JPS6073482A - Scintillation camera - Google Patents

Abstract

PURPOSE:To optimize linearity correction and energy correction and prevent linearity, etc., from sacrificing for nonuniformity correction by making the nonuniformity correction after executing the linearity correction and energy correction. CONSTITUTION:When the low-order seven digits of information stored in an address to which a random number generating circuit 6 outputs a random number of, for example, seven digits at random become smaller than the random number, a comparing circuit 7 supplies ''1'' to a timing signal generating circuit 8, and the most significant digit ''0'' is supplied from an nonuniformity correction memory 5 to put a hold and output circuit 4 in operation. An output circuit 3 generates position signals X' and Y' and an unblank signal and then the hold and output circuit 4 outputs the same position signals X' and Y' and unblank signal a specific time later. The probability that the low-order seven digits of information output successively are smaller than the random number corresponds to the ratio of the degree of nonuniformity appearing at a low side, and the position signals X' and Y' and unblank signal are added nearly according to the probability. The count number C of the position signal X' and Y' and unblank signal after the nonuniformity correction mentioned above is equal to a mean value M at every position.

Description

Detailed Description of the Invention (a) Industrial Application Field This invention detects radiation emitted from an object using a two-dimensional radiation position detector to take a minute IIi image of radioactive substances distributed within the object. Regarding the improvement of scintillation cameras.

(b) One problem with conventional scintillation cameras is non-uniformity, and the causes of this non-uniformity are, seventhly, inherent energy level fluctuations depending on position and spatial non-linearity. In the past, various proposals have been made to eliminate these causes and improve the non-uniformity (see Japanese Patent Publication No. 56-86377 and Japanese Patent Publication No. 56-86378 '4).

However, in all of these conventional methods, in order to achieve the best uniformity and property, it was necessary to sacrifice linearity to some extent and maintain the linearity in a state slightly worse than the best state. Furthermore, especially in the case of multiple nuclides and multiple energies, it is still difficult to achieve good uniformity even with energy correction and linearity correction compared to the case of single energy and one nuclide. Apart from these, special public service No. 52-137180
Although the publication describes improvement of uniformity, in this case there is a drawback that only a small count rate is necessarily obtained compared to the count rate obtained at the stage before uniformity correction.

(C) Objective The object of the present invention is to provide a synnarration camera that maintains the best linearity, provides the best uniformity, and does not cause deterioration of the body ratio characteristics.

(d) Configuration In the scintillation camera according to the present invention, the non-uniformity at each position is actually measured using the position signal and unrank signal written after each correction of linearity correction and energy correction. Correction information regarding whether the nonuniformity occurs on the higher or lower side than the average value and the extent of the nonuniformity is stored in the nonuniformity correction memory, and can be obtained when photographing the subject. By specifying an address using a position signal, correction information at that position is read out, and if the non-uniformity is one level higher than the average value, a position signal and an unranked signal are output with a probability corresponding to the ratio of the non-uniformity. In addition, when the non-uniformity is lower than the average value, a new position signal and unranked signal are added with a probability corresponding to the ratio of the non-uniformity.

(E) Embodiment In FIG. 1, when radiation is incident on the two-dimensional radiation position detector l, 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 includes an A/D converter, a linearity correction circuit, an energy correction circuit, etc., and the position signals X', Yo and amplifier are converted from analog signals to digital signals and corrected through these circuits. A rank signal is output. The position signals X', Yo and the amplifier 11 are sent to the output circuit 3 and the hold and output circuit 4. In this embodiment, the position signals X' and Yo are both 12 bits, and the -high and high 6 bins, i, are sent to the non-uniformity correction memory 5 to designate its address. In other words, here, the independent-take correction is not applied to each pixel individually, but is applied to each block containing B4x64 pixels, and the same correction 1F is applied to pixels included in the same block. It is. In this way, the correction information stored at the address is read out from the non-uniformity correction IF memory 5 which receives the address specification. In this example, this correction information is 8 hits, with the most significant digit being 1.
The bits are sent to the output circuit 3 and the timing signal generation circuit 8, and then to the lower 7-bit comparison circuit 7. The random number generation circuit 6 is triggered by the unranked 4.1 signal to generate a 7-bit random number, and sends this 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, and outputs these to output circuit 3 and timing signal generation circuit 8. send to The output circuit 3 outputs the most used information from the non-uniformity/gender correction memory 5 -l:, (iγ digit is "l".

output is prohibited only when the comparator circuit 7 sends the “l′ signal, and in other cases, the position signal X′ from the correction circuit 2 is
, Y' and the unranked signal are output as they are.

