JP4286807B2 - Radiation CT system - Google Patents

Description

  The present invention generates a scout image based on projection data obtained by, for example, irradiating a subject (patient) placed on a cradle from a radiation source and detecting the radiation that passes through the subject. The present invention relates to a radiation CT (Computerized tomography) apparatus and a data processing method thereof.

For example, a radiation imaging apparatus such as an X-ray CT imaging apparatus is known (for example, see Patent Document 1).
For example, this apparatus scans a set number of tomographic images perpendicular to the direction along the body axis (z-axis) of the subject by performing a scan such as a helical scan or an axial scan during the main scan. The above-described apparatus can take a tomographic image having a thickness of, for example, about a submillimeter, and can observe in-vivo information of a subject with submillimeter accuracy.

In general, before the main scan, a scout image is taken as a preparation stage for taking a tomographic image of the subject.
In this scan, for example, a gantry portion including an X-ray tube and an X-ray detector is rotated around the z axis (body axis of the subject), and the cradle on which the subject is placed is moved along the body axis direction. Move to shoot.

On the other hand, in scout imaging, the gantry portion including the X-ray tube and the X-ray detector is fixed without rotating around the z axis, and the cradle on which the subject is placed is moved for imaging.
In this scout imaging, an image along the body axis of the subject similar to simple X-ray imaging can be obtained. Since the position information of the subject is obtained in this scout imaging, the scout image is used for an imaging plan for determining an imaging range for the main scan, for example.
Specifically, for example, scout imaging may be performed from either one of the front image and the side image of the subject or from both directions.

As described above, scout imaging is performed as a preceding step of the main scan, and the movement start position and movement end position of the cradle along the body axis direction (z axis) are determined based on the obtained scout image.
Japanese Patent Laid-Open No. 10-314162

In general, the scout shooting range is defined within the movable range of the cradle (patient bed), but it is generally desirable that the shooting range during the above-described scout shooting be wide. This is because the imaging range at the time of the main scan cannot be set outside the scout imaging possible range.
Specifically, as shown in FIG. 12, for the scout imaging possible range ARI, a scout image is generated using projection data in a portion where the moving speed of the cradle is constant, and data at the time of acceleration / deceleration of the cradle is not used. . For this reason, generally, the shootable range ARI at the time of scout shooting is smaller than the cradle movable range ARC. For example, even if the cradle can move 1000 mm in the body axis direction (z-axis direction), the scout imaging range ARI is about 900 mm excluding the acceleration / deceleration movement range.

For example, when projection data obtained when the cradle moves at a constant speed is displayed in order as image data of one line in a scout image, the view (View) position along the z direction of each line image is at a constant interval. Therefore, it is possible to generate an appropriate image without causing a positional contradiction in the scout image.
However, since the projection position at the time of acceleration / deceleration does not have a fixed interval between the view positions along the z direction at the time of acquisition, if the projection data is simply arranged and displayed in order as one line image, the image position along the z direction is displayed. A scout image containing contradiction is generated.

That is, when a scout image at the time of acceleration / deceleration is simply generated by a conventional method, a scout image that is longer than the original length along the z-axis direction is generated. Therefore, an apparatus capable of obtaining a high-quality scout image even during acceleration / deceleration movement is desired.
Further, as described above, X-ray irradiation is performed in a range outside the imaging range, and therefore the X-ray irradiation time is relatively long.

  An object of the present invention is to provide a radiation CT apparatus capable of obtaining a high-quality scout image even when the cradle is accelerated or decelerated without increasing X-ray exposure during scout imaging, and data processing thereof It is to provide a method.

  Another object of the present invention is to provide a radiation CT apparatus capable of shortening the irradiation time of radiation during scout imaging, and a data processing method thereof.

  In order to achieve the above object, a radiation CT apparatus according to a first aspect of the present invention detects, by a detection means, radiation that is irradiated from a radiation generation means to a subject placed on a cradle and passes through the subject. A radiation CT apparatus for generating a scout image according to the obtained projection data, wherein the radiation control means controls the relative position of the radiation generation means, the detection means and the cradle, and the drive control means. An image for generating the scout image based on the projection data based on the detection result of the detection means and the relative position at the time of relative acceleration movement or deceleration movement of the radiation generation means and the detection means and the cradle. Generating means.

  The data processing method of the radiation CT apparatus according to the second aspect of the present invention is obtained by detecting, by the detection means, radiation that is irradiated from the radiation generation means to the subject placed on the cradle and passes through the subject. A data processing method of a radiation CT apparatus for generating a scout image according to projection data, the first step of controlling a relative position of the radiation generation means, the detection means, and the cradle, and the first The scout image is obtained based on the projection data based on the detection result of the detection means and the relative position at the time of relative acceleration movement or deceleration movement of the radiation generation means, the detection means and the cradle according to the step of A second step of generating

  According to the present invention, high-quality scout images can be obtained even during relative acceleration movement or deceleration movement of the radiation generation means and detector and the cradle on which the subject is placed during scout imaging. A radiation CT apparatus and a data processing method thereof can be provided.

  Further, it is possible to provide a radiation CT apparatus capable of shortening the irradiation time of radiation during scout imaging and a data processing method thereof.

[First Embodiment]
An X-ray CT apparatus 1 as a radiation CT apparatus according to an embodiment of the present invention includes an X-ray tube and a detector, which are radiation generating means, and a cradle on which a subject is placed at the time of scout imaging performed before a main scan. Projection data is collected even during acceleration movement or deceleration movement of relative linear movement along the body axis direction (z-axis direction), and a scout image is generated based on the collected projection data.
Embodiments according to the present invention will be described below with reference to the drawings.

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. FIG. 2 is a configuration diagram showing a main part of the X-ray CT apparatus 1 shown in FIG.
As shown in FIG. 1, the X-ray CT apparatus 1 according to the present embodiment includes a scanning gantry 2, an operation console 3, and a subject transport unit 4.
Each component is connected by, for example, a data communication line.

  The scanning gantry 2 scans the subject moving in the imaging space 29 by the subject transport unit 4 with X-rays based on the control signal CTL 30a from the operation console 3, for example, and uses the projection data of the subject as raw data. Then, a signal indicating the content is output to the operation console 3.

  The scanning gantry 2 scans the subject supported by the cradle 101 moved to the imaging space 29 by the cradle moving unit 102 of the subject transport unit 4 described later, and obtains projection data of the subject as raw data.

  As shown in FIG. 1, the scanning gantry 2 includes an X-ray tube 20, an X-ray tube moving unit 21, a collimator 22, an X-ray detector 23, a data collecting unit 24, an X-ray controller 25, a collimator controller 26, and a rotating unit 27. And a gantry controller 28.

  In the scanning gantry 2, an X-ray tube 20 and an X-ray detector 23 are arranged so as to sandwich an imaging space 29 into which a subject is carried. And the collimator 22 is arrange | positioned so that the X-ray from the X-ray tube 20 may be shape | molded.

  Each part of the scanning gantry 2 will be described.

  The X-ray tube 20 is, for example, a rotary anode type and irradiates X-rays. As shown in FIG. 2, the X-ray tube 20 irradiates X-rays having a predetermined intensity to the imaging region of the subject via the collimator 22 based on a control signal CTL 251 from the X-ray controller 25. The X-rays radiated from the X-ray tube 20 are formed into, for example, a cone shape by the collimator 22 and irradiated to the X-ray detector 23 through the subject. The X-ray tube 20 rotates around the subject about the body axis direction z of the subject by the rotating unit 27 in order to irradiate X-rays from the view direction around the subject during the main scan. During the scout imaging, the X-ray tube 20 does not rotate around the subject.

  As shown in FIG. 2, the X-ray tube moving unit 21 determines the radiation center of the X-ray tube 20 based on the control signal CTL 252 from the X-ray controller 25 and the body of the subject in the imaging space 29 in the scanning gantry 2. Move along the axial direction z.

