JP5349174B2 - Measurement program for measuring the distance between X-ray detection elements of an X-ray CT apparatus and an X-ray detector - Google Patents

Description

  The present invention relates to a measurement program for measuring the distance between an X-ray CT apparatus and an X-ray detector of an X-ray detector, and in particular, X-ray detection constituting an X-ray detector mounted on the X-ray CT apparatus. The present invention relates to a method for measuring a distance between elements.

  In Patent Document 1, an m × n channel matrix sensor is formed as a unit element array as a manufacturing method of a multi-slice detector in which a plurality of rows are arranged in two or more rows in the slice direction (direction orthogonal to the channel direction). A method of manufacturing an X-ray detector corresponding to multi-slice by tiling the element array in the slice direction is disclosed.

JP 2001-242253 A

  In an X-ray CT apparatus, high pitch accuracy is required for the arrangement of X-ray detection elements in order to suppress invalid exposure and improve the quality of a reconstructed image. On the other hand, in the manufacturing method as in Patent Document 1, the request has been satisfied by performing tiling with high accuracy. However, the number of tilings is increased due to the demand for further multi-slice of the X-ray CT apparatus. There has been a problem that it has become enormous and it has become difficult to ensure high pitch accuracy between the X-ray detection elements.

  Further, even if it is attempted to optically measure the pitch of the X-ray detection element in a state where the X-ray detection element is tiled, it is configured by a light reflecting member that determines the pitch of the X-ray detection element in the state after tiling. There is a problem that the channel separation layer is very difficult because it is covered by the light reflecting member on the surface and the collimator plate is present.

  Further, instead of directly measuring the pitch of the X-ray detection element directly, a reference is provided at a point that can be measured optically, and the distance between the reference is measured, or the measurement is performed using a three-dimensional measuring device. However, it is difficult to measure the pitch at the system delivery destination because a large-scale device is required to perform highly accurate measurement in a short time. Therefore, when repairing a failure of the X-ray detection element, the repair cost and time can be minimized by replacing the X-ray detection element in units of modules at the system delivery destination, as described above. Since it is difficult to measure the pitch after replacement, it is currently being replaced with a set of X-ray detectors that have been pitch-measured at the time of product manufacture, and there was a problem that it was very costly and time consuming. .

  The present invention has been made in view of the above problems, and an X-ray CT apparatus capable of measuring a pitch between channels of an X-ray detector without relying on optical measurement, and a channel pitch measurement program for the X-ray detector. The purpose is to provide.

  An X-ray CT apparatus according to the present invention includes an X-ray tube that generates X-rays and a plurality of X-ray detection elements arranged in a matrix in a channel direction and a slice direction, and transmits the X through the subject. An X-ray detector for detecting a line and outputting projection data; a rotating means for rotating the X-ray tube and the X-ray detector; and an image reconstruction means for performing an image reconstruction operation based on the projection data And a sinogram reading means for reading a sinogram based on projection data obtained by scanning an image with an attenuation body arranged between the X-ray tube and the X-ray detector, and a predetermined value based on the sinogram A density profile generating means for generating a density profile in which the density value of the attenuation body for each view is plotted in the channel direction; and a density profile for each of the density profiles for each predetermined view. The representative channel position over a plurality of views, with representative channel calculation means for calculating the representative channel where the representative point of the image is located and the corresponding channels between the X-ray detection elements to be measured on the density profile. The distance in the channel direction between the X-ray detection elements is calculated based on the change amount of the X-ray detection element, the ideal value of the change amount of the representative channel position, and the design value between the X-ray detection elements to be measured. And a distance calculating means.

  The “distance between X-ray detection elements” corresponds to the distance between channels when one X-ray detection element forms one channel.

  A measurement program for measuring the distance between X-ray detection elements of the X-ray detector according to the present invention is mounted on an X-ray CT apparatus, and a plurality of X-ray detection elements are arranged in a matrix in a channel direction and a slice direction. A measurement program for measuring a distance between the X-ray detection elements of an X-ray detector configured to detect the X-ray transmitted through a subject and output projection data, A sinogram reading step for reading a sinogram based on projection data obtained by scanning an attenuation body with an X-ray CT apparatus, and the density value of the attenuation body for each predetermined view is plotted against a channel based on the sinogram. A density profile generation step for generating a density profile and a density profile representative point for each of the density profiles for each predetermined view A representative channel calculating step for calculating a representative channel positioned; and a change amount of the representative channel position across a plurality of views sandwiching between channels corresponding to the X-ray detection elements to be measured on the density profile; A distance calculating step of calculating a distance in the channel direction between the X-ray detection elements based on an ideal value of the change amount of the representative channel position and a design value between the X-ray detection elements to be measured; Are executed by a computer.

