JPS593378A - Scintillation camera - Google Patents

Abstract

PURPOSE:To correct the nonuniformity in sensitivity in real time without sacrificing the sensitivity by constituting a titled camera in such a way that the window range of a pulse height analyzer is expanded and taking signals at the prescribed frequency according to the shift rate thereof. CONSTITUTION:The pulse height of an energy signal Z in a certain incident position of a scintillator 11 is assumed to be deviated to a high energy size. A shift rate DELTAZ is read out from a memory 27 for the shift rate of pulse height in this stage, and ''1'' is read out from a frequency conversion memory 29 at the frequency corresponding to the magnitude thereof. Since the rate DELTAZ is positive, the signal ''1'' is generated from a pulse generation circuit 31. A signal ADMIT. H is generated from an AND circuit 33 with respect the signal of a specified ratio. All of UNBLANK1 and the signals of a specified ratio among the UNBLANK3 from an auxiliary pulse height analyzer 18 are fed as a luminance signal to a display 25 which indicates a luminous spot.

Description

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

In general, scintillation cameras have sensitivity non-uniformity due to both spatial non-linearity and energy non-uniformity, and various proposals have been made to correct this. However, conventional methods had many problems such as sacrificing 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 photoelectric converter, PMT (
A large number of photomultipliers 13 are arranged. When radiation is incident on the front surface of the scintillator 11 and light emission occurs, the light is guided to each PMT 13 via the light guide 12 and converted into an electrical output. These PMTl 3
The output is led to a position and energy calculation circuit 14 where 1 position calculation and energy calculation are performed to obtain position signals X, Y and energy signal 2. The energy signal Z passes through a sample and hold delay circuit 15 to a main wave height analyzer 16. Low auxiliary wave height analyzer 17. It is sent to the high auxiliary wave height analyzer 18. These wave height analyzers 16, 17, and 18 detect that the wave height value of the energy signal Z is within the respective window ranges, and output UNBLANKI and UNBLANK2, respectively.
, UNBLANK3. Each window range is set first by the wind level setting circuit 19, and the second
As shown in the figure, for the main wave height analyzer 16, FiLL1~
LL2 for ULI range, low auxiliary wave height analyzer 17
~LLI range, UL for high auxiliary wave height analyzer 18
The range is from I to UL2. The window level setting circuit 19 can arbitrarily set the energy level (LBVEL) and window range (WINDOW) according to the nuclide of the radioisotope. WINDOW is L
It is set in chi for BVBL. LFiVEL is the center value of the window range. When LEVEL and WINDOW are set, if WINDOW is 20%, LLI
~ULI is 20%.

At this time, LL2 to LLI and ULI to UL2 are each about 5%, for example. O for UNBLANKI
The luminance signals are sent to the display device 25 as they are through the R circuit 22, but tJNBl and ANK2.3 are not sent as they are, but are gated by the AND circuits 20 and 21, and are gated by each of ADMIT-L and ADMIT-H. Only when the signal is allowed is the brightness signal passed through the OR circuit 22 and sent to the display device 25 as a luminance signal. Display! '25, the position signals X and Y are sent to sample and hold delay circuits 23.
．． 24, and a bright spot is displayed at a position determined by these.

By the way, the signal A for allowing UNBLANK2 and 3f
I) MIT-L and ADMIT-H are produced as follows. The position signals X and Y are respectively digitized (for example, 6 bits) by AD controllers 4-1.62 to sample and hold circuits 51 and 52't,
For example, the wave height shift amount memory 2 composed of P-ROM
7 as a signal specifying the read address. This wave height shift amount memory 27 stores the shift amount ΔZ of the wave height value of the energy signal regarding each position measured in advance, and the positive/negative shift amount Δ2 which is a signal for specifying either of the auxiliary wave height analyzers 17 or 18. A 1-bit signal corresponding to the address is written for each address specified by the position signals X and Y. On the other hand, the counter 28 is a self-propelled type, and is 1, for example, 0 to 2.
Until 55, the cycle of counting up and returning to zero is repeated at an independent timing that does not depend on the radiation incident event, and the output is the output of the shift amount Δ2 read from the wave height shift amount memory 27 (for example, 8
bits) and is sent to the frequency conversion memory 29 (for example, composed of a P-ROM) as a signal specifying a read address. 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 ratio between "1" and "0" is set in advance so that the larger the shift amount ΔZ is, the higher the probability that "1" will be read out for various count values. When "1" is read out, the pulse generation circuit 30 generates a signal ADMIT and the AND circuit 33.3
Sent to 4. On the other hand, 1 bit corresponding to the positive/negative of the shift amount Δ2 read from the wave height shift it memory 27
Is the signal NoJ? The pulses sent to the pulse generation circuit 31 and output from the pulse generation circuit 31 are sent to the AND circuit 33, and this J? The signal is inverted by an inverting circuit 32 and sent to an AND circuit 34. Therefore, 1 position signal X,
If the shift amount Δ2 of the energy signal wave height at the position defined by Y is positive (if it is shifted to the high energy side as shown by the dotted line in Figure 2), the signal AI is sent from the AND circuit 33.
When M I T , H is generated and the shift amount Δ2 is negative (shifted to the lower energy side as shown by the dashed line in FIG. 2), the AND circuit 34 generates the signal ADMIT-L. Note that timing control of each circuit in FIG. 1 is omitted for convenience of explanation.