As shown in FIG. 2, the collimator 22 is disposed between the X-ray tube 20 and the X-ray detector 23. The collimator 22 is composed of two plates each provided in the channel direction i and the column direction j.
Based on the control signal CTL 261 from the collimator controller 26, the collimator 22 moves the two plates provided in each direction independently, and blocks the X-rays emitted from the X-ray tube 20 in each direction. It is molded into a cone and the X-ray irradiation range is adjusted.

The X-ray detector 23 detects X-rays irradiated from the X-ray tube 20 and transmitted through the subject, and generates projection data of the subject based on the detection result.
The X-ray detector 23 rotates around the subject by the rotating unit 27 together with the X-ray tube 20 during the main scan. The X-ray detector 23 detects X-rays irradiated from around the subject and transmitted through the subject, and generates projection data. During scout imaging, the X-ray detector 23 does not rotate around the subject.

Further, as shown in FIG. 2, the X-ray detector 23 includes a plurality of detection elements 23a.
The X-ray detector 23 includes a channel direction i along the rotational direction in which the X-ray tube 20 rotates around the body axis direction z of the subject by the rotating unit 27 during the main scan, and the X-ray tube. The detection elements 23a are two-dimensionally arranged in an array in the column direction j along the rotation axis direction that is the central axis when the rotation unit 20 is rotated by the rotation unit 27.
The X-ray detector 23 forms a cylindrical concave curved surface by a plurality of detection elements 23a arranged two-dimensionally.

The detection element 23a constituting the X-ray detector 23 includes, for example, a scintillator (not shown) that converts detected X-rays into light, and a photodiode (not shown) that converts light converted by the scintillator into charges. The X-ray detector 23 is configured as a solid state detector.
The detection element 23a is not limited to this. For example, the detection element 23a may be a semiconductor detection element using cadmium tellurium (CdTe) or the like, or an ionization chamber type detection element 23a using xenon (Xe) gas.

The data collection unit 24 is provided for collecting projection data from the X-ray detector 23.
The data collection unit 24 collects projection data detected by each detection element 23 a of the X-ray detector 23 and outputs it to the operation console 3.
As shown in FIG. 2, the data collection unit 24 includes a selection / addition switching circuit (MUX, ADD) 241 and an analog-digital converter (ADC) 242.

The selection / addition switching circuit 241 selects projection data from the detection element 23a of the X-ray detector 23 in accordance with the control signal CTL303 from the central processing unit 30, or changes the combination and adds the results to analog. Output to digital converter 242.
The analog-to-digital converter 242 converts the projection data selected by the selection / addition switching circuit 241 or added in an arbitrary combination from an analog signal to a digital signal and outputs it to the central processing unit 30.

As shown in FIG. 2, the X-ray controller 25 outputs a control signal CTL 251 to the X-ray tube 20 in accordance with a control signal CTL 301 from the central processing unit 30 to control X-ray irradiation.
The X-ray controller 25 controls, for example, the tube current from the X-ray tube 20 and the irradiation time. Further, during the main scan, the X-ray controller 25 outputs a control signal to the X-ray tube moving unit in accordance with the control signal CTL 301 from the central processing unit 30, and sets the radiation center of the X-ray tube 20 in the body axis direction z. Control to move.

  As shown in FIG. 2, the collimator controller 26 outputs a control signal CTL 261 to the collimator 22 in response to the control signal CTL 302 from the central processing unit 30 to shape the X-rays emitted from the X-ray tube 20. 22 is controlled.

  As shown in FIG. 1, the rotating unit 27 has a cylindrical shape, and an imaging space 29 is formed therein. During the main scan, the rotating unit 27 rotates around the subject in the imaging space 29 around the body axis direction z in accordance with the control signal CTL 28 from the gantry controller 28.

  The rotating unit 27 includes, for example, an X-ray tube 20, an X-ray tube moving unit 21, a collimator 22, an X-ray detector 23, a data collection unit 24, an X-ray controller 25, a collimator controller 26, and the like. The positional relationship between the subject carried into the space 29 and each part relatively changes in the rotation direction. By rotating the rotation unit 27 during the main scan, the X-ray tube moving unit 21 can irradiate the subject from around the subject for each of a plurality of view directions. The line detector 23 can detect each view direction. The rotating unit 27 tilts in response to a control signal CTL 28 from the gantry controller 28. For example, the rotating unit 27 can be tilted along the body axis direction z with the isocenter of the imaging space 29 as the center.

  As shown in FIGS. 1 and 2, the gantry controller 28 outputs a control signal CTL 28 to the rotating unit 27 based on the control signal CTL 304 from the central processing unit 30 of the operation console 3, and rotates and tilts the rotating unit 27. (Tilt).

  The operation console 3 will be described.

  As shown in FIG. 1, the operation console 3 includes a central processing unit 30, an input device 31, a display device 32, and a storage device 33.

The central processing unit 30 is configured by a computer, for example, and comprehensively controls the entire apparatus of the X-ray CT apparatus 1.
As shown in FIG. 1, the central processing unit 30 includes a control unit 41 and an image generation unit 61.

For example, the control unit 41 performs overall control of each component of the apparatus by executing a program stored in the memory.
For example, the control unit 41 receives a scan condition input to the input device 31 by an operator, and outputs a control signal CTL 30a to each component based on the scan condition to execute a scan.
Specifically, the control unit 41 outputs a control signal CTL 30 b to the subject transport unit 4 and causes the subject transport unit 4 to transport the subject to the imaging space 29.
Further, the control unit 41 outputs a control signal CTL 301 to the X-ray controller 25 so that X-rays are emitted from the X-ray tube 20. And the control part 41 outputs the control signal CTL302 to the collimator controller 26, controls the collimator 22, and shape | molds X-ray | X_line. In addition, the control unit 41 outputs a control signal CTL 303 to the data collection unit 24 and controls to collect projection data obtained by the detection element 23 a of the X-ray detector 23.

The image generation unit 61 reconstructs an image of the tomographic plane of the subject based on the projection data collected by the data collection unit 24 of the scanning gantry 2.
For example, at the time of the main scan, the image generation unit 61 performs preprocessing such as sensitivity correction and beam hardening correction on projection data from a plurality of view directions by an axial scan or the like, and then performs reprocessing by a filter back projection method. A configuration is performed, and an image of a cross section of the subject is reconstructed and generated.
In addition, the image generation unit 61 generates a scout image based on data indicating a relative position and projection data based on a detection result of the detection unit when the cradle is relatively accelerated or decelerated by the drive control unit 111 described later. Generate.

  The input device 31 of the operation console 3 is composed of input devices such as a keyboard and a mouse, for example. The input device 31 inputs various information such as scan conditions and subject information to the central processing unit 30 based on an input operation by the operator.

  The display device 32 displays an image of the tomographic plane of the subject reconstructed by the image generation unit 61 under the control of the central processing device 30.

The storage device 33 is constituted by a memory, for example, and stores various data such as an image of a tomographic plane of the subject reconstructed by the image generation unit 61, a scout image generated at the time of scout imaging, a program, and the like.
In the storage device 33, the stored data is accessed to the central processing unit 30 as necessary.

  The subject transport unit 4 will be described. The subject transport unit 4 includes a so-called cradle.

The subject transport unit 4 is provided to transport the subject between the inside and the outside of the imaging space 29.
FIG. 3 is a configuration diagram of the subject transport unit 4 of the X-ray CT apparatus 1 shown in FIG.
As illustrated in FIG. 3, the subject transport unit 4 includes a table unit (also referred to as a cradle) 101, a cradle moving unit 102, and a drive control unit 111.

  The cradle 101 is provided to support the subject. The cradle 101 has a placement surface on which the subject is placed. In addition, as shown in FIG. 3, the cradle 101 has a horizontal direction H along the body axis direction z of the subject placed on the placement surface and a vertical direction perpendicular to the horizontal plane by the cradle moving unit 102. V is moved to V and carried into the photographing space 29.

  The cradle moving unit 102 is provided for moving the cradle 101. The cradle moving unit 102 moves the cradle 101 between the inner side and the outer side of the imaging space 29. The cradle moving unit 102 includes a horizontal moving unit 102a and a vertical moving unit 102b.

