JPH0119110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a uniformity correction device for a scintillation camera.

One of the basic performances of scintillation cameras is the uniformity of sensitivity (here simply referred to as uniformity).
There is. The factors that determine the upper limit of this uniformity are broadly classified into the scintillation camera body and the collimator that is used depending on the spatial resolution and sensitivity required for diagnosis. Research has progressed to elucidate the factors that determine the upper limit of uniformity and to find ways to improve it, and uniformity correction devices have been commercialized in general. Not enough improvement has been made.

FIG. 1 is a block diagram of a scintillation camera having a conventional uniformity correction device. That is, radiation from a subject (not shown) is projected onto a scintillator 2 via a collimator 1, and the light emission position due to the interaction between the scintillator 2 and the radiation is detected by a plurality of photomultiplier tubes 4 through an optically coupled light pipe 3. and convert it into an electrical signal. The output of the photomultiplier tube corresponding to the light emission position is determined by the position calculation circuit 5, which calculates the light emission position in two-dimensional coordinates by the XY calculation circuit 6, and calculates Z, which is the sum of the photomultiplier tube outputs for the purpose of selecting the energy of radiation. The computation and its pulse height analysis are performed by a pulse height analyzer 7. The calculation results of the light emission position obtained by the XY calculation circuit 6 include geometric uniformity depending on the arrangement of the collimator holes and walls, the unique light emission and uniformity of light diffusion of the scintillator, and the light pipe. 3. Uniformity of light transmission,
This includes the photosensitive uniformity of the photocathode of each tube of the photomultiplier tube 4, as well as the uniformity due to the nonlinearity of the XY calculation circuit 6, etc. Furthermore, the output of the pulse height analyzer 7 includes uniformity due to similar factors. A uniformity correction device 8 corrects these uniformities, and in this conventional example, it is composed of an XY correction coefficient matrix 9 for position calculation of two-dimensional coordinates and a Z correction matrix 10 for the purpose of correction of wave height distribution. ing. The corrected results are input to the display device 11 as two-dimensional coordinates and Z modulation to obtain a radiation image with improved uniformity.

In this case, the combination of other building blocks except collimator 1 is fixed and requires periodic calibration with the main purpose of correcting uniformity changes due to long-term gain drift of the photomultiplier tube. By implementing this, the function of the uniformity correction device can be fully demonstrated. However, although the collimator constituting the cinch camera is important for the uniformity of the cinch camera system, conventional uniformity correction devices are designed to be adapted to a single collimator. This is inconvenient in the following respects, considering the need to replace the collimator depending on the purpose of diagnosis. That is,
When changing the already installed collimator A to another collimator B according to the purpose of diagnosis, the following procedure must be followed.

1. Replace collimator A with collimator B.

2. Delete the correction data of the XY correction coefficient matrix 9 created in accordance with collimator A.

3. A planar radiation source prepared in advance that simulates ideal uniformity is installed in parallel in front of the collimator.

4. Take in radiation count data up to a fixed value to create correction coefficients for XY correction coefficient matrix 9 in accordance with collimator B.

5 Data processing to create correction coefficients.

6 Remove the plane source.

These steps typically take at least 30 minutes or more and are inefficient in collecting diagnostic data.
In this case, the same procedure and time are required when returning from collimator B to collimator A.

The present invention aims to improve these conventional drawbacks, and provides a scintillation camera with excellent uniformity depending on the type of collimator.

The gist of the present invention is that the camera is configured to read out a correction coefficient that matches the type of collimator from a plurality of uniformity correction coefficient matrices prepared in advance according to the type of collimator attached to the cinch camera, and perform correction. Furthermore, according to an advantageous embodiment of the present invention, the type of collimator is automatically detected, and the correction coefficient is automatically read out based on this detection signal. The details will be explained below.

