JP2003052685A - X-ray dose correction method and x-ray ct unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accomplish the correction of X-ray dose normally even when X rays incident into a reference channel is intercepted by an object to be examined. SOLUTION: When the X rays incident into the reference channel 27CR is intercepted by the object to be examined H while an X-ray detector 27 or the like turns about the center IC of the rotation, the reference data obtained from the reference channel 27CR is not used and instead, the X-ray projection data, obtained from the data channel 27CN at an end thereof opposite to the reference channel 27CR, are used to accomplish the correction of the X-ray dose.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray dose correction method and an X-ray CT (Computed Tomography) apparatus, and more particularly to a normal X-ray even when an X-ray incident on a reference channel is blocked by an object to be inspected. The present invention relates to an X-ray dose correction method and an X-ray CT apparatus capable of dose correction.

[0002]

2. Description of the Related Art FIG. 7 shows an object H to be inspected and an X-ray fan beam X when the object H is positioned for imaging.
It is a schematic diagram which shows the relationship of r. The object H to be inspected is positioned so that the X-rays not transmitted through the object H to be inspected enter the reference channel 27CR provided at the first end of the X-ray detector 27.

An X-ray tube, an X-ray detector 27, etc. (not shown) are rotated around a rotation center IC as shown by an arrow in the figure,
Reference data is collected in the reference channel 27CR for each rotation angle corresponding to each view, and X-ray projection data is collected in the data channel of the X-ray detector 27. After that, X-ray dose correction is performed to normalize the X-ray projection data obtained in each data channel with the reference data obtained in the reference channel, and this is used for generation of a tomographic image.

[0004]

It is premised that the reference channel 27CR receives X-rays that have not passed through the object H to be inspected. However, the inspection object H
When the position of is inadequate, the X-ray incident on the reference channel 27CR in some views may be blocked by the object H, as shown in FIG. However, if the X-ray incident on the reference channel 27CR is blocked by the object H to be inspected, the reference data will have an incorrect value, and the X-ray dose correction will not be performed properly. Therefore, an object of the present invention is to provide an X-ray dose correction method and an X-ray dose correction method capable of performing normal X-ray dose correction even when the X-ray incident on the reference channel is blocked by the inspection object.
It is to provide a line CT apparatus.

[0005]

SUMMARY OF THE INVENTION In a first aspect, the present invention provides a first X-ray detector having multiple data channels.
A reference channel is provided at the end to determine whether the reference data obtained in the reference channel is normal or abnormal. If it is determined to be normal, X obtained in each data channel
Normalize the line projection data with the reference data obtained from the reference channel, and if it is judged as abnormal, refer to the data obtained from the data channel of each data channel where the X-rays that have not transmitted through the inspected object are incident. There is provided an X-ray dose correction method characterized by performing the normalization using as data. X according to the first aspect
The dose correction method checks the reference data obtained in the reference channel. Then, in a normal case (when it is estimated that an X-ray that does not pass through the object to be inspected is incident on the reference channel), X-ray dose correction is performed using the reference data. On the other hand, in the case of an abnormality (when it is estimated that the X-rays that have passed through the object to be inspected are incident on the reference channel), the data can be obtained on the data channel on which the X-rays that have not penetrated the object to be inspected are incident. X-ray dose correction is performed using the obtained data as reference data. As a result, even when the X-ray incident on the reference channel is blocked by the object to be inspected, the X-ray dose can be corrected normally. It should be noted that it is preferable to select, for example, a data channel on the opposite side of the reference channel and the X-ray detector as the data channel into which the X-rays that have not transmitted through the device under test are incident. .

[0006] In a second aspect, the present invention provides the X structure as described above.
In the dose correction method, the reference data of the view at the start of scanning and the reference data of each view are compared, and if there is no difference or small, it is judged to be normal, and if the difference is large, it is judged to be abnormal. An X-ray dose correction method is provided. Generally, at the time of positioning an object to be inspected for imaging, X-rays that have not passed through the object to be inspected are incident on the reference channel. Therefore, in the X-ray dose correction method according to the second aspect, the reference data of the view at the start of scanning is regarded as the reference value, the reference data that is not much different from this is determined to be normal, and the reference data that is significantly different is determined to be abnormal. To do. In the present specification, "when there is no difference or small difference" includes "when the ratio is 1 or close to 1",
“When the difference is large” includes “when the ratio is larger than 1”.

