JPS61226676A - Method for correcting scattered radiation of radioactive ray position detector - Google Patents

Abstract

PURPOSE:To obtain the excellent picture quality with a good contract by correcting measured data on each position with the aid of the ratio of a higher part than the energy peak of said data relating to the same position to data on a part higher than the energy peak of reference data. CONSTITUTION:In terms of a memory 5, radioactive rays by energy (peak value of an energy signal Z) at a position where a reference radiation source 2 is placed are counted to obtain an energy vector B. If <99m>TC is employed as the reference radiation source 2, an energy vector A can be available at each position. The counted value of each energy of the energy vector B is multiplied by a coefficient (k) and standardized so that the counted value at the peak of the energy vector B can be equal to the peak counted value of the energy A. By obtaining an energy vector B', the ratio of the counted value (a) of reference data in a measurement energy window to the counted value b' in the standarized and measured data is taken, whereby b cor=bX(a/b'), that is, data b cor after correction, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a scattered radiation correction method for a radiation position detection device such as a scintillation camera.

Conventional technology: Radiation position detection devices such as scintillation cameras
This is to take an image of the distribution of RI (radioisotope). When a drug containing RI is administered to a subject and RI accumulates in an affected area, the radiation position detection device is directed toward the affected area. Then, the radiation emitted from R1 in the human body enters the radiation position detection device. Since this radiation position detection device detects the position of radiation, if the radiation is counted for each position, the degree of RI accumulation, that is, can be determined by counting radiation at each position.

A concentration distribution image can be obtained, which is useful for diagnosing the condition of the affected area.

Problems to be Solved by the Invention By the way, in this radiation position detection device, not only radiation is directly incident, but also scattered radiation is also incident. Since these scattered rays are counted in the same way as directly incident radiation, the obtained data will always include scattered rays.

However, with conventional radiation position detection devices, it has been impossible to remove or correct the influence of scattered radiation, or it has been inaccurate and insufficient. Conventional mocos have the problem of only being able to obtain images with a lot of background and poor contrast due to the influence of scattered radiation.

According to the present invention, data including scattered radiation can be corrected to remove the influence of scattered radiation, and the influence of scattered radiation is extremely small and the contrast is good.

It is an object of the present invention to provide a method for correcting scattered radiation for a radiation position detection device, which can obtain images of excellent quality with little background.

Means for Solving the Problems The scattered radiation correction method for a radiation position detection device according to the present invention collects reference data free of scattered radiation for each position using a reference radiation source in the radiation position detection device, and The method is characterized in that the measurement data obtained for each position is corrected based on the ratio of the portion of the measurement data higher than the energy peak and the data of the reference data of the portion higher than the energy peak for the same position.

The energy of the action scattered rays cannot theoretically be higher than the energy peak. In other words, when taking an energy spectrum, the data above the energy peak is
It can be considered the same regardless of whether there is a scatterer or not.

Therefore, reference data should be collected in advance without scattering objects.

When measurement data is actually obtained, the reference data and the data in the part of the measurement data higher than the energy peak are compared to find the ratio, and the measurement data is multiplied by this ratio to determine whether the measurement data is affected by the scattered radiation. Correction can be made to further remove the influence of the scattered radiation.

Embodiment An embodiment in which the present invention is applied to a scintillation camera will be described. First, as shown in Fig. 1, in the absence of scatterers, the reference radiation source 2 is placed at each position (represented by x, y) on the detection surface of the scintillation camera l. Then, the position signal x, Y and energy signal Z are output, and these signals are converted into digital signals by the A/D converter 3 and taken into the memory 5 via the CPU 4. Therefore, in this memory 5, the reference radiation source 2
Radiation is counted for each energy (peak value of the energy signal Z) at the position where it is placed, and an energy spectrum is obtained. By changing the position of the reference radiation source 2, this energy spectrum can be obtained for each position of, for example, 64x64 or 128x128.

If, for example, 'rc which emits 140 KeV gamma rays is used as the reference radiation source 2, an energy spectrum A having a peak at 140 KeV as shown in FIG. 2 can be obtained at each position. When data is collected under the above conditions, the influence of scattered radiation is negligible, and this energy spectrum A is the same as that of scintillation camera 1 for 140 KeV gamma rays.
It can be said that this spectrum shows the characteristics of the detection system. This energy spectrum A is used as reference data.

Next, as shown in FIG. 3, a collimator 6 is attached to the detection surface of the scintillation camera 1, and actual clinical data of the subject 7 is collected. In this case, the nuclide administered to the subject 7 is the same lIl'rC, and an energy spectrum is obtained for each position in the same manner as above. In actual clinical practice, scattered rays are generated by scatterers of the subject 7, and these scattered rays are also counted, so that an energy spectrum B as shown in FIG. 4 containing many scattered rays is obtained.

