JP2018068747A - Radiation tomography imaging device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a downtime of a radiation tomography imaging device.SOLUTION: An X-ray CT device incudes: a position z1 of a phantom provided to a holder attached to a cradle; a shift amount calculation part for calculating a positional shift amount LZ between the phantom and a referential position; a driving device for driving the cradle 41 so that the phantom 51 is positioned at the referential position based on the positional shift amount LZ; a gantry 2 for scanning the phantom 51 and collecting data of the phantom 51; a reconstruction part for reconstructing an image based on the data of the phantom 51 and the correction data required for an image reconstruction; and a control part for controlling, when an artifact is contained in the reconstructed image, each device and part in the gantry 2 to collect data required for proofing the correction data.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a radiation tomography apparatus that scans a subject using radiation, and a program applied to the radiation tomography apparatus.

  Conventionally, an X-ray CT apparatus is known as a radiation tomography apparatus that generates an image using X-rays. The X-ray CT apparatus has an X-ray tube that emits X-rays and an X-ray detector that detects X-rays. X-rays emitted from the X-ray tube pass through the subject and are detected by an X-ray detector. The X-ray detector detects transmitted X-rays of the subject and outputs an electrical signal corresponding to the intensity. The electrical signal output from the X-ray detector is received by the data collection unit and converted into X-ray data. An image is reconstructed based on the X-ray data.

When image reconstruction is performed, data obtained by imaging a subject is corrected using correction data (data) obtained by imaging a reference substance such as water or air. By this correction, a high quality image can be obtained. However, artifacts may occur in the reconstructed image due to the usage environment of the X-ray CT apparatus, the usage period of the X-ray CT apparatus, and the like, and the image quality may deteriorate. Therefore, a technique for performing calibration using a phantom in order to reduce artifacts is known (see, for example, Patent Document 1).

JP 2006-034306 A

In general, calibration using a phantom is a task that requires specialized knowledge, and thus there is a problem that it is difficult for a user (for example, a radiographer) of the X-ray CT apparatus to perform this task. Therefore, when the user finds an artifact, the user often contacts a field engineer and requests calibration. Upon receiving a request for calibration, the field engineer visits the hospital, performs analysis work for analyzing an image in which artifacts appear, and performs calibration based on the analysis result. Therefore, an image with reduced artifacts can be obtained.

However, in the above method, since the user contacts the field engineer and the field engineer who has received the contact needs to visit the hospital, it takes a long time to start the calibration work after finding the artifact. There is a problem. In addition, after arriving at the hospital, the field engineer needs to perform analysis work such as an image in which the artifact appears and the state of the X-ray CT apparatus, and determine whether the artifact can be reduced by calibration. In addition, if the field engineer determines that the artifact can be reduced by calibration, the phantom is installed in the cradle, and after the phantom is installed, the cradle is moved so that the phantom is positioned at a position suitable for scanning. It is also necessary to let them. A certain amount of time is required to perform such analysis work and phantom positioning. Therefore, when performing calibration, there is a problem that the downtime of the X-ray CT apparatus increases.

For these reasons, there is a demand for a technique capable of reducing the downtime of a radiation tomography apparatus such as an X-ray CT apparatus even when calibration is executed.

A first aspect of the present invention is a radiation tomography apparatus that scans a subject using radiation,
Deviation amount calculation means for calculating a positional deviation amount between the position of the phantom installed in the cradle or the position of the phantom installed in the holder attached to the cradle and a predetermined position where the phantom should be positioned; ,
Driving means for driving the cradle so that the phantom is positioned at the predetermined position based on the positional deviation amount;
Photographing means for scanning the phantom and collecting data of the phantom;
Reconstructing means for reconstructing an image based on the phantom data and correction data necessary for image reconstruction;
Control means for controlling the imaging means so that data necessary to calibrate the correction data is collected when artifacts are included in the reconstructed image;
A radiation tomography apparatus.
A second aspect of the present invention is a program applied to a radiation tomography apparatus that scans a subject using radiation, the deviation amount calculating means, the reconstruction means described in the first aspect of the present invention, And a program for realizing the control means.

  The amount of positional deviation between the position of the phantom and the predetermined position in the cavity is calculated, and the cradle moves so that the phantom is positioned at the predetermined position based on the calculated amount of positional deviation. Therefore, since the user does not need to position the phantom himself, the downtime of the radiation tomography apparatus can be shortened.

