JPH052956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation imaging device such as a scintillation camera.

In general, radiation imaging devices such as scintillation cameras have inherent energy non-uniformity, that is, sensitivity non-uniformity based on the position dependence of the energy signal wave height.

An object of the present invention is to provide a radiation imaging apparatus that can correct sensitivity non-uniformity based on the above energy non-uniformity in real time.

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, a large number of RMTs are connected to the back of scintillator 1 via light guide 2.
(Photomultiplier tubes) 3 are arranged, each PMT output is led to a position and energy calculation circuit 5 through a preamplifier 4, and position signals X, Y and energy signal Z are obtained. This configuration is similar to a normal scintillation camera. Position signals X, Y and energy signal Z are provided by sample and hold circuits 61 to 63.
are respectively captured and held in the AD converter 7.
1 to 73 are digital signals Xd, Yd and
Zd, and these signals Xd, Yd, Zd
Specify the address of PHA memory (wave height analysis memory) 8. For example, PHA memory 8 is dynamic
Consists of RAM, outputs 1-bit data,
The luminance signal is generated by the pulse signal generator 11.
UNBLANK is obtained and input to the display device 12 together with the position signals X and Y.

Examples of energy spectra are shown in FIGS. 2 and 3. In Figure 2, the photoelectric peak is ML1, and in this case, the upper and lower limits of the energy window are UL1 and UL1, respectively.
LL1 is fine. In Figure 3, the photoelectric peak is different from that in Figure 2 due to the difference in the radiation incident position.
In this case, if UL1 and LL1 are used as the upper and lower limits of the energy window, the sensitivity will decrease, so UL2 and LL2 should be used. In this way, the energy window for wave height analysis is changed depending on the position to correct the sensitivity non-uniformity based on the position dependence of the energy signal wave height.
PHA memory 8 is used.

For example, the PHA memory 8 includes each pixel of 64×64 and
When the energy of 512 KeV is divided by 0.5 KeV per channel, there are 64 x 64 x 1024 addresses corresponding to the peak values of 1024 channels, and each address has the content of "1" or "0". , wave height analysis conditions,
For example, the center level signal of the energy window
Each time the LEVEL and window width signal WINDOW are set, they are calculated using the following procedure and are written in advance before measurement. First, the peak shift of the energy signal Z at each position
Store it as 0. Let this peak shift data be f(x,y). Then, for example, the following calculations are performed using a calculation circuit 9 comprised of, for example, a microcomputer.

(MLx, y) = (LEVEL) × {1 + f (x, y)} ... (1) (ULx, y) = (MLx, y) × {1 + 1/2 × (WINDOW)} ... (2) ( LLx, y) = (MLx, y) × {1-1/2 × (WINDOW)} ...(3) Here, MLx, y, ULx, y, LLx, y correspond to each position x, y For example, ML1, UL1, LL1, ML2, UL shown in Figures 2 and 3
2.Same as LL2. In this calculation, each position x,
When ULx,y and LLx,y are obtained for y,
Addresses Xd, Yd regarding the location of PHA memory 8
For example, as shown in Figure 4, LLx,y
"1" is written for addresses Zd in the range of ZdULx,y, and "0" is written for addresses Zd in other ranges. This 1-bit data of "0" and "1" represents the wave height analysis result, and "1" indicates that the wave height value of the energy signal obtained at the position x, y is within the energy window determined for that position. , and "0" indicates that it is outside the energy window. Although Fig. 4 shows one set of energy windows for each position x, y, in the case of multiple spectra, it is possible to have multiple energy windows for each position x, y, so it is not necessary to use a pulse height analyzer as in the conventional case. There is no need to prepare multiple ones.

Position signals X, Y and energy signal Z for each event
are obtained and these digital signals Xd, Yd, Zd
are given to the PHA memory 8 as address information, and when an address is designated by these, the "1" or "0" stored at that address is read out. When "1" is read out, it is within the energy window, so the pulse signal generator 11 generates the brightness signal UNBLANK.
In this way, sensitivity non-uniformity based on the position dependence of the energy signal wave height can be corrected in real time for each event. Although omitted in FIG. 1 to simplify the explanation, it is assumed that each circuit is given an appropriate timing signal.

The above equation (1) is an equation based on the assumption that the position dependence of the energy signal wave height does not depend on the energy of the nuclide used, and the error caused by this approximation can be ignored in a normal optical system. However, even if this energy dependence cannot be ignored, it can be easily dealt with by adding a correction term. In other words, f(x, y) in the above formula (1)
can be obtained in advance by measuring with respect to a certain reference energy (for example, 140 KeV at ^{99 m} T _c ). If the center level signal of the energy window corresponding to this reference energy is LEVELO, then
MLx,y of other energies are (MLx,y)=(LEVEL)×{1+g(LEVEL−LEV
ELO)×f(x,y)}. Here g(LEVEL
−LEVLO) is a function of (LEVEL−LEVLO), for example, g(LEVEL−LEVLO)=1+k(LEVEL−LEVLO)
LEVELO) k: Can be approximated by a constant expression, etc.