  According to the present invention, a density profile of an attenuation body for each predetermined view is generated based on projection data of the attenuation body, and the distance between the X-ray detection elements is measured by calculating using the density profile and the design value. can do. Therefore, since it is possible to measure the pitch without using a high-precision and large distance measuring device between X-ray detection elements (hereinafter referred to as “element pitch”), X due to failure of the X-ray detection element at the system delivery destination. Measurement of the element pitch after replacement of the line detection element module becomes easy, and it is possible to recover from a detector failure in a short time and at low cost. Further, according to the present invention, it is possible to measure the variation in the element pitch of the X-ray detection element by the same method even when the detector is manufactured.

Front view of the X-ray CT apparatus according to the present embodiment Schematic diagram of a side cross section of an X-ray CT apparatus according to the present embodiment Unit configuration diagram of X-ray CT apparatus according to this embodiment Schematic diagram showing the arrangement (polygon) of X-ray detection element modules Schematic diagram showing a multi-slice X-ray detection element module A-A 'sectional view of the X-ray detection element module shown in FIG. Configuration diagram of element pitch measurement program The flowchart which shows the flow of a process of the element pitch measuring method which concerns on 1st embodiment. Attenuator layout in the first embodiment Relationship diagram of sinogram and view data in the first embodiment The schematic diagram which shows the processing content of the measuring method of the element pitch in 1st embodiment Relationship diagram of sinogram and view data in the second embodiment The schematic diagram which shows the processing content of the measuring method of the pitch between modules in 2nd embodiment

  Hereinafter, embodiments to which the present invention is applied will be described. Hereinafter, in all the drawings for explaining the embodiments of the present invention, those having the same function are denoted by the same reference numerals, and repeated explanation thereof is omitted.

  Hereinafter, a schematic configuration of the X-ray CT apparatus according to the present embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a front view of an X-ray CT apparatus according to the present embodiment, FIG. 2 is a schematic side sectional view of the X-ray CT apparatus according to the present embodiment, and FIG. 3 is an X-ray CT apparatus according to the present embodiment. FIG.

  As shown in FIG. 3, the X-ray CT apparatus M according to the present invention mainly includes a scanner unit 1, a table unit 14, and a console unit 12, and the scanner unit 1, table unit 14, and console unit 12. Are connected to each other by a signal cable 13.

  As shown in FIGS. 1 and 2, the scanner unit 1 of the X-ray CT apparatus M includes a rotating plate 2 that rotates about the subject 11, and a top plate 14 t on which the subject 11 is placed at the center. Is provided with an opening 1h. An X-ray tube device 3 in which an X-ray tube that emits X-rays for scan measurement is placed on the rotating plate 2 and heat generated in the X-ray tube device 3 are efficiently radiated. The heat radiation device 4, the X-ray collimator 5 that narrows the X-rays from the X-ray tube device 3 to a predetermined thickness, and the halation on the image fixed under the X-ray tube device 3 are controlled and the X-ray exposure is reduced. Compensation filter 6 for attenuating the intensity of X-rays, X-ray detector 7 for receiving X-rays transmitted through subject 11 and outputting an electrical signal (projection data) corresponding to the X-ray intensity, and X-ray detection An amplification circuit device 8 that amplifies the electrical signal of the device 7 to an appropriate level and converts it into digital data for performing image reconstruction calculation, and a control device 10 that controls the movement of the rotating plate motor 9 are mounted. .

  Although not shown, the console unit 12 of the X-ray CT apparatus M generates a CT image by reconfiguring projection data and an input device such as a keyboard and a trackball for inputting parameters and operation instructions. Image reconstruction program, measurement program for measuring the distance between the X-ray detection elements of the X-ray detector according to the present embodiment (hereinafter referred to as “element pitch”), and elements output from the measurement program Various types of programs such as a data interpolation / correction program for interpolating / correcting projection data between channels for which projection data cannot be obtained based on the pitch, reconstructed images, and element pitches output from the measurement program From storage devices such as hard disks and memories, control / arithmetic units consisting of CPUs and MPUs, and reconstructed images and measurement programs Comprising a display unit for displaying display data indicating the force is an element pitch. The program is loaded into the memory and executed by the CPU or MPU to realize its function.