It is a figure which shows schematically the structure of the hardware of the X-ray CT apparatus which concerns on this form. It is a side view of a gantry and a table of an X-ray CT apparatus. It is a functional block diagram of the operation console of the X-ray CT apparatus which concerns on this form. It is a figure which shows roughly the program and data which are memorize | stored in the memory | storage device 63. It is a flowchart which shows the flow of a process in the X-ray CT apparatus which concerns on this form. It is explanatory drawing of an example of the installation method of a phantom. It is a figure which shows the deviation | shift amount LZ between the position z1 of the present phantom, and the reference position z0 of the phantom. It is a figure which shows the cradle after moving only deviation | shift amount LZ. Using the correction data _D 1 to D _W, a (kVp, SFOV, FS) schematically illustrates an image of a plurality of slices obtained for each combination of. It is explanatory drawing of the parameter | index calculated for every image. It is explanatory drawing of a determination result. It is explanatory drawing of an example of calibration. It is a figure which shows roughly a mode that the correction data Dc1 obtained by the detailed calibration was overwritten by the correction data _DW . The reconstructed image using the correction data D ₁ ~D _W-1 and correction data Dc1 obtained by calibration is a diagram schematically showing. It is a figure which shows roughly the value of the 2 parameter | index (average value m and standard deviation (sigma)) calculated for every image. It is a figure which shows a determination result. It is a figure which shows roughly an example in which the parameter | index exceeding a reference value appeared. It is a figure which shows a mode that the correction data Dc2 obtained by the 2nd detailed calibration was overwritten by the correction data Dc1. It is a figure which shows a determination result. It is explanatory drawing of some examples of the calibration different from detailed calibration.

  Hereinafter, although the form for inventing is demonstrated, this invention is not limited to the following forms.

  FIG. 1 is a diagram schematically illustrating a hardware configuration of an X-ray CT apparatus 1 according to the present embodiment, and FIG. 2 is a side view of a gantry and a table of the X-ray CT apparatus 1.

  As shown in FIG. 1, the gantry 2 includes an X-ray tube 21, an aperture 22, a collimator device 23, an X-ray detector 24, a data acquisition system 25, a rotation unit 26, A high voltage power supply 27, an aperture driving device 28, a rotation driving device 29, and a control unit 30 are included. A combination of the X-ray tube 21, the aperture 22, the collimator device 23, the X-ray detector 24, the data collection unit 25, the rotation unit 26, the high voltage power supply 27, the aperture drive device 28, and the rotation drive device 29 is combined. This corresponds to an example of the photographing means in the present invention.

  The rotating part 26 is supported rotatably. The X-ray tube 21, the aperture 22, the collimator device 23, the X-ray detector 24, and the data collection unit 25 are mounted on the rotation unit 26.

  The X-ray tube 21 and the X-ray detector 24 are arranged to face each other across the imaging space where the subject 5 is placed, that is, the cavity 2B of the gantry 2.

  The aperture 22 is disposed between the X-ray tube 21 and the cavity 2B. The aperture 22 shapes X-rays emitted from the X-ray focal point of the X-ray tube 21 toward the X-ray detector 24 into a fan beam or a cone beam.

  The collimator device 23 is disposed between the cavity 2B and the X-ray detector 24. The collimator device 23 removes scattered radiation incident on the X-ray detector 24.

  The X-ray detector 24 has a plurality of X-ray detection elements arranged two-dimensionally in the spreading direction and thickness direction of the fan-shaped X-ray beam radiated from the X-ray tube 21. Each X-ray detection element detects transmitted X-rays of the subject 5 arranged in the cavity 2B, and outputs an electrical signal corresponding to the intensity.

  The data collection unit 25 receives an electrical signal output from each X-ray detection element of the X-ray detector 24, converts it into X-ray data, and collects it.

  The imaging table 4 has a cradle 41 and a driving device 42. The subject 5 is placed on the cradle 41. The driving device 42 drives the cradle 41 so that the cradle 41 moves up and down in the y direction, and further drives the cradle 41 so that the cradle 41 moves in the z direction.

The high voltage power supply 27 supplies a high voltage and current to the X-ray tube 21.
The aperture driving device 28 drives the aperture 22 to deform its opening.
The rotation drive device 29 drives the rotation unit 26 to rotate.
The control unit 30 controls each device and each unit in the gantry 2, the drive device 42, and the like.

  The operation console 6 receives various operations from the operator 9. The operation console 6 includes an input device 61, a display device 62, a storage device 63, and an arithmetic processing device 64. In this example, the operation console 6 is configured by a computer.

  Here, as shown in FIG. 1, the body axis direction of the subject 5, that is, the conveyance direction of the subject 5 by the imaging table 4 is the z direction. The vertical direction is the y direction, and the horizontal direction orthogonal to the y direction and the z direction is the x direction.

  FIG. 3 is a functional block diagram (block diagram) of the operation console of the X-ray CT apparatus according to the present embodiment.

  The operation console 6 of the X-ray CT apparatus according to the present embodiment includes a deviation amount calculation unit 71, a reconstruction unit 72, an index calculation unit 73, a determination unit 74, a generation unit 75, and a functional block for realizing the above functions. A count unit 76 and the like are included.

