JP2012135371A - X-ray ct apparatus - Google Patents

Abstract

When calculating an optimum tube current value in an X-ray CT apparatus, accurate cross-sectional information of a subject is easily obtained.
An X-ray CT apparatus includes a top plate control means 10 for controlling a top plate on which a subject is placed to a desired height, and a subject by X-ray from a direction parallel to the height direction of the top plate. Obtained by the projection image calculation unit 32 that calculates the cross-sectional information of the subject using the perspective projection, and the height information and cross-section information calculation unit obtained from the top plate control means when the subject is placed. Suitable for X-ray CT imaging of the subject based on the projection image correction unit 33 for obtaining the corrected cross-sectional information based on the cross-sectional information of the subject and the corrected cross-sectional information obtained by the corrected cross-sectional information calculating unit. And a tube current adjusting unit 34 for adjusting the X-ray irradiation amount.
[Selection] Figure 1

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus, and more particularly to an X-ray CT apparatus including an X-ray automatic exposure mechanism that controls a tube current of an X-ray tube.

  In the X-ray CT apparatus, the X-ray generation amount of the X-ray tube at the time of capturing a tomographic image is calculated from a positioning image (scout image) before capturing the tomographic image. The amount of X-ray generation is adjusted by controlling the tube current of the X-ray tube. Controlling the tube current of the X-ray tube using the scout image can optimize the X-ray dose irradiated to the subject and the image quality of the tomographic image to be reconstructed as an X-ray automatic exposure mechanism. X-ray CT apparatus has been provided.

  In Patent Document 1, by using a scout image from one direction (0 degree direction), a projection area and a minor axis calculated from the scout image are obtained, and a major axis of a subject regarded as an ellipse is calculated. The tube current value of the optimum X-ray tube is calculated.

  In Patent Document 2, the shift amount between the geometric center and the rotation center of the scanning section is calculated from the projection area value (projection area) and the projection measurement value (projection measurement value) calculated from the scout image. Based on the shift amount, the measured projection area can be corrected to the reference projection area, and the optimum tube current value of the X-ray tube can be calculated.

JP 2001-43993 A JP 2009-160394 A

  However, in Patent Document 1, it is necessary to make the center of the imaging region of the subject coincide with the rotation center (isocenter) of the X-ray CT apparatus. If the isocenter is different, there is a possibility that an inappropriate tube current value of the X-ray tube is calculated.

  In Patent Document 2, the projection area is corrected using the shift between the center of the imaging region of the subject and the isocenter of the X-ray CT apparatus as a shift amount. For the calculation of the shift amount, Complex and high-speed processing such as analysis of the projection data just before is necessary.

  The present invention provides an X-ray CT apparatus capable of easily obtaining accurate cross-sectional information of a subject when calculating an optimum tube current value in the X-ray CT apparatus.

  An X-ray CT apparatus according to a first aspect includes a top plate control means for controlling a top plate on which a subject is placed to a desired height, and a subject X from a direction parallel to the height direction of the top plate. Obtained by the cross-section information calculation unit that calculates the cross-section information of the subject using the projection seen through the line, and the height information and cross-section information calculation unit obtained from the top plate control means when the subject is placed Suitable for X-ray CT imaging of the subject based on the corrected cross-sectional information obtained by the corrected cross-sectional information calculated by the corrected cross-sectional information calculated by the corrected cross-sectional information obtained from the cross-sectional information of the subject to be obtained An X-ray dose adjustment unit for adjusting the dose of X-rays.

The X-ray CT apparatus according to the second aspect further comprises storage means for storing the correlation between the height information of the top board obtained from the top board control means and the cross-sectional information of the subject according to the top board height, The corrected cross-section information calculation unit is corrected using the correlation stored in the storage unit based on the height information of the top plate obtained from the top plate control unit and the cross-section information of the subject obtained by the cross-section information calculation unit. Obtain cross-sectional information.
In the X-ray CT apparatus according to the third aspect, the correlation stored in the storage means includes correlation data or a correlation equation indicating a relationship between reference cross-section information serving as a reference in advance and height information of the top plate, and corrected cross-section information. The calculation unit calculates cross-sectional information of the subject based on the correlation data or the correlation equation.