The horizontal moving unit 102a moves the cradle 101 in the horizontal direction H. The horizontal moving unit 102a includes, for example, a roller driving mechanism (not shown), and drives the roller by an actuator to move the cradle 101 in the horizontal direction H.
In the present embodiment, the horizontal direction H that is the moving direction of the horizontal moving unit 102a and the body axis (z-axis direction) are defined to be the same direction.

  The vertical movement unit 102b moves the cradle 101 in the vertical direction V. The vertical movement unit 102b includes, for example, an arm-type drive mechanism (not shown), and moves the cradle 101 in the vertical direction V by changing the angle between two intersecting arms.

  The drive control unit 111 receives, for example, the control signal CTL30b of the central processing unit 30, and drives the cradle moving unit 102a to move it at a set speed such as cradle 101 acceleration movement, constant speed movement, or deceleration movement. .

  FIG. 4A is a diagram for explaining the movement start position of the table unit (cradle) 101. FIG. 4B is a diagram for explaining the movement end position of the cradle 101.

  At the start of movement of the cradle 101, for example, as shown in FIG. 4A, the X-ray tube moving unit 21 and the X-ray detector 23 are positioned near the chest of the subject. The cradle 101 starts moving from the movement start position along the body axis (z-axis) direction of the subject. For example, as shown in FIG. 4B, the X-ray tube moving unit 21 or the X-ray detector. The movement ends when 23 is located near the abdomen of the subject.

FIG. 5 is a flowchart for explaining the operation of the X-ray CT apparatus 1 shown in FIG. FIG. 6 is a diagram for explaining the operation of the X-ray CT apparatus 1 shown in FIG.
The operation at the time of scout imaging of the X-ray CT apparatus 1 will be described with reference to FIGS.

In step ST1, the central processing unit 30 fixes the X-ray tube 20 and the X-ray detector 23 without rotating at the time of scout imaging.
In step ST2, the central processing unit 30 controls the drive control unit 111 to move the table unit (cradle) 101 to the linear movement start position CS1 as shown in FIG.
In step ST3, the central processing unit 30 controls the drive control unit 111 to start linear movement of the cradle 101 as shown in FIG.
In step ST4, the central processing unit 30 controls the drive control unit 111 to accelerate the linear moving speed of the cradle 101 based on a predetermined function. In the present embodiment, a case where the predetermined function is linear with respect to time as shown in FIG. 6 will be described.
This predetermined function associates each time with the linear moving speed by a calculation formula format or a table format.

In step ST5, the central processing unit 30 accelerates the projection data D0 (z, View, j, i) represented by the linear movement position z, the view position view, the detector number j, and the channel number i. Collected by the line detector 23.
Further, the central processing unit 30 generates a scout image as will be described later based on the projection data collected by the X-ray detector 23 during the acceleration movement and the position of the cradle 101.

  In step ST6, central processing unit 30 determines whether or not the linear movement speed of cradle 101 has reached, for example, a constant speed (predetermined speed) Vc shown in FIG. 6, and as a result of the determination, has not reached the constant speed. If it is determined, the process returns to step ST4 to collect data. On the other hand, if the constant speed Vc is reached in the determination in step ST6, the process proceeds to step ST7.

  In step ST7, when determining that the cradle 101 has reached a constant speed, the central processing unit 30 controls the drive controller 111 to move the cradle 101 in the z-axis direction at a constant speed Vc from the constant speed start position CS2. It moves along with a constant speed.

In step ST8, the central processing unit 30 collects projection data D0 (z, View, j, i) by the X-ray detector 23 while the cradle 101 is moving at a constant speed.
Further, the central processing unit 30 generates a scout image as will be described later based on the projection data collected by the X-ray detector 23 during the constant speed movement and the position of the cradle 101.

  In step ST9, the central processing unit 30 determines whether or not the cradle 101 has moved to the constant speed end position SE1, and proceeds to the processing of step ST10 when determining that the cradle 101 has moved to the constant speed end position SE2. If it is determined that it has not moved to the end position SE2, the process returns to step ST4, and data collection at a constant speed is continued.

In step ST10, the central processing unit 30 controls the drive control unit 111 to decelerate the linear moving speed of the cradle 101 based on a predetermined function.
For example, as shown in FIG. 6, a case where the predetermined function is linear with respect to time will be described.

In step ST11, the central processing unit 30 uses the X-ray detector 23 to collect projection data D0 (z, view, j, i) during which the cradle 101 is decelerating.
Further, the central processing unit 30 generates a scout image as described later based on the projection data collected by the X-ray detector 23 during the deceleration movement and the position of the cradle 101.

  In step ST12, the central processing unit 30 determines whether or not the cradle 101 has reached the stoppable speed, and if it determines that the cradle 101 has not reached the stoppable speed, the process returns to step ST10 and further decelerates. On the other hand, if it is determined in step ST12 that the cradle 101 has reached the stoppable speed, the process proceeds to step ST13.

  In step ST13, the central processing unit 30 controls the drive control unit 111 to stop the linear movement of the cradle 101 along the body axis direction (z-axis direction) at the movement stop position CE2.

In step ST14, the central processing unit 30 performs an imaging plan for determining an imaging range at the time of the main scan based on the generated scout image.
In step ST15, the central processing unit 30 performs the main scan imaging based on the imaging plan generated in step ST14.

  FIG. 7 is a flowchart for explaining an operation of obtaining a scout image when the cradle of the X-ray CT apparatus 1 shown in FIG. 1 moves at a constant speed. 8A to 8D are diagrams for explaining projection data and a scout image. FIG. 8A is a diagram for explaining the projection data D0 collected during the constant speed movement. FIG. 8B is a diagram for explaining a scout image generated based on the projection data D0 shown in FIG.

In step ST102, the central processing unit 30 performs an initial process for generating a scout image.
In step ST104, the central processing unit 30 obtains projection data D0 (n) at the nth view position.
In step ST106, the central processing unit 30 performs correction processing such as cone beam reconstruction weighting on the projection data D0 (n) at the nth view position.
In step ST108, the central processing unit 30, for example, based on the projection data D0 (n) obtained at the nth view position as shown in FIG. 8A, as shown in FIG. The nth line image data L0 (n) in the scout image is generated, and the nth line image data L0 (n) is added to the scout image.

  In step ST110, the central processing unit 30 determines whether or not the line image data from step 102 to ST108 described above has been generated for all view positions that are moving at a constant speed. If it is determined that line image data has not been generated for all view positions, the process returns to step ST104. On the other hand, if it is determined in step ST110 that line image data has been generated for all view positions during constant speed movement, the process proceeds to step ST112.

  In step ST112, the central processing unit 30 causes the display device 32 to display the scout image obtained during the constant speed movement.

  FIG. 8C is a diagram for explaining the projection data D0 collected during the acceleration movement. FIG. 8D is a view for explaining a scout image generated based on the projection data D0 shown in FIG. FIG. 9 is a flowchart for explaining an operation of generating a scout image when the cradle of the X-ray CT apparatus 1 shown in FIG. 1 is accelerated or decelerated.

  The difference between the operation shown in FIG. 9 and the operation shown in FIG. 7 is that the operation shown in step ST107 is performed between step ST106 and step ST108. The difference will be mainly described.

In step ST102, the central processing unit 30 performs initial processing for generating a scout image during acceleration movement or deceleration movement.
In step ST104, the central processing unit 30 obtains projection data D0 (n) at the nth view position.
In step ST106, the central processing unit 30 performs correction processing such as cone beam reconstruction weighting on the projection data D0 (n) at the nth view position.

During constant speed movement, the position of the projection data D0 (n) at the nth view position and the position of the nth line image data L0 (n) in the scout image are the same.
However, as shown in FIGS. 8C and 8D, the acquisition position of the nth projection data D0 (n) during acceleration movement or deceleration movement and the nth line image in the scout image. The position of the data L0 (n) does not match.

  Therefore, in step ST107, the central processing unit 30 determines the (n−1) th projection data D0 (n) located in the vicinity of the image position of the nth line image data L0 (n) along the z-axis direction. -1) and the nth projection data D0 (n), and based on the (n-1) th projection data D0 (n-1) and the nth projection data D0 (n), The n′th line image data L0 (n ′) is generated by weighted addition processing.

