JPH06105295B2 - Scattered ray correction method of ECT device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ECT device (emission type) in which a compound labeled with a radioisotope (RI) is administered to a patient and a two-dimensional distribution thereof is obtained as a tomographic image. The present invention relates to a computer tomography apparatus), and more particularly to a method for correcting data having an error due to its scattered rays.

Radiation emitted from labeled compounds administered to patients is
As it passes through the patient's body to the outside, it may be absorbed and attenuated in the body, or scattered to provide erroneous information. Various methods for correcting these have been sought, but among them, a method for correcting scattered rays has not been established, and various methods have been tried.

For example, in the case of PET (positron ECT), a portion 7 containing RI in the ring-shaped detector array 1 as shown in FIG. 10A.
Taking the profile data on the X-axis passing through the center when the phantom 6 having the part 8 and the part 8 not containing is arranged, it becomes as shown in FIG. It can be seen that there is data obtained by mistake. Therefore, assuming that the data of the portion 9 outside the phantom 6 is only erroneous data due to scattered rays, obtain the average value of this portion 9 and subtract this average value from the entire profile data to correct the scattered rays. That is why.

Problems to be Solved by the Invention However, the correction method shown as the above conventional example has a problem that the accuracy is poor because it simply subtracts a constant value uniformly.

Regarding other various conventional correction methods, it takes time and effort to collect the correction data, the cost increases due to the need for a special device, or the correction accuracy is poor. There is a problem that the data processing for correcting the subject data takes time.

The present invention does not require any time or labor to collect the correction data, does not require a special device for that, is inexpensive, has a high correction accuracy, and uses the correction data to obtain the actual subject data. An object of the present invention is to provide a scattered radiation correction method for an ECT device, which can perform data processing for correction in a short time.

Means for Solving the Problems In the scattered radiation correction method of the ECT apparatus according to the present invention, the radiation source is arranged so as to occupy one point in the plane to obtain a tomographic image,
The data of this radiation source was collected for the condition with and without scatterers in the surroundings, and the filter function for scattered radiation correction was obtained from the relationship between these data, and for the data obtained for the actual subject. The feature is that the scattered radiation is corrected by applying this filter function.

Action Collecting point source data with and without scatterers in the surroundings gives a blurred image due to scatterers in the presence of scatterers, so the profile data is also compared to the case without scatterers. It becomes blunt. If you take the ratio of these two data, you can see that it can be used as data to restore the original data to the data blurred by scattered radiation.

Therefore, the scattered radiation can be corrected by approximating the ratio of these two data by a certain function and applying this function as a filter function to the actual data of the object.

In general, when the image is reconstructed by backprojecting the profile data, each profile data is filtered. Therefore, at the same time, the above-mentioned scattered radiation correction filter function can be actuated. Less time is needed for

Example An example applied to PET will be described. First, the first
As shown in FIG. A, the linear radiation source 2 is arranged in the ring-type detector array 1 perpendicularly to the tomographic plane. Then, it is substantially the same as placing a point source on the fault plane. Then, data collection is performed in this state. The profile data in the X direction is as shown in FIG. 1B.

Next, as shown in FIG. 2A, the scatterer 3 is placed around the line source 2. The scatterer 3 is made of water or acrylic having a scattering characteristic similar to that of a human body. If data is collected in this state, a part of the radiation emitted from the radiation source 2 is scattered by the scatterer 3, and the data is blurred, and the same X
The profile data of the direction is scatterer 3 as shown in FIG. 2B.
It is almost the same as the data when there is no (Fig. 1B), but it becomes a little wider than that and spreads.

The Fourier transforms of the profile data shown in FIGS. 1B and 2B are almost the same as shown in FIGS. 3 and 4, respectively, and if they are appropriately scaled and then overlapped, they almost overlap each other. Only the difference due to the scattered ray component appears in the low frequency part. Therefore, by taking the ratio of the data after the Fourier transform, the data as shown in FIG. 5A is obtained.

By the way, the data shown in FIG. 5A can be considered as correction data for returning the data including an error due to scattered radiation to the original error-free state. Therefore, if the data of FIG. 5A is approximated by a certain function, a function as shown in FIG. 5B is obtained, and this function can be used as a scattered radiation correction filter function. The data in the case without the scatterer shown in FIG. 1B is the scatterer 3 shown in FIG. 2B.
It can also be created by curve fitting from the data in the case of.

When the scattered radiation correction filter function is obtained in this way, the scattered radiation can be corrected by applying the function to the profile data collected for the actual subject to perform filtering. Since image reconstruction is usually performed by back-projecting profile data after filtering the profile data, it is sufficient to apply the above scattered radiation correction filter function at the same time when performing the filtering. Therefore, it is possible to shorten the time required for the data processing required.

