JPH0636028B2 - Positron CT correction method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a correction method for correcting emission data collected in a positron CT so as to remove the influence of scatter coincidence.

Conventional technology In positron CT, when the positron disappears, 18
Information on the position of the positron is obtained by simultaneously detecting the two γ-rays emitted in the 0 ° direction, and from this, the RI (radioisotope) concentration distribution image of the positron-emitting nuclide is reconstructed.

However, the emitted γ-rays are scattered in the subject, and coincidence counting (scattering coincidence counting) due to the scattering is inevitable, and the collected emission data always includes this scattering component. Therefore, various methods for correcting the scattering coincidence count have been conventionally proposed.

Problems to be Solved by the Invention However, the conventional method for correcting the scatter coincidence count is a method of subtracting a constant value or a method of deducing the scatter component from the response of the line source in the phantom and subtracting it from the reconstructed image. Yes, because it is not a correction that corresponds to the actual subject, correct correction cannot be made if the shape of the subject changes.
There is a drawback that.

It is an object of the present invention to provide a positron CT correction method capable of accurately correcting the scatter coincidence count even if the shape of the subject is different.

Means for Solving the Problems In the correction method of the positron CT according to the present invention, first, R
A line source is rotated around the untreated I subject and co-counting data is collected at each location. From this coincidence count data, only the data on the location of the line source is taken out to obtain absorption correction data and a correction function for correcting the scattering of emission data is obtained. Then, emission data collected when RI is administered to the subject is absorption-corrected using the absorption-correction data, and the correction function is acted on to perform simultaneous scatter counting included in the emission data itself. I try to remove the ingredients.

When the line source is rotated around the subject to which the RI is not administered, the coincidence counting data is collected at each location, and only the data of the location where the line source is present is extracted from this coincidence counting data. , Most of the scattered coincidence counting components can be removed. Therefore, if absorption correction data is obtained using this data, it will not be affected by scattering coincidence counting. Further, since the coincidence counting data described above is also emission data of the line radiation source whose location is known, the component of the scatter coincidence counting contained in the data itself can be known. Therefore, the correction function for removing the scatter coincidence counting component Can be asked. Therefore, if RI is administered to the subject, emission data is collected, and if this emission data is absorption-corrected using the absorption correction data, absorption correction with less influence of scattering can be performed. The component of the scattering coincidence count included in the emission data itself can be removed by applying the correction function of.

Example First, a blank scan is performed. As shown in FIG. 1, a line source (line-shaped γ-ray source extending in a direction orthogonal to the detector ring 1, that is, a direction parallel to the body axis of the subject 2) 3 is rotated in the detector ring 1. Then, the data of coincidence counting is collected at the place of each step. At this time, the subject 2 is not placed in the detector ring 1.

Next, the actual subject 2 is placed and the absorption data of this subject 2 is collected (RI has not yet been administered to this subject 2). As shown in FIG. 1, the line radiation source 3 is rotated around the subject 2, and the data of coincidence counting is collected at the position of each step as described above. Since the γ-rays emitted from the line source 3 pass through the subject 2 and then enter the detector ring 1, the collected data can be regarded as data transmitted through the subject 2, that is, transmission data. . Since the γ-rays are absorbed as they pass through the subject 2, it means that the transmission data represents the absorption at each part of the subject 2. Therefore, by comparing the absorption data with the blank scan data, absorption correction data can be obtained.

By the way, the object 2 is a scatterer as well as an absorber. Therefore, the above transmission data also includes the data of scattered coincidence counting. For example, the sinogram of this transmission data when the line source 3 is at the position shown in FIG. 1 becomes as shown in FIG. The data at θ = 0 ° is as shown by P in FIG. 4, and there is a skirt portion due to the scattered coincidence count data around the peak due to the true coincidence count data at the place where the line source 3 should be. Occurs. Since the location of the line source 3 is known, only the data corresponding to that location is taken out, and the data when no other line source 3 is present is removed as a scatter coincidence count. The sinogram of the data thus obtained is as shown in FIG. 3, and transmission data in which most of the scattered components are removed by removing the foot portion can be obtained. Further, by extracting only the part where the line radiation source 3 exists, the coincidence coincidence count data included in the skirt part is also removed. Therefore, if the absorption correction data is obtained using the transmission data subjected to such an operation, the absorption correction data having a high SN can be obtained.

At the same time, a correction function for scattering correction of emission data as shown in FIG. 5 is obtained from this transmission data. In this case, it is not seen as the obtained data and transmission data, but as the emission data of this line source 3 when the line source 3 is located at a certain place. For example, at the position shown in FIG.
If there is, the data at θ = 0 ° in the sinogram will consist of only true coincidence counting data without scattering unless the object 2 which is a scatterer is used, as shown by Q in FIG. However, due to the existence of the subject 2, the scatter coincidence count data is included and the result becomes as shown in FIG. 4P. Therefore, a correction function as shown in FIG. 5 that allows the data Q to be reproduced only by true coincidence counting when the correction function is superimposed and integrated on the data P is provided for each angle of the sinogram at least at several positions of the line source 3. Ask for each.

In this way, after obtaining the absorption correction data and the correction function, the line source 3 is removed, RI is administered to the subject 2, and this is performed in the same manner as in the normal positron CT. Gamma rays emitted from RI are simultaneously detected to collect data (collection of emission data).

Then, the collected emission data is absorption-corrected using the absorption-correction data described above, and further the above-mentioned correction function is superimposed and integrated on the corrected data to correct the scattering coincidence count. . Sinogram θ
If the measured emission data of the object 2 at = 0 ° is as shown in FIG. 6, absorption correction data is used to perform absorption correction to obtain emission data after absorption correction. Scattering correction of emission data is performed by superimposing and integrating the correction function of FIG. By reconstructing an image as usual using the data thus corrected, it is possible to obtain an image with a high SN in which the influence of scattering is eliminated in a double sense.

EFFECTS OF THE INVENTION According to the present invention, the scatter coincidence count is also corrected for the absorption correction data, and the absorption correction of the emission data of the subject is performed using the corrected absorption correction data. Since the scatter coincidence count included in itself is corrected, the scatter coincidence count can be corrected with extremely high accuracy. Furthermore, since these corrections are made using the actual measurement data of the actual subject,
The correction can be performed corresponding to the actual subject, and the accurate correction can be performed regardless of the shape of the subject. Also, since the coincidence count in the absorption correction data is reduced, the SN is improved,
In particular, it is most suitable for correcting the simultaneous coincidence counting of the abdomen.

[Brief description of drawings]

FIG. 1 is a front view of an apparatus for explaining an embodiment of the present invention, FIG. 2 is a graph showing a sinogram of measured data, FIG. 3 is a graph showing a sinogram of corrected data, and FIG. Diagram for explaining the relationship between the actual measurement data at a specific angle of the sinogram and the true coincidence counting data,
FIG. 5 is a diagram showing a correction function, and FIG. 6 is a diagram showing actual measurement data of a subject after RI administration at a specific angle of a sinogram. 1 ... Detector ring, 2 ... Subject 3 ... Line source

Claims (1)

[Claims] 1. A line radiation source is rotated around a subject to which RI has not been administered, and coincidence counting data is collected at each location, and from the coincidence counting data, the data of the location of the line radiation source is collected. The absorption correction data is obtained by obtaining only the absorption correction data by obtaining only the correction function for correcting the scattering of the emission data, and calculating the emission data collected when RI is administered to the subject as the absorption correction data. A method for correcting a positron CT in which the absorption coincidence correction is performed by using, and the above-mentioned correction function is actuated so as to remove the scattered coincidence counting component included in the emission data itself.