In the X-ray CT apparatus according to the fourth aspect, the corrected cross-section information calculation unit calculates cross-section information at a plurality of positions in the body axis direction of the subject.
In the X-ray CT apparatus according to the fifth aspect, the correlation data or the correlation equation stored in the storage means further includes the total height obtained by adding the height information in the minor axis direction of the subject to the height information of the top plate, and this total. Correlation data or correlation equation with the cross-sectional information of the subject according to the height is included, and the corrected cross-section information calculation unit is corrected using the correlation stored in the storage means based on the total height and the cross-sectional information of the subject. Find cross-section information.

The height information in the minor axis direction of the subject of the X-ray CT apparatus according to the sixth aspect is calculated based on the weight, height, age, and part of the subject.
For the height information in the minor axis direction of the top plate of the X-ray CT apparatus according to the seventh aspect, the projection obtained by seeing through the subject with X-rays from the direction perpendicular to the height direction of the top plate or the subject thickness is obtained. Calculation is based on the image taken by the body thickness detector.

  The X-ray CT apparatus of the present invention can calculate the optimum tube current value of the X-ray tube based on the corrected corrected cross-sectional information by correcting the cross-sectional information of the subject by a simple method. For this reason, there is an advantage that accurate X-ray automatic exposure can be performed.

1 is a block diagram of a configuration of an X-ray CT apparatus 100. FIG. 2 is a perspective view of the imaging table 10 and the scanning gantry 20. FIG. (A) is the figure which showed the positional relationship of the X-ray tube 21, the multi-row X-ray detector 24, and the subject HB. (B) is the figure which showed the projection area S of (a). (A) is a diagram showing the positional relationship between the subject HB and the X-ray tube 21 and the multi-row X-ray detector 24 when the subject center position HC and the rotation center GC are greatly different. (B) is a diagram showing individual projection areas S of (a). It is the graph which showed the relationship between the projection area S and the top-plate height h. 3 is a flowchart showing an imaging procedure of the X-ray CT apparatus 100. It is the figure which showed that the position of the subject center position HC changes with the subject thickness BB of the subject HB. It is the graph which showed the relationship between the body thickness b in the abdominal part abd (M) of a 40-year-old male, and the body weight HW for every height. It is the figure which showed the scout side view image SS of the whole body from a 90 degree | times direction. 2 is a perspective view of a scanning gantry 20 in which an infrared camera 40 is installed. FIG.

The best mode for carrying out an X-ray CT apparatus according to the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to the embodiment.
(First embodiment)
<Overall configuration of X-ray CT apparatus>

  FIG. 1 is a block diagram of a configuration of an X-ray CT apparatus 100 according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 collects X-ray detector data collected by the scanning gantry 20 and an input device 2 such as a keyboard or a mouse that receives input from the operator, a central processing unit 3 that executes image reconstruction processing, each control, and the like. The data collection buffer 5 is provided. Further, the operation console 1 includes a monitor 6 for displaying a tomographic image reconstructed from projection data obtained by preprocessing X-ray detector data, a program, X-ray detector data, projection data, or X-ray tomography. And a storage device 7 for storing various data such as images. The photographing condition is input from the input device 2 and stored in the storage device 7. The imaging table 10 includes a top plate 12 on which the subject HB is placed and taken in and out of the opening of the scanning gantry 20. The top 12 is moved up and down (Y-axis direction) and horizontally (Z-axis direction) by a driving device such as a motor built in the imaging table 10.

  The position where the top 12 is moved up and down and the position where it is moved horizontally are detected by a top position detecting unit 13 built in the imaging table 10. The detection value in the Y-axis direction (hereinafter referred to as the top height h) of the top position detector 13 is used so that the gantry and the top 12 do not interfere with each other. In the present embodiment, the top height h is also used to calculate the reference projection area S0 calculated by the projection image correction unit 33 described later. The position information of the horizontal movement of the top 12 is used for the horizontal shooting position of the scout image. Further, the position information of the horizontal movement of the top 12 is used in a plurality of scanning methods such as a conventional scan, a helical scan, a variable pitch helical scan with a variable pitch, and a helical shuttle scan that performs a helical scan in a reciprocating manner.

