JPH0424674B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a scintillation camera.

A scintillation camera has a configuration in which a large number of photoelectric converters (usually photomultipliers are used) are arranged on the back of the scintillator via a light guide, and an energy signal is obtained from the sum of the outputs of these photoelectric converters. Therefore, the position dependence of the energy signal is significant, for example, when scintillation occurs between adjacent photoelectric converters, the sum of all photoelectric converter outputs is different when it occurs directly below the photoelectric converter. (also called energy non-uniformity) is unavoidable. In other words, when we take the spectrum (frequency distribution) of the energy signal, as shown in Figure 1, there is a shift between the solid line and the dotted line depending on the scintillation position, and the window width W in the energy signal analyzer varies. If the number of incident radiation is different, and if an image is taken in which radiation is uniformly generated at all points on a plane, a non-uniform image will be obtained that is uneven depending on the position. Therefore, various proposals have been made to correct this energy non-uniformity, but all of the conventional methods are based on the measurement results obtained by imaging a specific pattern before using it for actual clinical imaging. A correction coefficient is calculated for each position using is taken. Therefore, it is necessary to take the trouble of calculating and writing correction coefficients during off-time, and it is also difficult to deal with changes over time.

In view of the above, this invention eliminates the need for troublesome work during off-time by dynamically applying the correction amount for energy non-uniformity correction based on incident data obtained during actual shooting.
The present invention aims to provide a scintillation camera that corrects energy non-uniformity in real time by dealing with changes over time.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, a large number of photomultipliers 13 are arranged on the back side of a scintillator 11 via a light guide 12, and scintillation light generated when radiation such as γ rays is incident on the scintillator 11 is transmitted to each photomultiplier 13. This output is led to the position and energy calculation circuit 14, where position signals X, Y and energy signal Z are output.
The energy signal Z is input to an analyzer 15 and an unblank signal is generated from the analyzer 15 when it is within a set window. This unblank signal and the position signals X, Y are input to a display device 16 such as a CRT device, and when the unblank signal is input, the position signals X, Y on the display screen are input.
A dot is displayed at the position indicated by Y. Assuming that the window in this analyzer 15 is fixed as set by the window setting device 17, it will be similar to a conventional scintillation camera.

In an embodiment according to the invention, this analyzer 1
5 window, AD conversion circuit 21, memory 2
The change is made by a 2(+1) addition circuit 23, a subtraction circuit 24, an addition circuit 25, a level generation circuit 26, and a timing circuit (not shown). First, the energy level (center value of the window) corresponding to the nuclide is set according to the measured radiation by external manual operation using the window setting device 17, and the window width is set as a ratio such as a percentage above and below the energy level. settings (see Figure 5). The memory 22 stores position signals X, Y
For each address (Xi, Yi), as shown in FIG. 3, there is a section 31 for storing the energy level and upper data (described later). It has a section 32 and a section 33 for storing lower data (described later). Initially, the contents of this memory 22 are all cleared, and when the energy level and window width are set with the window setter 17, the set energy level is uniformly written to each storage section 31 at each address.

Then, when actual imaging is performed and radiation is incident on the scintillator 11, the energy level is read out from the memory 22 by addressing with digital position signals X and Y obtained for each event of radiation incidence, and this energy level is read out from the memory 22. The level is sent to level generation circuit 26. This level generation circuit 2
6 is composed of a level calculation circuit and a DA conversion circuit, and calculates the energy level and upper level (upper limit value of the window) based on the energy level and the window width data (ratio to the energy level) from the window setting device 17. Each lower level (lower limit value of the window) is created as a voltage level, and these are sent to the analyzer 15.

The analyzer 15, as shown in FIG. When this energy signal Z enters the upper half of the window (between the energy level and the upper level), an upper signal is output, and the upper signal is output when the energy signal Z enters the upper half of the window (between the energy level and the upper level). and the lower level), a lower signal is outputted and input into the memory 22. When this upper signal or lower signal is input (+
1) The adder circuit 23 operates to add (+1) the contents of the storage section 32 or 33 at the address specified by the digital position signals X and Y at this time. In other words, the contents of memory sections 32 and 33 (upper data, lower data) represent the number of times the energy signal Z enters the upper and lower halves of the window, respectively, and in this sense functions as a counting circuit. It turns out.

