at a constant period in synchronization with the heartbeat increases the target tube current at each position z0 to z3 in the body axis direction of the heart Hc, as shown in FIG. 4B. It corresponds to. In the non-helical scan, when scanning at each position z0 to z3, if the scan is performed after t1 from the peak of the signal intensity, the time interval Tc of the time interval Tc is the same as in FIGS. 4A and 4B. The position is converted into a position in the body axis direction.

  FIG. 5 shows a method of specifying the target tube current mAz based on the relative position of the subject H and the X-ray tube 20 in the body axis direction (step S2). The upper graph shows the target tube current mAz, the horizontal axis is the position in the body axis direction, and the vertical axis is the tube current. The lower diagram schematically shows the heart Hc, spine Hb, and rib Hr of the subject H, where the horizontal axis is the position in the body axis direction and the vertical axis is the position in the y direction (see FIG. 2). The scales of the upper and lower horizontal axes are the same.

  The amount of X-ray absorption at each part of the subject H is higher in the spine Hb and rib Hr than in the heart Hc. Therefore, in order to reduce the exposure while improving the image quality in the fault where the spine Hb and the rib Hr exist, the X-ray intensity is relatively large at the position in the body axis direction where the spine Hb and the rib Hr exist, It is desirable to make it relatively small at other positions. Therefore, the target tube current mAz indicated by the solid line is set so as to increase or decrease according to the position of the rib Hr or the like.

  An appropriate technique may be used for setting the target tube current mAz with respect to the body axis direction of the subject. For example, an image of a subject called a so-called scout image is acquired in advance, and a user sets a target tube current mAz with respect to a position in the body axis direction via the operation console 3 based on the image, and a storage device 33, the central processing unit 30 may appropriately read and specify the tube current mAz stored in the storage device 33 based on the relative position of the subject H and the X-ray tube 20 in the body axis direction.

  FIG. 6 shows a method of specifying the target tube current mAθ based on the tube angle (step S3). FIG. 6A shows a state in which the X-ray tube 20 rotates around the subject H and is irradiated with X-rays. When the subject H is viewed in the body axis direction, since the cross section of the subject H has anisotropy, the X-ray absorption amount of the subject H varies depending on the tube angle. For example, between the positions θ0 and θ2 and the positions θ1 and θ3, the X1-ray absorption amount is large because the X1-ray transmission distance is longer at the positions θ1 and θ3. Therefore, as shown in FIG. 6B, if the X-ray intensity is relatively low at the positions θ0 and θ2, and the X-ray intensity is relatively large at the positions θ1 and θ3, the exposure dose is reduced. The image quality can be improved.

  An appropriate technique may be used for setting the target tube current mAθ based on such a tube angle. For example, scout images are acquired in advance from two or more view directions, the ellipticity of the subject is specified based on the images, and the target tube current mAθ is set with respect to the tube angle based on the ellipticity. . The specification of the ellipticity based on the scout image and the setting of the target tube current mAθ with respect to the tube angle based on the ellipticity may be performed by the user via the operation console 3, or the central processing unit 30 may use a predetermined calculation formula or data. You may calculate based on a table.

  FIG. 7 shows a method for specifying the target tube current mAp based on the target tube current mAz based on the position in the body axis direction and the target tube current mAθ based on the tube angle, and the horizontal axis represents the body axis direction. The vertical axis represents the tube current. The target tube current mAp is specified in the process of specifying the final target tube current mAa (step S4). However, the target tube current mAa may be specified directly from the target tube currents mAt, mAz, and mAθ without specifying the target tube current mAp.

  The target tube current mAp is specified by reflecting the increase or decrease of the other tube current with respect to one tube current of the target tube currents mAz and mAθ. For example, it is specified by the following formula.

      mAp = mAz × mAθ / mAθ_max (1)

  This calculation formula is obtained by dividing the product of the target tube current mAz and the target tube current mAθ by the maximum value mAθ_max of the target tube current mAθ. According to this calculation formula, as shown in FIG. 7, mAp that increases or decreases with the increase or decrease of the target tube current mAθ is calculated with the target tube current mAz as an envelope. Instead of mAθ_max, an appropriate value may be multiplied, or an appropriate value may be added for correction.

