JPH0425511B2 - - Google Patents

Description

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

In general, scintillation cameras have sensitivity non-uniformity based on both spatial non-linearity and energy non-uniformity, and various proposals have been made to correct this. However, the conventional method had many problems such as a sacrifice in sensitivity.

In view of the above, an object of the present invention is to provide a scintillation camera that can correct sensitivity non-uniformity due to energy non-uniformity in real time without sacrificing sensitivity.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a large number of PMTs (photomultipliers) 13, which are photoelectric converters, are arranged on the back side of a scintillator 11 via a light guide 12. When radiation is incident from the front surface of the scintillator 11 and light is emitted, the light is guided to each PMT 13 via the light guide 12 and converted into an electrical output. The outputs of these PMTs 13 are led to the position and energy calculation circuit 14, where position and energy calculations are performed, and the position signals X,
Y and an energy signal Z are obtained. The energy signal Z is sent through a sample and hold delay circuit 15 to a main wave height analyzer 16, a low auxiliary wave height analyzer 17, and a high auxiliary wave height analyzer 18. These wave height analyzers 16,
17 and 18 detect that the peak value of the energy signal Z is within the respective window ranges, and output UNBLANK1, UNBLANK2, and UNBLANK2, respectively.
Generate each of UNBLANK3. Each window range is given by a window level setting circuit 19, and as shown in FIG.
For the high auxiliary wave height analyzer 18, the range is from LL2 to LL1, and for the high auxiliary wave height analyzer 18, the range is from UL1 to UL2. The window level setting circuit 19 sets the energy level (LEVEL) according to the nuclide of the radioactive isotope.
and window range (WINDOW) can be set arbitrarily. WINDOW is set as a percentage of LEVEL. LEVEL is the center value of the window range. When LEVEL and WINDOW are set, if WINDOW is 20%, LL1 to UL
1 is 20%, and at this time LL2 to LL1 and UL
1 to UL2 are each about 5%, for example.
UNBLANK1 goes through the OR circuit 22 and is sent as a brightness signal to the display device 25, but UNBLANK2 and 3 are not sent as they are, but are gated by AND circuits 20 and 21, respectively, and ADMIT・L and ADMIT・H are respectively gated. The display device 2 passes through the OR circuit 22 only when permitted by
5 as a luminance signal. Position signals X and Y are sent to the display device 25 through sample and hold delay circuits 23 and 24, respectively, and a bright spot is displayed at a position determined by these signals.

By the way, the signals ADMIT.L and ADMIT.H for allowing UNBLANK2 and UNBLANK3 are generated as follows. The position signals X and Y pass through sample and hold circuits 51 and 52, respectively, to the AD converter 6.
1 and 62, respectively (for example,
6 bits) and is sent as a signal specifying a read address to a pulse height shift amount memory 27 composed of, for example, a P-ROM. This wave height shift amount memory 2
7 includes a wave height shift amount ΔZ of the energy signal regarding each position measured in advance and an auxiliary wave height analyzer 17;
A 1-bit signal corresponding to the positive or negative of the shift amount ΔZ, which is a signal for specifying one of the 18 positions, is written for each address specified by the position signals X and Y. On the other hand, the counter 28 is self-propelled, and repeats a cycle in which it sequentially counts up from 0 to 255 at an independent timing that does not depend on the radiation incident event, and then returns to zero, and its output is the wave height shift amount. The output of the shift amount ΔZ read from the memory 27 (e.g. 8 bits) and the frequency conversion memory 2 as a signal specifying the read address.
9 (consisting of, for example, P-ROM). The frequency conversion memory 29 stores 1-bit data regarding the frequency for each address designated by the output of the counter 28 and the read wave height shift amount ΔZ, as shown in FIG. For example, the larger the shift amount ΔZ, the higher the probability that "1" will be read for various count values.
The ratio of "0" to "0" is set in advance. When “1” is read out, the pulse generation circuit 30 sends a signal.
ADMIT is generated and sent to AND circuits 33 and 34.
On the other hand, the 1-bit signal corresponding to the positive/negative of the shift amount ΔZ read from the wave height shift amount memory 27 is sent to the pulse generation circuit 31, and the pulse output from this pulse generation circuit 31 is sent to the AND circuit 33. This pulse is inverted by an inverting circuit 32 and sent to an AND circuit 34. Therefore, if the shift amount ΔZ of the energy signal wave height at the position defined by the position signals
The signal ADMIT・H is generated from the circuit 33, and if the shift amount ΔZ is negative (if it is shifted to the lower energy side as shown by the dotted line in FIG. 2), the AND circuit 3
4 produces the signal ADMIT.L. Note that timing control of each circuit in FIG. 1 is omitted for convenience of explanation.