Generally, in scintillation cameras, the position dependence of the energy signal wave height has the spatial frequency based on the PMT array as the main component, and positions showing the same shift of the photoelectric peak appear repeatedly. So the second
In this embodiment, the PHA memory address is shared for each position showing the same peak shift, thereby reducing the PHA memory capacity, simplifying the address, and shortening the PHA memory write calculation time.

This second embodiment will be explained with reference to FIGS. 5 and 6. The configuration after sending the data read from the AD converters 71 to 73 and the PHA memory 108 to the pulse signal generator 11 is the same as that shown in FIG. The address of address data memory 107 is designated by digital signals Xd and Yd from AD converters 71 and 72, and the obtained address data Ad, together with digital signal Zd from AD converter 73, designates the address of PHA memory 108. In this embodiment, a large number of positions exhibiting the same peak shift are commonly tied together and represented by one position a, and the address data memory 1
07 converts the addresses Xd and Yd of the respective positions x and y into the address Ad of the representative position a.
The PHA memory 108 is located at position x, as shown in FIG.
Instead of y, data "1" and "0" are written for each address Ad related to representative position a. This writing is performed by the calculation circuit 109 and the correction memory 110, and the positions x and y of the first embodiment are converted to the representative position a and the peak shift data f(x,
The only difference is that y) is replaced with f(a), and the calculation process etc. are the same as in the first embodiment.

In addition, in the first and second embodiments above, the wave height analysis accuracy or energy non-uniformity correction accuracy is
To improve memory capacity without increasing it,
The energy signal Z may be subjected to analog or digital subtraction and multiplication processing before being used as the address signal Zd of the PHA memory.
Furthermore, by dividing the PHA memory into multiple blocks, setting an energy window for each block, and determining from which block the data that generates the brightness signal UNBLANK is output, multi-nuclide measurement becomes possible. Instead of dividing this PHA memory into multiple blocks, by increasing the data depth of the PHA memory to 2 bits or more, for example, “01”, “10”, and “11” are the first and second blocks, respectively.
It is also possible to perform multispectral or multinuclide measurements, such as by indicating that the signal is within the second and third energy windows, and "00" indicates that it is outside these ranges.

As described above with respect to the embodiments, according to the present invention, as an energy signal wave height analysis means for determining whether or not the energy signal wave height is within a predetermined energy window, the position signal and the energy signal wave height are used. Because it uses a single memory configured to read out in real time data representing the analysis result of whether the wave height at that position falls within the window, which is addressed and pre-stored at that address. It is very easy to increase the speed, and it has an extremely simple configuration, and sensitivity non-uniformity due to energy non-uniformity can be improved in real time. The wave height analysis means is constructed by storing data representing the wave height analysis results in a memory for each address specified by the position signal and the energy signal wave height, and reading out the data based on the position signal and the energy signal wave height. Therefore, this wave height analysis means can be seen as essentially having the configuration of a multi-channel analyzer, and has a high degree of freedom in setting conditions of the energy window, such as being able to handle multiple spectra and multi-nuclide measurements.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention;
2 and 3 are energy spectrum graphs, FIG. 4 is a diagram showing the contents of the PHA memory 8, FIG. 5 is a block diagram showing the main part of the second embodiment, and FIG. 6 is a PHA memory 108. FIG. 1...Scintillator, 2...Light guide, 3...
PMT, 4...Preamplifier, 5...Position and energy calculation circuit, 61-63...Sample hold circuit,
71-73...AD converter, 8,108...PHA memory, 9,109...calculation circuit, 10,110...correction memory, 11...pulse signal generator, 12...display device, 107...address data memory.

Claims (1)

[Claims] 1. Radiation imaging comprising means for obtaining a position signal and an energy signal for each event of radiation incidence, and means for analyzing an energy signal wave height to determine whether the wave height of the energy signal is within a predetermined energy window. In the apparatus, the analysis means includes data representing an analysis result of whether or not each wave height value of the energy signal at each position is within the window, based on the position dependence of the energy signal wave height measured in advance. , are stored for each address specified by the position signal and the energy signal wave height, and the position signal and the energy signal wave height obtained for each radiation incident event are input as an address designation signal and stored at the address. A radiation imaging device comprising a memory, from which data representing the above-mentioned analysis results that have been analyzed is read out in real time.