  FIG. 8 shows a method for specifying the target tube current mAa from the target tube currents mAt, mAz, and mAθ. The horizontal axes of the graphs G1, G2, and G3 are time, the position in the body axis direction of the X-ray tube 20 with respect to the subject H, and the tube angle. The scale is adjusted to match. Therefore, the horizontal axis of the graph G4 may be regarded as any of time, position in the body axis direction, and tube angle. The vertical axis represents the tube current.

  The target tube current mAa is specified by reflecting the increase or decrease of the other tube current with respect to one tube current of the target tube currents mAa and mAp. For example, it is specified by the following formula.

      mAa = mAp × mAt / mAt_max (2)

  This calculation formula is obtained by dividing the product of the target tube current mAp and the target tube current mAt by the maximum value mAt_max of the target tube current mAt. According to this calculation formula, the target tube current mAa that increases or decreases as the target tube current mAt increases or decreases is calculated using the target tube current mAp as an envelope. If mAp is calculated by equation (1), as shown in FIG. 8, the target tube current mAa increases and decreases with the increase and decrease of the target tube currents mAt and mAθ using the target tube current mAz as an envelope. It should be noted that instead of mAt_max, an appropriate value may be multiplied, or an appropriate value may be added for correction. Further, mAa may be directly calculated from mAt, mAz, and mAθ without specifying mAp by using an arithmetic expression obtained by substituting Expression (1) for Expression (2).

  When calculating the target tube current mAa, each target tube current mAt, mAz, mAθ needs to be at the same time point (same position). Each target tube current at the same time point may be specified by an appropriate method before the start of scanning or after the start of scanning. For example, before the start of scanning, from various values such as the initial position and conveyance speed of the cradle 41, the initial position and rotation speed of the rotation unit 27, and the correlation between the movement start timing of the cradle 41 and rotation unit 27 and the heartbeat timing. As shown in the horizontal axis of FIG. 8, parameters (time, body axis direction position, tube angle) for changing each target tube current are converted to the same scale, and each target tube current at the same time point is specified. Good. In this case, the identification may be performed by the user or the central processing unit 30. Further, during the scan, the central processing unit 30 identifies the current heartbeat phase, the position in the body axis direction, the tube angle, and identifies each target tube current corresponding to the identified value. As shown in FIG. 8, the target tube currents at the same time may be specified without converting the parameters for changing the target tube currents to the same scale.

  According to the above embodiment, since the tube current is modulated in synchronization with the heartbeat of the body motion and the tube current is modulated based on the relative position between the X-ray tube 20 and the subject H, a specific heartbeat motion is specified. Exposure can be reduced while obtaining a tomographic image in phase with high image quality. Further, since the actual target tube current is specified based on the product of the target tube current based on the heartbeat of body movement and the target tube current based on the relative position between the X-ray tube 20 and the subject H, a simple method is used. The tube current can be appropriately modulated.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The X-ray CT apparatus is not limited to the helical scan type, and may be a non-helical scan. In the case of non-helical scan, the target tube currents mAt, mAz, and mAθ are specified as in the helical scan except that X-rays are not irradiated during movement in the body axis direction, and the final results are based on these products. A target tube current mAa can be specified. The detector may be a single detector type in which detection elements are arranged in a line in the channel direction, or a multi-detector type in which detection elements are arranged in a direction orthogonal to the channel direction (column direction). Good.

  The control of the radiation intensity may be performed by an appropriate method, and is not limited to the control of the tube current. For example, the tube voltage may be used as a control variable for determining the radiation intensity, and the tube voltage may be specified depending on various parameters such as the position in the body axis direction, similar to the tube current.

  A first target tube current and a second target tube current are specified, a third target tube current is specified based on a product of the first and second target tube currents, and the tube current is In the process of modulating the tube current so that the target tube current is 3, not only when the first, second and third target tube currents are directly specified for the tube current, but also in proportion to the tube current. When specifying the first, second and third control amounts or radiation intensity for various control amounts or radiation intensity itself, that is, indirectly specifying the first, second and third target tube currents Including cases.

  The time based on the predetermined state of the subject can be any time as long as exposure can be suppressed while obtaining an appropriate image quality by modulating the intensity of radiation irradiated to the subject over time. Including. For example, it may be the elapsed time since administration of the contrast agent. Further, the periodic motion of the subject region is not limited to the contraction motion of the heart, and may be, for example, the periodic motion of the lung (respiration motion).

