JPH0462034B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field
This invention relates to an improvement of a scintillation camera for capturing distribution images of radioactive substances distributed in a subject by detection with a dimensional radiation position detector.

(b) Prior Art One problem with scintillation cameras is non-uniformity, and the causes of this non-uniformity are mainly variations in the inherent energy level depending on position and spatial non-linearity. In the past, various proposals have been made to eliminate these causes and improve non-uniformity (Japanese Patent Publication No. 86377/1983 and Japanese Patent Publication No. 1986-86377).
(See Publication No. 86378). However, in all of these conventional methods, in order to obtain the best uniformity, it was necessary to sacrifice linearity to some extent and maintain the linearity in a state slightly worse than the best state. In addition, especially with multiple nuclides and multiple energies,
Even with energy correction and linearity correction, it is still difficult to obtain good uniformity compared to the case of single energy and one nuclide. In addition to these, the special public
Although Japanese Patent No. 137180 talks about improving uniformity, in this case there is a drawback that only a small counting rate is always obtained compared to the counting rate obtained at the stage before uniformity correction.

(c) Purpose It is an object of the present invention to provide a scintillation camera which has the best uniformity while maintaining the best linearity, and which does not cause deterioration of count rate characteristics.

(d) Configuration The scintillation camera according to the present invention has the following features:
Using the position signal and unblank signal after linearity correction and energy correction in the correction circuit, we actually measure the non-uniformity at each position in advance,
Based on this, the level of non-uniformity information indicating whether the non-uniformity at each position is higher or lower than the average value and the extent of the non-uniformity relative to the average value. Non-uniformity ratio information indicating whether the ratio is equal to or less is stored for each address corresponding to each position in the non-uniformity correction memory. Then, when the position signal and unblank signal are obtained from the correction circuit when photographing the subject,
The position signal specifies an address in the non-uniformity correction memory, and non-uniformity level information and non-uniformity ratio information regarding that position are read out. This non-uniformity ratio information is compared with a random number signal from a random number generation circuit, and depending on the comparison result and the fact that the non-uniformity level information indicates high, a position signal and an unblank signal are sent from the correction circuit. output is prohibited. Therefore, at locations where the heterogeneity is higher than the average value,
The output is thinned out with a probability according to the ratio of the degree of non-uniformity to the average value. On the other hand, when the heterogeneity level information indicates low, depending on the comparison result between the heterogeneity ratio information and the random number signal,
Since the temporarily held position signal and unblank signal from the correction circuit are output with a certain time delay, at a position where the non-uniformity is lower than the average value, the average value of the degree of non-uniformity is output. The same output is newly added with a probability according to the ratio.

(E) Embodiment In FIG. 1, when radiation is incident on the two-dimensional radiation position detector 1, position signals X, Y, an energy signal and an unblank signal are generated, and these are sent to the correction circuit 2. The correction circuit 2 has an A/
A position signal that includes a D converter, a linearity correction circuit, an energy correction circuit, etc., and is converted from an analog signal to a digital signal and corrected through these circuits.
X', Y' and an unblank signal are output.
The position signals X', Y' and the unblank signal are sent to an output circuit 3 and a hold and output circuit 4. In this embodiment, the position signals X' and Y' are both 12 bits, and the upper 6 bits are sent to the non-uniformity correction memory 5 to designate its address.
In other words, here, the non-uniformity correction is not to apply different corrections to each pixel, but to apply the same correction to pixels including 64×64 pixels. In this way, the correction information stored at the address is read out from the non-uniformity correction memory 5 that received the address designation. In this embodiment, this correction information is 8 bits, the most significant 1 bit is sent to the output circuit 3 and the timing signal generation circuit 8, and the lower 7 bits are sent to the comparison circuit 7.
sent to. The random number generation circuit 6 is triggered by the unblank signal and generates a 7-bit random number,
This is sent to the comparison circuit 7. Comparison circuit 7 compares these two inputs, outputs "1" if the random number is larger, and outputs "0" if the random number is larger.
Output circuit 3 and timing signal generation circuit 8
send to The output circuit 3 prohibits output only when the most significant digit of the information read from the nonuniformity correction memory 5 is "1" and a "1" signal is sent from the comparison circuit 7, and in other cases, the correction circuit position signal X′ from 2,
Outputs Y′ and unblank signal as is.
The timing signal generation circuit 8 holds the output and sends it to the output circuit 4 only when the most significant digit of the information read from the non-uniformity correction memory 5 is "0" and a "1" signal is sent from the comparison circuit 7. , the position signals X', Y' and the unblank signal from the correction circuit 2 are output after being held for a certain period of time.

In this embodiment, the non-uniformity correction memory 5 is
It is a PROM (programmable read-only memory), and the information to be stored at each address is determined as follows. First, a radiation source that is uniform over the entire surface is used and detected by the two-dimensional radiation position detector 1. According to the corrected position signals X', Y' and the unblank signal obtained from the correction circuit 2, since the subject is uniform, a uniform image must be obtained over the entire surface. However, in reality, no matter how well the correction is performed, non-uniformity remains, and the number of counts at each position C
increases and decreases with respect to the average value M as shown in FIG. To correct this, if the count number C _p at point P exceeds the average value M, the output position signals X', Y' and unblank are Just thin out the signals. Conversely, if the count number C _q at point Q is lower than the average value M, the output position signal is
In addition to X', Y' and unblank signals, new position signals X', Y' and unblank signals may be added. Therefore, in this embodiment, the position signals X', Y' and the unblank signal are thinned out or added at a probability corresponding to the ratio of deviation from the average value M.