  The scanning gantry 20 includes an X-ray tube 21, an X-ray controller 22, a multi-row X-ray detector 24, and a data acquisition device (DAS: Data Acquisition System) 25. The X-ray controller 22 controls the voltage / current supplied to the X-ray tube 21. The gantry rotating part 15 is rotatable via a bearing. When a rotation motor (not shown) rotates, the rotation is transmitted to the gantry rotation unit 15 via a belt (not shown), and the gantry rotation unit 15 rotates. Further, the scanning gantry 20 performs communication with the rotating unit controller 26 that controls the gantry rotating unit 15 rotating around the body axis of the subject HB, and communication with the rotating unit controller 26 and transmission and reception of signals with the top 12. And a controller 29. An X-ray irradiation space into which the subject HB is inserted is formed inside the gantry rotating unit 15, and the center thereof becomes the rotation center GC of the gantry rotating unit 15.

  The central processing unit 3 includes a projection image calculation unit 32, a projection image correction unit 33, a tube current adjustment unit 34, an image reconstruction unit 38, and a control unit 39.

  The projection image calculation unit 32, as one of the cross-sectional information of the subject HB, projects the projection area S in the Z-axis direction of the top 12 based on the projection data detected by the multi-row X-ray detector 24 during the scout imaging. Is calculated.

  The projection image correction unit 33 corrects the projection area S, which is one of the cross-sectional information of the subject HB calculated by the projection image calculation unit 32, and calculates a reference projection area S0.

  The tube current adjusting unit 34 calculates an optimum tube current value from the reference projection area S0 calculated by the projection image correcting unit 33. By transmitting the tube current value obtained by the tube current adjusting unit 34 to the X-ray controller 22, an optimum tube current value in each Z-axis direction of the top 12 is set in the X-ray tube 21. The projection image calculation unit 32, the projection image correction unit 33, and the tube current adjustment unit 34 are used to automatically control the tube current when the subject HB is irradiated with X-rays by a helical scan or the like. This method of controlling the tube current is called an X-ray automatic exposure mechanism, and details thereof will be described later.

  The image reconstruction unit 38 fixes the X-ray tube 21 and the multi-row X-ray detector 24, reconstructs a scout image obtained by moving the top 12 in the Z-axis direction while irradiating X-rays, A tomographic image such as a helical scan obtained by irradiating X-rays while rotating the tube 21 and the multi-row X-ray detector 24 and moving the top 12 in the Z-axis direction is created.

  The control unit 39 performs communication with the input device 2, the monitor 6, the storage device 7, each controller, and other controls related to the X-ray CT apparatus 100 in general.

  FIG. 2 is a perspective view of the imaging table 10 and the scanning gantry 20. As shown in FIG. 2, the top 12 is placed on the top of the imaging table 10. The imaging table 10 includes an elevation drive device and a horizontal drive device (not shown) inside, and moves the top 12 up and down in the Y-axis direction and horizontally moves in the Z-axis direction. A driving device (not shown) such as a motor is used to move the imaging table 10 up and down and horizontally. The driving amount by the driving device is detected by a top plate position detector 13 such as an encoder. The top height h is acquired by the top position detector 13.

  The scanning gantry 20 includes a light source such as a laser light, and includes a laser light LX indicating the center in the X-axis direction and a laser light LY indicating the center in the Y-axis direction. The intersection of the laser light LX and the laser light LY is the rotation center GC of the gantry rotating unit 15 of the scanning gantry 20.

  The operator lays the subject HB on the top 12 and moves the imaging table 10 up and down and horizontally to visually align the center of the subject HB with the laser light LX and laser the center of the thickness of the subject HB. Set to light LY. By aligning the center of the width of the subject HB and the center of the thickness with the rotation center GC, the target part of the subject HB can be stored in the imaging region in the FOV (field of view) set by the operator.

<Description of automatic X-ray exposure mechanism>
The X-ray CT apparatus 100 of the present invention can reconstruct a tomographic image having an optimal image quality by irradiating an X-ray with an optimal X-ray dose to an imaging region of the subject HB by an X-ray automatic exposure mechanism. it can.