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the whole structure of the X-ray CT apparatus of the 1st Embodiment of this invention. The figure which shows the relative position of the subject and X-ray tube in the X-ray CT apparatus of FIG. The conceptual diagram of the modulation method of the tube current of the X-ray CT apparatus of FIG. The figure which shows the modulation method of the tube current based on the heartbeat of the X-ray CT apparatus of FIG. The figure which shows the modulation | alteration method of a tube current based on the relative position of the subject of the X-ray CT apparatus of FIG. The figure which shows the modulation | alteration method of the tube current based on the tube angle of the X-ray CT apparatus of FIG. The figure which shows the modulation method of the tube current based on the tube current specified by the modulation method of FIG.5 and FIG.6. The figure which shows the modulation method of the tube current based on the tube current specified by the modulation method of FIGS.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... X-ray tube, H ... Subject, 23 ... X-ray detector, 2 ... Scanning gantry, 41 ... Cradle, 4 ... Imaging table, 5 ... Body motion detection means, 30a ... Rotation position specification means, 30b ... Body axis Direction position specifying means, 30, 25... Modulating means.

Claims (9)

A scanning gantry comprising a radiation source for irradiating the subject with radiation, and rotating the radiation source around a body axis of the subject;
A cradle on which the subject is placed; a table for moving the cradle in the body axis direction of the subject;
Body motion detecting means for detecting a periodic motion of the subject;
Rotational position detecting means for detecting the rotational position of the radiation source relative to the subject;
Body axis direction position detecting means for detecting the position of the radiation source in the body axis direction relative to the subject;
The tube of the radiation source based on the position detected by at least one of the rotational position detecting means and the body axis direction position detecting means and the phase of the periodic motion detected by the body motion detecting means. Modulation means for modulating the current;
A radiation CT apparatus comprising: The radiation CT apparatus according to claim 1, wherein the modulation unit modulates the tube current so that the tube current of the radiation source increases or decreases in a specific phase of the periodic motion. The modulating means is configured to increase or decrease the tube current when the position detected by at least one of the rotational position detecting means and the body axis direction position detecting means is within a predetermined range. The radiation CT apparatus according to claim 1, wherein the tube current is modulated. The modulation means identifies a first target tube current that increases or decreases according to the phase of the periodic motion, and a second target tube current that increases or decreases according to a change in the detected position. The third target tube current is specified based on the first and second target tube currents, and the tube current is modulated so that the tube current becomes the third target tube current. The radiation CT apparatus according to item 1. A radiation source for irradiating the subject with radiation;
Moving means for moving the radiation source relative to the subject;
Control means for controlling the intensity of radiation emitted by the radiation source;
With
The control means controls the intensity of the radiation so as to change the intensity of the radiation in accordance with a lapse of time based on a predetermined state of the subject and a change in a relative position of the radiation source with respect to the subject. Radiation CT device. The radiation source irradiates a predetermined site that periodically moves the subject,
The radiation CT apparatus according to claim 5, wherein the time based on the predetermined state is a phase of the periodic motion. The moving means is
Rotational movement means for rotating the radiation source relative to the subject around a predetermined axis of the subject;
Linear moving means for moving the radiation source relative to the subject in the direction of the predetermined axis;
With
The control means controls the intensity of the radiation source so as to change the intensity of the radiation source according to a change in at least one of a rotational position of the radiation source with respect to the subject and a relative position in the axial direction. The radiation CT apparatus according to claim 5 or 6. The control means is specified based on a first target radiation intensity that increases or decreases with the passage of time based on the predetermined state and a second target radiation intensity that increases or decreases with a change in the relative position. The radiation CT apparatus according to claim 5, wherein the intensity of the radiation is controlled so that a target radiation intensity of 3 is obtained. A radiation control method for controlling the radiation intensity of the radiation source of a radiation CT apparatus for reconstructing an image by collecting projection data of the subject at a plurality of positions while moving the radiation source relative to the subject,
A radiation control method for a radiation CT apparatus, wherein the radiation intensity is changed in accordance with a lapse of time based on a predetermined state of the subject and a change in a relative position of the radiation source with respect to the subject.

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