  Next, the configuration of the X-ray detector 7 will be described with reference to FIGS. 4, 5, and 6. FIG. 4 is a schematic diagram showing the arrangement (polygon) of the X-ray detection element module, and FIG. 5 is a schematic diagram showing the multi-slice X-ray detection element module. Of these, (a) is a schematic view seen from the front. A figure is shown and (b) is a mimetic diagram seen from the side. FIG. 6 is a cross-sectional view taken along the line A-A ′ of the X-ray detection element module 20 shown in FIG. 5.

  As shown in FIGS. 4 and 5, the X-ray detector 7 combines a scintillator array 21 that generates light by irradiation of radiation and a photoelectric conversion element 22 that converts light generated by the scintillator array 21 into current. An X-ray detection element module 20 having four unit element arrays 28 in which 6 × 6 unit elements are arranged on the detection element module substrate 23 along the slice direction is arranged in a substantially arc-shaped polygon. As shown in FIGS. 5 and 6, each X-ray detection element module 20 includes several channels of photoelectric conversion elements 22 arranged on a detection element module substrate 23, a scintillator array 21 stacked thereon, and a detection circuit. The scintillator array 21 is separated by a light reflecting member 25 corresponding to a plurality of channels of the photoelectric conversion element 22. Further, a light reflecting member 26 that prevents the outflow of light to other than the corresponding photoelectric conversion elements is also provided on the surface of the scintillator array 21. 5 indicate an example of the element pitch (corresponding to the joint pitch of the X-ray detection element module 20 in the second embodiment).

  Further, a collimator plate 27 for controlling the X-ray dose incident on each scintillator array 21 and reducing scattered radiation is disposed on the X-ray entrance side of the further divided scintillator array 21. Without this collimator plate 27, the output of the channel for detecting scattered X-rays increases, and the amount of attenuation of the subject on the measurement path is apparently measured, which is an error. If there is such an error, the density resolution of the reconstructed image reconstructed using these data is lowered. In particular, in a subject with a large attenuation rate, the amount of scattered X-rays with respect to the X-ray dose via the measurement path is relatively large, so that a decrease in density resolution becomes a problem.

  Next, the element pitch measurement program according to the present embodiment will be described with reference to FIG. FIG. 7 is a block diagram of the element pitch measurement program.

  The element pitch measurement program according to the present embodiment includes a sinogram reading unit 71 that reads a sinogram as a basis for generating a density profile, and parameters for setting parameters such as the position of the element pitch to be measured and the number of views for generating the density profile. A setting unit 72; a density profile generation unit 73 that generates a density profile based on the read sinogram; a representative channel calculation unit 74 that calculates a channel number indicating a representative value of each density profile; and a representative channel position of each density profile A distance calculation unit 75 that calculates a distance (element pitch) between the X-ray detectors based on an ideal value of the change amount of the representative channel position, an ideal value of the change amount of the representative channel position, and a design value of the element pitch to be measured; And an output unit 76 for outputting data indicating the calculated element pitch. . The output unit 76 may output the calculated element pitch to the display device of the console unit 12. Further, when the storage device of the console unit 12 stores a projection data interpolation / correction program, for example, a program for interpolating / correcting unequal pitch projection data into equal pitch projection data, the projection data interpolation / correction program is stored. Alternatively, the calculated element pitch may be output and the projection data may be interpolated / corrected.

  Next, the element pitch measurement method of this embodiment is demonstrated based on FIGS. FIG. 8 is a flowchart showing a process flow of the element pitch measurement method according to the first embodiment, FIG. 9 is an attenuation body arrangement diagram in the first embodiment, and FIG. 10 is a diagram of sinogram and view data in the first embodiment. FIG. 11 is a schematic diagram showing the processing contents of the element pitch measurement method in the first embodiment.

