JPH0390134A - X-ray ct device - Google Patents

Abstract

PURPOSE:To improve radiation measuring accuracy of an X-ray CT detector by providing a plurality of X-ray detectors with at least one detector formed into structure shielded for X-rays. CONSTITUTION:An accelerated electron by an accelerator 1 collides against a target 2, and an X-ray beam 12 is irradiated from the target 2. A sample 14 is placed on a CT scanner 4 and translation rotation-scanned, and permeability of an X-ray is measured from all the directions by a detector arranged behind a collimator 5. The detector is such that solid or liquid scintillator 6 is combined with a photomultiplier or photoelectric transfer element 7, and its output is input to an AD converter 9 through an amplifier 8 and fetched to a computer 10. Of the detectors, the one is shielded for the X-rays to serve as a base line monitor 13. In the base line monitor 13, a fluctuation amount, in which a base line of a detector output essentially being 0, when radiation is not incident upon the detector, is changed by fluctuation and electromagnetic noise or the like of a power supply and the base line caused by a high voltage power supply 3 or the like of the accelerator 1, is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for improving measurement accuracy in a detector of an X-ray computed tomography device.

[Conventional technology]

Conventional detectors, as described in Japanese Patent Application Laid-open No. 55-65174, package the radiation detector with a flexible material such as a button.
In a structure in which a slit for radiation incidence is opened on the side, one or more radiation detectors other than the radiation detector provided on the slit through which radiation enters are installed above and at least one below the radiation detector on the slit. A compensating detector was installed in each location, and the compensating detector was designed to detect radiation that passed through the shielding material portion other than the slit.

The output of a radiation detector that measures radiation incident through the slit includes a background component that is detected by the radiation detector after passing through a shielding material portion other than the slit. Only this background component was measured by a compensation detector to improve the measurement accuracy of the radiation incident through the slit.

Mata, XwACT detector, JP-A-62-72328
As described in the publication, in addition to the detector that measures the X-rays that have passed through the sample, a detector that monitors fluctuations in the X-ray intensity of the X-ray source is installed, and the output of each X-ray detector is monitored as an X-ray source monitor. It was designed to be corrected using the output of the detector to remove the effects of fluctuations in X-ray intensity.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account fluctuations in the detector's power supply, fluctuations in the ground line, or fluctuations in the baseline of the detector due to electromagnetic noise, resulting in a problem in which the measurement accuracy of the detector decreases. Ta. The baseline of a detector is the output of the detector when X-rays incident on the detector are completely blocked, and originally it should be at OV. However, when measuring high-energy X-rays, the baseline fluctuates due to fluctuations in the power supply voltage caused by the high-voltage power supply of the electron beam accelerator, fluctuations in the ground line, and electromagnetic noise. These fluctuations can be significantly eliminated by stabilizing the power supply, installing noise filters, and electromagnetic shielding, but it is impossible to eliminate them completely. The influence of this baseline fluctuation appeared as an error in the radiation measurement value measured by the detector, and ultimately caused deterioration of the tomographic image.

The present invention aims to improve the radiation measurement accuracy of an X@CT detector, and further aims to improve the image quality of tomographic images.

[Means to solve the problem]

In order to achieve the above objective, a plurality of xmcr detectors are provided, at least - detectors are shielded against radiation to measure only the baseline fluctuations of the detectors, and the others are The baseline measurement value is corrected for the measurement value of the radiation measurement detector.

Further, when a combination of a scintillator and a photoelectric conversion element is used as a radiation detector, only the photoelectric conversion element is used as a baseline detector in a dim state in order to measure the baseline.

[Effect]

When multiple radiation detectors are installed, each detector is placed facing the XI source so as to measure the X-rays from the X-ray source, but at least - of the radiation detectors are placed facing the I'm sorry. When using a combination of a scintillator and a photoelectric conversion element as a radiation detector, the detector that is resistant to radiation should be one that does not include a scintillator and only has a photoelectric conversion element that is resistant to light. According to
Radiation protection can be made easier. The output of all detectors is collected into a data acquisition device. Here, first, measurement values of all the detectors are collected multiple times with all the detectors shielded from X-rays. At this time, the output of all detectors should be 0 because the X-rays are being suppressed.
However, in reality, only a small amount of output is obtained, and the output fluctuates. For each detector output, the output of the detector that is originally resistant to radiation and the output of the detector that is originally oriented toward the X-ray source, collected at the same time, is compared. By comparing the measured values collected a plurality of times as described above, the correlation between the detector, which is originally resistant to radiation, and the xsvA regular detection detector is determined. In normal measurements where the shielding of the XIIA measurement detector is removed, the output of the radiation-shielded detector is calculated from the measured values of the X-ray measurement detector based on the correlation with each detector previously determined. By subtracting the corrected value, the true X-ray measurement value can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, electrons accelerated by an accelerator 1 collide with a target 2, and the target 2 is irradiated with an X-ray beam 12. A sample 14 is placed on the CT scanner 4, and the sample 14 is scanned in translation and rotation, and the transmittance of X-rays is measured from all directions. Measurement is performed by a detector placed behind the collimator 5. The detector is a combination of a solid or liquid scintillator 6 and a photomultiplier tube, or a photoelectric conversion element 7 such as a photodiode. 7
The output passes through the preamplifier 8, enters the AD converter 9, and is taken into the computer 10. Of the detectors, at least
- Individuals are X-ray resistant and baseline monitor 1
Set it to 3. In the baseline monitor 13, the baseline of the detector output, which should be O when no radiation is incident on the detector, changes due to fluctuations in the power supply and ground line caused by the high-voltage power supply 3 of the accelerator 1, electromagnetic noise, etc. Measure the amount of variation. The output of the baseline monitor 13 also passes through the preamplifier 8 to the AD converter 9 and is collected by the computer 10 in the same way as other detectors. The computer 10 corrects each detector output based on the output of the baseline monitor 13, performs image reconstruction calculations to obtain a CT tomographic image, and displays the tomographic image on the display 11. To correct baseline fluctuations, first, an X-ray shielding material is installed in front of the collimator 5, and a primary shielding material is used to shield the X-rays incident from the slit.
Accelerator 1 accelerates electrons and causes them to collide with target 2
Generate a line. Since the X-ray beam 12 is shielded by a barrier placed in front of the collimator and does not pass through the slit of the collimator 5, the X-ray beam is not detected by the detector. The outputs of each detector and the output of the baseline monitor 13 at this time are collected in the computer 10. This data collection samples the output of all detectors including the baseline monitor 13 at the same time.Since the X-rays have not reached each of the nine detectors, the output of each detector should be 0. As described above, due to the influence of the accelerator high-voltage power supply 3 and the like, the output does not become O but has a certain level, and the output level fluctuates.