Assume that radiation is incident on a certain position of the scintillator 11 in the above configuration. 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 wave height shift fish memory 27
The shift amount ΔZ at this position read from is zero, and “0” is always read from the frequency conversion memory 29. Therefore, no matter how many radiations are incident on this position, the signal AI)
MIT-H, At) MIT-L are always connected to V
This means that it will not occur with a "probability of zero". Therefore, from the low auxiliary wave height analyzer 17 and the high auxiliary wave height analyzer 18,
2. Even if UNBLANK3 occurs, AND circuit 2
0.21, and in the end only UNBLANKl from the main wave height analyzer 16 is sent to the display device 25.

Therefore, the energy signal Z is in the range from LLI to ULI in Fig. 2.
When the wave height reaches , 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 Figure 2. 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, at this time, since the shift amount ΔZ 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 ADMI is output from the AND circuit 33 for a certain percentage of them.
T@H will occur. Therefore, in this case, LLI
All of the UNBLANKl indicating that the wave height of the energy signal 2 is in the range of ~ULI, and the UN from the high auxiliary wave height analyzer 18 indicating that the wave height is in the range of ULI~UL2.
A certain percentage of HLANK3 is sent to the display device 25 as a luminance signal.

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.
The signal ADMIT·L is generated at a frequency corresponding to the shift amount Δ2. Therefore, at this time, in addition to all of UNBLANKl, UNB from the low sleeve auxiliary wave height analyzer 17 generated in response to the wave height of the energy signal Z entering LL2 to LLI is
A certain proportion of LANK2 is sent to the display device 25 as a luminance signal. Therefore, at this time, all of the times that the range falls within the range LL1 to ULI are displayed as bright spots, and a certain percentage (frequency) of the number of times that the range falls within the ranges of LL2 to I, Ll is displayed as the bright spot. That will happen.

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
Since it is configured to import items in a wide range at a predetermined frequency depending on the shift amount, items in the original wind range are not excluded, so without sacrificing the feeling.
Sensitivity non-uniformity that lags behind energy non-uniformity can be corrected in real time.

Note that the frequency can be converted from the shift amount ΔZ by 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, by integrating the wave height shift amount memory 27 and the frequency conversion memory 29, the shift amount ΔZ
1b at a predetermined frequency based on the pre-measured shift amount for each position.
The ratio of rlJ and rOJ of it signal is determined 1 b
It is also possible to use a memory in which the it signal is written so that a signal relating to the frequency of "0" or "1" can be directly obtained from the position signal and the count value.

In addition, the window range of the main wave height analyzer 16 is narrowed so that the auxiliary wave height analyzer 17.18 is used even when the shift amount is zero, and the accuracy is improved by providing a larger number of auxiliary wave height analyzers 17.18. You can do it like this.

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. .

Also, energy window setting conditions (LEVEL).

The contents of the wave height shift amount memory 27 and the frequency conversion memory 29 are rewritten in accordance with WINL) OW), or a gain adjustment circuit for the shift amount ΔZ read out is inserted between these settings. Shift amount Δ depending on conditions
You may try to reduce or enlarge Z, or change the window range (EL2, LJL2) of the auxiliary wave height analyzer 17°J8. Like this W I N I
The reason why it is changed according to the setting of JOW 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. Also l,
Changing the above according to E V EL is because if the radiation energy is high, the energy resolution will be degraded (and WIN
This is because the change in sensitivity becomes small under conditions where the ratios of IJOW and shift amount Δ2 are the same. Even if the energy of the incident radiation changes slightly, 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 contents of the wave height shift amount memory 27 may be fixed. If the energy changes, the average depth of absorption within the scintillator lJ 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), so it is necessary to deal with this. If so, 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 applicant Shimadzu Corporation

Claims (2)

[Claims] (1) A scintillator, a number of sources through which light emission in this scintillator is guided, a converter, and a position and energy signal that outputs position and energy signals by measuring and transmitting the outputs of these many photoelectric converters. an arithmetic circuit, a main wave height analyzer that generates an unranked signal when the wave height of the energy signal is within a predetermined energy window range, and a wave height of the energy signal that has an energy window range adjacent to the energy window and de ranges. a plurality of auxiliary wave height analyzers each generating an unblank signal when is within each of these energy window ranges; a shift amount storage means in which an auxiliary Oshima analyzer designation signal is stored and whose read address is specified by the position signal; a means for converting the read shift amount into a frequency; and a display device which receives an unrank signal from an auxiliary wave height analyzer designated by the specified signal together with the unrank signal at a frequency determined by the frequency conversion means and displays a point at a position designated by the position signal. synnarration camera. (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. a dominant wave height analyzer that produces an unranked signal when the wave height is within a predetermined energy window range; and a main wave height analyzer having an energy wind range adjacent to said energy wind range, and wherein the wave height of the energy signal is within each of these energy window ranges. The position signal specifies a plurality of auxiliary wave height analyzers each generating an unranked signal at a certain time, and an auxiliary wave height analyzer designation signal determined based on a wave height shift amount of the energy signal for each position measured in advance. A signal is generated for each address, and a signal corresponding to the frequency added by the measured shift amount of each position is stored for each address specified by the position signal and the random signal, and a storage means whose reading address is specified by a signal and a random signal, and an unrank signal from an auxiliary wave height analyzer specified by the read designation signal together with an unrank signal from the main wave height analyzer is read out. A scintillation camera comprising a display device that displays a point at a position specified by the position signal that is input at a frequency that is inputted.