  Next, processing for obtaining the view position (number) from the position of the cradle 101 by calculation will be described.

  The position L along the moving direction of the cradle 101 is obtained by calculation as shown in the cradle speed S, the view position V, and Expression (1).

  Further, the view position V at the cradle position L (mm) is obtained by calculating an inverse function V of the position L = P (V) along the moving direction of the cradle 101 as shown in Expression (2).

  V = Q (L) (2)

[First example]
For example, when the speed S (v) of the cradle 101 is as shown in Equation (3), the position L = P (V) along the body axis (z-axis) direction of the cradle is as shown in Equation (4). It is obtained by calculation using the constant a.
Further, the view position V is obtained by calculation using a constant C as shown in Expression (5).

  S (v) = a × v (3)

[Second specific example]
For example, a case will be described in which the cradle speed S (v) is accelerated until it reaches a constant speed b, moves for a set time at the constant speed b, and then decelerates.
Specifically, the speed S (v) of the cradle is equal to the constant position a when the view position v is v <V1, and the view position v is V1 ≦ V. When v ≦ V2, constant velocity motion is performed using the constant b as shown in the equation (7), and when the view position v is V2 <v, the constant c is used as shown in the equation (8). A constant acceleration motion (deceleration motion) is performed until becomes zero.

  S (v) = a × v; (v <V1) (6)

  S (v) = a × V1 = b; (V1 ≦ v ≦ V2) (7)

  S (v) = b−c × (v−V2); (V2 <v) (8)

  Then, with respect to the cradle speed S (v) shown in the equations (6) to (8), integration is performed from 0 to V with respect to the view position v as shown in the equation (1), and the equation (2) is obtained. As described above, the view position V (view) at the position L (mm) of the cradle is obtained by performing an operation for generating an inverse function.

  Hereinafter, as shown in FIG. 9, in step ST108, the central processing unit 30 converts the n′th line image data L0 (n ′) generated by the interpolation processing into the n′th line of the scout image. As image data, the n'th line image data is added to the scout image.

  In step ST110, the central processing unit 30 determines whether or not the line image data from step 102 to ST108 described above has been generated for all view positions during acceleration movement or deceleration movement. If it is determined that line image data has not been generated for all view positions during the middle or decelerating movement, the process returns to step ST104. On the other hand, if it is determined in step ST110 that line image data has been generated for all view positions during acceleration movement or deceleration movement, the process proceeds to step ST112.

  In step ST112, the central processing unit 30 causes the display device 32 to display a scout image obtained during acceleration movement or deceleration movement.

  As described above, the central processing unit 30 includes the (n−1) th projection data D0 (n−1) and the nth image data that are located in the vicinity of the image position of the nth line image data L0 (n). Projection data D0 (n) is obtained, and based on the (n-1) th projection data D0 (n-1) and the nth projection data D0 (n), the nth line image data L0 is obtained. Since (n) is generated by interpolation processing, a high-quality scout image that does not extend along the body axis direction (z-axis direction) in the scout image can be generated.

Further, as shown in FIG. 6, in the X-ray CT apparatus 1 according to the present embodiment, the cradle movement range ARC is the same as the scout imaging range ARI and is the range from the acceleration movement start position CS1 to the deceleration movement end position CE2, Since it becomes smaller than the cradle movement range ARC of the general CT apparatus as shown in FIG. 12, the X-ray irradiation time for the subject can be reduced.
Further, since the cradle movement range ARC is relatively small, it is possible to reduce the restraint time for the examination on the subject.

[Second Embodiment]
The second embodiment according to the present invention will be described below.

  The X-ray CT apparatus 1a according to the second embodiment of the present invention generates a scout image using projection data obtained by MDCT (Multi detector row CT) in which a plurality of X-ray detectors 23 are arranged. In such MDCT, a plurality of images can be taken by one scan. The CT apparatus 1a according to the second embodiment includes a multi-detector, reduces the scan time during scout imaging, and reduces the exposure dose. Hereinafter, description will be given with reference to the drawings.

FIG. 10 is a diagram for explaining the operation of the X-ray CT apparatus 1a according to the second embodiment of the present invention.
The X-ray CT apparatus 1a according to the present embodiment has a cradle movement range by a geometric arrangement configuration of the X-ray tube 20 and the multi-row X-ray detectors 23 arranged in a matrix as shown in FIG. X-rays are also irradiated outside the ARC, and projection data is collected by the multi-row detector 23. Then, based on the collected projection data, for example, as shown in FIG. 10, a scout image is generated based on the projection data obtained during acceleration or deceleration.

  When generating the nth line image data L0 (n), the central processing unit 30 specifies a view position and a row (ROW) position corresponding to the nth line image data L0 (n) Interpolation processing is performed based on the projection data D0 (n) at the specified view position and low position, and a scout image is generated based on the processing result.

  FIG. 11 is a flowchart showing a specific example of the operation of the X-ray CT apparatus according to the second embodiment of the present invention. The operation of the X-ray CT apparatus according to the present embodiment will be described with reference to FIG. Since the operation during the constant speed movement is a general process, a description thereof will be omitted, and the operation during the acceleration movement or the deceleration movement will be described.

In step ST102, the central processing unit 30 performs an initial process for generating a scout image.
In step ST104a, in the central processing unit 30, the X-ray detector 23 at the nth view position and the mth row position obtains projection data (n, m) during acceleration movement or deceleration movement.

Here, the central processing unit 30 obtains the number of views (position) and the row position of the detector row from the position of the cradle.
For example, the central processing unit 30 sets the number of detector rows t (from the detector center to the body axis z direction), the width dp (mm) of one row of detectors, the cradle movement start position Ls, and the cradle movement end position Le. Thus, when the cradle center position L is smaller than the movement start position Ls of the cradle (L <Ls), the cradle center position L is generated by the calculation shown in Expression (9). Here, the value of the view position V is 0.

  When the cradle center position L is larger than the movement end position of the cradle (L> Le), the central processing unit 30 generates the detector row number t by the calculation shown in Equation (10). Here, the view position V value is Vend.

  As described above, the central processing unit 30 obtains the view position and the row position based on the number of detector rows t obtained from the equations (9) and (10), the equation (2), and the like.

  In step ST106a, the central processing unit 30 adds weighted addition such as cone beam reconstruction weight to the projection data (n, m) by the X-ray detector 23 at the mth row position and the nth view position. Apply processing.

  In step ST107a, the central processing unit 30 determines the n'th line in the scout image based on the obtained projection data (n, m) at the mth row position and the nth view position. The (n−1) th projection data D0 (n−1) and the nth projection data D0 (n) located in the vicinity of the image position of the image data L0 (n ′) are obtained, and the (n− 1) Based on the nth projection data D0 (n-1) and the nth projection data D0 (n), the n'th line image data L0 (n ') is generated by interpolation processing.

  In step ST108a, the central processing unit 30 sets the n'th line image data L0 (n ') generated by the interpolation processing as the n'th line image data in the scout image, and the n'th line image data. Add line image data to the scout image.

  In step ST109, central processing unit 30 determines whether or not the processing from steps 104a to ST108a described above has been performed for all low positions during acceleration movement or deceleration movement, and as a result of the determination, no processing is performed. If it is determined, the process returns to step ST104a. On the other hand, if it is determined in step ST109 that processing has been performed for all the row positions, the process proceeds to step ST110.

  In step ST110, the central processing unit 30 determines whether or not the line image data for the above-described steps 104a to ST108a has been generated for all view positions during acceleration movement or deceleration movement. If it is determined that line image data has not been generated for all view positions during the middle or decelerating movement, the process returns to step ST104a. On the other hand, if it is determined in step ST110 that line image data has been generated for all view positions during acceleration movement or deceleration movement, the process proceeds to step ST112.

  In step ST112, the central processing unit 30 causes the display device 32 to display a scout image obtained during acceleration movement or deceleration movement.