The deviation amount calculation unit 71 calculates a later-described deviation amount LZ (see FIG. 7).
The reconstruction unit 72 reconstructs an image based on data obtained by scanning and correction data necessary for image reconstruction.
The index calculator 73 calculates an average value m and a standard deviation σ, which will be described later.
The determination unit 74 determines whether each of the average value m and the standard deviation σ is included in the allowable value range.
The generation unit 75 generates correction data necessary for image reconstruction.
The counting unit 76 counts the number of times calibration is performed to calibrate the correction data.

  The deviation amount calculation unit 71 is an example of the deviation amount calculation means in the present invention. The reconstruction unit 72 is an example of a reconstruction unit in the present invention. The index calculation unit 73 is an example of an index calculation unit in the present invention. The determination unit 74 is an example of a determination unit in the present invention. The generation unit 75 is an example of a generation unit in the present invention. The count unit 76 is an example of a counting unit in the present invention.

  The operation console 6 functions as each functional block when the arithmetic processing unit 64 executes a predetermined program. The predetermined program is stored in the storage device 63 (see FIG. 4).

FIG. 4 is an explanatory diagram of the storage device 63.
The storage device 63 stores programs PG _{1 to} PG _U. At least one program of these programs PG ₁ ~PG _U is a program executed by the processor 64. Further, the storage device 63 stores correction data D _{1 to} D _W. The correction data D _{1 to} D _W represent correction data necessary for image reconstruction. The correction data D _{1 to} D _W include, for example, data for correcting the characteristics of the X-ray tube, data for correcting the characteristics of the X-ray detector 24 and the like. The image of the subject 5 is reconstructed based on the data obtained by scanning the subject 5 and the correction data D _{1 to} D _W.

The program _PG 1 _{~PG U} and the correction data _D 1 to D _W shown in FIG. 4, an externally connected storage device or storage medium in the operation console 6 90 may be stored (see FIG. 1), stores The device 63 and the storage device or storage medium 90 may be distributed and stored. Details of the function of each part of the operation console 6 will be described together with the description of the processing flow in the X-ray CT apparatus.

  The X-ray CT apparatus according to the present embodiment is not a field engineer but an X-ray CT apparatus when a situation occurs in which calibration for calibrating correction data (see FIG. 4) necessary for image reconstruction occurs. The user (for example, a photography engineer) can perform calibration by himself / herself. Therefore, an effect that the downtime of the X-ray CT apparatus can be reduced is obtained. The following describes what processing is performed by the X-ray CT apparatus when a situation in which calibration must be performed occurs in the present embodiment.

  FIG. 5 is a flow chart showing the flow of processing in the X-ray CT apparatus according to the present embodiment.

  The X-ray CT apparatus needs to execute calibration for calibrating correction data (see FIG. 4) as necessary. Situations that require calibration include, for example, when an artifact appears in an image taken with an X-ray CT apparatus, when a periodic inspection of the X-ray CT apparatus is performed, and when an X-ray tube is replaced. In this embodiment, when it is considered that the user needs to execute calibration, the calibration is executed according to the following flow. Hereinafter, each step executed in the flow will be described.

  In step S1, the user installs a phantom. FIG. 6 is an explanatory diagram of an example of a method for installing the phantom 51.

  The user operates an operation unit provided on the gantry 2 or the imaging table 4 and inputs an instruction necessary to raise and lower the cradle 41 in a vertical direction (y direction) to a predetermined height. When this instruction is input, the control unit 30 (see FIG. 1) moves the imaging table 4 so that the cradle 41 moves up and down to a predetermined height.

  After the cradle 41 moves up and down, the user attaches the holder 50 to the one end 41 a of the cradle 41 and installs the phantom 51 on the holder 50. In this embodiment, the phantom 51 is the water phantom 51, but it is also possible to use a phantom containing a substance different from water. Although FIG. 6 shows an example in which the phantom 51 is installed in the holder 50, the phantom 51 can be installed in the cradle 41 instead of the holder 50. After installing the phantom 51, the process proceeds to step S2.

  In step S <b> 2, the user uses the input device 61 (see FIG. 1) to input a command (command) indicating an instruction for causing the phantom 51 to be scanned. The command is input by a simple operation such as pressing a predetermined button of the input device 61, for example.

  In step S3, the cradle 41 moves so that the phantom 51 is positioned at a predetermined position in response to the command input in step S2 (see FIGS. 7 and 8).

