JPH0812247B2 - ECT device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a nuclear medicine diagnostic device, and more particularly, to an ECT device (emission type computer tomography device) which administers a single photon emitting nuclide or a positron emitting nuclide into a subject and obtains a distribution image thereof as a tomographic image. .

[Prior art]

Since the ECT device has a relatively small amount of data and a large amount of statistical noise, when an image is reconstructed from the collected projection data by the backprojection method, after applying a convolution integral filter with a maximum frequency limit, backprojection is performed. I try to do it. However, the maximum frequency of this filter is not constant, and unless it is changed according to the total count value, the diameter of the subject, the distribution of RI (radioisotope), etc., an appropriate image that is easy to see cannot be obtained. Therefore, conventionally, an image is first reconstructed by using one of the filters, and if the image has a lot of noise, the highest frequency of the filter is lowered and the image is reconstructed again. Therefore, depending on the case, it is necessary to repeat such an image reconstruction operation many times.

[Problems to be Solved by the Invention]

Repeating image reconstruction by changing the filter as in the past requires a very long calculation time and requires a long time to obtain an image with a high S / N ratio, which is extremely inefficient. was there. According to the present invention, an optimum one having the highest frequency is automatically selected as a convolution integral filter used at the time of image reconstruction so that an image having a high S / N ratio can be obtained by one image reconstruction. The object is to provide an improved ECT device.

[Means for solving problems]

In the ECT device according to the present invention, a means for obtaining a total count of collected data, a means for inputting an imaging site and a radiopharmaceutical used as imaging conditions, various total counts, an imaging site and an optimum maximum frequency for each radiopharmaceutical A means for storing a predetermined convolution integral filter, a means for obtaining a filter of the optimum maximum frequency from the storage means by the above-mentioned total count, imaging region and radiopharmaceutical, and the above-obtained filter for the collected data. It is special to have a means for operating and reconstructing an image.

[Action]

The noise ratio of the reconstructed image can be expressed by the following equation. Here, rms is the ratio of noise expressed by the square root of the root mean square, D is the source diameter, and N is the total count. That is, the rms of the image is proportional to the 2/3 power of the diameter of the RI distribution in the subject and inversely proportional to the 1/2 power of the total count. Therefore, it is understood that the maximum frequency of the filter for obtaining an appropriate rms can be obtained if the diameter of the subject, the RI distribution and the total count value are known. So, in advance, the total number of possible
For radiographic conditions such as nuclides (radioactive agents) and radiographic sites,
The maximum frequency of the optimum filter is found and determined so that rms becomes appropriate, and this is tabulated and stored. When actually taking an image of the subject, enter the imaging conditions such as the imaging site and radiopharmaceutical, and obtain the total count after collecting the data, and from this, find the optimum frequency filter from the stored table. You can ask. Therefore, when this filter is applied to the collected data to perform superimposition integration and then backprojection, it is close to the optimum.
A reconstructed image with S / N ratio can be obtained.

【Example】

In an ECT apparatus according to an embodiment of the present invention, as shown in the figure, an output of a detector 1 for detecting radiation emitted from a subject is guided to a data collecting apparatus 2, and collected data is stored in a data memory 3, The total count of this data is obtained by counting with the counter 4. On the other hand, prior to data collection for such an actual subject, the condition input device 5 inputs the radiographic agent administered to the imaging site and the subject. The total count value obtained when all the data is collected is
When it is given to the CPU 6, the filter of the optimum maximum frequency is read from the filter table memory 7 in accordance with the total count value and the inputted imaged region and radiopharmaceutical. In other words, the optimum maximum frequency for total counts, imaging sites (head, heart, liver, etc.) and radiopharmaceuticals (FDG, CO, CO _2, etc.) that can occur in various clinical ECT scans actually performed is empirical. Therefore, it is determined in advance, tabulated and stored in the memory 7. In this table, the maximum frequency is shown by the resolution (unit: mm) in the real space. The filter read from the table of the memory 7 is applied to the projection data collected by the CPU 6 and is subjected to superimposition integration, and then sent to the image reconstructing device 8 to be processed by the back projection method. Is reconstructed. If the maximum filter frequency cannot be stored as a table for all total count values, the maximum frequency corresponding to the actual total count value is interpolated from the maximum frequency of the total count values adjacent to the total count value. It is possible to obtain it by using the following equation, or to use the curve that most closely approximates it. Further, in the above, the imaging site and the radiopharmaceutical are input as the imaging conditions, but it is also conceivable to input age or medical condition as the imaging conditions. Further, in the above embodiment, the processing is performed by hardware,
Of course, it can be processed by software.

【The invention's effect】

According to the ECT device of the present invention, before image reconstruction,
Based on the input imaged region and radiopharmaceutical and the automatically obtained total count, various total counts and a superposition integral filter in which the optimum maximum frequency is determined for each imaged region and radiopharmaceutical are stored in advance. Since the total count, the optimum maximum frequency superimposition integral filter for the radiographed region and the radiopharmaceutical are obtained from the storage means and the image is reconstructed using this, the image reconstruction is not performed once and The image of the optimum S / N ratio can be easily obtained by the image reconstruction processing.

[Brief description of drawings]

The figure is a block diagram of an embodiment of the present invention. 1 ... Detector, 2 ... Data collection device, 3 ... Data memory, 4 ... Counter, 5 ... Condition input device, 6 ... CP
U, 7 ... Filter table memory, 8 ... Image reconstruction device.

Claims (1)

[Claims] 1. A means for obtaining a total count of collected data,
Means for inputting the imaging site and radiopharmaceutical used as imaging conditions, various total counts, means for storing the superimposition integral filter in which the optimum maximum frequency is determined for each imaging site and radiopharmaceutical, and the above total count, An ECT apparatus comprising: a means for obtaining a filter having an optimum maximum frequency from the storage means according to an imaged region and a radiopharmaceutical; and means for reconstructing an image by applying the obtained filter to collected data.