  When setting the optimum tube current of the X-ray tube 21, it is preferable to match the center of thickness of the subject HB with the rotation center GC during scout imaging from the 0 degree direction or the 180 degree direction. The 0 degree direction or the 180 degree direction is a direction parallel to the height direction of the top 12. In the present embodiment, scout shooting from the 0 degree direction will be described, and description of scout shooting from the 180 degree direction will be omitted. FIG. 3 is an explanatory diagram when scout shooting from the 0 degree direction is performed.

  When scout imaging from the 0 degree direction is performed by the X-ray CT apparatus 100, the image reconstruction unit 38 reconstructs a scout image from the information of the multi-row X-ray detector 24. At the same time, the projection image calculation unit 32 calculates the projection area S for each position in the Z-axis direction from the information of the multi-row X-ray detector 24.

FIG. 3A is a diagram showing a positional relationship between the X-ray tube 21 and the multi-row X-ray detector 24 and the subject HB at the time of scout imaging. Specifically, assuming that the subject HB is elliptical water, the projection image calculation unit 32 (see FIG. 1) uses the relational expression shown in Equation 1. Here, the thickness of the subject HB is the subject thickness BB, the X-ray absorption coefficient of the subject HB is μ, the X-ray irradiation amount irradiated from the X-ray tube 21 is I0, and the X-ray dose transmitted through the subject HB (transmission) X dose) is I.
μBB = −ln (I / I0) (1)

  When the projection image calculation unit 32 graphs the result of Equation 1 for each multi-row X-ray detector 24, a graph as shown in FIG. 3B can be calculated. The projection image calculation unit 32 calculates the projection area S by integrating values for each channel of the multi-row X-ray detector 24. The projection area S is calculated in the entire region in the Z-axis direction of the scout image, or is calculated for each Z-axis position of the imaging range in which the CT image is acquired. The tube current adjusting unit 34 is called a target standard deviation value (target SD) from the value of the projection area S, and obtains the image quality of a tomographic image reconstructed with an optimum CT value. Calculate the value. Since the target standard deviation value and the tube current value of the X-ray tube 21 have a strong correlation, the optimum tube current value obtains an accurate projection area S.

  As shown in FIG. 3A, the accurate projection area S is determined by the center of the subject thickness BB in the Y-axis direction (hereinafter referred to as the subject center position HC) and the rotation center GC of the scanning gantry 20. It is preferable that they match. As described with reference to FIG. 2, the operator visually adjusts the subject center position HC to the rotation center GC of the scanning gantry 20 with the laser light LY. For this reason, the subject center position HC of the subject thickness BB may not match the rotation center GC of the scanning gantry 20 in the Y-axis direction.

  FIG. 4A shows the positional relationship between the X-ray tube 21 and the multi-row X-ray detector 24 and the subject HB when the subject center position HC and the rotation center GC in the Y-axis direction are greatly different for easy understanding. FIG. FIG. 4B is a diagram showing the individual projection areas S of FIG. As shown in FIG. 4A, the description will be made specifically with respect to the positions of the subject HB at three positions.

  One place drawn by a dotted line is an example in which the subject HB is arranged on the top 12 with the top height h0. The subject center position HC0 of the subject HB coincides with the rotation center GC. One place is an example in which the subject HB is arranged on the top 12 having the top height h1. At this time, the subject center position HC1 of the subject HB is above the rotation center GC. The other place is an example in which the subject HB is arranged on the top 12 with the top height h2. The subject center position HC2 of the same subject HB is below the rotation center GC.

  The reference projection area S0 shown in FIG. 4B is the projection area S when the subject center position HC and the rotation center GC match. The calculated value of the projection image calculation unit 32 in the subject HB at the subject center position HC1 is calculated as the projection area S1 because the area projected on the multi-row X-ray detector 24 becomes wide. Further, the calculated value of the projection image calculation unit 32 in the subject HB at the subject center position HC2 is calculated as the projection area S2 because the region projected onto the multi-row X-ray detector 24 becomes narrow.