7 and 8 are explanatory diagrams of positioning of the phantom 51. FIG.
First, as shown in FIG. 7, the deviation amount calculation unit 71 (see FIG. 3) calculates a deviation amount LZ between the current position z1 of the phantom 51 and the reference position z0 where the phantom 51 is to be positioned. . The reference position z0 of the phantom 51 is, for example, the isocenter of the cavity 2B. However, a position shifted from the isocenter of the cavity 2B can be set as the reference position z0 of the phantom 51. As a method for obtaining the shift amount LZ, for example, there is a method using a camera (not shown). When using a camera, the area including the phantom 51 is photographed with the camera. After shooting by the camera, the current position of the phantom 51 is specified by applying image recognition technology to the image data obtained by the camera. Therefore, since the current position of the phantom 51 can be specified, the deviation amount calculation unit 71 can calculate the deviation amount LZ.

  The shift amount LZ may be obtained by a method that does not use a camera. As a method of obtaining the shift amount LZ without using a camera, there is a method of executing a scan. In this case, the deviation amount calculation unit 71 can calculate the deviation amount LZ based on the data obtained by scanning.

  The control unit 30 controls the driving device 42 (see FIG. 1) so that the cradle 41 moves by the shift amount LZ. The drive device 42 moves the cradle 41 in the horizontal direction (z direction) by the shift amount LZ. FIG. 8 is a view showing the cradle 41 after being moved by the shift amount LZ. The phantom 51 can be positioned at the reference position z0 by moving the cradle 41 by the shift amount LZ.

  In this embodiment, after the cradle 41 is moved up and down to a predetermined height in the y direction, the user installs the phantom 51 (step S1) and moves the cradle 41 in the z direction, thereby moving the phantom 51 to the reference position x0. (Step S3). However, before the cradle 41 is moved up and down to a predetermined height, the user installs the phantom 51, and after the user installs the phantom 51, the cradle 41 is positioned in the y direction and so that the phantom 51 is positioned at the reference position x0. It may be moved in the z direction. Moreover, the imaging table 4 is not limited to the structure shown in FIG. 2 etc., For example, the imaging table which has a structure which can move a cradle to ay direction and az direction by swinging a support | pillar (swing). May be used.

After positioning the phantom 51 as shown in FIG. 8, the process proceeds to step S4.
In step S4, a phantom scan for obtaining an image of the phantom 51 is executed. In the phantom scan, a phantom scan is executed while adjusting a plurality of parameters. For example, kVp representing the tube voltage of the X-ray tube, SFOV (scan FOV) representing the width of the data collection range, and FS (Focal Spot representing the size of the X-ray focal point) are adjusted as parameters when performing the phantom scan. )and so on. Hereinafter, an example of performing a phantom scan while adjusting these three parameters (kVp, SFOV, and FS) will be described. However, it should be noted that one or more of the above three parameters can be replaced with another parameter. Further, the number of parameters is not limited to three, and may be one, two, or four or more.

In this embodiment, the above three parameters kVp, SFOV, and FS are changed as follows.
(1) kVp is a parameter that can be changed to p = 1 to n, that is, n values (kV1, kV2, kV3,... KVn). For example, n can be set to n = 3.
(2) SFOV is a parameter that can be changed to two SFOVs, that is, a small SFOV and a large SFOV. The small SFOV represents an SFOV for scanning a narrow area, and the large SFOV represents an SFOV for scanning a wide area.
(3) The parameter FS is a parameter that can be changed to two FSs, that is, a small FS and a large FS. The small FS indicates that the X-ray focal spot size is small, and the large FS indicates that the x-ray focal spot size is large.

Therefore, in this embodiment, the phantom scan is executed while changing (kVp, SFOV, FS) as follows.
(KV, SFOV, FS) = (kV1, small SFOV, small FS)
= (KV1, Small SFOV, Large FS)
= (KV1, large SFOV, small FS)
= (KV1, large SFOV, large FS)
= (KV2, Small SFOV, Small FS)
= (KV2, Small SFOV, Large FS)
= (KV2, large SFOV, small FS)
= (KV2, large SFOV, large FS)
・
・
・
・
= (KVn, Small SFOV, Small FS)
= (KVn, small SFOV, large FS)
= (KVn, large SFOV, small FS)
= (KVn, large SFOV, large FS)

  In this embodiment, there are n ways for kVp, two ways for SFOV, and two ways for FS. Therefore, there are n × 2 × 2 = 4n combinations of (kVp, SFOV, FS).