In the above configuration, radiation is transmitted to the scintillator 11
Suppose that it is incident on a certain position. Assume that at this position there is no shift in the energy signal wave height, and the energy spectrum is as shown by the solid line in FIG. Then, the shift amount ΔZ at this position read from the wave height shift amount memory 27 is zero, and "0" is always read from the frequency conversion memory 29. Therefore, no matter how many pieces of radiation are incident on this position, there is no signal.
Both ADMIT・H and ADMIT・L always occur, that is, with a “probability of zero”, they do not occur. Therefore, even if UNBLANK2 and UNBLANK3 are generated from the low auxiliary wave height analyzer 17 and the high auxiliary wave height analyzer 18, they will be blocked by the AND circuits 20 and 21.
Eventually, only UNBLANK1 from the main wave height analyzer 16 is sent to the display device 25. Therefore, LL in Figure 2
When the wave height of the energy signal Z falls within the range of 1 to UL1, a bright spot is displayed on the display device 25.

Assume that radiation is incident on another position of the scintillator 11. It is assumed that it has been previously measured that at this incident position, the wave height of the energy signal Z shifts to the high energy side, and the energy spectrum becomes as shown by the dotted line in FIG. At this time, the shift amount ΔZ is read out from the wave height shift amount memory 27, and "1" is read out from the frequency conversion memory 29 at a frequency corresponding to its magnitude. Further, since the shift amount ΔZ at this time is positive, a signal of "1" is generated from the pulse generation circuit 31.
As a result, when a large number of radiations are incident on this position, a signal ADMIT.H is generated from the AND circuit 33 for a certain percentage of the radiations.
Therefore, in this case, UNBLANK1 indicates that the wave height of the energy signal Z is in the range of LL1 to UL1.
All of , and a certain percentage of UNBLANK3 from the high auxiliary wave height analyzer 18 indicating that it is in the range of UL1 to UL2 are displayed as a luminance signal on the display device 2.
5, and a bright spot is displayed.

Furthermore, when radiation is incident at a position where the energy spectrum shifts to the lower energy side as shown by the dashed line in FIG. Occurs at a frequency depending on ΔZ. Therefore, in this case, in addition to all of UNBLANK1, UNBLANK from low auxiliary wave height analyzer 17 generated in response to the wave height of energy signal Z entering LL2 to LL1
2 is sent to the display device 25 as a luminance signal. Therefore, at this time, LL1 to UL1
All of the times that fall within the range are displayed as bright spots, and a certain percentage (frequency) of the times that fall within the range of LL2 to LL1 are displayed as bright spots.

In this way, even when there is non-uniformity in the energy signal wave height depending on the incident position, the window range of the wave height analyzer can be expanded to the high energy side or the low energy side, and the expanded range can be adjusted according to the shift amount. Since the configuration is configured to capture data at a predetermined frequency, the original window range is not excluded, so sensitivity non-uniformity based on energy non-uniformity can be corrected in real time without sacrificing sensitivity. I can do it.

Note that the frequency can be converted from the shift amount ΔZ using other configurations such as using a random number generator instead of the self-running counter 28 and specifying the address of the frequency conversion memory 29 based on the output of the random number generator.
In particular, the wave height shift amount memory 27 and the frequency conversion memory 29 are integrated, and the 1-bit signal is converted into a 1-bit signal according to a frequency determined based on a pre-measured shift amount for each position, without writing the shift amount ΔZ. It is also possible to use a memory in which a 1-bit signal with a predetermined ratio of 1 and 0 is written, so that a signal related to the frequency of 0 or 1 can be directly obtained from the position signal and count value. can.