In other words, the count number C at position (i, j) is
If Cij is positive, the most significant digit of the 8-bit information is set to "1", and the remaining 7 lower digits are integers from 0 to 127 obtained by converting (M/Cij) x 127 into an integer. It is a numerical value. Also, Cij
When −M is 0 or negative, the most significant digit is set to “0” and the remaining 7 lower digits are 0 to
Take an integer value of 127. The correction information thus obtained is written to the address corresponding to position (i, j).

Assume that after such writing is completed, the address (i, j) of the non-uniformity correction memory 5 is designated by the obtained position signals X', Y' during normal photographing of a subject. Then, the information stored at this address is read out, and if non-uniformity occurs on the over side at the position (i, j) corresponding to this address, the most significant digit becomes "1".
The random number generation circuit 6 generates a 7-bit random number, that is, 0 to 127.
Outputs one of the integers at random. Therefore, when comparing the lower seven digits of the above-mentioned read information and this random number, the probability that the former is smaller than the latter corresponds to the ratio of the excess. Therefore, the probability that "1" is generated from the comparator circuit 7 and that the output circuit 1 is inhibited corresponds to the ratio of the exceeded amount.

Additionally, if the most significant digit of the information read from the specified address is "0", the position (i, j) corresponding to this address is a location where non-uniformity occurs on the lower side. Become. If the lower 7 digits of the information read at this time are smaller than the random number, the comparison circuit 7 gives "1" to the timing signal generation circuit 8, and the non-uniformity correction memory 5 gives the most significant digit "0". ” is given, a signal is generated from this timing signal generation circuit 8, which causes the hold and output circuit 4 to operate. Therefore, first, position signals X', Y, and an unblank signal are generated from the output circuit 3, and after a certain period of time, the same position signals X', Y' and an unblank signal are generated from the hold and output circuit 4. .
The probability that the lower seven digits of the read information will be smaller than the random number corresponds to the ratio of the degree of non-uniformity that appears on the lower side, and with this probability, the position signals X', Y' and the unblank signal will be newly generated. It will be added.

The position signal after undergoing non-uniformity correction in this way
X″, Y″ and unblank signal count number C
is equal to the average value M in FIG. 2 at all positions. Since non-uniformity correction is performed after linearity correction and energy correction in this way, linearity correction and energy correction can be optimized separately from non-uniformity correction. There is no need to sacrifice linearity etc. to correct the linearity. Furthermore, the counting rate will not increase or decrease due to non-uniformity correction. Furthermore, it is also possible to simplify linearity correction and energy correction compared to the conventional method.

In addition, in the above embodiment, the non-uniformity correction memory 5 is
Although it is configured with PROM, it may also be configured with RAM (random access memory) and controlled by a microcomputer or the like. Furthermore, the position signal to be newly added is not the same as the original position signal, but may be one in which a weighted variable is added to the original position signal.

(F) Effect The scintillation camera according to this invention has the following effects:
Depending on whether the heterogeneity appears higher or lower than the average value, the signal can be thinned out or added with a probability corresponding to the ratio of the degree of heterogeneity to the average value. Therefore, the counting rate becomes approximately equal to the average value, and fine and highly accurate non-uniformity correction can be realized without increasing or decreasing the counting rate, making it possible to obtain an excellent image.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a graph showing the count C at each position to explain the operation. 1... Two-dimensional radiation position detector, 2... Correction circuit,
3...Output circuit, 4...Hold and output circuit, 5
... Non-uniformity correction memory, 6... Random number generation circuit, 7...
Comparison circuit, 8...timing signal generation circuit.

Claims (1)

[Claims] 1. A two-dimensional radiation position detector, a correction circuit into which a position signal and an unblank signal outputted from the detector are input and outputs a position signal and an unblank signal after linearity correction and energy correction, and the above correction circuit. Based on the heterogeneity measured in advance using the output of The non-uniformity correction memory stores the non-uniformity ratio information representing the ratio of the degree to the average value for each address corresponding to each position, and the non-uniformity correction memory stores the non-uniformity ratio information representing the ratio of the degree of A random number generation circuit generates a random number signal in response to an unblank signal from the circuit, and a random number signal is read out from the non-uniformity correction memory by addressing using a position signal obtained from the correction circuit when photographing an object. Average
A comparison circuit that compares the sex ratio information and the random number signal, and the nonuniformity level information that is addressed and read out by the comparison circuit output and the correction circuit output position signal when photographing the subject indicates high. an output circuit that prohibits the position signal and unblank signal from the correction circuit from being output according to the control signal; and an output circuit that temporarily holds the position signal and the unblank signal from the correction circuit, and It operates for a predetermined period of time in response to the fact that the nonuniformity level information read out by the address designation of the output hold and output circuit, the output of the comparison circuit, and the output position signal of the correction circuit at the time of photographing the subject indicates low. A scintillation camera characterized by comprising a timing generation circuit that sends a control signal to the hold and output circuit to output each held signal after the elapse of time.