FIG. 2 shows a block diagram of an embodiment of the uniformity correction apparatus of the present invention. In the configuration of this embodiment, a collimator 1, a scintillator 2, a light pipe 3,
The photomultiplier tube 4, position calculation circuit 5, XY calculation circuit 6, pulse height analyzer 7, uniformity correction device 8, and display device 11 are basically the same as those of a conventional scintillation camera. The difference from the conventional example is that the uniformity correction device 101 is made into a plurality of units instead of the conventional single unit.
XY correction coefficient matrices 9-1 and 9-2,
A correction matrix selection circuit 102 that selects one of these plurality of XY correction coefficient matrices according to a collimator type signal 211, which will be described later, and a conventional Z
This is at a newly constructed point in the correction matrix 10.
Furthermore, a collimator type signal 21 that controls the newly configured correction matrix selection circuit 102 is added.
1 is a collimator type detector 103 newly installed near the collimator 1 attached to the scintillator 2.
obtain by.

The collimator type detector 103 detects the type of collimator after the change every time a new collimator is changed. The type detection signal 211 switches the switches forming the correction matrix selection circuit 102, and selects the XY correction coefficient matrices 9-1, 9-2.
Select the appropriate matrix in . The selected correction coefficient matrix is connected to the output 401 of the XY calculation circuit 6, uniformity correction is performed correctly on the changed collimator, and the corrected data can be displayed on the display device 11.

It will be explained in further detail. Collimators are classified into various types depending on sensitivity and resolution. They are called high-sensitivity collimators and high-resolution collimators. Furthermore, collimators are classified according to the energy of the source. The radiation source is 140KeV
There are technesium Tc-99m, 90KeV, 180KeV gallium Ga-67, 135KeV, 167KeV thallium Te-201, 160KeV, 364KeV iodine I-123, 131, etc. Collimators have different thicknesses and structures depending on each energy.

Next, the relationship between the collimator and the correction coefficient will be described. When the sources are the same (when the energy is the same),
Even if the collimator is changed, the correction coefficient of the Z matrix, which is energy information for each event from the radiation source, does not change, and only the XY correction coefficient changes. When the energy changes by changing the radiation source, the collimator is changed, and both the Z matrix correction coefficient and the XY matrix correction coefficient change. However, the change in the correction coefficient of the Z matrix is generally small;
For practical purposes, it can be ignored. Therefore, normally it is sufficient to prepare one Z matrix. However, the correction coefficient of the Z matrix may change depending on the width of the window W to be captured, and in this case, it is necessary to prepare multiple Z matrices. . Furthermore, if Z correction is to be performed without being ignored in practice, a plurality of Z matrices are similarly required.

Next, data filing of correction coefficients will be described. Now, assume that a high-sensitivity collimator A and a high-resolution collimator B are mutually used as collimators. First, attach collimator A. After installing, select compatibility matrix 9-1.
Next, a plane radiation source (using a plane phantom) is installed and an operation button (not shown) is turned on. This captures uniformity information from the planar source. After taking in the information, the information is processed to calculate true correction coefficients, and a matrix is formed as correction coefficients in the XY correction matrix 9-1. In the above processing and calculation, the captured information is reciprocated for each point of XY and used as a correction coefficient for uniformity.

The above processing is similarly performed for the collimator B, and is captured and stored as a correction coefficient in the XY matrix 9-2. The matrices 9-1 and 9-2 thus obtained are selected for each installation of the corresponding collimator and are used for matrix correction calculations for uniformity.

FIG. 3 is a diagram showing a detailed embodiment of the collimator type detector 103. Collimator type detector 10
3 is a code 201 that is optically composed of bright and dark parts and represents the type of collimator attached to the collimator.
It consists of a detecting section 203 provided close to a label 202 indicating , and a logic circuit 210 that takes in the output of the detecting section 203 and performs logical processing. Furthermore, the detection unit 203 has two detection units that independently detect both the dark and bright areas of the label. The two detection units have exactly the same configuration, and include light sources 204A and 204.
B. a light guide 205A optically coupled to the light source;
205B, light guides 207A, 207B, which receive the light emitted from the light guide, projected and reflected from the dark and bright areas of the label 202;
Photodetector 20 that detects light from 7A and 207B
It consists of 8A and 208B.

Logic circuit 210 includes photodetectors 208A, 208
A discriminator 209A that takes the detection output of B and identifies whether it is a reflection from a dark area or a bright area based on the magnitude relationship with a reference value (threshold level).
209B, the output of the disc discriminator 209A and the inverted output via the inverter 209C are each used as one input, and the disc discriminator 209
It consists of two-input NAND gates 209D and 209E whose other input is the output of B.