In the phantom scan, the phantom scan is performed while changing the combination of (kVp, SFOV, FS) to 4n ways. In this embodiment, it is assumed that the image of the phantom 51 is acquired as a multi-slice image. Therefore, in this embodiment, data for obtaining images of a plurality of slices can be collected for each combination of (kVp, SFOV, FS) by executing a phantom scan. The reconstruction unit 72 (see FIG. 3) sequentially reconstructs the tomographic images corresponding to the slices almost in real time based on the data obtained by the phantom scan and the correction data registered in advance (see FIG. 4). Configure. Therefore, by using the correction data _D 1 to D _W, it can be reconstituted for each combination, an image of a plurality of slices of (kVp, SFOV, FS). 9, the correction data using the _{D 1 ~D W, (kVp,} SFOV, FS) schematically shows an image of a plurality of slices obtained for each combination of. In FIG. 9, for convenience of explanation, it is assumed that the pattern of the combination of (kVp, SFOV, FS) is represented by the following three combinations H1, H2, and H3.
Combination H1: (kV1, small SFOV, small FS)
Combination H2: (kV1, small SFOV, large FS)
Combination H3: (kVn, large SFOV, large FS)

  In the multi-slice, for example, an image of 64 slices and an image of 128 slices can be obtained, but in FIG. 9, only an image of 3 slices is shown due to space limitations. After image reconstruction, the process proceeds to step S5.

In step S5, the index calculation unit 73 (see FIG. 3) calculates an index value for detecting an artifact for each image. FIG. 10 is an explanatory diagram of an index for detecting an artifact. An existing technique can be used as a method for calculating the index value. For example, one or a plurality of regions are set in the in-vivo region of the image, and the average value m of the CT value and the standard deviation σ of the CT value are obtained for each region, and each of the average value m and the standard deviation σ is indicated It can be. In the following, it is assumed that the average value m and the standard deviation σ are used as indexes. For convenience of explanation, FIG. 10 shows an example in which two regions r1 and r2 are set for each image, and the average value m and the standard deviation σ are calculated for each of the regions r1 and r2. ing.
After calculating the average value m and the standard deviation σ, the process proceeds to step S6.

In step S6, the determination unit 74 (see FIG. 3) determines whether or not the values of the two indexes (average value m and standard deviation σ) calculated in step S5 are within an allowable value range. To do. In this embodiment, the reference value mth for determining whether or not the calculated value of the average value m is included in the allowable value range and the calculated value of the standard deviation σ is included in the allowable value range. A reference value σth for determining whether or not is set in advance. The determining unit 74 compares the calculated value of the average value m with the reference value mth to determine whether or not the calculated value of the average value m is included in the allowable value range, and further, the standard deviation σ Is compared with the reference value σth to determine whether or not the calculated value of the standard deviation σ is included in the allowable value range. In this embodiment, the reference value mth of the average value m represents the upper limit value of the average value m, and the reference value σth of the standard deviation σ represents the upper limit value of the standard deviation σ. Therefore, the determination unit 74 determines that the calculated value of the average value m is included in the allowable value range when the calculated value of the average value m is less than or equal to the reference value mth, while the calculated value of the average value m When the value exceeds the reference value mth, it is determined that the calculated value of the average value m is not included in the allowable range. Similarly, when the calculated value of the standard deviation σ is equal to or smaller than the reference value σth, the determination unit 74 determines that the calculated value of the standard deviation σ is included in the allowable value range, while calculating the standard deviation σ. When the value exceeds the reference value σth, it is determined that the calculated value of the standard deviation σ is not included in the allowable range. FIG. 11 is an explanatory diagram of the determination result. In FIG. 11, the calculated value surrounded by ○ represents that it is equal to or less than the reference value (included in the range of allowable values), and the calculated value indicated by × exceeds the reference value. (Not included in the range of acceptable values). For example, referring to the images IM11, IM12, and IM13 obtained by scanning in the combination H1: (kV1, small SFOV, small FS), the calculated values of the average value m and the standard deviation σ for any image Is below the reference value (included in the range of acceptable values). Therefore, artifacts are sufficiently reduced in the images IM11, IM12, and IM13 obtained by the combination H1: (kV1, small SFOV, small FS). However, in the combination H2: (kV1, small SFOV, large FS) and the combination H3: (kVn, large SFOV, large FS), some calculated values exceed the reference value. For example, in the combination H2: (kV1, small SFOV, large FS), the calculated value of the average value m in the region r2 of the image IM21 exceeds the reference value. Therefore, in the combinations H2 and H3, it is considered that there is a possibility that artifacts that cannot be ignored appear in the image. Therefore, when the calculated values of the average value m and the standard deviation σ include those that exceed the reference value, the determination unit 74 determines all or part of the correction data D _{1 to} D _W (see FIG. 4). It is determined that it is necessary to execute calibration for calibrating. If it is determined that the calibration needs to be executed, the process proceeds to step S7.

In step S7, the calibration for calibrating the whole or a part of the correction data D ₁ to D _W is executed. In the following, for convenience of description, among the correction data D ₁ to D _W, and only the correction data D _W is the calibration target. However, the present invention is calibration of the target, the correction to be limited to the data D _W are not, correction data D _W and may be a target of correction data for calibrating the different correction data, two or more correction data (For example, two correction data D ₁ and D ₂ and all correction data D _{1 to} D _W ) may be used as correction data to be calibrated.