  The projection area S1 shows a value larger than the reference projection area S0, and the projection area S2 shows a value smaller than the reference projection area S0. That is, the X-ray tube current value when the same subject HB is placed at the subject center position HC1 is large, and the X-ray tube current value when the subject HB is placed at the subject center position HC2 is small. This causes a change in the image quality of the CT image and a difference in the exposure dose of the subject HB even when the same subject HB is imaged by a helical scan or the like.

  In order to correct the above difference, the projection image correcting unit 33 corrects the projection area S when the subject center position HC of the subject HB is acquired in an arrangement different from the rotation center GC. Specifically, the projection image correction unit 33 corrects the projection area S1 or the projection area S2 calculated by the projection image calculation unit 32 to the reference projection area S0 at the reference position HC0 where the subject center position HC matches the rotation center GC.

  FIG. 5 is a graph showing the relationship between the projection area S and the top height h. In FIG. 5, the vertical axis represents the top plate height h, and the horizontal axis represents the corrected projection area Ps. As shown in FIG. 4, when the subject center position HC0 of the subject HB coincides with the rotation center GC, the projection area S0 is obtained, but the subject HB is close to the X-ray tube 21. At the top height h1, the projection area S1 is large. In addition, the projection area S2 is small at the top height h2 where the subject HB is close to the multi-row X-ray detector 24.

  The correlation data SH or the correlation equation between the top height h and the projection area S of the top 12 shown in FIG. (See FIG. 1). The positions of the rotation center GC in the Y-axis direction and the X-axis direction are stored in advance in the storage device 7 as device information. The correlation data SH or the correlation equation may be a separate data or formula for male / female, or may be a separate data or formula for each age.

  When the projection image calculation unit 32 calculates the projection area S1, and the top plate position detection unit 13 incorporated in the imaging table 10 sends the top plate height h1 to the projection image correction unit 33 (see FIG. 1), the projection image is obtained. The correction unit 33 obtains a reference projection area S0 at the rotation center GC (reference position HC0), which is the corrected projection area Ps, based on the correlation data SH or the correlation equation.

  When the projection image calculation unit 32 calculates the projection area S2, and the table top position detection unit 13 built in the imaging table 10 sends the table height h2 to the projection image correction unit 33, the projection image correction unit 33 calculates the correlation data SH. Alternatively, a reference projection area S0 that is the corrected projection area Ps is obtained based on the correlation equation.

  The tube current adjusting unit 34 (see FIG. 1) calculates the optimum tube current value of the X-ray tube 21 from the corrected projection area Ps calculated by the projection image correcting unit 33. By transmitting the calculated tube current value to the X-ray controller 22, the tube current from which the target standard deviation value of the CT value at each position in the horizontal direction (Z-axis direction) of the top 12 is obtained is supplied to the X-ray tube 21. Flowing.

  According to the series of tube current value determination methods shown above, the X-ray CT apparatus 100 allows the subject HB to be detected with the optimum tube current value even when the top 12 is placed at an arbitrary height during scout imaging. Can be taken with a helical scan.

  FIG. 6 is a flowchart showing an imaging procedure of the X-ray CT apparatus 100. The CT imaging apparatus described above obtains the tube current value of the X-ray tube 21 by the procedure shown in FIG. 6 and reconstructs a tomographic image. In the present embodiment, a case will be described in which a scout image is taken from the 0 degree direction in which the tubes are arranged at 0 degrees.

  In step A1, the operator places the subject HB on the top 12 and performs alignment. The operator visually adjusts the center of the width of the subject HB to the laser light LX shown in FIG. 2, and matches the center of the thickness of the subject HB to the laser light LY. The center of the width of the subject HB and the center of the thickness are approximately matched with the rotation center GC.

  In step A2, the operator selects an imaging region and performs scout image imaging from the 0 degree direction. The image reconstruction unit 38 attaches the top plate height h to the scout image to be photographed. Alternatively, the image reconstruction unit 38 stores the top height h in the storage device 7 as a separate file.

  In step A3, the operator sets an imaging range in the Z-axis direction (horizontal direction) of the subject HB. For setting the shooting range, a shooting start position, a shooting end position, and FOV are set using a scout image.

  In step A4, the projection image calculation unit 32 obtains the projection area S at each coordinate position in the Z-axis direction from the projection data of the scout image.

