JPH0528535Y2 - - Google Patents

Description

[Detailed explanation of the idea] Industrial applications This invention relates to a positron CT device.

Conventional technology In a positron CT device, inside the detector ring,
A subject who has been administered positron-emitting nuclide RI (radioisotope) is placed in the test, and radiation from the RI in the subject's body is detected. When the positron disappears, two gamma rays are emitted in a 180° direction, so they simultaneously enter each part of the detector ring. Therefore, by performing coincidence counting, it can be seen that RI exists on the line connecting the two incident positions.
In this way, location information is accumulated in RI,
RI within one slice plane is processed by a computer using an image reconstruction algorithm.
Reconstruct the distribution image (tomographic image).

Incidentally, in recent years, there has been a demand for higher spatial resolution of positron CR devices. This is required not only in the slice in-plane direction but also in the slice thickness direction (axial direction). That is, it is required to increase the spatial resolution between slices at different positions in the axial direction when multiple slices are simultaneously imaged by forming the detector ring in multiple layers.

As shown in Fig. 3, the three-layer detector ring 11,1
2,13, the sensitivity distribution on the axis Z will be 1 to 5. Sensitivity distributions 1, 3, and 5 of the direct slice can be obtained by calculating the simultaneous coefficient that two gamma rays emitted in the 180° direction enter one detector ring through the path shown in A. , the cross-slice sensitivity distributions 2 and 4 are obtained by simultaneously counting the incidence of two γ-rays into each of the two adjacent detector rings as shown in path B.
In this way, images of five slices can be obtained simultaneously by the three layers of detector rings 11 to 13, but in the case of cross slices 2 and 4, the solid angle at which the detector ring is viewed from the center of the slice on the Z axis is smaller. The sensitivity of the entire slice (corresponding to the area of each distribution) is twice that of direct slices 1, 3, and 5, and the peak is twice that of direct slices 1, 3, and 5.
It's twice as many as 5.

Therefore, by using six layers of detector rings 11 to 16 whose thickness in the Z direction is 1/2 as shown in Fig. 4, 11 sensitivity distributions 1 to 11 can be obtained on the Z axis, and 11 slices can be obtained simultaneously. It becomes possible to take pictures of

In other words, in order to increase the spatial resolution in the axial direction,
The thickness of the detector ring is made thinner.

Problems that the invention aims to solve However, although simply reducing the thickness of the detector ring increases the spatial resolution in the axial direction, the sensitivity deteriorates significantly. For example, in the example of FIG. 4 above, slices 1 to 11
At each center position (in the Z-axis direction), the solid angle of the detector ring seen from the Z-axis is 1/2 of that in Figure 3, so the peak is 1/2, and the sensitivity is 0. Since the width of the slice is also 1/2, the sensitivity of the entire slice is 1/4 of that shown in Figure 3. This is the same for direct slicing and cross slicing. Therefore, in order to obtain the same image quality as in the case of Figure 3, if the amount of RI to be administered is the same,
This will require four times as much time.

Therefore, when a configuration is adopted to increase the spatial resolution in the axial direction, the sensitivity deteriorates significantly in the conventional method, and to compensate for this, the measurement time must be increased, and the measurement time for dynamic measurements etc. is limited. In this measurement, a problem arises in that it is not possible to obtain a large number of counts per slice, and an image with a good S/N ratio cannot be obtained.

The purpose of this invention is to provide an improved positron CT device that can increase sensitivity as necessary even when a configuration with increased spatial resolution in the axial direction is adopted.

Means for Solving the Problems The positron CT device according to this invention has a multi-layered detector ring and a simultaneous detection system for detecting simultaneous incidence of radiation into one layer and two adjacent layers of the detector ring. It has a counting circuit, a memory that simultaneously collects data regarding the direct slice and the cross slice, and an adder that adds the data regarding at least two adjacent slices.

Effect Since data regarding at least two adjacent slices are added, if this added data is used as data for one slice, the amount of data regarding one slice will increase. At this time, since data of a plurality of slices at different positions in the axial direction are added, the spatial resolution in the axial direction is somewhat degraded and the number of slices is also reduced.