However, even if this energy spectrum B includes the influence of scattered radiation, it only appears in the region below the peak, and should be negligible in the region above the peak. This is because it is theoretically impossible for scattered rays generated from gamma rays that are originally 140 KeV to exceed 14QKeV, and there are only a certain number of scattered rays that exceed 140 KeV due to energy resolution. . In other words, the total counts in the shaded areas in FIGS. 2 and 4 should be the same.

Therefore, so that the count value at the peak of energy spectrum B matches the peak count value of energy spectrum A, the count value at each energy of energy spectrum B is normalized by multiplying by a coefficient k. Obtain the energy spectrum B′ as shown, take the ratio of the count value a in the reference data within the measurement energy window and the count value b° in the normalized measurement data, and from this, b c
or = bX (a/b') corrected data l
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Note that the reason for the standardization as described above is that the actual count values differ due to differences in measurement time and the like in each measurement, so it is necessary to match them.

In this way, corrected data can be obtained for all X and Y positions.

Although the case where a nuclide with one energy peak is used has been described above, the same applies to the case of a nuclide with two, three or more peaks. For simplicity, we will explain the case of In, which has two energy peaks at 245 KeV and 171 KeV.
As shown in the figure, standard data without scattered radiation is collected for each position to obtain a standard energy spectrum as shown in Figure 6, and then actual clinical data is obtained as shown in Figure 3. Obtain an energy spectrum as shown in Figure 7. In these two energy spectra, it can be said that the influence of scattered radiation is negligible in the region above 245 KeV, so 245
The clinical energy spectrum is normalized by multiplying it by a coefficient k so that the count value at the peak of KeV matches the reference value, and a normalized clinical energy spectrum B' as shown in FIG. 8 is obtained. Then, by the following calculation, the corrected 245
In-window data b for KeV.

In-window data b2 for car and 171KeV
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bx cor=bxX (ax/bx')b 2
cor= b 2 X (ax/bi')a,,a
, are reference data, al is the in-window count value of 245KeV, a2 is the in-window count value of 171Ke■, bz
, b2 is the clinical data, b is the in-window count value of 245 KeV, bw is the in-wind count value of 171 KeV, b
lo and b2° are counts obtained by normalizing bt and bt.

In addition, in the energy spectrum of the reference data shown in FIG. 6, the peak at 171 KeV has a
It is unavoidable that the line contains some influence of scattering within the detection system of the scintillation camera 1, as shown in the dotted line. Since the effects are not included in the energy spectrum of this reference, this external scattering effect (which is much larger) can be compensated for, resulting in an image of good quality with good contrast.

In order to avoid the influence of scattering of this 245 KeV γ-ray in the detection system of the scintillation camera 1 from being included in the 171 KeV reference data, it is possible to avoid including the influence of scattering of this 245 KeV γ-ray in the detection system of the scintillation camera 1 by having a single energy peak near 245 KeV.
255KeV) as the reference source 2, or 171
Reference source 2 with a single energy peak near KeV
This is possible by using

The above correction operation may be performed by software under the control of the CPU 4, or may be performed by hardware if speed is required.

Furthermore, the present invention can be applied to all radiation position detection devices such as ring-type ECT devices (devices that arrange radiation detectors in a ring shape around a subject and reconstruct 81 distributed tomographic images using a computer). .

Effects of the Invention According to this invention, it is possible to perform correction to remove the influence of scattered radiation from data containing scattered radiation.Therefore, the image quality is excellent, with very little influence of scattered radiation, good contrast, and little background. In particular, in the case of an ECT device using a single photon-emitting nuclide, this invention can remove the influence of scattered radiation, which is extremely effective in improving image quality and dramatically improving quantitative performance. improves.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration for obtaining reference data in an embodiment of the present invention, FIG. 2 is a graph showing the energy spectrum of the reference data, and FIG. 3 is a block diagram showing the configuration for obtaining actual clinical data. Fig. 4 is a graph showing the energy spectrum of clinical data, Fig. 5 is a graph superimposing the standard energy spectrum and the normalized clinical energy spectrum, and Fig. 6 is the standard data obtained in other examples. 7th graph showing the energy spectrum of
The figure shows the energy spectrum of clinical data in another example. Figure 8 is a graph in which the standard energy spectrum and the normalized clinical energy spectrum in another example are superimposed. l...Scintillation camera 2...Reference radiation source 3
...A/D converter 4...CPU5...
・Memory 6...Collimator 7・
・・Subject

Claims (1)

[Claims] (1) Collect standard data free of scattered radiation for each position using a reference radiation source in the radiation position detection device, and compare the measured data obtained for each position regarding the actual subject with the measured data for the same position. 1. A scattered radiation correction method for a radiation position detection device, characterized in that correction is performed based on a ratio of data of a portion higher than an energy peak of the reference data to data of a portion higher than the energy peak of the reference data.