FIG. 12 is an explanatory diagram of an example of calibration.
FIG. 12 is a diagram schematically illustrating an example of detailed calibration for performing detailed calibration. Detailed calibration is composed of a processes P1 to Pa corresponding to all combinations of (kVp, SFOV, FS). In the detailed calibration, a scan is executed in each of the a processes. Then, correction data used for image reconstruction is generated based on the data obtained by scanning. The a processes P1 to Pa include, for example, a process for small SFOV phantom calibration, a process for large SFOV phantom calibration, a process for air calibration, and the like.

  In the small SFOV phantom calibration process, the phantom 51 is positioned at a position above the isocenter by a predetermined distance, and a phantom scan for acquiring an image of the phantom 51 is executed. In the large SFOV phantom calibration process, the phantom 51 is positioned at a position below the isocenter by a predetermined distance, and a phantom scan for acquiring an image of the phantom 51 is executed. In the air calibration process, scanning is performed without the phantom 51 being installed between the X-ray tube 21 and the X-ray detector 24.

As described above, in the detailed calibration, scanning is executed in the a processes P1 to Pa. The generation unit 75 (see FIG. 3) generates correction data Dc1 used for image reconstruction based on data obtained by scanning. The correction data Dc1 is overwritten on the correction data D _W (see FIG. 4) to be calibrated. FIG. 13 schematically shows how the correction data Dc1 obtained by the detailed calibration is overwritten on the correction data _DW .

In this way, calibration for calibrating the correction data _DW is executed. After executing calibration, the process proceeds to step S8.

  In step S8, the counting unit 76 (see FIG. 3) counts the number of calibration executions v. Here, since the calibration is executed only once, the counting unit 76 counts v = 1. After counting the number of calibration executions v, the process returns to step S3, and the phantom 51 is positioned at the reference position z0 (see FIG. 8). Then, the process proceeds to step S4.

In step S4, a phantom scan is executed. The reconstruction unit 72, and data obtained by phantom scan, the correction data _{D 1 ~D W-1,} based on the correction data Dc1 obtained by the calibration in step S7 (see FIG. 13), Perform image reconstruction. Therefore, it is possible to reconstruct an image of a plurality of slices for each combination of (kVp, SFOV, FS) using the correction data Dc1 obtained by calibration. FIG. 14 schematically shows an image reconstructed using the correction data D _{1 to} D _W-1 and the correction data Dc1 obtained by calibration. After image reconstruction, the process proceeds to step S5.

  In step S5, the index calculation unit 73 calculates an index for detecting an artifact for each image. FIG. 15 schematically shows two index values (average value m and standard deviation σ) calculated for each image. After calculating the average value m and the standard deviation σ, the process proceeds to step S6.

  In step S6, the determination unit 74 determines whether or not the calculated values of the average value m and the standard deviation σ are included in the allowable value range. FIG. 16 is a diagram schematically illustrating an example of a determination result. In FIG. 16, a value surrounded by a circle represents that it is equal to or less than a reference value (included in an allowable value range). In FIG. 16, all the calculated values of the average value m and the standard deviation σ are surrounded by circles. Therefore, it is determined that the calibration by the detailed calibration is successful, and the flow is finished.

  On the other hand, even if the correction data Dc1 obtained by the detailed calibration is used, the calculated values of the average value m and the standard deviation σ may include those exceeding the reference value. FIG. 17 is a diagram schematically illustrating an example in which the calculated values of the average value m and the standard deviation σ include those exceeding the reference value. In FIG. 17, a value surrounded by a circle represents that it is equal to or less than a reference value (included in an allowable value range), and a value indicated by × exceeds the reference value ( Not included in the range of acceptable values). For example, in the combination H1: (kV1, small SFOV, small FS) and the combination H3: (kVn, large SFOV, large FS), all the calculated values of the average value m and the standard deviation σ are below the reference value (acceptable) Included in the range of values). However, in the combination H2: (kV1, small SFOV, large FS), some calculated values of the average value m and the standard deviation σ exceed the reference value. Therefore, the determination unit 74 determines that calibration needs to be executed again. If it is determined that the calibration needs to be executed again, the process proceeds to step S7.

  In step S7, a second calibration is executed to calibrate the correction data Dc1. By executing the second calibration, correction data Dc2 is obtained. The correction data Dc2 is overwritten on the correction data Dc1 obtained by the first calibration. FIG. 18 shows a state where the correction data Dc2 obtained by the second detail calibration is overwritten on the correction data Dc1.

  After performing the second calibration, the process proceeds to step S8, and the number of calibration executions v is counted. Here, since the calibration has been executed twice, the count unit 76 counts v = 2. After counting the number of times of execution of calibration v, the process returns to step S3 to center the phantom 51, execute phantom scan in step S4, and obtain correction data Dc2 obtained by the second detail calibration (see FIG. 18). ) To reconstruct the image. After reconstructing the image, the process proceeds to step S5, and the average value m and the standard deviation σ are calculated for each image. Then, the process proceeds to step S6.