Therefore, in cases such as dynamic measurements where the measurement time cannot be long, such addition is performed to improve the S/N.
One way to use this method is to obtain images of high image quality with a high ratio, and if the measurement time can be long, do not perform such addition and take advantage of the high axial resolution to obtain images of many slices. It can be performed using a positron CT device.

Embodiment In FIG. 1, six thin layers of detector rings 11 to 16 are stacked, and these are connected to a coincidence circuit 21 to calculate coincidence in the same layer and in two adjacent layers. A simultaneous count is made between the two. Then, position information of direct slices and cross slices (same as in FIG. 4) is accumulated in the memory 23 for each slice. After a certain period of time, direct slice 1, 3, 5, 7, 9, 1
1, cross slice 2, 4, 6, 8, 10 (4th
Data for a total of 11 slices (see figure) are collected in the memory 23.

Therefore, during dynamic measurement, an adder 25 adds data of two adjacent direct slices 1 and 3 and a cross slice 2 between them under the control of the CPU 22. Addition is performed similarly for other direct slices and cross slices. That is, addition of slices 3, 4, and 5, addition of slices 5, 6, and 7, addition of slices 7, 8, and 9, and addition of slices 9, 10, and 11 are performed, respectively. This results in five slices 1 shown in Figure 1.
~5 data are obtained, and the sensitivities are the same as direct slices 1, 3, and 5 in Figure 3, respectively, and direct slices 1, 3, and 5 in Figure 4, respectively.
5, it will be four times as much as...

In this way, the original three slices of data are combined into one slice of data, which is processed by the image processing unit 24 using an image reconstruction algorithm such as a back projection method to obtain five slices of images. This image data is stored in the external storage device 26 or displayed on the display device 27.

In this case, there were 11 slices before addition, but there are 5 slices after addition, so the number of slices is halved and the spatial resolution in the Z-axis direction is also halved.
Since the sensitivity can be quadrupled, it is possible to obtain images of excellent image quality with a high S/N ratio even in dynamic measurements where a long measurement time cannot be taken, and this is effective in such cases.

Therefore, if the measurement time can be longer,
By not performing the above addition, image reconstruction can be performed in a mode with high axial resolution and a large number of slices by taking advantage of the configuration that has high spatial separation in the Z-axis direction, and the measurement time for dynamic measurements etc. can be reduced. For measurements that cannot be made for a long time, it is possible to reduce the axial resolution to some extent and reduce the number of slices, while increasing the sensitivity and obtaining an image with a high S/N ratio.

Note that data addition between slices as shown in FIG. 2 is also possible. First, as shown in FIG. 2A, the sensitivities of the 11 slices of data originally obtained are made equal. This is corrected by reducing data related to highly sensitive cross slices. Then, the data of slices 1 and 2 in FIG. 2A are added to obtain new slice 1 data. By sequentially adding adjacent slices in FIG. 2A in this way, ten new slices 1 to 10 as shown in FIG. 2B are obtained. In this case, the response in the Z-axis direction becomes trapezoidal, the sensitivity is twice the original value, and the number of slices remains almost unchanged at 10.

Effects of the invention According to the positron CT device of this invention, even when the axial thickness of the detector ring is made thinner and the axial spatial resolution is increased, the sensitivity can be increased as necessary, and the dynamic It is convenient because it enables measurement and can be used differently depending on the measurement.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of this invention, FIGS. 2A and B are diagrams showing the Z-axis direction sensitivity distribution for other embodiments, and FIGS. 3 and 4 are diagrams showing the detector ring arrangement and Z-axis direction. FIG. 6 is a schematic diagram showing the relationship with the axial sensitivity distribution. 11-16...Detector ring, 21...Coincidence circuit, 22...CPU, 23...Memory, 24
...image processing device, 25...adder, 26...external storage device, 27...display device.

Claims (1)

[Scope of utility model registration request] a plurality of layers of detector rings and one of the detector rings;
a coincidence circuit for detecting simultaneous incidence of radiation in one layer and in two adjacent layers; a memory for simultaneously collecting data regarding the direct slice and the cross slice;
A positron CT device having an adder that adds data regarding two slices.