JPH0462493A - Scintillation camera - Google Patents

Abstract

PURPOSE:To make accurate corrections regarding miscounting in real time by counting the incidence of radiation entering a specific energy window for each picture element and performing counting operation for each picture element every time a position signal and an energy signal are generated. CONSTITUTION:On a memory 8, '1' is added to an address specified with signals X and Y every time an energy signal Z is generated, and incident gamma rays are counted as to all energy. On a memory 7, data are gathered for a period of 10msec and integrated counted number data on each picture element is sent to a correcting circuit 10. Namely, the correction of the omission of counting is made at extremely short time intervals of 10msec, so the omission correction is accurately made in real time.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a scintillation camera, and particularly to a counting loss correction technique for a scintillation camera.

[Conventional technology]

When counting a large number of sequentially incident gamma rays for each pixel in a scintillation camera, as the timing of gamma ray incidence approaches, the interval between gamma ray detection signals shortens, making it impossible to process them. Dropping occurs. That is, if the signal decomposition time is τ, there is a relationship between the true gamma ray incident count number Rin and the actually counted count number Ro as follows: Ro = Rin −e−”n. Conventionally, only the number of counts of gamma ray detection signals that fall within a predetermined energy window is corrected for missing counts in accordance with the counting rate.

[Problem to be solved by the invention]

However, simply performing counting loss correction only for the number of counts within a predetermined energy window will only result in inaccurate correction because counting loss will occur even when the signal within the energy window overlaps with the signal outside the window. There's a problem. An object of the present invention is to provide a scintillation camera that can perform accurate counting correction.

[Means to solve the problem]

In order to achieve the above object, the scintillation camera according to the present invention includes a means for emitting light in response to incident radiation, a photoelectric conversion means for converting the illumination into an electric signal, and a position signal and an energy signal from the output of the photoelectric conversion means. means for detecting a signal within a predetermined energy window by analyzing the wave height of the energy signal; and means for counting for each pixel indicated by the position signal in response to the signal detection. 1 counting means, a second counting means for counting each pixel indicated by the position signal each time the position signal and the energy signal are generated, and counting down according to the count value of the second counting means. a correction coefficient storage means in which correction coefficients are stored in advance; and a second counting means for each pixel corresponding to the count value of each pixel in the first counting means obtained within a relatively short time interval. a correction means that performs a count-off correction by applying a correction coefficient read from the correction coefficient storage means according to the count value at each time interval; and a correction means that adds the corrected count value for each pixel. means are provided.

[For production]

In the first counting means, a pixel-by-pixel count is performed for radiation incident that falls within a predetermined energy window. On the other hand, in the second counting means, each time a position signal and an energy signal are generated, counting is performed for each pixel indicated by the position signal. That is, a count is made of the radiation incidence for each pixel over the entire energy range. Then, a correction coefficient is read out according to the number of counts in the entire energy range, and the number of counts within the energy window is corrected for missing counts using this correction coefficient. Therefore, since it is possible to perform counting loss correction using a correction coefficient that corresponds to all cases in which signal overlap that causes counting loss occurs, accurate correction can be performed. Moreover, since this count loss correction is performed on the count value in the first counting means at relatively short time intervals,
It can be done in real time.