[0007] In a third aspect, the present invention provides an X having the above structure.
In the dose correction method, the average value of the reference data of multiple views is compared with the reference data of each view, and if there is no difference or a small difference, it is determined to be normal, and if the difference is large, it is determined to be abnormal. An X-ray dose correction method is provided. In general, only a part of the whole view has X-rays transmitted through an object to be inspected and incident on the reference channel. Therefore, if the average of the reference data of a plurality of views is obtained, it is considered that the reference data does not deviate significantly from the appropriate value. Therefore, in the X-ray dose correction method according to the third aspect, the average value of the reference data of a plurality of views is regarded as a reference value, reference data that is not much different from this is determined to be normal, and reference data that is significantly different is determined to be abnormal. To do.

[0008] In a fourth aspect, the present invention provides the X-structure of the above construction.
In the dose correction method, the average value of the reference data obtained by the calibration scan and the reference data of each view are compared.If there is no difference or a small difference, it is judged as normal, and if the difference is large, it is judged as abnormal. A characteristic X-ray dose correction method is provided. In general, only a part of the whole view has X-rays transmitted through an object to be inspected and incident on the reference channel. Therefore,
If the average of the reference data obtained by the calibration scan is calculated, it is considered that the reference data does not deviate significantly from the appropriate value. Therefore, in the X-ray dose correction method according to the fourth aspect, the average value of the reference data obtained by the calibration scan is regarded as the reference value, the reference data having no great difference from this is determined to be normal, and the reference data having a large difference is determined. Judge as abnormal.

[0009] In a fifth aspect, the present invention provides the X-structure of the above construction.
In the dose correction method, the maximum value of the reference data during scanning is compared with the reference data of each view, and if there is no difference or small difference, it is judged as normal, and if the difference is large, it is judged as abnormal. An X-ray dose correction method is provided. The value of the reference data is larger when the X-rays that have not passed through the inspected object enter the reference channel than when the X-rays that have passed through the inspected object enter the reference channel. Therefore, the maximum value of the reference data is considered to be proper reference data. Therefore, in the X-ray dose correction method according to the fifth aspect, the maximum value of the reference data is regarded as the reference value, reference data that is not much different from this is determined to be normal, and reference data that is significantly different is determined to be abnormal.

According to a sixth aspect, the present invention provides an X having the above construction.
In the dose correction method, the maximum frequency value of the reference data during scanning is compared with the reference data of each view, and if there is no difference or a small difference, it is judged as normal, and if the difference is large, it is judged as abnormal. An X-ray dose correction method is provided. In general, only a part of the whole view has X-rays transmitted through an object to be inspected and incident on the reference channel. Therefore, the maximum frequency value of reference data, that is, the value of reference data that appears most frequently is considered to be proper reference data. Therefore, in the X-ray dose correction method according to the sixth aspect, the maximum frequency value of the reference data is regarded as the reference value, reference data that is not much different from this is determined to be normal, and reference data that is significantly different is determined to be abnormal.

In a seventh aspect, the present invention provides an X-ray detector having a number of data channels, a reference channel provided at a first end of said X-ray detector, and a reference obtained by said reference channel. Reference data evaluation means for determining whether the data is normal or abnormal, and when the reference data evaluation means is determined to be normal, the X-ray projection data obtained in each data channel is normalized by the reference data obtained in the reference channel, and abnormal If it is determined that the X-ray dose correction unit performs the normalization by using as the reference data the data obtained in the data channel in which the X-rays that have not passed through the inspected object are incident, among the respective data channels. Provided is an X-ray CT apparatus characterized by the above. The X-ray CT apparatus according to the seventh aspect can suitably implement the X-ray dose correction method according to the first aspect.