When a large number of images are taken and the counts of each upper data and lower data are statistically sufficient, there is no deviation of the energy signal Z with respect to a certain position and the spectrum of the energy signal Z is centered around the energy level. Assuming that the energy level is vertically symmetrical and the center value of the upper level and lower level, as shown in Figure 5, the values of the upper data and lower data correspond to the area of each diagonal line. It should be the same. Energy signal Z
If deviates due to position dependence, the spectrum curve in FIG. 5 will shift to the right or left, so symmetry around the energy level will disappear, and either the upper data or the lower data will be larger than the other. The upper data and lower data are read out from the memory 22 for each event, and sent to the subtraction circuit 24, where one is subtracted from the other to obtain data regarding the level shift. The data regarding this level shift is added in an adder circuit 25 with the data regarding the energy level read out from the memory 22 and sent to the memory 22 again to update the energy level in the storage section 31 of the address in question. In this way, for example, if the spectrum curve of the energy signal Z shifts to the right in FIG. 5, there will be more upper data than lower data,
A level shift amount (correction amount) corresponding to the difference is added to the original energy level, and the energy level in FIG. 5 is shifted to the right and moved to the center of the shifted spectrum curve. Therefore, the energy level corrected for each position (each address) is read out from the memory 22, and the level generation circuit 26 generates the energy level as a voltage level.
By creating an upper level and a lower level and supplying them to the analyzer 15, the window can be corrected for each position in response to energy non-uniformity at each position.

Note that the storage sections 32 and 33 that store the upper data and lower data of the memory 22 essentially function as a counting circuit, so a counting circuit provided for each address can be used as a specific circuit. May be used.

Also, in the above explanation, the spectrum curve, upper level, and lower level are symmetrical with respect to the energy level, but depending on the spectrum curve and window settings, they may be asymmetrical (both counts are not the same). case) may become a normal state. In such a case, the subtraction circuit 24 does not simply perform subtraction, but also performs subtraction with non-linearity, which is necessary to restore the relative relationship of the window to the shifted spectrum curve to the normal one. Calculation is performed to obtain a level shift amount (correction amount).

Since this correction amount differs for each position, it is necessary to read it out and change the window for each event of radiation incidence, but updating to calculate the correction amount does not necessarily have to be performed for each event, but can be done every time sufficient data has been accumulated. Alternatively, once the correction amount is updated, the (+1) addition operation is stopped and used for a certain period of time, and when changes over time appear, the (+1) addition operation is stopped again.
1) It is also possible to perform an addition operation, obtain data, and update the correction amount.

Further, in this embodiment, the window is changed according to the position dependence of the energy signal Z, but since the relationship between the energy signal Z and the window is relative, the window is not changed but the window is changed depending on the position dependence of the energy signal Z. It is also possible to shift or enlarge or reduce the object itself, in short, it is sufficient to change the relative relationship between the two.

In addition, when using a nuclide with multiple energy peaks such as ⁶⁸ Ga, storage section 3 of the memory 22 is used to enable counting in multiple windows.
This can be easily dealt with by adding 2 or 33 or a counting circuit.

As described above with respect to the embodiments, according to the present invention, it is possible to obtain the correction amount for correcting energy non-uniformity at any time or at any time even during actual clinical imaging. It requires no effort and can respond to changes over time.

[Brief explanation of drawings]

Fig. 1 is a graph showing an energy spectrum, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a conceptual diagram showing storage divisions of each address in memory, and Fig. 4 is a block diagram showing an example of an analyzer. Figure 5 shows the energy level, upper level,
It is a graph of an energy spectrum for explaining the relationship between a lower level, upper data, and lower data. 11... scintillator, 12... light guide, 13... photo multiplier, 14... position and energy calculation circuit, 15... analyzer,
16...display device, 17...window setting device,
21...AD conversion circuit, 22...memory, 23...
...(+1) Addition circuit, 24...Subtraction circuit, 25...
...addition circuit, 26...level generation circuit.

Claims (1)

[Claims] 1. A scintillator, a large number of photoelectric converters arranged on the back side of the scintillator via a light guide, and a position and energy calculation circuit that receives the outputs of the large number of photoelectric converters and outputs a position signal and an energy signal. , an analyzer that detects that the energy signal is within a set window and outputs an unblank signal; and an analyzer that detects that the energy signal is within a set window and outputs an unblank signal; In a scintillation camera, the scintillation camera includes a display device that displays a point at the indicated position, and a circuit that detects for each position that an energy signal has entered each of the upper and lower windows obtained by dividing the window, and the upper and lower windows that are obtained by dividing the window. A counting circuit that counts the number of times an energy signal enters each of the windows at each position, and when the correlation between the respective counted values regarding the upper and lower windows at each position deviates from a predetermined correlation, this deviation is resolved. A circuit that stores the relative correction amount of the window with respect to the energy signal required for each position, reads out the correction amount using the position signal obtained for each radiation incident event, and uses this correction amount to calculate the energy for each event. A scintillation camera characterized by comprising a circuit that changes the relative relationship between a signal and a window.