The scattered radiation correction filter function is obtained from the data obtained when the point radiation source is placed at one central position. However, this scattered radiation correction filter function is data collected at other positions. It seems that it doesn't change much even if asked from. However, for more accuracy, it is also desirable to determine for some positions.

By the way, in the above scattered ray correction method, the accuracy is deteriorated when the influence of scattered rays from other than the tomographic plane cannot be ignored. In such a case, the above-mentioned correction filter function may be corrected by estimating the scattered radiation component from outside the tomographic plane.
This includes, for example, the
10 Use a phantom 6 as shown in FIG. As aforementioned,
This phantom 6 has a portion 7 including RI and a portion 8 not including RI.
, And the profile data on the X axis is shown in FIG. 10B.
Therefore, the data of the portion 9 where RI does not originally exist is the data of the scattered radiation component. Therefore, the scattered ray component from outside the tomographic plane is estimated from the data of this portion 9 and the above scattered ray correcting filter function is corrected. For example, the correction filter function as shown in FIG. 5C is obtained by correcting the data amount of the portion 9.

In the above, the case of performing scattered ray correction on the actual subject data was explained, but since the influence of scattered rays that collects absorption correction data appears, it is also used to remove the error due to scattered rays from the absorption correction data. it can. That is, the absorption correction data is first collected by placing the ring-shaped radiation source 4 in the ring-shaped detector array 1 as shown in FIG. 6, and then collecting the ring-shaped radiation as shown in FIG. The actual subject 5 is placed in the source 4, data is collected, and their ratio is obtained. That is, since the influence of absorption by the subject 5 does not appear in the data in the case of FIG. 6 and the influence of absorption by the subject 5 appears in the data in the case of FIG. This is because it becomes the data for use. However, the data in the case of FIG. 7 is affected by the radiation emitted from the ring-shaped radiation source 4 being scattered by the subject 5. Therefore, as shown in FIG. 8 and FIG.
The data for the case where there is no subject 5 and the case where there is the subject 5 are collected, and similarly to the above, Fourier transform is performed on these data and a scattered radiation correction filter function is created from the ratio. Scattered rays can be corrected by applying this filter function to the data obtained in FIG. 7 for filtering. In this way, absorption correction data that excludes the influence of scattered radiation can be obtained.

EFFECTS OF THE INVENTION According to the scattered radiation correction method of the ECT apparatus according to the present invention, the correction data only needs to be collected once, and it takes time and effort to collect the correction data for each subject each time. Never. Further, for that reason, a special device is not required, and the correction data can be easily obtained at a low cost. Further, the accuracy of correction can be improved as compared with the case where a constant value is simply subtracted. Further, it is possible to perform the data processing for correcting the data of the actual subject using the correction data in a short time.

[Brief description of drawings]

FIGS. 1 to 5 are for explaining one embodiment of the present invention, and FIG. 1A is a schematic diagram showing that data is collected in a state where there is no scatterer of a linear source, FIG. 1B is a graph showing one profile data obtained in FIG. 1A, FIG. 2A is a schematic view showing collecting data in a state where a scatterer of a linear source is collected, and FIG. B is A in FIG.
A graph showing one profile data obtained in FIG. 3, FIGS. 3 and 4 are graphs showing data obtained by Fourier transforming the data of FIGS. 1B and 2B, and FIG. 5A is FIGS. 4 is a graph showing the ratio of the data in FIG. 4, FIGS. 5B and 5C are graphs showing the correction filter function, FIG. 6,
FIGS. 7, 8 and 9 are schematic diagrams showing the arrangement of a radiation source and a subject, respectively, for explaining the application of the present invention to scattered radiation correction of absorption correction data, and FIG. 10A is a schematic diagram showing the arrangement of phantoms, and FIG. 10B is a graph showing one profile data obtained in FIG. 10A. 1 ... Ring type detector array, 2 ... Line source 3 ... Scatterer, 4 ... Ring source 5 ... Subject, 6 ... Phantom

Claims (2)

[Claims] 1. A radiation source is arranged so as to occupy one point in a plane where a tomographic image is to be obtained, and data of this radiation source are collected with and without a scatterer around them. The filter function for scattered radiation correction is obtained from the relationship between the data of
A scattered radiation correction method for an ECT device, characterized in that this filter function is applied to the data obtained for an actual subject to correct scattered radiation. 2. The filter function is corrected by data obtained in a region where the radiation source does not exist when the radiation source is placed in a plane to obtain the tomographic image. A scattered radiation correction method for an ECT device according to claim 1.