[0012] In an eighth aspect, the present invention provides the X structure as described above.
In the line CT apparatus, the reference data evaluation means compares the reference data of the view at the start of scanning with the reference data of each view, determines that there is no difference or a small difference, and determines that the difference is large, and determines that the difference is abnormal. Provided is an X-ray CT apparatus characterized by making a determination. The X-ray CT apparatus according to the eighth aspect can suitably implement the X-ray dose correction method according to the second aspect.

According to a ninth aspect, the present invention provides an X having the above construction.
In the line CT apparatus, the reference data evaluation unit compares the average value of the reference data of a plurality of views with the reference data of each view, determines that there is no difference or a small difference, and normal if there is a large difference. Provided is an X-ray CT apparatus characterized by making a determination. In the X-ray CT apparatus according to the ninth aspect, the X-ray CT apparatus according to the third aspect is used.
The dose correction method can be suitably implemented.

According to a tenth aspect of the present invention, in the X-ray CT apparatus having the above structure, the reference data evaluation means compares the average value of the reference data obtained by the calibration scan with the reference data of each view. Provided is an X-ray CT apparatus, which is characterized as normal when there is no difference or small and as abnormal when the difference is large. The X-ray CT apparatus according to the tenth aspect can preferably implement the X-ray dose correction method according to the fourth aspect.

According to an eleventh aspect of the present invention, in the X-ray CT apparatus having the above structure, the reference data evaluation means compares the maximum value of the reference data during scanning with the reference data of each view, and a difference is found. There is provided an X-ray CT apparatus characterized in that it is determined to be normal when it is not present or small, and is determined to be abnormal when the difference is large. First above
The X-ray CT apparatus according to the first aspect can preferably implement the X-ray dose correction method according to the fifth aspect.

In a twelfth aspect of the present invention, in the X-ray CT apparatus having the above-mentioned configuration, the reference data evaluation means compares the maximum frequency value of the reference data during scanning with the reference data of each view to obtain a difference. There is provided an X-ray CT apparatus characterized in that it is judged to be normal when there is no or small, and it is judged to be abnormal when the difference is large. The X-ray CT apparatus according to the twelfth aspect can suitably implement the X-ray dose correction method according to the sixth aspect.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail with reference to the embodiments of the invention shown in the drawings. The present invention is not limited to this.

FIG. 1 is a block diagram 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 and a table 10 to be inspected.
And a scanning gantry 20.

The console 1 includes an input device 2 for receiving an operator's instruction input and information input, and a CPU 3 for executing scan processing, various correction processing, image reconstruction processing, and the like.
A control interface 4 for exchanging control signals and the like with the object table 10 and the scanning gantry 20, an X-ray data acquisition interface 5 for collecting data acquired by the scanning gantry 20, and a tomographic image reconstructed from the data. A display 6 for displaying and a storage device 7 for storing programs, data and tomographic images are provided.

The scanning gantry 20 is obtained by an X-ray tube 21, an X-ray controller 22, a collimator 23, a collimator controller 24, an X-ray detector 27 having a large number of channels, and an X-ray detector 27. The data collection unit 28 that collects data and the rotation controller 29 that rotates the X-ray tube 21, the X-ray detector 29, and the like are provided.

FIG. 2 is a schematic diagram showing the X-ray tube 21, collimator 23 and X-ray detector 27. The X-rays emitted from the X-ray tube 21 pass through the aperture of the collimator 23 to become a flat X-ray fan beam Xr, and enter the reference channel 27CR of the X-ray detector 27 and the data channels # 1 to #N. The X-ray detector 27 has a reference channel 27CR and data channels # 1 to #N, and these channels are arranged in an arc shape.

FIG. 3 is a flow chart of imaging processing by the X-ray CT apparatus 100. In step S1, the inspection object H is placed on the inspection object table 10. In step S2, X
The object table 10 is moved so that the imaging position of the object H is aligned with the position of the linear fan beam Xr.