(Step S1)
The sinogram reading unit 71 reads a sinogram used for measuring the element pitch (S1). In the present embodiment, a columnar rod 31 that is an attenuation body configured in a columnar shape using a uniform material (a general structural material such as iron, aluminum, and plastic) is used in a scan range 32 shown in FIG. A sinogram obtained by setting up outside and taking one rotation is read. The reason for installing the rod 31 outside the scan range 32 is to measure the element pitch within the entire channel range including the peripheral portion of the X-ray detector 7. FIG. 10 shows a sinogram generated from projection data obtained by photographing with the rod 31 placed outside the scan range 32. The vertical axis of the sinogram of FIG. 10 indicates the rotation angle, and the horizontal axis indicates the fan beam direction, that is, the channel direction. Hereinafter, the rotation angle is referred to as a view, and data at each angle is referred to as view data. By installing the rod 31 outside the scan range 32, the profile of the rod 31 is measured over all channels in the sinogram of FIG.

  Further, two sinograms 33 and 34 of the rod 31 are shown in the sinogram of FIG. The sinogram 33 is a sinogram in which projection data of a view in which the rod 31 is photographed in a state closer to the X-ray tube 3 than the X-ray detector 7 during the scan photographing, and the sinogram 34 is a rod in the scan photographing. 31 is a sinogram in which projection data of a view taken in a state closer to the X-ray detector 7 than the X-ray tube 3 is plotted. In the step of generating a density profile, which will be described later, compared to the sinogram 33, it is more accurate to use the sinogram 34 in which the change in the channel direction of the rod 31 per unit view (for example, 6 views) is more gradual. Can be measured.

  The sinogram reading unit 71 may read the projection data of the rod 31 instead of reading the sinogram, and generate a sinogram based on this.

(Step S2)
Parameters necessary for measuring the element pitch are set (S2). As parameters, for example, there are two channel numbers corresponding to the element pitch to be measured, and a slice position where the element pitch to be measured is located. This is because, as shown in FIG. 5, the element pitch can change when the slice position changes even in the same channel. The operator inputs parameters to be set from the input device of the console unit 12, and the parameter setting unit 72 sets the parameters based on the input values. The parameter setting unit 72 may set necessary parameters by reading various parameters stored in advance in the storage device of the console unit 12 in addition to the input from the operator. This step is omitted when parameter setting is unnecessary.

(Step S3)
The density profile generation unit 73 uses the sinogram 34 to generate a density profile in which the density value of the rod 31 for each view is plotted against the channel (S3). The density profile may be obtained for each view or for each of a plurality of views. The sinogram 33 may be used when generating the concentration profile.

(Step S4)
The representative channel calculation unit 74 calculates, for each density profile generated in step S3, the number of the representative channel where the representative point of each density profile is located (S4). In this embodiment, the center of gravity of each density profile is used as a representative point, and the number of the center of gravity channel is obtained. The representative point may be a channel position where the density profile is a peak value or a channel position where the half point width of the density profile is the middle point.

(Step S5)
The distance calculation unit 75 designs the amount of change in the positions of the two gravity center channels obtained from the two profiles sandwiching the element pitch to be measured by the distance calculation unit 75, the ideal value of the amount of change, and the element pitch design. The target element pitch is measured based on the value (S5). The distance calculation unit 75 selects two views that satisfy the condition that the density profile of the rod 31 does not include between the channels to be measured while sandwiching between the channels corresponding to the element pitch to be measured on the density profile. To do. For example, in FIG. 10, when the measurement target is between the 440 channel and the 441 channel, the view 1434 and the view 1440 are two views selected so as to satisfy this condition. Then, the change amount ΔG (i) of the center of gravity channel position between these two views is compared with the geometrical theoretical value ΔG (ideal) to determine the element pitch to be measured by the following formula (1) ( Measure according to 2). The geometric theoretical value ΔG (ideal) corresponds to the amount of change in the center-of-gravity channel position between the two selected views when the element pitch to be measured is provided according to the design value.

Channel Gap = − {ΔG (i) −ΔG (ideal)} × P [mm] (1)
Element pitch to be measured = Channel Gap + P (2)
However, deviation from the design value of the element pitch to be measured: Channel Gap
Element pitch (design value): P [mm]
Center of gravity channel position change (theoretical value): ΔG (ideal)
Change in the center of gravity channel position when the channel corresponding to the element pitch to be measured is sandwiched: ΔG (i)

  The processing in this step will be described with reference to FIG. FIG. 11 is a schematic diagram showing the contents of processing when the channel corresponding to the element pitch to be measured is between 440 channel and 441 channel. In this example, the projection data of the rod 31 is displayed in 6 views. Plotting every other time generates a density profile for the two views 1434, 1440.