According to this configuration, the label 202 and the detection unit 2
03 are in the positional relationship as shown in the figure, the discriminators 209A and 209B generate outputs that are logically different from each other. That is, if one output is "1", the other output is "0". Therefore, since different logic signals are generated from the NAND gates 209D and 209E, the presence of the label can be identified. Note that the logic circuit 210 can have various logics. For example, the outputs of 209A and 209B may be used for direct identification. Logic for direction detection or more accurate label detection may be incorporated. Furthermore,
The pattern configuration of the bright and dark areas in the label can also be varied.

Furthermore, an embodiment of incorporating this detector 203 into a scintillation camera is shown in FIG. That is, a shield container 301 showing a partial cross-sectional view of a radiation detection section of a scintillation camera, a collimator 1 corresponding to the collimator 1 in FIG.
In the conventional configuration consisting of a container 302 that collectively houses the scintillator 2, light pipe 3, and photomultiplier tube 4 shown in the figure, a third
A label 202 indicating the type of collimator explained in the figure with a code 201 is attached.
Furthermore, a logic circuit 210 is provided that generates logic signals of the type of detector 203 and collimator described in FIG. The collimator 1 has a necessary collimating hole 100 formed in its inner circumference.

In this case, the collimator 1 is illustrated in a state where it is separated from the container 302 containing the scintillator, but in practical use, the collimator 1 is attached close to it by screws 303 for attaching it. Furthermore, if there is a part between the detection unit 203 and the label 202 that blocks light, the detection unit 2
The detection ability in 03 is lost. Therefore, there is a space between the detection section 203 and the label 202, and the shield container 301 forms a notch in that space. However, this notch is minute and can be seen as a kind of slit hole.

Figure 5 shows the XY correction coefficient matrix 9-1, 9
This is an embodiment showing input/output switching of 2. XY
A switch 402 for switching the input 401 is provided before the correction coefficient matrices 9-1 and 9-2, and a switch 403 for switching the output is provided after the matrices 9-1 and 9-2. This switch 40
Switching between 2 and 403 is performed by the logic circuit output 211 of the detector 103. When matrix 9-1 is selected, upper switches 402A and 403A are turned on, and when matrix 9-2 is selected, lower switches 402B and 403B are turned on.

According to this embodiment, when there are two collimators and the two are to be used separately, the type of the collimator is automatically read and the corresponding correction coefficient matrix can be automatically selected. Note that there is generally no limit to the number of types of collimators. Furthermore, the correction coefficient matrix may be selected manually by eliminating the detector. At this time, the correction coefficient matrix is not limited to the XY matrix, and can also be selected for the Z matrix.

According to the present invention, it has become possible to easily correct uniformity.

[Brief explanation of drawings]

Fig. 1 is a diagram of a conventional example, Fig. 2 is an embodiment of the present invention, Fig. 3 is an embodiment of a collimator type detector circuit, and Fig. 4 is an embodiment of incorporating the detector into a scintillation camera. FIG. 5 is an embodiment diagram of a switching circuit. 1...Collimator, 2...Collimator type detector,
102...Correction matrix selection circuit, 9-1, 9-
2...XY correction coefficient matrix.

Claims (1)

[Scope of Claims] 1. A plurality of photomultiplier tubes optically coupled to a scintillator, a position calculation circuit for determining the light emitting position of the scintillator, and a collimator that projects radiation emitted from the subject onto the scintillator surface. In the scintillation camera configured, the scintillation camera includes: a memory storing coefficients for correcting uniformity of the scintillation camera according to the type of the collimator to be attached to the scintillation camera; A scintillation camera comprising means for selecting a corresponding coefficient from the memory according to the type of collimator attached to the camera, and reading and processing the selected coefficient as correction data. 2. The selection of the coefficient according to the type of collimator is an operation performed by automatically reading a mark indicating the type provided on the collimator and automatically selecting the coefficient based on the read detection signal. The scintillation camera described in Section 1. 3 The coefficient according to the type of collimator mentioned above is
A scintillation camera according to claim 1 or 2, which is used for a matrix.