In step S3, the rotation controller 29
The X-ray tube 21 and the X-ray detector 27 are rotated by the X-ray tube 21 to generate X-rays, the reference channel 27CR of the X-ray detector 27 collects the reference data, and the data channels # 1 to #N are used. Collect X-ray projection data. In step S4, reference data and X
The line projection data is AD-converted by the data collection unit 28 and is taken into the CPU 3 via the X-ray data collection interface 5. In step S5, offset data for each channel is subtracted from the reference data and the X-ray projection data (offset correction). In step S6, the reference data and the X-ray projection data are logarithmically converted.

In step S7, it is determined whether the reference data is normal or abnormal. If it is determined that the reference data is abnormal, step S8
If it is determined to be normal, the process proceeds to step S10. The judgment is made by any of the following methods.

(1) The reference data of the view at the start of scanning and the reference data of each view are compared, and if the ratio is more than 1 apart, that is, if the difference is large, it is judged as abnormal, and the ratio is 1 or 1. When it is close to, that is, when there is no difference or a small difference, it is determined to be normal. For example, the reference data of the view at the start of scanning is Ref (1), the reference data of the nth view is Ref (n), and ε
When is a small value obtained empirically, if Ref (n) / Ref (1) | <(1-ε), Ref (n) is judged as abnormal, and if not, it is judged as normal.

(2) The average value of the reference data of a plurality of views is compared with the reference data of each view, and if the ratio is more than 1 apart, that is, if the difference is large, it is judged as abnormal and the ratio is 1 or 1. When it is close to, that is, when there is no difference or a small difference, it is determined to be normal. For example, let AvRef be the average value of the reference data for each view for one rotation,
If Ref (n) is the reference data of the nth view and ε is a small value obtained empirically, if Ref (n) / AvRef | <(1-ε), then Ref (n) is judged as abnormal. , If not, it is determined to be normal.

(3) The average value of the reference data obtained by the calibration scan executed for adjustment before the scan for obtaining the tomographic image generation data is compared with the reference data of each view, and the ratio is 1 If they are far apart, that is, if the difference is large, it is judged as abnormal,
When the ratio is 1 or close to 1, that is, there is no difference or a small difference, it is determined to be normal. For example, let AvCalRef be the average value of the reference data of each view for one rotation obtained by the calibration scan, and set the reference data of the nth view to
Ref (n), and if ε is a small value obtained empirically, if Ref (n) / AvCalRef | <(1-ε), then Ref (n) is judged as abnormal, otherwise it is judged as normal. To do.

(4) The maximum value of the reference data during scanning is compared with the reference data of each view, and if the ratio is more than 1 apart, that is, if the difference is large, it is judged as abnormal and the ratio is 1 or 1. When it is close to, that is, when there is no difference or a small difference, it is determined to be normal. For example, the reference data of the nth view is Ref (n), and the maximum value of the reference data from the first view at the start of scanning to the nth view during scanning is max {Ref (1), Ref (n)}. , Ε is a small value obtained empirically, if Ref (n) / max {Ref (1), Ref (n)} ｜ <(1-ε), then Ref (n) is judged to be abnormal, If not, it is determined to be normal.

(5) The maximum frequency value of the reference data during scanning is compared with the reference data of each view, and if the ratio is more than 1 apart, that is, if the difference is large, it is judged as abnormal and whether the ratio is 1 or not. When it is close to 1, that is, when there is no difference or a small difference, it is determined to be normal. For example, the nth
Ref (n) is the reference data of the view, and maxf {Ref (1), Ref (n)} is the maximum frequency value of the reference data from the first view at the start of scanning to the nth view during scanning.
If ε is a small value obtained empirically, then if Ref (n) / maxf {Ref (1), Ref (n)} ｜ <(1-ε), Ref (n) is judged to be abnormal. , If not, it is determined to be normal.

In step S8, the n-th data channel 27CN on the opposite side of the reference channel 27CR.
It is determined whether the X-ray projection data D (N, n) of the view can be used as reference data, and if it can be used, step S9.
If it cannot be used, the collected data is regarded as invalid and the process is terminated. The method of determining whether or not it can be used is the same as the method of determining whether the reference data is normal or abnormal. Instead of using Ref (n), D (N, n) is used. It can be determined that "it can be used", and instead of "abnormal", it can be determined that "it cannot be used".