Furthermore, even if the window range of the main wave height analyzer 16 is narrowed and the shift amount is zero, the auxiliary wave height analyzer 17,
18, or a larger number of auxiliary wave height analyzers 17, 18 may be provided to improve accuracy.

Further, in the above embodiment, the data regarding the frequency written in the frequency conversion memory 29 is determined according to the absolute value of the shift amount ΔZ, but it may be written differently depending on the sign of the shift amount ΔZ. .

Energy window setting conditions (LEVEL,
WINDOW), the contents of the wave height shift amount memory 27 and the contents of the frequency conversion memory 29 may be rewritten according to the setting conditions, or a gain adjustment circuit for the read shift amount ΔZ may be inserted between these. The shift amount ΔZ may be reduced or enlarged, or the window ranges LL2 and UL2 of the auxiliary wave height analyzers 17 and 18 may be changed. The reason why it is changed in accordance with the WINDOW setting in this way is that, in general, when the window range is expanded, the change in sensitivity becomes smaller even if the shift amount of the energy signal wave height is the same. Further, the reason why it is changed as described above according to LEVEL is that when the radiation energy is high, the energy resolution becomes high and the sensitivity change becomes small under the condition that the ratio of WINDOW and shift amount ΔZ is the same. Furthermore, even if the energy of the incident radiation changes, the ratio of the shift amount ΔZ at each position can be approximated as being approximately constant, so the contents of the wave height shift amount memory 27 may be fixed in this sense, but strictly speaking, the energy of the incident radiation If the change occurs, the average depth of absorption within the scintillator 11 changes, so there is some energy dependence (this depends on the configuration of the optical system, for example, the presence or absence of a mask in the light guide 12, etc.). This is because it is desirable to change the value and frequency of the shift amount ΔZ to be used depending on LEVEL.

As described above with respect to the embodiments, according to the present invention, sensitivity non-uniformity based on energy non-uniformity can be corrected in real time without sacrificing sensitivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a graph showing an energy spectrum, and FIG. 3 is a schematic diagram showing the contents of a frequency conversion memory. 11... scintillator, 12... light guide, 13... PMT, 14... position and energy calculation circuit, 25... display device.

Claims (1)

[Claims] 1. A scintillator, a number of photoelectric converters to which light emission from the scintillator is guided, and a position and energy calculation circuit that calculates and outputs position signals and energy signals based on the outputs of these many photoelectric converters. a main wave height analyzer that generates an unblank signal when the wave height of the energy signal is within a predetermined energy window range; and a main wave height analyzer that generates an unblank signal when the wave height of the energy signal is within a predetermined energy window range; A plurality of auxiliary wave height analyzers each generating an unblank signal when within the window range, a wave height shift amount of the energy signal for each position measured in advance, and an auxiliary wave height analyzer designation determined based on this wave height shift amount. a shift amount storage means in which a signal is stored and whose read address is specified by the position signal; a means for converting the read shift amount into a frequency; A scintillation camera comprising a display device which receives an unblank signal from the auxiliary wave height analyzer specified by the frequency converter at a frequency determined by the frequency conversion means and displays a point at a position specified by the position signal. 2. A scintillator, a large number of photoelectric converters to which the light emitted from the scintillator is guided, a position and energy calculation circuit that calculates and outputs position signals and energy signals from the outputs of these large number of photoelectric converters, and a position and energy calculation circuit that calculates and outputs position signals and energy signals, and a main wave height analyzer that generates an unblank signal when it is within a predetermined energy window range; and a main wave height analyzer that has an energy window range adjacent to the energy window range and when the wave height of the energy signal is within each of these energy window ranges. a plurality of auxiliary wave height analyzers that generate unblank signals, respectively, and an auxiliary wave height analyzer designation signal determined based on the amount of wave height shift of the energy signal for each position measured in advance for each address specified by the position signal. and a signal corresponding to the frequency determined by the measured shift amount of each position is stored for each address specified by the position signal and the random signal, and is read out using the position signal and the random signal. The unblank signal from the auxiliary wave height analyzer specified by the read designated signal is inputted at the read frequency, and the unblank signal from the main wave height analyzer is inputted to the memory means to be addressed, and the unblank signal from the auxiliary wave height analyzer specified by the read designation signal is A scintillation camera consisting of a display device that displays a point at a position specified by a position signal.