The timing signal generation circuit 8 holds the output only when the lowest 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, and the output circuit 4・The position signal X' from the correction circuit 2
, Yo, and unranked signals are output after being held for a certain period of time.

In this embodiment, the non-uniformity correction memory 5 is a FROM (programmable read Φ-only memory), and the cleavage information to be stored in each of these seven traces is determined as follows. First, uniform radiation over the entire surface is used, and this is detected by a two-dimensional radiation position detector l. According to the corrected position signals X', Yo and unranked signal 5- thus obtained by 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 count number C at each position fluctuates above and below the average value M as shown in FIG. To correct this, if the count number Cp at point P exceeds the average value M, the output position signals X', Y' and unranked signal All you have to do is thin out the . Conversely, if the count number Cq at point Q is lower than the average value M, the output position signal X',
In addition to Y' and the unranked signal, new position signals X', Y' and the unranked signal may be added. Therefore, in this embodiment, the position signals X', Y' and the unranked signal are thinned out or added at a probability corresponding to the ratio of deviation from the average value M.

That is, the count number C at position (i, D is Cij
Then, when there is one C4j-M, the most significant digit of the 8-pin information is “l゛°, and the remaining 7 least significant digits are O~ which is the integer of CM/Ci D X l 27 It is an integer value of 127. Also, Cij
When -M is O or negative, the most significant digit is ``0'', and the remaining 7 lower digits are an integer value from 0 to 127 obtained by converting ((2C4j-M)/Ci N X127 into an integer) The correction information thus obtained is written to the address corresponding to position (i, j).

Suppose that after such writing is completed, the address (i, j) of the non-uniformity correction memory 5 is designated by the obtained positional values X' and Y' when photographing a normal subject. Then, the information stored in this address is read out, and if the non-uniformity is 41 on the over side at the position corresponding to this address (i, D, then the highest digit) is l". The random number generation circuit 6 randomly outputs a 7-bit random number, that is, any integer from O to 127. Therefore, the lower 7 of the read information in "2" is output at random.
Comparing the digit and this random number, the probability that the former is smaller than the latter corresponds to the ratio of the excess. Therefore, "1 pass" is generated from the comparator circuit 7, which causes the output circuit l
The probability of being prohibited corresponds to the ratio of O/<S.

Also, if the most significant digit of the information read from the specified address is 0, the position corresponding to this address (
i, D is where the non-uniformity occurs on the lower side. If the lower seven digits of the information read at this time are smaller than the random number, the comparator circuit 7 sends the timing signal generator circuit 8 a signal of "1'°."

The most significant digit is 0 from the non-uniformity correction memory 5.
'' is given, a signal is generated from this timing signal generation circuit 8, which causes the hold and output circuit 4 to operate. After - daylight savings time has elapsed, the hold and output circuit 4 generates the same signal (X', Y'-) and an unrank signal. The probability of this corresponds to the ratio of the degree of non-uniformity on the lower side, and with this probability the position signals X', Y' and the unranked signal will be newly added.

In this way, the position after receiving 1 complement i1E unevenly is
', Y'' and the count number C of the unblank signal are:
It becomes 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, it is possible to optimize linearity correction and energy correction separately from non-uniformity correction. There is no need to sacrifice linearity etc. for compensation. Further, the counting rate will not increase or decrease due to non-uniformity correction. Furthermore, it is also possible to simplify the linearity correction i[: and the energy correction compared to the conventional method.

Incidentally, in the above embodiment, the non-restrictive auxiliary IF memory 5 is FRO.
Although it is configured with M, 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 may not be the same as the original position signal, but may be a signal obtained by adding a weight i and a change if.

(f) Effects With the synnarration camera according to the present invention, uniformity can be maximized without deteriorating linearity, etc., and excellent images can be taken without any increase or decrease in counting rate.

[Brief explanation of drawings]

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

Claims (1)

[Claims] (1) A two-dimensional radiation position detector, a linearity correction circuit,
In a scintillation camera that includes an energy correction circuit, the non-uniformity at each position was actually measured using the position signal and unrank signal obtained after receiving each of the above compensation pressures, and the non-uniformity at each position was confirmed. Correction information regarding whether the nonuniformity occurs above or below the average value and the ratio of the degree of nonuniformity to the average value is stored in the nonuniformity correction memory. By specifying an address using the position signal obtained when photographing the subject, correction information at that position is read out, and if the non-uniformity is higher than the average value, the position signal is read out with a probability corresponding to the ratio of the non-uniformity. and unranked signals are not output, and when the non-uniformity is lower than the average value, a new position signal and unranked signal are added with a probability corresponding to the ratio of the non-uniformity. A scintillation camera featuring