  The density profile (from channel 432 to 440 channel) 40 in the 1434 view and the density profile (from channel 441 to 448 channel) 41 in the 1440 view are the element pitches to which the center of gravity channels of the density profiles 40 and 41 are measured. It is a density profile of two views sandwiching and not including the corresponding 440 channel and 441 channel.

In step S4, the representative channel calculation unit 74 calculates the centroid channel number of each density profile, the centroid channel of the density profile 40 is G ₁₄₃₄ = 4366.5845 (channel), and the centroid channel of the density profile 41 is G ₁₄₄₀ = 444.5000 (channel).

  Therefore, the element pitch corresponding to the 440-441 channel is measured by assuming that the center-of-gravity channel obtained from the plotted projection data is moving at an equal speed between the six views.

Change amount of center of gravity channel position: ΔG (i) = G ₁₄₄₀ −G ₁₄₃₄ (3)
Using this change amount, the element pitch to be measured can be obtained from the equations (1) and (2). For example, if ΔG (ideal) = 8.00735 and P = 1.000 (mm / channel), the deviation Channel Gap from the ideal value is
Channel Gap = − {(444.5000−436.5845) −8.00735} × 1.000 = 0.092 (mm)
It becomes. Therefore, the distance (element pitch) P _{440-441 in} the channel direction between the X-ray detection elements to be measured is
P _440-441 = 0.092 + 1 = 1.092 (mm)
Thus, the element pitch corresponding to the 440-441 channel pitch is 1.092 mm.

(Step S6)
The output unit 75 outputs the element pitch calculated in step S5 according to the usage mode (S6). When the projection data is interpolated / corrected using the element pitch, the output unit 75 stores the projection data in the storage device of the console unit 12 so that the projection data interpolation / correction program can be read when necessary, or the projection data During the execution of the interpolation / correction program, the data may be delivered from the output unit 75, or display data indicating the element pitch may be generated and displayed on the display device of the console unit 12.

  According to the present embodiment, the element pitch can be measured using the projection data of the rod 31 without depending on the optical measurement method. This eliminates the need for an optical measuring device. Also, the element pitch can be measured when the X-ray detector element module 20 constituting the X-ray detector 7 is replaced at the system delivery destination.

<Second embodiment>
In the X-ray detector 7 according to the second embodiment, the distance between the adjacent X-ray detection element modules 20 (hereinafter referred to as “seam pitch”) is sufficiently larger than the detection element pitch variation in the X-ray detection element module 20. This is applied when the joint pitch of the X-ray detector element module 20 is the element pitch to be measured. In this embodiment, instead of the geometric theoretical value of the first embodiment, the amount of change in the representative channel position between views that do not sandwich the joint of the X-ray detection element module 20 is used.

  Hereinafter, the second embodiment will be described with reference to FIGS. FIG. 12 is a diagram showing the relationship between sinogram and view data in the second embodiment, and FIG. 13 is a schematic diagram showing the processing contents of the inter-module pitch measurement method in the second embodiment.

In the second embodiment, in addition to the two views specified in step S5 of the first embodiment, a plurality of views that do not sandwich the seam of the X-ray detection element module 20 are specified. Then, based on the change amount of the center-of-gravity channel position between the plurality of views, the change amount ΔG (measure) between views where the joint of the X-ray detection element module 20 is not sandwiched is measured. This ΔG (measure) is replaced with the geometrical theoretical value ΔG (ideal) in the first embodiment, and a deviation from the design value of the element pitch to be measured is measured according to the following equation (4).
Channel Gap = − (ΔG (i) −ΔG (measure)) × P [mm] (4)
However, the element pitch to be measured: Channel Gap
X-ray detector element module joint pitch (design value): P [mm]
Amount of change between views without X-ray detector element module seam: ΔG (measure)
Amount of change between views with X-ray detection element module seam in between: ΔG (i)

  FIG. 13 is a density profile in which projection data is plotted every 6 views based on the sinogram of FIG. 12, and the seam of the X-ray detection element module 20 is between the 440 channel and the 441 channel. Therefore, ΔG (measure) is measured using two density profiles on each of the right and left sides, a total of four density profiles across the joint.

  The representative channel calculation unit 74 calculates the center-of-gravity channel for each of the density profile 42 (from 425 to 432 channels) in the 1428 view and the density profile 43 (from 449 to 456 channels) in the 1446 view in the above S4. ing.