  In step S6, the determination unit 74 determines whether or not the calculated values of the average value m and the standard deviation σ are included in the allowable value range. FIG. 19 shows the determination result. In FIG. 19, the value surrounded by ○ represents that it is equal to or less than the reference value (included in the range of allowable values), and the value indicated by × exceeds the reference value ( Not included in the range of acceptable values). For example, in the combination H1: (kV1, small SFOV, small FS) and the combination H3: (kVn, large SFOV, large FS), all the calculated values of the average value m and the standard deviation σ are below the reference value (acceptable) Included in the range of values). However, in the combination H2: (kV1, small SFOV, large FS), some calculated values of the average value m and the standard deviation σ exceed the reference value.

  Therefore, the determination result of FIG. 19 shows that although the calibration was executed twice, some calculated values of the average value m and the standard deviation σ still exceed the reference value. As described above, the fact that the calculated value of the index exceeds the reference value in spite of the execution of the calibration twice means that even if the detailed calibration is further executed, the artifact is reduced to an allowable level. It is thought that can not be obtained. Therefore, if the calculated value of the average value m or the standard deviation σ includes a value exceeding the reference value even though the calibration has been executed twice, the X-ray CT apparatus will detect artifacts in the detailed calibration. The user is warned of a warning indicating that it cannot be reduced. As a method of notifying the warning, there are a method of visually informing the user of the warning using the display device 62 (see FIG. 1) and a method of informing the user of the warning by sound. If this warning occurs, the process proceeds to step S9.

In step S9, the user contacts a field engineer (FE). Upon receiving a report from the user, the field engineer visits the facility where the X-ray CT apparatus is installed and identifies the cause of the artifact.
In this way, the flow in which the flow is executed ends.

  In this embodiment, after the user instructs calibration (step S2), the phantom 51 is automatically positioned in response to this instruction (step S3). After the phantom 51 is positioned, calibration is performed. Is executed (step S7). Accordingly, the user himself / herself does not have to perform a work necessary for calibration such as positioning of the phantom 51, and therefore the downtime of the X-ray CT apparatus can be shortened.

  In the present embodiment, the index (average value m and standard deviation σ) for detecting the artifact is calculated for the image obtained by the phantom scan (step S5). Based on the index value, It is determined whether or not to execute calibration (step S6). Accordingly, since the user does not need to select a process necessary for calibration, the downtime of the X-ray CT apparatus can be further shortened.

  In the above description, when detailed calibration is executed, an example in which a processes P1 to Pa corresponding to all combinations of (kVp, SFOV, FS) are executed is described. However, in some cases, only a part of the a processes P1 to Pa may be executed. For example, considering the index determination results shown in FIG. 11, in combination H2: (kV1, small SFOV, large FS) and combination H3: (kVn, large SFOV, large FS), the average value m and the standard deviation σ Although the calculated value of the part exceeds the reference value, in the combination H1: (kV1, small SFOV, small FS), all the calculated values of the average value m and the standard deviation σ are below the reference value. Therefore, when the determination result as shown in FIG. 11 is obtained, only the calibration process corresponding to the combinations H2 and H3 is executed out of the a processes P1 to Pa, and the calibration corresponding to the combination H1 is performed. This process may not be executed. Thus, it is necessary for calibration while maintaining the effect of reducing artifacts by executing the calibration process only for the combinations where the calculated value of the average value m or the standard deviation σ exceeds the reference value. Time can be shortened.

  In the above description, the detailed calibration is executed in step S7. However, it is not always necessary to execute the detailed calibration (see FIG. 20).

FIG. 20 is an explanatory diagram of some examples of calibration different from the detail calibration.
FIG. 20 shows three examples of simple calibration, manual calibration, and machine learning calibration as examples of calibration different from detailed calibration in addition to detailed calibration.

  The simple calibration includes only a part of the a processes included in the detailed calibration. In FIG. 20, processes included in the simple calibration are indicated by symbols “Pi”, “Pi + 1”,... “Pj”. The process included in the simple calibration is selected by the user before the flow shown in FIG. 5 is started.

  In manual calibration, after the user confirms the determination result obtained in step S6, the user selects a process to be executed from the a processes P1 to Pa included in the detailed calibration. Execute this selected process. When performing manual calibration, the user first selects a process to be performed in manual calibration. Then, the user operates the input device 61 to input a command for instructing execution of manual calibration including the selected process. When this command is input, the control unit 30 controls each device and each unit in the gantry 2 so that data necessary for calibration of correction data by manual calibration is collected.