As described above, in the present embodiment, the interpolation processing is performed based on the projection data by the plurality of X-ray detectors 23 positioned outside the cradle movement range along the movement direction (z direction). Since the scout image is generated according to the processing result, the photographing range can be further reduced.
Specifically, as shown in FIG. 10, the imaging range ARI can be made larger than the cradle movement range ARC.
In addition, since the moving range ARC of the cradle is smaller than the shooting range ARI, the scan time at the time of scout shooting can be shortened. In addition, the exposure dose can be reduced.

  Further, there may be a plurality of projection data at different view positions or different row positions corresponding to the n'th line image data in the scout image. Or there may be a plurality of data corresponding to close positions. In such a case, a scout image with higher image quality can be obtained by using all or part of a plurality of projection data at different view positions or different low positions for interpolation processing.

Further, as described above, the photographing range ARI can be set to be equal to or larger than the moving range of the cradle.
Further, since the cradle movement range ARC is shorter than the imaging range ARI, the restraint time for imaging the subject is shortened.
In addition, since a scout image corresponding to a range that is not less than the movable range ARC of the cradle can be created, an imaging plan for the main scan can be performed beyond the movable range ARC of the cradle.
For the same reason as described above, the plan for the X-ray tube current (Auto mA) can be performed in a wider imaging range than before, and the exposure can be further reduced.
Further, even if the cradle speed is constant, image noise can be reduced by using all corresponding data at the same position.
Further, even when the cradle speed is constant, the X-ray exposure can be reduced by using all corresponding data at the same position.
In addition, since the data density of the acceleration / deceleration part is large with respect to the distance, the X-ray tube current in the acceleration / deceleration part can be reduced by using a large amount of overlapped part data, thereby reducing the exposure. it can.

[Third Embodiment]
The third embodiment according to the present invention will be described below.

  In the present embodiment, when the subject is scanned by the X-ray CT apparatus 1, the operation of the control unit 41 of the central processing unit 30 controlling each unit is different. Except for this point, the present embodiment is the same as the first embodiment. For this reason, description is abbreviate | omitted about the overlapping part.

  FIG. 13 is a flowchart showing a process flow of scout data collection in the third embodiment according to the present invention. Moreover, FIG. 14 is a figure which shows the time change of a scout scan in 3rd Embodiment concerning this invention. In FIG. 14, FIG. 14A is a diagram showing the moving speed v of the cradle 101 corresponding to time t, the vertical axis is the moving speed v of the cradle 101, and the horizontal axis is the time t. FIG. 14B shows the moving speed v of the cradle 101 in correspondence with the moving position z of the cradle 101. The vertical axis indicates the moving speed v of the cradle 101, and the horizontal axis indicates the moving position z of the cradle 101. It is. FIG. 14C is a diagram showing the tube current value I supplied to the X-ray tube 20 at the movement position z of the cradle 101, where the vertical axis is the tube current value I and the horizontal axis is the movement position z of the cradle 101. is there.

  First, in step P1, as shown in FIG. 13, the X-ray tube 20 and the X-ray detector 23 are rotated in the direction of taking a scout image and stopped.

  In Step P2, the cradle 101 of the subject transport unit 4 is started to move linearly in the z direction.

In step P3, If now moving speed target speed v _c of the cradle 101, the X-ray in X-ray tube current value proportional to the moving speed as the X-ray tube current is the X-ray tube current I _c of the target gradually To output.

Here, as shown in FIG. 14 (a), during the movement from the movement start time t ₀ when the cradle 101 is stopped until the first hour t ₁ after a predetermined time, the moving velocity v of the cradle 101 is predetermined constant speed v is accelerated cradle 101 so that the _c of moving. That is, as shown in FIG. 14 (b), during the period from the movement start position z ₀ of the cradle 101 is stopped, until the constant speed movement start position z ₁ cradle 101 starts moving at a constant velocity v _c The cradle 101 is accelerated and moved at a constant acceleration. Then, in this case, as shown in FIG. 14 (c), to be proportional to correspond to the moving speed v of the cradle 101, to increase the tube current value I to the X-ray tube 20 to a predetermined value I _c Scan the subject. That is, the product of the X-ray irradiation time per unit length in the direction in which the cradle 101 moves with respect to the scanning gantry 2 and the tube current value to the X-ray tube 21 is made constant, and the cradle 101 with respect to the scanning gantry 2 is made constant. The X-ray controller 21 controls the X-ray tube 21 so that the X-ray irradiation amount per unit length in the direction in which the X-axis moves is constant.

  In step P4, scout image X-ray transmission data is collected.

At step P5, moving the cradle 101 at a constant predetermined speed v _c.

Here, as shown in FIG. 14 (a), from the first hour t ₁ described above, until a second time t ₂ after a predetermined time, to move the cradle 101 at a constant predetermined speed v _c. That is, as shown in FIG. 14 (b), during the period from a constant speed movement start position z ₁ described above, to constant velocity movement end position z ₂ cradle 101 has finished moving at a constant velocity v _c, I constant moving the cradle 101 at a predetermined speed _{v c.} Then, in this case, as shown in FIG. 14 (c), as the predetermined value I _c of the tube current value I constant in the X-ray tube 20, scanning a subject.

  In Step P6, the cradle moving speed is reduced.

Here, as shown in FIG. 14A, the moving cradle 101 is stopped so that the cradle 101 stops between the second time t ₂ and the third time t ₃ after a predetermined time elapses. Is decelerated at a constant rate. That is, as shown in FIG. 14 (b), the constant speed movement end position z ₂ described above, during the period until the stop position z ₃ where the cradle 101 is stopped, and stops by decelerating the cradle 101 at a constant deceleration . Then, in this case, as shown in FIG. 14 (c), to be proportional to correspond to the moving speed v of the cradle 101, the constant tube current values I to X-ray tube 20 from a predetermined value I _c Reduce the rate and scan the subject. Note that the cradle moving speed may be decelerated at a position where the cradle position z satisfies the following mathematical formula (11).

  In step P7, when the end point of the scout image X-ray transmission data collection is reached, the X-ray transmission data collection is terminated.

  In step P8, the data collection is finished, the X-ray output is stopped, and the cradle 101 is stopped so that the set movement amount L of the cradle satisfies the following formula (12).

  When the subject is scout scanned as described above, as shown in FIG. 14C, the X-ray tube current is controlled to correspond to the speed in the acceleration / deceleration section.

  When performing a scout scan of the subject as described above, acceleration / deceleration is nonlinear (non-linear) in addition to the case where acceleration / deceleration is controlled linearly as shown in FIG. You may go to

    FIG. 15 is a diagram illustrating the control of the X-ray tube current when the speed change of the cradle 101 is nonlinear. In FIG. 15, FIG. 15A is a diagram showing the moving speed v of the cradle 101 corresponding to the moving position z of the cradle 101, the vertical axis is the moving speed v of the cradle 101, and the horizontal axis is the cradle 101. This is the moving position z. FIG. 15B is a diagram showing the tube current value I supplied to the X-ray tube 20 at the movement position z of the cradle 101, where the vertical axis is the tube current value I and the horizontal axis is the movement position z of the cradle 101. is there.

  As shown in FIG. 15, when acceleration / deceleration is performed in a non-linear manner, for example, the acceleration / deceleration is changed like an S-shaped curve, and the X-ray tube current control is matched to the speed even when the ride is performed comfortably. Change it like an S curve. Also at this time, the X-ray tube current is controlled in proportion to the speed so that the X-ray irradiation dose per unit length in the z direction is constant.

  The data collection pulses used to trigger this scout data collection can be roughly divided into the following two methods.

(1) z-direction distance equidistant data collection pulse: The interval between data collection pulses is constant on the z-direction distance.

(2) Data collection pulse for a fixed time: The interval between data collection pulses is a fixed interval in the time direction.

  FIG. 16 is a diagram illustrating a case of z-direction distance equidistant data collection pulses. In FIG. 16, FIG. 16A is a diagram showing the relationship between the moving speed v of the cradle 101 and the time interval Δt at which data is collected. The vertical axis is the moving speed v of the cradle 101 and the horizontal axis is the horizontal axis. Time t. FIG. 16B is a diagram showing the relationship between the tube current value I supplied to the X-ray tube 20 and the time interval Δt for collecting data, where the vertical axis represents the tube current value I and the horizontal axis. Is time t. FIG. 17 is a diagram showing how a scout image is reconstructed in the case of z-direction distance equidistant data collection pulses.