In step S9, the n-th data channel 27CN on the opposite side of the reference channel 27CR.
The X-ray projection data D (N, n) of the view is set as the reference data Ref (n) of the nth view. Then, the process proceeds to step S10.

In step S10, the X-ray projection data of the nth view of each data channel is set as reference data Re.
Subtract from f (n) (X dose correction).

In step S11, the sensitivity correction data for each channel is subtracted from the X-ray projection data after the X-ray dose correction (X-ray sensitivity correction). In step S12, a filter function is superimposed on the X-ray projection data subjected to the X-ray sensitivity correction, and back projection is performed to create a tomographic image. In step S13, a tomographic image is displayed on the display 6.

FIG. 4 shows the object H to be inspected at the time of positioning the object H to be imaged (step S2 in FIG. 3).
It is a schematic diagram which shows the relationship between X-ray fan beam Xr. The object H to be inspected is positioned so that the X-rays that have not passed through the object H to be inspected enter the reference channel 27CR.

As shown in FIG. 5, an X-ray tube and an X-ray detector 2 are provided.
7 and the like are rotated about the rotation center IC as a rotation center as shown by an arrow in the figure, reference data is collected in the reference channel 27CR for each rotation angle corresponding to each view, and the X-ray is detected in the data channel of the X-ray detector 27. Projection data is collected. When the X-ray incident on the reference channel 27CR in a certain view is not blocked by the object H to be inspected, the reference data of this view is used for the X-ray dose correction.

As shown in FIG. 6, when the X-ray incident on the reference channel 27CR in a certain view is blocked by the object H to be inspected, the reference data of this view is not used and the X-ray obtained by the data channel 27CN is not used. The projection data is used as X-ray dose correction as reference data.

According to the X-ray CT apparatus 100, the X-ray dose can be normally corrected even when the X-ray entering the reference channel 27CR is blocked by the object H to be inspected. Since the reference channel 27CR is provided only on the first end side of the X-ray detector, the FOV (Fiel
d Of View) can be widened.

In the above embodiment, the X-ray projection data of one channel (data channel 27CN) at the end opposite to the reference channel 27CR was used for X-ray dose correction, but the X-ray projection data of a plurality of channels at the opposite end to the reference channel 27CR. May be used for X-ray dose correction. In this case, the SN ratio can be improved.

In the above embodiment, logarithmic conversion (see FIG.
After step S6), X-ray dose correction (step S1 in FIG. 3) is performed.
Although 0) is performed, X-ray dose correction may be performed before logarithmic conversion.

[0040]

The X-ray dose correction method and X-ray CT of the present invention
According to the apparatus, the X-ray dose can be normally corrected even when the X-ray incident on the reference channel is blocked by the object to be inspected.

[Brief description of drawings]

FIG. 1 is a block diagram of an X-ray CT apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an X-ray tube, a collimator and an X-ray detector.

FIG. 3 is a flowchart showing a photographing process according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a relationship between an object to be inspected and an X-ray fan beam when the object to be inspected is positioned for imaging.

FIG. 5 is a schematic diagram showing a case where an X-ray incident on a reference channel is not blocked by an object to be inspected.

FIG. 6 is a schematic diagram showing a case where an X-ray incident on a reference channel is blocked by an object to be inspected.

FIG. 7 is a schematic diagram showing the relationship between the inspection object and the X-ray fan beam when the inspection object is positioned for imaging.

FIG. 8 is a schematic diagram showing a case where an X-ray incident on a reference channel is blocked by an object to be inspected.

