JPH0423232B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scintillation camera.
Analog images from scintillation cameras are subjected to AD conversion for data processing, or camera-specific spatial distortion correction is performed.
In this case, the nonlinearity of the AD converter that performs AD conversion of the position signal causes stripes in the image, which is an important problem.

The object of the present invention is to provide a scintillation camera that solves the above problems by adding a simple circuit.

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, the detector 1 is well known, so a detailed explanation thereof will be omitted, but it consists of a scintillator, a photomultiplier, a position calculation circuit, an energy calculation circuit, etc., and indicates the incident position according to the incident radiation. It outputs analog position signals X and Y, an analog energy signal Z corresponding to the energy of the incident radiation, and an unblank signal. The energy signal Z is input to the sample and hold circuit 33, while it is guided to the attenuator 7, and the attenuated output αZ is input to the analog subtracters 21 and 22, where the output αZ is subtracted from the position signals X and Y, respectively. Ru. The obtained outputs (X-αZ) and (Y-αZ) are input to AD converters 41 and 42 through sample and hold circuits 31 and 32, respectively, and the obtained digital signals
Dig (X-αZ) and Dig (Y-αZ) are register 5
It is held at 1,52. On the other hand, the energy signal Z held in the sample and hold circuit 33 is guided to the AD converter 43, and the obtained digital signal DigZ
is held in the register 53. The upper bit data DigαZ of DigZ is sent to digital adders 61 and 62.
is added to the lower bits of Dig(X-αZ) and Dig(Y-αZ). Here, the output αZ of the attenuator 7 converts this αZ into the AD converter 41, 42
The digital signal converted by is the above-mentioned DigZ
The attenuation rate of the attenuator 7 is adjusted so that it is equal to the upper bit data DigαZ. Therefore, the outputs of the digital adders 61 and 62 become DigX and DigY because the αZ portion is canceled.

Here, with the configuration shown in Fig. 1, AD converters 41, 4
The reason why the nonlinearity of No. 2 is improved will be briefly explained using FIG. 2. Figure 2 shows 4-bit AD
An example of the input/output characteristics of the converter is shown, and the analog input signal V corresponds to the position signal X or Y in FIG. In FIG. 2, it is assumed that the output code "0111" is generated in a wide range where the analog input signal V is around _V1 . In other words, when this AD converter is used, the probability that the code "0111" will occur is much higher than the probability that other codes will occur. If the AD converters 41 and 42 have such characteristics, simply this AD converter 4
If the position signals X and Y are simply digitized using 1 and 42, if an image is constructed using these digital position signals, stripes will appear in the image. According to the configuration shown in Figure 1, this is corrected; in other words, the analog input V ₁ is once shifted to the analog input (V ₁ - αZ) and then AD converted, and then converted into a digital signal corresponding to this αZ.
Since DigαZ is added, even if the analog input is _V1 , parts of the AD conversion characteristics other than _V1 are used. Although the energy signal αZ has a certain frequency distribution characteristic, it is generally generated randomly. Therefore, the analog input near _V1 is also distributed approximately equally to various parts of each step of the AD conversion characteristic, and the probabilities of each code occurring are averaged and made equal. In other words, the probability that the code "0111" is output is approximately the same as that of the others. Therefore, the above-mentioned stripes are hardly observed. Since the analog signal αZ and its digital signal DigαZ are canceled, there is almost no deterioration in AD conversion accuracy.

Furthermore, whenever the energy signal Z is randomly generated, it takes a specific frequency distribution as shown in Fig. 3, and in order to extract only the energy signal Z that falls within the window W, the frequency distribution is far outside this window W. Such an energy signal Z is originally not generated from the detector 1. the result,
Upper bit of digital output of AD converter 43
When using DigαZ, these bits do not all occur randomly. Taking this into consideration, the output αZ of the attenuator 7 is
is subtracted by the signal C from the analog signal source 9 in the analog subtracter 8 to obtain (αZ-C), and on the other hand, the upper bit DigαZ of the digital signal DigZ of the energy signal Z is also subtracted by the signal C from the analog signal source 9 in the digital subtracter 10. Digital output from 11
Make DigC subtract. And Dig{X-
(αZ-C)} and Dig(αZ-C) are added by digital adders 61 and 62 to cancel the part (αZ-C) (the other configuration is the same as in FIG. 1). With this configuration, the part of DigαZ that always has the same code will not be used, and the position signals X and Y will be changed to {X-(αZ-
C)}, AD converter 4 in the form of {Y-(αZ-C)}
It is possible to more randomly distribute the conversion characteristics to other parts of the conversion characteristics of 1 and 42, and the output probability of each code can be more averaged.

In addition, in this specification, when an analog quantity is subtracted before AD conversion and a digital quantity corresponding to the analog quantity is added after AD conversion, the words "subtraction" and "addition" are used as intermediate words. This term is used to mean that additions and subtractions are canceled, and therefore, in actual circuit configuration, the analog subtracters 21 and 22 can be replaced with analog adders, and the digital adders 61 and 62 can be replaced with digital subtracters. Of course.

Further, in each of the embodiments described above, the attenuator 7 may be provided separately for the X signal and the Y signal and adjusted separately.

As described above with respect to the embodiments, according to the present invention, stripes in a digital image that are observed when there is nonlinearity in the conversion characteristics of an AD converter that performs AD conversion of a position signal are caused by deterioration in AD conversion characteristics. It is possible to resolve the problem without causing any problems, and the quantitative nature of diagnosis can be improved. Furthermore, since the non-linearity of the AD converter is corrected, it is possible to more accurately obtain uncorrected data when correcting the spatial distortion of a scintillation camera, so the correction vector for each pixel at each position is also more accurate. can be obtained accurately, and as a result, spatial distortion of the image can also be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a graph showing AD conversion characteristics, FIG. 3 is a graph showing frequency distribution of energy signals, and FIG. 4 is a block diagram of a modified example. 1...Detector, 21,22,8...Analog subtracter, 31,32,33...Sample hold circuit, 41,42,43...AD converter, 51,5
2, 53...Register, 61, 62...Digital adder, 7...Attenuator, 9...Analog signal source, 10...Digital subtracter, 11...Digital signal source.

Claims (1)

[Claims] 1. A detector that outputs an analog position signal representing the incident position in response to incident radiation and an analog signal energy signal corresponding to the energy of the incident radiation, and subtracting a part of the energy signal from the position signal. an analog subtracter, a position signal AD converter for AD converting the output of the analog subtracter, an energy signal AD converter for AD converting the energy signal, and an AD converter for the energy signal.
A scintillation camera comprising: a digital adder that adds a digital output corresponding to a part of the energy signal among the digital outputs of the converter to the digital output of the position signal AD converter.