The center of gravity channel number of the density profile 42 is G ₁₄₂₈ = 428.5781 (channel), and the center of gravity channel number of the density profile 43 is G ₁₄₄₆ = 452.5083 (channel).

  The density profile 40 of 1434 views and the density profile 41 of 1440 views are the same as in the first embodiment.

  By assuming that the center-of-gravity channel obtained from the plotted projection data is moving at an equal speed between 18 views (3 × 6 views), the element pitch corresponding to the 440-441 channel is measured.

  The amount of change ΔG (i) between views sandwiching the joint of the X-ray detection element module 20 is the same as in the first embodiment, and is obtained by the above-described equation (3).

A change amount ΔG (measure) between views that do not sandwich the joint of the X-ray detection element module 20 is obtained by the following equation (5).
ΔG (measure) = {(G ₁₄₄₆ −G ₁₄₄₀ ) + (G ₁₄₃₄ −G ₁₄₂₈ )} / 2 (5)
Alternatively, ΔG (measure) = G ₁₄₄₆ −G ₁₄₄₀ and ΔG (measure) = G ₁₄₃₄ −G ₁₄₂₈ may be used.

When P = 1.0 mm / Channel and substituting Equation (3) and Equation (5) into Equation (4),
Channel Gap =-{(444.5000-436.5845)-(452.5083-444.5000 + 436.5845-428.5781) / 2} x 1.000 = 0.092 (mm)
Therefore, the deviation from the design value between 440-441 channels is 0.092 mm.

Substituting this into equation (2) of the first embodiment,
P _440-441 = 0.092 + 1 = 1.092 (mm)
Thus, the element pitch corresponding to the 440-441 channel is 1.092 mm.

  According to the present embodiment, since the movement amount of the center of gravity channel position when the joint of the X-ray detection element module 20 is not sandwiched using the projection data, the geometrical theoretical value is unknown as in the first embodiment. Even in such a case, the desired distance between the X-ray detection element modules can be measured.

<Third embodiment>
In the second embodiment, the material and the size of the attenuation body are not limited. However, in the third embodiment, as the attenuation body, the width in the channel direction of the concentration profile of the attenuation body is the X-ray detection element module 20. A rod 31 having a width equal to or less than the width is used.

  By limiting the material to metal, attenuation suitable for generation of the concentration profile can be obtained. Furthermore, the size of the attenuation body is configured so that the width in the channel direction of the concentration profile of the attenuation body is equal to or less than the width of the X-ray detection element module 20, so that the X-ray detection module seam to be measured is The density profile of the rod 31 is not applied to the adjacent X-ray detection module joint. According to this embodiment, since the density profile with sufficient attenuation can be generated in a shape that does not straddle the seam of the X-ray detection element module 20, the seam pitch of the X-ray detection element module 20 can be measured more accurately. Can be improved.

<Fourth embodiment>
The fourth embodiment reads projection data obtained by photographing a plurality of rotations in S1 of the first and second embodiments, and uses projection data obtained by dividing the projection data for the plurality of rotations by the number of rotations. , S2 and subsequent processes are performed. Although the variation between views causes the element pitch measurement accuracy to deteriorate, according to this embodiment, by averaging projection data for a plurality of rotations, the variation between views is reduced and the element pitch is measured. Accuracy can be improved.

<Fifth embodiment>
In the fifth embodiment, the projection data captured by setting the rod 31 in the scan range 32 in S1 of the first and second embodiments is read. By arranging the arrangement of the rod 31 within the scan range 32, the measurement of the element pitch around the X-ray detector 7 becomes inconvenient, but the measurement accuracy at the center of the X-ray detector 7 having a strong influence on image quality is increased. It can be improved.

1: scanner unit, 1h: opening, 2: rotating plate, 3: X-ray tube device, 4: heat radiation device, 5: X-ray collimator, 6: compensation filter, 7: X-ray detector, 8: amplifier circuit device , 9: motor for rotating plate, 10: control device, 11: subject, 12: console unit, 13: signal cable, 14: table unit, 14t: top plate, 20: X-ray detection element module, 21: scintillator Array: 22: Photoelectric conversion element, 23: Detection element module substrate, 24: Connector, 25: Light reflection member (separation layer), 26: Light reflection member (surface), 27: Collimator plate, 28: Unit element array, 31 : Cylindrical rod, 32: scan range, 33: profile, 34: profile, 40: density profile, 41: density profile, 42: density profile, 43: density profile , M: X-ray CT system