[Explanation of symbols]

3 CPU 5 X-ray data acquisition interface 20 Scanning gantry 21 X-ray tube 27 X-ray detector 27CR Reference channel 27C1 to 27CN Data channel 100 X-ray CT apparatus

Continued front page    (72) Inventor Akihiko Nishide             127, 4-7 Asahigaoka, Hino City, Tokyo             GE Yokogawa Medical System Co., Ltd.             Within (72) Inventor Masatake Nakai             127, 4-7 Asahigaoka, Hino City, Tokyo             GE Yokogawa Medical System Co., Ltd.             Within F-term (reference) 4C093 AA22 BA03 CA09 CA13 FC23

Claims (12)

[Claims] 1. A reference channel is provided at the first end of an X-ray detector having a large number of data channels, and it is determined whether the reference data obtained by the reference channel is normal or abnormal. The X-ray projection data obtained in the channel is normalized with the reference data obtained in the reference channel, and when it is judged as abnormal, in the data channel in which the X-rays that have not transmitted through the inspected object are incident An X-ray dose correction method, characterized in that the obtained data is used as reference data to perform the normalization. 2. The X-ray dose correction method according to claim 1, wherein the reference data of the view at the start of scanning is compared with the reference data of each view, and if there is no difference or a small difference, it is determined as normal, and the difference is An X-ray dose correction method characterized in that when it is large, it is determined to be abnormal. 3. The X-ray dose correction method according to claim 1, wherein the average value of the reference data of a plurality of views is compared with the reference data of each view, and if there is no difference or a small difference, it is determined as normal, and the difference is An X-ray dose correction method characterized in that when it is large, it is determined to be abnormal. 4. The X-ray dose correction method according to claim 1, wherein the average value of the reference data obtained by the calibration scan is compared with the reference data of each view, and if there is no difference or a small difference, it is determined to be normal. The X-ray dose correction method is characterized in that when the difference is large, it is determined to be abnormal. 5. The X-ray dose correction method according to claim 1, wherein the maximum value of the reference data during scanning is compared with the reference data of each view, and if there is no difference or a small difference, it is determined as normal, and the difference is An X-ray dose correction method characterized in that when it is large, it is determined to be abnormal. 6. The X-ray dose correction method according to claim 1, wherein the maximum frequency value of the reference data during scanning is compared with the reference data of each view, and if there is no difference or a small difference, it is determined as normal, and the difference An X-ray dose correction method, which is characterized in that it is determined to be abnormal when the value is large. 7. An X-ray detector having a large number of data channels, a reference channel provided at a first end of the X-ray detector, and whether reference data obtained by the reference channel is normal or abnormal. Reference data evaluating means, and X obtained in each data channel when the reference data evaluating means determines that the reference data is normal.
Normalize the line projection data with the reference data obtained from the reference channel, and if it is judged as abnormal, refer to the data obtained from the data channel of each data channel where the X-rays that have not transmitted through the inspected object are incident. An X-ray CT apparatus comprising: an X-ray dose correction unit that is used as data to perform the normalization. 8. The X-ray CT apparatus according to claim 7, wherein the reference data evaluation means compares the reference data of the view at the start of scanning with the reference data of each view, and if there is no difference or a small difference, An X-ray CT apparatus characterized in that it is judged to be normal and, if the difference is large, to be abnormal. 9. The X-ray CT apparatus according to claim 7, wherein the reference data evaluation means compares the average value of the reference data of a plurality of views with the reference data of each view, and if there is no difference or a small difference, An X-ray CT apparatus characterized in that it is judged to be normal and, if the difference is large, to be abnormal. 10. The X-ray CT apparatus according to claim 7, wherein the reference data evaluation means compares the average value of the reference data obtained by the calibration scan with the reference data of each view and determines whether there is a difference. An X-ray CT apparatus characterized in that when it is small, it is determined to be normal, and when the difference is large, it is determined to be abnormal. 11. The X-ray CT apparatus according to claim 7, wherein the reference data evaluation means compares the maximum value of the reference data during scanning with the reference data of each view, and if there is no difference or a small difference, An X-ray CT apparatus characterized in that it is judged to be normal and, if the difference is large, to be abnormal. 12. The X-ray CT apparatus according to claim 7, wherein the reference data evaluation means compares the maximum frequency value of the reference data during scanning with the reference data of each view, and if there is no difference or a small difference. The X-ray CT apparatus is characterized in that is determined to be normal, and is determined to be abnormal if the difference is large.