JPH0452422B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in scintillation cameras using AD converters.

Generally, a scintillation camera has a scintillator 11 and a photoelectric converter 12, as shown in FIG.
and a position and energy calculation circuit 13 that calculates the position and energy of the incident radiation based on the output of this photoelectric converter, and obtains position signals X, Y and energy signal Z from this position and energy calculation circuit 13. There is, but the position signals X and Y are AD
When calculating a correction amount by accessing a memory for linearity correction using the converted digital signal, there are the following problems. First, AD converter 2
1 and 22, stripes appear in the image. This means that if there is nonlinearity in the AD converter,
For example, the probability that an output code corresponding to a certain input value will occur is significantly lower than other codes, or conversely, an output code that should correspond to one input step may span two or three input steps and its output This is because the probability that a code will appear is two or three times that of other codes, and the data will no longer be smooth. Second, due to the configuration of optical systems such as scintillators, light guides, and photoelectric converters, even if a uniform image is taken, there are sparse parts and dense parts in the image, that is, spatial non-linearity. However, in areas where this non-uniformity is large, if the minimum pixel correction amount is calculated by interpolation, the non-uniformity will remain at the level of this interpolated pixel. Put it away. That is, in digital interpolation calculation, the digital space before and after correction does not become a mapping, so that stripes occur depending on the final display pixel level. This is particularly noticeable in areas where differential nonuniformity is large, that is, areas where the correction amount and correction amount change rate are large.

In view of the above, it is an object of the present invention to provide a scintillation camera that can improve the problem caused by the non-linearity of the first AD converter and at the same time improve the second problem of non-uniformity. With the goal.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, analog position signals X and Y are subtracted by random numbers ΔR _X and ΔR _Y in analog subtracters 31 and 32 before AD converters 21 and 22, respectively. These random numbers are digital random numbers obtained by random number generators 41 and 42 triggered by an unblank signal output from the pulse height analyzer 14 that analyzes the pulse height of the energy signal Z, and are converted into analog numbers by DA converters 51 and 52. This is what I did. This signal (X
-ΔR _X ) and (Y-ΔR _Y ) are AD-converted. this
Each signal after AD conversion is sent to the correction calculation circuit 15. The correction calculation circuit 15 has a memory that stores correction amounts for linearity correction, etc., and accesses this memory with digital values of (X-ΔR _X ) and (Y-ΔR _Y ) to calculate the correction amount. Read out ΔX and ΔY. These correction amounts ΔX and ΔY are position (X-ΔR _X , Y-ΔR _Y )
Since _{it is} related to ΔX ( _X - _ΔR Then, this correction amount is sent to the A converter 21,
22 output. Therefore, the signals after addition are (X-ΔR _X ) +ΔX (X-ΔR _X , Y-ΔR _Y ) (Y-ΔR _Y ) +ΔY (X-ΔR _X , Y-ΔR _Y ), respectively. This signal is sent to digital adders 71 and 72.
The digital values of random numbers ΔR _X and ΔR _Y , which are the same as the random numbers mentioned above, are added. Therefore, the signal after addition
X′, Y′ are X′=(X−ΔR _X )+ΔX(X−ΔR _X , Y
−ΔR _Y )+ΔR _X ……(1) Y′=(Y−ΔR _Y )+ΔY( _X −ΔR
−ΔR _Y )+ΔR _Y ...(2). Therefore, the random numbers ΔR _X and ΔR _Y will be canceled after all.

Since random numbers are subtracted and added before and after AD conversion and are eventually canceled, the AD converters 21 and 22 have non-linearity.
For example, even if there are output codes whose probability of appearing is lower than other output codes, or whose probability of appearing is two or three times higher than other output codes, the input corresponding to these output codes is random. This can prevent the output data from losing smoothness, and can prevent the first problem of stripes appearing in the image mentioned above.
problems will be improved.