Claims (10)

An X-ray tube that generates X-rays;
An X-ray detector configured by arranging a plurality of X-ray detection elements in a matrix in the channel direction and the slice direction, detecting the X-ray transmitted through the subject, and outputting projection data;
Rotating means for rotating the X-ray tube and the X-ray detector;
Image reconstruction means for performing image reconstruction calculation based on the projection data,
A sinogram reading means for reading a sinogram based on projection data obtained by scanning a scan with an attenuation body arranged between the X-ray tube and the X-ray detector;
Based on the sinogram, a concentration profile generation means for generating a concentration profile in which the concentration value of the attenuation body for each predetermined view is plotted with respect to a channel;
Representative channel calculation means for calculating a representative channel where a representative point of the density profile is located for each density profile for each predetermined view;
The change amount of the representative channel position across a plurality of views across the channels corresponding to the measurement target on the density profile, the ideal value of the change amount of the representative channel position, Distance calculation means for calculating a distance in the channel direction between the X-ray detection elements based on a design value between the X-ray detection elements to be measured;
An X-ray CT apparatus comprising: The distance calculation means calculates a value obtained by multiplying the difference between the change amount of the representative channel position and the ideal value by the design value as a deviation amount from the design value of the distance between the X-ray detection elements, Calculating the distance between the X-ray detection elements by adding the design value to the deviation amount;
The X-ray CT apparatus according to claim 1. The ideal value is a geometric theoretical value of a change amount of the representative channel position when the X-ray detection elements to be measured are arranged according to the design value, or the measurement target on the concentration profile. The amount of change in the representative channel position over a plurality of views that do not sandwich the corresponding channels between the X-ray detection elements.
The X-ray CT apparatus according to claim 1 or 2 , wherein The X-ray CT apparatus further includes projection data interpolation / correction means for interpolating or correcting projection data between channels where the projection data cannot be obtained based on the calculated distance between the X-ray detection elements,
The image reconstruction means performs an image reconstruction calculation based on the projection data after interpolation or correction.
The X-ray CT apparatus according to any one of claims 1 to 3 . The X-ray CT apparatus further includes display means for displaying the calculated distance between the X-ray detection elements.
The X-ray CT apparatus according to any one of claims 1 to 4 , wherein: The X-ray detector includes an X-ray detection element module configured to include a substrate, a plurality of channels of photoelectric conversion elements arranged on the substrate, and a scintillator array stacked on the photoelectric conversion elements. It is configured by arranging in the channel direction with a gap,
The distance calculating means calculates a gap between the X-ray detection element modules as a distance between the X-ray detection elements .
X-ray CT apparatus according to any one of claims 1 to 5, characterized in that. The attenuation body is configured by using a metal cylindrical body whose width in the channel direction of the concentration profile of the attenuation body is equal to or less than the width of the X-ray detection element module.
The X-ray CT apparatus according to claim 6 . The sinogram reading means reads the sinogram based on projection data obtained by setting the attenuation body outside a scan range and performing a scan shooting.
X-ray CT apparatus according to any one of claims 1 to 7, characterized in that. The sinogram reading means reads the sinogram obtained by averaging the projection data obtained by scanning the attenuation body a plurality of times.
X-ray CT apparatus according to any one of claims 1 to 7, characterized in that. An X-ray mounted on an X-ray CT apparatus, configured by arranging a plurality of X-ray detection elements in a matrix in the channel direction and the slice direction, and detecting the X-ray transmitted through the subject and outputting projection data A measurement program for measuring a distance between the X-ray detection elements of a detector,
A sinogram reading step for reading a sinogram based on the projection data obtained by scanning the attenuation body with the X-ray CT apparatus;
A concentration profile generating step for generating a concentration profile in which the concentration values of the attenuation body for each predetermined view are plotted with respect to the channel based on the sinogram;
A representative channel calculating step for calculating a representative channel where a representative point of the density profile is located for each density profile for each predetermined view;
The change amount of the representative channel position across a plurality of views across the channels corresponding to the measurement target on the density profile, the ideal value of the change amount of the representative channel position, A distance calculating step of calculating a distance in the channel direction between the X-ray detection elements based on a design value between the X-ray detection elements to be measured;
Is a measurement program for measuring the distance between X-ray detection elements of an X-ray detector.

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