  The z-direction distance equidistant data collection pulse is a z-direction coordinate such as an encoder signal, graticule signal, or magnet scale signal attached to the cradle 101 of the subject transport unit 4 or a pulse that is a source thereof or a divided signal of the signal. And so on. Here, the data collection time Δt is made to correspond to the moving speed v of the cradle 101 so as to obtain projection data at every fixed distance interval at which the cradle 101 moves relative to the scanning gantry 2. That is, as shown in FIG. 16, the data collection time Δt for one view (one line) changes from a gradually long time width on the time axis to a short time width along with the acceleration during acceleration, and gradually decreases during deceleration. It changes from time width to longer time width with deceleration. At a constant speed, the data collection time Δt has a constant time width and data collection is performed.

  When an image of a scout image is reconstructed from this view data, as shown in FIG. 17, one view becomes data of one line having a width Δz in the z direction of the scout image as it is. Or, if multiple views become one line of data with a width of Δz in the z direction of the scout image, perform bundling processing, averaging processing, weighted addition processing, etc. of multiple constant view data in the z direction or time direction. Process it to be one line of data.

FIG. 18 is a diagram illustrating a flow of creating data of each line of a scout image in the case of a constant interval width data pulse in the z direction.
Here, n is an integer, z _s is the start Z coordinate of the weighted addition range, z _e is the end Z coordinate of the weighted addition range, and z _i is the scout view data Z coordinate in the weighted addition range. Yes, S (i) is the weighted and added scout view data, that is, the bundled scout view data (scout projection data), and w _i is the weighting coefficient for the view data.

  As shown in FIG. 18, in step C1, n = 0 is set.

In step C2, z _s = n · Δz and z _e = (n + 1) Δz.

In step C3, look for view data for the range of _{z s ≦ z i ≦ z e} .

In step _{C4, z s ≦ z i ≦} z e in the range of view data data (n ₁₎ for extracting ~data (n _m).

  In the case of a data acquisition pulse with a constant interval width in the z direction due to an encoder signal, etc., if the data acquisition system is made so that the data of one view of the acquired data becomes one line of the scout image as it is, a constant speed is obtained. For each part, acceleration part, and deceleration part, "one view of data collection" is always extracted and becomes "one line of scout image" as it is.

Similarly, in the case of a data acquisition pulse with a constant interval width in the z direction by an encoder signal, etc., the data collected for the n _m views is bundled or averaged or weighted to form one line of the scout image. If a data collection system is created, a fixed number of _nm views are always extracted for the constant speed portion, acceleration portion, and deceleration portion, and the bundle processing or averaging processing or weighting is extracted. Adds to make a “one line of scout image”.

In step C5, view data in the range of z _s ≦ z _i ≦ z _E is obtained by bundling processing, averaging processing, or weighted addition as shown in the following formula (13) or formula (14).

Data of 1 views and data collection, if it is not one line of scout, to create each line data of the scout image, bundled data from multiple views of a certain number n _m which is the data acquisition or average By processing or weighted addition, the data of each line of the scout image can be reconstructed. An example of the weighting coefficient in the average or weighted addition is shown in FIG.

  In step C6, it is determined whether all scout view data has been collected. If yes, exit; if no, go to step C7.

  In step C7, n = n + 1. Then, the process returns to step C2.

  From the viewpoint of the irradiated X-ray dose, when the speed is slow during acceleration and deceleration, a small X-ray dose and X-ray with an X-ray tube current are irradiated in proportion to the speed. Further, at a constant speed portion where the speed is high, an X-ray dose and an X-ray current corresponding to the X-ray tube current are increased in proportion to the speed.

  The speed at a constant speed is v (mm / s), the speed at acceleration / deceleration is k · v (mm / s) (where 0 ≤ k ≤ 1), and the X-ray tube current at a constant speed is a ( Assuming mA), the X-ray tube current during acceleration / deceleration is k · a (mA).

  The X-ray dose R at a unit length Δz (mm) at a constant speed is equivalent to mA · s, and is represented by the following formula (15).

  Further, the X-ray dose R at the unit length Δz (mm) during acceleration / deceleration is equivalent to mAs, and is expressed by the following formula (16), which is the same as the X-ray dose during a constant speed.

  In other words, if the X-ray dose and X-ray tube current are controlled in proportion to the velocity, the X-ray dose per unit length in the z direction will be the same, and the S / N of the image noise of the obtained scout image will be the z direction In addition, the acceleration / deceleration part and the constant speed part are uniform, and the image quality is constant.

  FIG. 19 is a diagram showing a case of data collection pulses at regular intervals. In FIG. 19, FIG. 19A is a diagram showing the relationship between the moving speed v of the cradle 101 and the time interval Δt for collecting data, the vertical axis is the moving speed v of the cradle 101 and the horizontal axis is the horizontal axis. Time t. FIG. 19B is a diagram showing the relationship between the tube current value I supplied to the X-ray tube 20 and the time interval Δt for collecting data, where the vertical axis represents the tube current value I and the horizontal axis. Is time t. FIG. 19C is a diagram showing the relationship between the moving speed v of the cradle 101 and the interval Δz of the position of the cradle 101 when data is collected. The axis is the cradle movement position z. FIG. 20 is a diagram illustrating a state in which a scout image is reconstructed in the case of a constant time interval data collection pulse.

  As shown in FIG. 19, the fixed time data collection pulse is realized by a fixed period width clock signal in the time direction such as an internal clock. Here, the control unit 41 controls the scanning gantry 2 so as to obtain projection data at regular time intervals at which the cradle 101 moves relative to the scanning gantry 2. As shown in FIG. 19, the data collection time Δt for one view (one line) is a constant time for both the acceleration and deceleration and the constant speed in the constant time data collection pulse. In other words, when considering the z-direction distance coordinate system, the z-direction width Δz of one view (one line) during acceleration changes from a narrow z-direction width to a wide z-direction width during acceleration, and one view (1) during deceleration. The data is collected while the z-direction width Δz of the line changes from a wide z-direction width to a narrow z-direction width.

  When a scout image is reconstructed from this view data, as shown in FIG. 20, a plurality of eye views are bundled together at a higher speed during acceleration / deceleration, and the width of the scout image in the z direction is 1 As a line data, at a constant speed, one view becomes one line data of the width Δz of the scout image as it is. Or, when a plurality of views become data of one line of a scout image, bundling processing, averaging processing, and weighted addition processing are required for view data during acceleration / deceleration. However, the number of views to be added is not a fixed number.

  FIG. 21 is a diagram showing a flow of data creation for each line of a scout image in the case of a data acquisition pulse for a certain period of time.

  As shown in FIG. 21, in step C11, n = 0.

  In Step C12, the following mathematical formula (17) is satisfied.

In step C13, look for view data for the range of _{z s ≦ z i ≦ z e} .

In step _{C14, z s ≦ z i ≦} z range _e of view data data (n ₁₎ for extracting ~data (n _k).

  In the case of a data acquisition pulse for a fixed time, the number n (t) of collected view data that changes to one line of a scout image at a constant speed portion and an acceleration / deceleration portion varies. In other words, if the n (t) view data collected is a single line with a width in the z direction of the scout image of Δz, n (t) is a function of time t. This n (t) varies depending on the acceleration / deceleration pattern.

In step C15, determining the view data in the range of z _s ≦ z _i ≦ z _e by the following equation (18) or formula (19).

  The data of each line of the scout image can be reconstructed by averaging or weighted adding the data of a plurality of views of the n (t) views collected in order to create each line data of the scout image.

  An example of the weighting coefficient for averaging or weighted addition is shown in FIG.

  In step C6, it is determined whether all scout view data has been collected. If YES, the process ends. If NO, go to Step C7.

  In step C7, n = n + 1. Then, the process returns to step C2.