The reason why the second problem regarding non-uniformity is improved is as follows. As shown in Figure 3, point P
Correction amount ΔX (X, Y), ΔY (X,
By calculating Y) and adding this correction amount, the corrected point P ₀ ' is obtained as shown by the dotted line. If the coordinates of this P ₀ ' are (X ₀ ', Y ₀ '), then X ₀ '=X+ΔX (X, Y) Y ₀ '=Y+ΔY (X, Y). Random numbers ΔR _x for X and Y of this point P,
When ΔR _Y is subtracted, its coordinate becomes point Q. When the correction amount regarding this point Q is added, it becomes the output of the adders 61 and 62, which becomes the point Q'. Then, when we add random numbers ΔR _X and ΔR _Y to this point Q,
becomes P ₁ ′. The coordinates of this P ₁ ' are as shown in equations (1) and (2) above. Therefore, even though the position signal of point P is obtained, point P ₁ ' is obtained which is corrected by the correction amount related to the surrounding position Q. And in the part where the correction amount change rate is large, the correction amount ΔX
(X, Y), ΔY (X, Y) and correction amount ΔX ( _X -ΔR
Since the difference _between Y _- ΔR _Y ) and ΔY ( _X - _ΔR In some parts, even if the correction is made using the correction amount related to the surrounding points, the correction amount will not change, so the point will end up being P ₀ '. In this way, in a portion where the rate of change in the amount of correction is large, the positions after correction can be spread out and averaged, so that uniformity can be improved.

In the above embodiment, the random numbers are subtracted before the AD converters 21 and 22, and the random numbers are added later.
Conversely, if you add before and subtract after, the result is exactly the same.
Further, in the above embodiment, the adders 61 and 62 add the correction amounts ΔX and ΔY, and then the adders 71 and 72 add the random numbers ΔR _X and ΔR _Y , but the same effect can be obtained even if the order is reversed.

As described above with respect to the embodiments, the stillation camera according to the present invention includes an analog adder/subtracter that adds or subtracts an input analog value to an analog position signal in front of an AD converter;
After the AD converter, there is a digital adder/subtracter that adds or subtracts the input digital value to the digital position signal in the opposite way to the analog adder/subtracter, and sends the generated random number analog value to the analog adder/subtracter and A random number generator that sends digital values of the same random number to the digital adder/subtractor, and linearity correction depending on the position indicated by the digital position signal output from the AD converter and before input to the digital adder/subtractor. ,
It is characterized in that it includes a digital position signal correction circuit that corrects the digital position signal after the AD converter. By adding and subtracting the same random numbers before and after the AD converter and ultimately obtaining a digital position signal that cancels those random numbers, it is possible to improve the negative effects of the nonlinearity of the AD converter, and at the same time, the random numbers can be canceled. By correcting the position signal using the digital position signal added with , it is possible to improve the non-uniformity of the image. That is, according to the present invention, even if the linearity of the AD converter is poor, the adverse effects thereof can be removed, and at the same time, it is possible to improve the uniformity of the image. Furthermore, in areas where the rate of change in correction amount is large and uniformity is poor, uniformity is improved by averaging with a degree of variation that matches the large rate of change in correction amount, and where the rate of change in correction amount is small and uniformity is good. It is equivalent to not adding any processing to some parts, and it is possible to improve uniformity while minimizing deterioration in resolution and linearity as a whole.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a schematic diagram for explaining the operation. 11...Scintillator, 12...Photoelectric converter,
13... Position and energy calculation circuit, 14... Wave height analyzer, 15... Correction calculation circuit, 21, 22...
...AD converter, 31, 32...Analog subtractor,
41, 42...Random number generator, 51, 52...DA
Converter, 61, 62, 71, 72...digital adder.

Claims (1)

[Claims] 1. A scintillation camera comprising a scintillator, a photoelectric converter, a position and energy calculation circuit, and an AD converter that converts analog position signals obtained from the position and energy calculation circuit into digital position signals to obtain digital position signals, an analog adder/subtractor that adds or subtracts an input analog value to the analog position signal in front of the AD converter;
After the AD converter, there is a digital adder/subtracter that adds or subtracts the input digital value to the digital position signal in the opposite way to the analog adder/subtracter, and sends the generated random number analog value to the analog adder/subtracter and A random number generator that sends digital values of the same random number to the digital adder/subtractor, and linearity correction depending on the position indicated by the digital position signal output from the AD converter and before input to the digital adder/subtractor. ,
A scintillation camera comprising: a digital position signal correction circuit that corrects a digital position signal after the AD converter.