  In step A5, the projection image correction unit 33 acquires the top plate height h from the top plate position detection unit 13, and uses the projection area S at each coordinate position in the Z-axis direction obtained by the projection image calculation unit 32 as a reference projection. The area is corrected to S0. Since the top position detector 13 uses an encoder in the imaging table 10 or the like, it is not necessary to provide a new detector.

  In step A6, the tube current adjusting unit 34 obtains the target standard deviation value of the CT value from the corrected projection area Ps (reference projection area S0) at the coordinate position in the Z-axis direction. Set.

  In step A <b> 7, the operator starts CT imaging of the imaging range under the imaging conditions set by the tube current adjustment unit 34.

In step A8, the image reconstruction unit 38 creates a CT image by reconstructing an image from the projection data of the multi-row X-ray detector 24.
In step A9, the control unit 39 displays a CT image on the monitor 6.
Note that the same steps as described above can also be performed when a scout image is taken from a 180-degree direction in which the tubes are arranged at 180 degrees.

(Second Embodiment)
In the X-ray CT apparatus 100 of the second embodiment, not only the top height h detected by the top position detector 13 but also the subject thickness BB (BB0, BB3) or the body thickness b (half of the subject thickness BB) Also using b0, b3), the projection image correction unit 33 corrects the projection area S obtained by the projection image calculation unit 32 to the reference projection area S0.

  FIG. 7 is an explanatory diagram when performing scout shooting from the 0 degree direction. When scout imaging from the 0 degree direction is performed by the X-ray CT apparatus 100, the projection image calculation unit 32 calculates the projection area S for each position in the Z-axis direction from the information of the multi-row X-ray detector 24. The subject thickness BB varies depending on the body shape of the subject HB, and the subject thickness BB varies depending on the site in the Z-axis direction (such as the chest or abdomen) even for the same subject HB. For example, the hatched subject in FIG. 7 has a subject thickness BB0 and a body thickness b0. A subject height H0 obtained by combining the top height h and the body thickness b0 detected by the top position detector 13 coincides with the rotation center GC of the gantry rotation unit 15. On the other hand, the subject indicated by the dotted line has a subject thickness BB3 and a body thickness b3. A subject height H3 obtained by combining the top height h and the body thickness b3 is a position closer to the X-ray tube 21 than the rotation center GC. That is, since the subject height H3 does not coincide with the rotation center GC, in order to correct the reference projection area S more accurately, it is better to add the body thickness b (b0, b3) to the top height h.

  The body thickness b which is half of the subject thickness BB of the second embodiment may be actually measured and input from the input device 2 by the operator, but is calculated from the weight HW, height HH, age and part of the subject HB. May be. For example, FIG. 8 is a graph showing the relationship between the body thickness b and the body weight HW in the abdomen abd (M) of a man in his 40s, for each height HH. As shown in the figure, when the body thickness is b3, the height is 140cm, the weight is HW1, the height is 160cm, the weight is HW2, and the height is 180cm, the weight is HW3. Show. In this way, the body thickness b can be calculated from the body weight HW, the height HH, the age, and the part of the subject HB. The correlation data SH or correlation equation of the body thickness b is stored in the storage device 7 in advance. The weight HW, height HH, and age of the subject HB can be acquired as attribute information of the subject HB from an operator input or a network. The part is input by the operator selecting a target part for CT imaging.

  The projection image correction unit 33 calculates the body thickness b from the input body weight HW, height HH, age, and part of the subject HB, obtains the top height h from the top position detector 13, and obtains the subject height H Is calculated, a difference from the height of the rotation center GC in the Y-axis direction is obtained, and the projection area S obtained by the projection image calculation unit 32 is corrected to the reference projection area S0 from the difference.

  The storage device 7 stores correlation data SH or a correlation equation between the projection area S and the top height h, and separately stores correlation data or a correlation equation between the body weight HW of the subject HB and the body thickness b. May be. Further, correlation data or a correlation formula between the subject height H obtained by adding the body thickness b to the top height h and the projection area S may be stored.