  From the viewpoint of the irradiated X-ray dose, the X-ray dose at the unit length Δz (mm) is the same as during the z-direction distance equidistant data collection pulse, both during constant speed and during acceleration / deceleration. Is equivalent to mA · S, is expressed by the following formula (20), is constant, and is the same as in the case of a data acquisition pulse for a certain period of time.

  In other words, the X-ray dose per unit length in the z direction is the same if the X-ray dose and the X-ray tube current are controlled in proportion to the speed even in the case of a data acquisition pulse for a certain period of time. The S / N of noise is uniform in the acceleration / deceleration part and constant speed part in the z direction, and the image quality is constant.

  FIG. 23 is a flowchart showing an outline of operations of scout data collection and image reconstruction of the X-ray CT apparatus 100 of the present invention.

  In step S1, as described above, first, the X-ray tube 20 and the X-ray detector 23 are rotated by a set angle with respect to the subject and stopped. A scout scan operation is performed while linearly moving the cradle 101 of the subject transport unit 4, and X-ray detector data D0 (view, j, i) represented by a view angle view, a detector row number j, and a channel number i. ) Is added to the table linear movement z-direction position Ztable (view), and X-ray detector data is collected.

  In step S2, the X-ray detector data D0 (view, j, i) is preprocessed and converted into projection data. As shown in FIG. 24, the preprocessing includes step S21 offset correction, step S22 logarithmic conversion, step S23 X-ray dose correction, and step S24 sensitivity correction.

  In step S3, the preprocessed channel data is arranged in a line in the x direction, and further, the scout image is obtained by arranging the line data in the z direction as the cradle of the imaging table advances in the z direction.

  In the description of the data acquisition pulse used for the scout image data acquisition trigger, the view data acquisition method using two types of data acquisition pulses, the z-direction distance equidistant data acquisition pulse and the constant time data acquisition pulse, and its view Describes the image reconstruction method for one line of scout image data, and realizes the image quality that makes the S / N constant of the image noise in the z direction at that time, and further requires the reduction of exposure dose and optimization He stated that the X-ray irradiation dose should be proportional to the speed of the table.

  However, the above-described data collection method and image reconstruction method for one line of scout image data from view data have been described on the premise of one row of X-ray detectors. Next, an example of data processing for image reconstruction of a multi-row X-ray detector when the X-ray detector becomes a multi-row X-ray detector is shown below. From the viewpoint of data collection, this is the same as the case of the X-ray detector in one row.

In the case of a single row of X-ray detectors, a scout image was created simply by arranging the X-ray detector data of one view collected at each time in the z direction. However, in the case of the multi-row X-ray detector 23, as shown in FIG. 25, the X-ray detector data of the ch channel at time t _i and the 1 row of k columns are represented as d (ch, k, t _i ) Then, the scout image S (ch, t _i ) is calculated at each time and each column in consideration of improving the S / N by adding the data of a plurality of views as shown in the following equation (21). The X-ray detector data of the line detector 23 is added to reconstruct the scout image.

  In this case, a weighting factor may be applied as shown in the following formula (22) in order to increase the time resolution.

  In step S4, post-processing such as image filter superimposition and data value conversion is performed on the scout image to obtain a final scout image D31 (x, y).

  In post-processing image filter superimposition processing, if the final scout image is D31 (x, y), the data after image filter convolution is D32 (x, y), and the image filter is Filter (x, y), This is performed as shown in Equation (23).

  When an edge enhancement type filter is used for this image filter, it can be converted into a scout image that is easy to see visually.

  The obtained scout image is displayed on the display device 32.

When the scout image is displayed on the display device 32, if the scout image S (ch, t _i ) is displayed as it is on the monitor screen M (x, y), the X-ray detector has an arc shape as shown in FIG. Appears to be distorted on the monitor screen. In order to avoid this, arc-to-line conversion is performed as shown in FIG. 26, and the data det (ch) of each channel of the arc-shaped X-ray detector is changed to X-ray detector data P (x) rearranged on the X-axis. Can be matched.

  In this case, det (ch) is converted to P (x) so as to satisfy the following formula (24). Here, fcd is the distance between the X-ray focal point and the rotation center, fdd is the distance between the X-ray focal point and the detector, and Δp indicates the detector channel pitch.

  By performing such address conversion, the corresponding data is interpolated or weighted to rearrange the X-ray detector data at equal intervals on the x-axis. This rearrangement by address conversion can suppress the geometric distortion on the scout image that occurs because the X-ray detector has an arc shape.

  By arranging this X-ray detector data P (x) in the x-axis direction of the screen and P (x) that can be collected in time series in the y-axis direction of the screen, the scout image is displayed on the monitor screen M (x, y) Can be displayed.

  As described above, when the subject is scanned in this embodiment, the horizontal moving unit 102a of the cradle moving unit 102 accelerates or decelerates the horizontal direction H in the imaging space 29 of the cradle 101 supporting the subject. Let me move. Then, the scanning gantry 2 scans projection data from the subject in association with at least one of the movement position and the movement time of the cradle unit 101 that is accelerated and decelerated by the horizontal moving unit 102a of the cradle moving unit and moves in the imaging space 29. Acquired by performing a scan. Here, the X-ray controller determines the tube current to the X-ray tube 21 so that the X-ray irradiation amount irradiated to the subject per unit time is proportional to the moving speed at which the cradle 101 moves relative to the scanning gantry 2. Control. Thereafter, the image generation unit 61 generates an image of the tomographic plane of the subject based on the projection data acquired in association with at least one of the movement position and the movement time of the cradle 101.

  As described above, in the present embodiment, the cradle 101 is used because the scanning gantry 2 performs scanning so that the moving speed at which the cradle 101 moves is proportional to the amount of X-ray irradiation applied to the subject per unit time. The amount of X-ray irradiation per unit length in the moving direction is constant. For this reason, the S / N of the image noise of the scout image is constant between the positions in the moving direction of the cradle 101, and a constant image quality can be realized. In addition, the X-ray tube current is controlled in proportion to the speed, the X-ray irradiation dose per unit length in the z direction is controlled to be constant, and the X-ray tube current is not output more than necessary. Optimization of radiation dose can be realized.

  Therefore, according to the present embodiment, compared to the cradle movable range, it is possible to realize a scout image photographing possible range in the scout scan as wide as possible in the z direction, and X-ray exposure reduction in the scout scan, and Image noise uniformity in the z direction in the image quality of a scout image can be realized.

  Note that the present invention is not limited to this embodiment, and can be arbitrarily modified.

  For example, even when the cradle speed is constant, there may be a plurality of projection data corresponding to (or in the vicinity of) the same position in consideration of all view positions and low positions. Therefore, when the n'th line image of the scout image is created when the cradle speed is constant, the line image may be generated by interpolation using all projection data in the vicinity of the position. Thus, by generating a scout image using a plurality of projection data, image noise in the scout image can be reduced, and a higher-quality scout image can be obtained.

  Specifically, the drive control unit 111 relatively moves the cradle at a constant speed under the control of the central processing unit 30, and the image generation unit 61 corresponds to the image data of the nth line in the scout image. Based on a plurality of projection data obtained as a result of detection by the X-ray detector 23 at the view position and the low position, image data of the nth line in the scout image is generated, and the scout image is generated based on the generation result. It may be generated.

  Further, since image noise can be reduced, the amount of X-ray irradiation can be reduced, and exposure can be reduced.

  Further, in the above-described embodiment, the operation according to the present invention described above is performed on the assumption that the view interval is constant and the interval of the data acquisition time is constant because the view interval is constant. It is not something that can be done.

For example, the scout image may be generated by synchronizing the data acquisition time and the z-direction position (that is, by making the data acquisition time interval non-uniform).
Specifically, in the central processing unit 30, the image generation unit 61 corresponds to the nth line image data in the scout image based on the relative position along the moving direction of the cradle by the drive control unit 111. The data acquisition time of the projection data by the X-ray detector 23 is determined, and a scout image is generated based on the projection data obtained at the determined data acquisition time.
By doing so, a high-quality scout image without distortion can be obtained.

  Further, the image reconstruction method of the scout image by the multi-row X-ray detector may be as shown in the embodiment or may be another similar method.