  In machine learning calibration, an X-ray CT apparatus is made to learn a process suitable for reducing artifacts by using a machine learning method before the flow is executed. Based on this, the optimal process is executed.

  In this way, various calibrations can be executed in addition to the detailed calibration.

  Further, when the calibration is executed in step S7, the user may be able to select any of detailed calibration, simple calibration, manual calibration, and machine learning calibration.

  In this embodiment, even if the calibration is executed twice, if the calculated value of the index exceeds the reference value, a warning is notified to the user. However, the number of times calibration is performed is not limited to two, and may be one or three or more times.

  In this embodiment, two indices, that is, an average value m and a standard deviation σ are used as indices for detecting artifacts. However, only one of the average value m and the standard deviation σ may be used as an index. In addition, the index is not limited to the average value m and the standard deviation σ, and the average value m or the standard deviation σ may be replaced with another feature amount. Three or more indices may be used in addition to the above-described another feature amount.

  Although the present embodiment is an X-ray CT apparatus, the present invention is also applicable to a radiation tomography apparatus that uses radiation other than X-rays, for example, gamma rays.

  A program for causing a computer to function as each means for performing control and processing in the X-ray CT apparatus and a recording medium on which the program is recorded are also an example of embodiments of the invention.

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 2 Gantry 2B Cavity part 4 Imaging table 5 Subject 6 Operation console 21 X-ray tube 22 Aperture 23 Collimator apparatus 24 X-ray detector 25 Data acquisition part 26 Rotation part 27 High voltage power supply 28 Aperture drive apparatus 29 Rotation Drive device 30 Control unit 41 Cradle 42 Drive device 50 Holder 61 Input device 62 Display device 63 Storage device 64 Processing unit 71 Deviation amount calculation unit 72 Reconfiguration unit 73 Index calculation unit 74 Determination unit 75 Generation unit 76 Count unit 90 Storage medium

Claims (10)

A radiation tomography apparatus that scans a subject using radiation,
Deviation amount calculation means for calculating a positional deviation amount between the position of the phantom installed in the cradle or the position of the phantom installed in the holder attached to the cradle and a predetermined position where the phantom should be positioned; ,
Driving means for driving the cradle so that the phantom is positioned at the predetermined position based on the positional deviation amount;
Photographing means for scanning the phantom and collecting data of the phantom;
Reconstructing means for reconstructing an image based on the phantom data and correction data necessary for image reconstruction;
Control means for controlling the imaging means so that data necessary to calibrate the correction data is collected when artifacts are included in the reconstructed image;
A radiation tomography apparatus. Index calculating means for calculating a value of an index for detecting the artifact of the image;
A determination unit that compares the value of the index with a reference value of the index, and determines whether to execute calibration for calibrating the correction data based on the comparison result;
The control means includes
The radiation tomography apparatus according to claim 1, wherein when the determination unit determines to execute the calibration, the imaging unit is controlled so that data necessary to calibrate the correction data is collected. An input device that is operated by a user and inputs a command for instructing execution of calibration for calibrating the correction data;
The radiation tomography apparatus according to claim 1, wherein when the command is input, the control unit controls the imaging unit such that data necessary for calibrating the correction data is collected. The calibration includes a plurality of processes for calibrating the correction data,
The plurality of processes are:
A process of performing a scan of the phantom with the phantom set to a position corresponding to a first SFOV;
A process in which scanning of the phantom is executed in a state where the phantom is set at a position corresponding to a second SFOV for scanning data in a wider range than the first SFOV;
A process in which scanning is performed without using the phantom;
The radiation tomography apparatus according to claim 2, comprising:   The radiation tomography apparatus according to claim 2, wherein calibration selected by a user from a plurality of calibrations for calibrating the correction data is executed.   The radiation tomography apparatus according to claim 1, wherein the imaging unit performs a scan of the phantom while changing a plurality of parameters.   For the first combination of the plurality of parameters, all calculated values of the index are less than or equal to the reference value, and for the second combination of the plurality of parameters, at least one calculated value of the index is When the reference value is exceeded, the control unit does not execute the process corresponding to the first combination among the plurality of processes, and executes the process corresponding to the second combination. The radiation tomography apparatus according to claim 6, wherein the imaging unit is controlled.   The plurality of parameters include at least one of a parameter representing a tube voltage of an X-ray tube, a parameter representing a width of a data collection range, and a parameter representing a size of an X-ray focal point. Or the radiation tomography apparatus of 7. A gantry having a cavity that constitutes an imaging space on which the subject is placed;
The radiation tomography apparatus according to claim 1, wherein the predetermined position is an isocenter of the hollow portion.
is there, A program applied to a radiation tomography apparatus that scans a subject using radiation,
The program for implement | achieving the deviation | shift amount calculation means and reconstruction means of Claim 1.