(Third embodiment)
In the second embodiment, the subject thickness BB is obtained using information such as the weight HW of the subject HB. In the third embodiment, the subject thickness BB is obtained using a scout image from the 90-degree direction. The configuration of the X-ray CT apparatus 100 of the third embodiment is the same as that of the first embodiment.

  In the third embodiment, in step A2 described in the flowchart of FIG. 6, a 90 ° scout side image SS in the same range as the 0 ° scout image is captured. The scout side view SS is taken while the X-ray tube 21 is disposed at 90 degrees and the top 12 is moved horizontally. For example, when a scout side image SS of the whole body is photographed, a scout side image SS of the subject HB as shown in FIG. 9 can be formed.

  The projection image correcting unit 33 detects the subject thickness BB at the Z-axis coordinate position from the scout side image SS, and calculates the body thickness b that is ½ of the subject thickness BB. Alternatively, the body thickness b can be calculated by obtaining a deviation amount between the rotation center GC and the center of the subject from the scout side image SS and adding the deviation amount and the height of the rotation center GC. As shown in FIG. 9, the body thickness b changes at the coordinate position of the Z axis. For example, the body thickness is b1 at the Z-axis coordinate position corresponding to the head, and the body thickness is b2 at the Z-axis coordinate position corresponding to the chest, and the Z-axis corresponding to the abdomen. In the position Z3 in the coordinate position, the body thickness is b3. Further, the projection image correcting unit 33 calculates the interval c between the top 12 and the boundary of the subject HB. For example, the interval c1 is at the head position Z1, the interval c2 is at the chest position Z2, and the interval c3 is at the abdomen position Z3. In addition, the projection image correction unit 33 obtains the top height h from the top position detection unit 13 and calculates the subject height H. That is, the subject height H is the total value of the body thickness b, the interval c, and the top height h.

The projection image correction unit 33 calculates the subject height H in all the parts where the scout image and the scout side image SS are taken, thereby calculating the projection area S for each coordinate position in the Z-axis direction obtained by the projection image calculation unit 32. Is corrected to the reference projection area S0. As a result, the tube current adjusting unit 34 can obtain the target standard deviation value of the CT value at the coordinate position in the Z-axis direction even when imaging a plurality of parts from the head to the abdomen at a time. The current value can be set.
(Fourth embodiment)

The X-ray CT apparatus 110 of the fourth embodiment uses a body thickness detector to determine the subject thickness BB.
The body thickness detector is composed of a sensor capable of measuring the boundary of the subject thickness BB, such as a thermography camera or an infrared camera 40. The case where the infrared camera 40 is installed in the X-ray CT apparatus 110 will be described below.

  The infrared camera 40 is a sensor capable of confirming the boundary of the subject HB through the clothes such as thin examination clothes. In the gantry of the X-ray CT apparatus 110, as shown in FIG. 10, an infrared camera 40 is installed at a position of 90 degrees of the scanning gantry. The imaging field of view of the infrared camera 40 is formed in a slit shape.

  At the same time that the operator performs scout imaging from the 0 degree direction, the infrared camera 40 images the side surface of the subject HB from the 90 degree direction. The infrared camera 40 can form a side image of the subject HB as shown in FIG. 9 from the image passing through the slit and the moving top plate 12. The projection image correction unit 33 forms an infrared side image of the subject HB by collecting an infrared image at the coordinate position of the top plate 12 from the infrared image through the slit and information on the installation location of the infrared camera 40. Further, the projection image correcting unit 33 calculates the subject thickness BB for each coordinate position of the Z axis from the infrared side image, and calculates the body thickness b by halving the subject thickness BB.

  The projection image correction unit 33 calculates the subject height H from the top plate height h detected by the top plate position detection unit 13 and the body thickness b calculated by the infrared camera 40, and is obtained by the projection image calculation unit 32. The projection area S at the coordinate position in the Z-axis direction is corrected to the reference projection area S0.

The projection image correcting unit 33 can calculate the subject height H in all the parts obtained by photographing the infrared side image, and thereby, a plurality of parts can be CT at a time by taking one scout image from the 0 degree direction. Even in the case of imaging, the tube current adjustment unit 34 can set the tube current value of the X-ray tube 21 that can obtain the target standard deviation value of the CT value at the coordinate position in the Z-axis direction.
In the above-described embodiment, the correlation data or the correlation equation is stored in the storage device 7, but the correlation may be calculated for each photographing.