  In this embodiment, an edge-enhanced image filter is superimposed on the scout image to convert it into an easy-to-see scout image, but various filter coefficients can be considered for this, but all have the same effect. Can be put out.

  Although this embodiment is written based on a medical X-ray CT apparatus, a scout scan such as an X-ray CT-PET apparatus or an X-ray CT-SPECT apparatus combined with an industrial X-ray CT apparatus or another apparatus. Available at.

  The present invention is a radiation CT that generates a scout image based on projection data obtained by irradiating a subject (patient) placed on a cradle from a radiation generation source and detecting the radiation transmitted through the subject. Applicable to equipment.

FIG. 1 is a block diagram showing the overall configuration of an X-ray CT apparatus 1 as a radiation CT apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a main part of the X-ray CT apparatus 1 shown in FIG. FIG. 3 is a configuration diagram of the subject transport unit 4 of the X-ray CT apparatus 1 shown in FIG. FIG. 4 is a diagram for explaining the operation of the subject transport unit 4 of the X-ray CT apparatus 1 shown in FIG. (A) is a figure showing an example of a movement start position at the time of scout photography. (B) is a figure showing an example of a movement end position at the time of scout photography. FIG. 5 is a flowchart for explaining the operation of the X-ray CT apparatus 1 shown in FIG. FIG. 6 is a diagram for explaining the operation of the X-ray CT apparatus 1 shown in FIG. FIG. 7 is a flowchart for explaining an operation of obtaining a scout image when the cradle of the X-ray CT apparatus 1 shown in FIG. 1 moves at a constant speed. In FIG. 8, (a) to (d) are diagrams for explaining projection data and a scout image. (A) is a figure for demonstrating the projection data D0 collected at the time of constant speed movement. (B) is a figure for demonstrating the scout image produced | generated based on the projection data D0 shown to (a). (C) is a figure for demonstrating the projection data D0 collected at the time of acceleration movement. (D) is a figure for demonstrating the scout image produced | generated based on the projection data D0 shown to (c). FIG. 9 is a flowchart for explaining an operation of generating a scout image when the cradle of the X-ray CT apparatus 1 shown in FIG. 1 is accelerated or decelerated. FIG. 10 is a diagram for explaining the operation of the X-ray CT apparatus 1a according to the second embodiment of the present invention. FIG. 11 is a flowchart showing a specific example of the operation of the X-ray CT apparatus according to the second embodiment of the present invention. FIG. 12 is a diagram for explaining the operation of a general X-ray CT apparatus. FIG. 13 is a flowchart showing a process flow of scout data collection in the third embodiment according to the present invention. FIG. 14 is a diagram showing temporal changes in scout scanning in the third embodiment according to the present invention. FIG. 15 is a diagram showing the control of the X-ray tube current when the speed change (acceleration) of the cradle of the imaging table is non-linear. FIG. 16 is a diagram illustrating a case of z-direction distance equidistant data collection pulses. FIG. 17 is a diagram showing how a scout image is reconstructed in the case of z-direction distance equidistant data collection pulses. FIG. 18 is a diagram illustrating a flow of creating data of each line of a scout image in the case of a constant interval width data pulse in the z direction. FIG. 19 is a diagram showing a case of data collection pulses at regular intervals. FIG. 20 is a diagram illustrating a state in which a scout image is reconstructed in the case of a data acquisition pulse at regular intervals. FIG. 21 is a diagram showing a flow of data creation for each line of a scout image in the case of a data acquisition pulse for a certain period of time. FIGS. 22A and 22B are diagrams illustrating examples of weighting factors when image reconstruction is performed on scout image data, where FIG. 22A illustrates an average weighting factor and FIG. 22B illustrates a weighted addition weighting factor. ing. FIG. 23 is a flowchart showing a schematic operation of the X-ray CT apparatus according to the embodiment of the present invention. FIG. 24 is a flowchart showing details of the preprocessing. FIG. 25 is a diagram showing an example of scout image reconstruction in the case of a multi-row X-ray detector. FIG. 26 is a diagram showing an arc / straight line change in the case of an arc-shaped multi-row X-ray detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus, 2 ... Scanning gantry, 3 ... Operation console, 4 ... Subject conveyance part, 20 ... X-ray tube, 21 ... X-ray tube moving part, 22 ... Collimator, 23 ... X-ray detector, 24 Data collection unit, 25 X-ray controller, 26 Collimator controller, 27 Rotating unit, 28 Gantry controller, 30 Central processing unit, 31 Input device, 32 Display device, 33 Storage device, 41 Control Reference numeral 61: Image generation unit, 101: Cradle, 102: Cradle moving unit, 111: Drive control unit, 241: Selection / addition switching circuit (MUX, ADD), 242: Analog-digital converter (ADC).

Claims (11)

A radiation CT apparatus that generates a scout image according to projection data obtained by detecting, by a detection means, radiation that is irradiated from a radiation generation means to a subject placed on a cradle and transmitted through the subject,
Drive control means for controlling the relative positions of the radiation generating means and the detection means and the cradle;
At the time of relative acceleration movement or deceleration movement of the radiation generation means, the detection means and the cradle by the drive control means, the projection data based on the detection result of the detection means and the relative position are used. Image generation means for generating a scout image, wherein image data of one line in the scout image is obtained from projection data by the detection means during acceleration or deceleration movement of the cradle by the drive control means. Radiation comprising: selecting line projection data for generating, and generating the scout image by generating image data of one line of the scout image by interpolation based on the selected line projection data CT device. The image generation means is configured to select one of the scout images out of projection data by the detection means when the cradle is accelerated or decelerated based on a view position corresponding to the relative position of the cradle. The radiation CT apparatus according to claim 1, wherein line projection data for obtaining line image data is selected. The detection means includes at least a plurality of detection means arranged along the moving direction of the cradle,
3. The radiation according to claim 1, wherein the image generation unit generates the scout image based on projection data by the plurality of detection units located outside the moving range of the cradle along the moving direction. CT device. The image generating means generates image data of the nth line based on a relative position of the cradle when generating image data of the nth line in the scout image. Projection data by the detection means of the view position or the low position of the scout image is specified, and image data of the nth line in the scout image is generated by interpolation calculation based on the specified projection data, and the scout image Generate
The radiation CT apparatus as described in any one of Claim 1 to 3. The drive control means relatively moves the cradle at a constant speed,
The image generation means is configured to generate an nth image of the scout image based on a plurality of projection data by the detection means of the view position and the low position corresponding to the image data of the nth line in the scout image. The radiation CT apparatus according to any one of claims 1 to 4 , wherein the image data of the line is generated, and the scout image is generated based on a result of the generation. The image generation means determines a data acquisition time of projection data by the detector corresponding to the nth line image data in the scout image, and the projection data obtained at the determined data acquisition time The radiation CT apparatus according to claim 1, wherein the scout image is generated on the basis of the above. As radiation dose per unit length in the direction in which the cradle is moved relative to the radiation generating means and said detecting means becomes constant, according claim 1 having a radiation control unit for controlling the radiation generating means Item 7. The radiation CT apparatus according to any one of Items 6 . The radiation generating means such that a product of a radiation irradiation time per unit length in a direction in which the cradle moves with respect to the radiation generating means and the detecting means and a tube current value to the radiation generating means is constant. The radiation CT apparatus as described in any one of Claims 1-6 which has a radiation control part which controls this. A radiation control unit that controls the radiation generation unit so that a radiation irradiation amount irradiated to the subject per unit time is proportional to a moving speed at which the cradle moves with respect to the radiation generation unit and the detection unit; The radiation CT apparatus according to claim 1, comprising: The control part which controls the said radiation generation means and the said detection means so that the said projection data may be acquired for every fixed time interval when the said cradle moves with respect to the said radiation generation means and the said detection means. Item 10. The radiation CT apparatus according to any one of Items 9. The control part which controls the said radiation generation means and the said detection means so that the said projection data may be acquired for every fixed distance interval to which the said cradle moves with respect to the said radiation generation means and the said detection means. Item 10. The radiation CT apparatus according to any one of Items 9.

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