This baseline level fluctuation occurs randomly, but
If we observe a certain time variation, the variation will appear within a certain range. Therefore, simultaneous sampling of all detectors is performed thousands to hundreds of times and the fluctuations in the baseline level of each detector are recorded. This baseline fluctuation occurs due to fluctuations in the power supply voltage, etc., and therefore fluctuates in the same way in all detectors. In other words, the upper and lower baseline levels fluctuate simultaneously in all detectors. However, since the sensitivity of each detector and preamplifier is not necessarily the same for all detectors, the width of the baseline level fluctuation of each detector is not equal. Therefore, the baseline monitor 1
Examine the correlation between the value of 3 and the value of each detector. Then, as shown in FIG. 2, there is a proportional relationship between the value of the baseline monitor 13 and the output of each detector, and if the output of the nth detector is yn and the value of the baseline monitor is X, then V n = a a X ・
...Aaln, from which the relationship (1) is found, is the proportionality coefficient between the output of the n-th detector and the output of the baseline monitor 13. After determining a and l for all detectors, the shingle provided in front of the collimator 5 is removed.

In normal X-ray measurements, the output of each detector is
The output of the baseline monitor 13 is also collected by the preamplifier 8 through the AD converter 9 and collected by the computer 10.
and are collected by the computer 10 through the AD converter 9. The calculator 10 corrects the output of each detector by subtracting the output of the baseline monitor 13 and the baseline level of each detector determined from equation (1), thereby obtaining the true detector output. A clear tomographic image can be obtained by performing image reconstruction calculations based on the true measurement values obtained above.

Another embodiment of the invention is shown in FIG. The difference between FIG. 3 and FIG. 1 is that the baseline monitor 13 has a photoelectric conversion element 7.
This was done only for the time being. Since the baseline monitor 13 measures only baseline fluctuations without detecting X-rays, a configuration including only the photoelectric conversion element 7 without the scintillator 6 is sufficient and can be configured at low cost. At this time, as with other detectors, sufficient care must be taken regarding the intensity and light of the baseline monitor 13. The method for correcting baseline fluctuations is exactly the same as the first embodiment.According to this embodiment, by removing the influence of baseline fluctuations from the measured values of X-ray transmission data of X-ray CT, 81!
This has the effect of improving the accuracy of fixed values, and has the effect of improving the image quality of tomographic images.

〔Effect of the invention〕

According to the present invention, the influence of baseline fluctuations can be removed from X-ray CT data.

This has the effect of improving the accuracy of X-ray transmission data.

This improves the image quality of tomographic images and enables tomography of thick materials with higher X-ray transmittance than in the past.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention, FIG. 2 is a correlation diagram between a baseline monitor and each detector, and FIG. 3 is an explanatory diagram of another embodiment of the present invention. 1... Electron beam accelerator, 2... Target, 3...
Accelerator high-voltage power supply, 4...CT scanner, 5...Collimator, 6...Scintillator, 7...Photoelectric conversion element, 8...Pre-Figure 1//0 Figure Baseline Monia Upper Blade No. Figure 3

Claims (1)

[Claims] 1. An X-ray source consisting of an electron beam accelerator and a target and a sample, or a CT scanner, an X-ray detector, and the output of the detector that scans the X-ray source and detector in translation and rotation. In an X-ray CT apparatus comprising a computer that collects images and performs image reconstruction calculations, a plurality of the X-ray detectors are provided, and at least one detects X-rays;
An X-ray CT device characterized by always having a shrunken structure. 2. The X-ray CT apparatus according to claim 1, wherein a plurality of combinations of scintillators and photoelectric conversion elements are provided as detectors, and at least one of the detectors includes only the photoelectric conversion element. CT device. 3. In the X-ray CT apparatus according to claim 1, the correlation between the constantly suppressed detector output when no X-rays are incident on all of the X-ray detectors and the other X-ray detectors is calculated. An X-ray CT apparatus characterized in that the product of the suppressed detector output and the proportionality coefficient obtained by the correlation is always subtracted from each detector output when measuring X-ray transmission data. . 4. In the X-ray CT apparatus according to claim 1, the radiation source includes γ.
An X-ray CT device characterized by using radiation or neutron beams.