DESCRIPTION OF SYMBOLS 1 ... Operation console, 2 ... Input device 3 ... Central processing unit, 5 ... Data collection buffer 6 ... Monitor, 7 ... Memory | storage device 10 ... Imaging table, 12 ... Top plate 13 ... Top plate position detection part 14 ... Display part, 15 ... Gantry rotation unit 20 ... Scanning gantry, 21 ... X-ray tube 22 ... X-ray controller, 24 ... X-ray detector 26 ... Rotation unit controller, 29 ... Control controller 32 ... Projection image calculation unit (section information calculation)
33 ... Projection image correction unit (cross-section information correction)
34 ... Tube current adjusting unit 38 ... Image reconstruction unit 39 ... Control unit 100 ... X-ray CT apparatus, 110 ... X-ray CT apparatus b ... Body thickness (half of subject thickness)
BB ... Subject thickness c ... Interval GC ... Center of rotation h ... Top height H ... Subject height HB ... Subject HC ... Subject center position HH ... Height, HW ... Weight LX ... Laser light, LY ... Laser light S ... Projection area SH ... Correlation data S0 ... Reference projection area SS ... Scout side view

Claims (10)

A top plate control means for controlling the top plate on which the subject is placed to a desired height;
A cross-section information calculation unit for calculating cross-section information of the subject from a direction parallel to the height direction of the top plate using a projection obtained by seeing through the subject with X-rays;
When the subject is placed, corrected cross-sectional information is obtained based on the height information of the top plate obtained from the top plate control means and the cross-sectional information of the subject obtained by the cross-section information calculation unit. A corrected cross-section information calculator,
An X-ray dose adjustment unit that adjusts the X-ray dose suitable for X-ray CT imaging of the subject based on the corrected cross-sectional information obtained by the corrected slice information calculation unit;
An X-ray CT apparatus comprising: Storage means for storing the correlation between the height information of the top plate obtained from the top plate control means and the cross-sectional information of the subject according to the top plate height;
The corrected cross-section information calculation unit calculates the correlation stored in the storage unit based on the height information of the top plate obtained from the top plate control unit and the cross-section information of the subject obtained by the cross-section information calculation unit. The X-ray CT apparatus according to claim 1, wherein the X-ray CT apparatus is used to obtain corrected sectional information. The correlation stored in the storage means includes correlation data or a correlation equation indicating a relationship between reference cross-section information serving as a reference in advance and height information of the top plate,
The X-ray CT apparatus according to claim 2, wherein the corrected cross-section information calculation unit calculates the cross-section information of the subject based on the correlation data or the correlation equation.   The X-ray CT apparatus according to claim 1, wherein the corrected cross-section information calculation unit calculates the cross-section information at a plurality of positions in the body axis direction of the subject. The correction information calculation unit obtains corrected cross-section information based on the total height obtained by adding the height information of the minor axis direction of the subject to the height information of the top plate and the cross-section information of the subject. The X-ray CT apparatus according to any one of claims 1 to 4. The X-ray CT apparatus according to claim 5, wherein the height information of the subject in the minor axis direction is a radius of the subject in the minor axis direction. The storage means is a correlation data or a correlation formula between the total height obtained by adding the height information in the minor axis direction of the subject to the height information of the top plate and the cross-sectional information of the subject according to the total height The X-ray CT apparatus according to claim 5 or 6. The X-ray CT apparatus according to any one of claims 5 to 7, wherein the height information of the subject in the minor axis direction is calculated based on the weight, height, age, and part of the subject.   The height information in the minor axis direction of the top plate is obtained by a projection obtained by seeing the subject through X-rays from a direction perpendicular to the height direction of the top plate, or by a body thickness detector for obtaining the subject thickness. The X-ray CT apparatus according to claim 5, wherein the X-ray CT apparatus is calculated based on the obtained image.   The X-ray CT apparatus according to any one of claims 1 to 9, wherein the X-ray irradiation amount adjustment unit adjusts a tube current supplied to an X-ray tube that irradiates the X-rays.