【Example】

Hereinafter, a scintillation camera according to an embodiment of the present invention will be described in detail with reference to the drawings. 1st
In the figure, gamma rays emitted from a subject (not shown) pass through a collimator 1, enter a scintillator 2, and emit light. The light is transmitted through a large number of photomultipliers (PM
T) 3 and generates a signal whose magnitude corresponds to the amount of incident light. This signal is sent to the arithmetic circuit 5 with weighting through the preamplifier 4, and the weighting is added to the X-direction position signal X.
A Y-direction position signal Y and an energy signal Z are obtained. The wave height of this energy signal Z is analyzed in a pulse height analyzer 6, and if the wave height is within a predetermined energy window, an output is generated from the pulse height analyzer 6. In other words, if the energy spectrum is as shown in Figure 2, an energy window of 20% is usually set around the peak, and analysis is performed to determine whether the wave height of energy signal 2 falls within this window. is done and the output will be produced if it is contained. When this output from the pulse height analyzer 6 is generated, "1" is added to the address specified by the signal XY in the memory 7, and the incident gamma rays within the energy window are counted for each pixel. On the other hand, in the memory 8, each time the energy signal Z is generated, "1" is added to the address specified by the signals will be done. The memory 7 collects the above data for a period of 10 m5ec, for example, and sends the cumulative count data for each pixel to the correction circuit 10. On the other hand, in the memory 8, data is collected during a period longer than the above-mentioned period, for example, 1 second, and a correction coefficient corresponding to the accumulated count number for each pixel is read from a table 9 configured in a ROM or the like. This correction coefficient is applied to the count from the memory 7 in the correction circuit 10. For example, regarding a certain pixel, the cumulative count per 10m5ec for those that fall within the above 20% window and the 10m5ec for those that fall within the 100% window.
Assuming that the time trends of the cumulative counts for each period are as shown in Figure 3 A and B, at a certain point T, 20% of the previous 10 m5ec period.
Assume that the cumulative count of things entering the window is Ct' (this can be obtained from the memory 7). It is assumed that the cumulative count number for the 100% window in the period from 1 second before time T is represented by the area of the shaded portion, and is Q. On the other hand, total count number (100% wind count number)
As shown in the curve in Figure 4, Ro is the number of incident gamma rays per unit time due to counting, and the counting rate, c p
s : count per 5econd) Ri
As n increases, the linear correspondence thereto disappears and it begins to decrease. That is, when the count number Q is obtained as described above, the actual number of incident gamma rays should be P. Therefore, by storing a correction coefficient corresponding to this curve in the table 9 in advance, reading out the correction coefficient (P/Q) corresponding to Q, and applying it to Q, the true value P can be obtained. This correction coefficient (P/Q) is applied to the Callan I number Ct in the correction circuit 10, and Ct
/Q) = Ct' + αt is calculated. 6Ct" is an integer, and Ct is the remainder. The value of Ct' is added to the address of the corresponding pixel in the main memory 11, and the value of Ct is It is added to the address of the corresponding pixel. Then, these additions are performed every lQmsec, and when the integrated value of Ct becomes 1 or more, the arithmetic circuit 13 detects it and stores it in the value of the main memory 11. 1" is added, and at the same time, "1" is subtracted from the submemory 12. Here, the reason why the total number of counts Q is used to find the correction coefficient is that the weighting of counts occurs at the stage of the arithmetic circuit 5, and the pulse height analyzer 6 determines that it falls within the 20% window. This is because it does not occur between those who have been treated. In other words, counting loss occurs not only when signals entering the 20% window overlap each other, but also when signals entering the window and signals outside the window overlap each other. This is because it corresponds more to the counting rate of all counts than the counting rate of . In addition, to calculate the correction coefficient, we used the total number of counts Q in an integrated time (1 second) longer than the integrated time (10 m5ec > This is because it is more preferable to use a correction coefficient that corresponds to the counting rate.In other words, if the counting rate per short unit time such as 10 m5ec is converted to the counting rate per second (cps) and the correction coefficient is calculated, , correction coefficient is 10m5ec
This is because the value varies greatly from time to time, resulting in only inaccurate correction. Therefore, the correction for missing counts is performed at very short time intervals of 10 m5 ec, so accurate correction for missing counts can be performed in real time.

【Effect of the invention】

According to the scintillation camera of the present invention, accurate correction regarding omitted counting can be performed in real time.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a graph showing the energy spectrum, Fig. 3 is a graph showing the temporal change in the number of counts, and Fig. 4 is the true number of incident gamma rays and the number of counts. This is a graph showing the relationship between 1...Collimator, 2...Scintillator, 3...
Photo multiplier, 4... preamplifier, 5...
Weighting is done by arithmetic circuit, 6... pulse height analyzer, 7.8...
Image collection memory, 9...Correction coefficient table, 10
... Correction circuit, 11... Main memory for image collection,
12... Sub-memory for image collection 213... Arithmetic circuit.

Claims (1)

[Claims] (1) means for emitting light in response to incident radiation; photoelectric conversion means for converting the light into an electrical signal; means for obtaining a position signal and an energy signal from the output of the photoelectric conversion means; and means for obtaining a position signal and an energy signal from the output of the photoelectric conversion means; means for analyzing and detecting a signal within a predetermined energy window; first counting means for counting each pixel indicated by the position signal in response to the signal detection; a second counting means for counting each pixel indicated by the position signal each time a pixel is generated; a correction coefficient storage means in which a count correction coefficient corresponding to the count value of the second counting means is stored in advance; The count value of each pixel in the first counting means obtained within a relatively short time interval is read out from the correction coefficient storage means according to the count value of the second counting means for the corresponding pixel. 1. A scintillation camera, comprising: a correction means for performing count-off correction by applying the corrected correction coefficient at each time interval, and a means for adding the corrected count value for each pixel.