JP3309614B2 - Radiation camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiographic camera such as a scintillation camera for taking a radiographic substance concentration distribution image.

[0002]

2. Description of the Related Art In a radiation camera such as a scintillation camera, the direction of incident radiation is regulated by a collimator, and then radiation such as gamma rays is incident on a detector. A signal representing the position is output, and the event occurrence signal is accumulated (counted) for each position to capture a radiation image (radioactive substance concentration distribution image).

In this radiation camera, a uniform radiation image should be obtained when the radioactive substance is uniformly distributed, but in practice, only a radiation image having uneven density is obtained. This means that in the entire system including the collimator, there is non-uniformity such that the same count is not obtained depending on the position. Therefore, conventionally, in order to correct this non-uniformity, an image is taken using a uniform surface radiation source, the non-uniformity is measured, and weighting correction of the count value for each position is performed based on the data. I do it. In other words, it shoots a uniform area source,
It measures how much the count value differs for each position, and weights and corrects the count value for each position so that these count values become constant.

[0004]

However, obtaining a uniform surface radiation source is very difficult in practice, at least on a commercial basis, which results in errors in the data collected for uniformity correction. As a result, there is a problem that uniformity correction cannot be performed accurately.

[0005] Data collection for uniformity correction (to capture data by capturing a uniform surface radiation source) is usually performed by a user himself at a facility such as a hospital where a radiation camera such as a scintillation camera is installed. There are many.
In that case, as shown in FIG.
The liquid source is put in a flat container 31 to manufacture the container. As the radiation source, Tc-99m or the like is usually used because it is inexpensive and easily available. The liquid source and water are injected into the rectangular and flat closed container 31 from the injection port 33, and are stirred so as to be uniform. In addition, this injection port 33
Is provided at one corner of the rectangular / flat container 31,
Air vent holes 32 are provided at other corners on the diagonal line.

[0006] The uniform surface radiation source thus produced cannot be made very uniform in practice because it is difficult to completely stir the radiation source and water in the closed vessel 31. Normally, the concentration of the radiation source is highest near the injection port 33, and the concentration gradually decreases toward the air vent hole 32.

SUMMARY OF THE INVENTION In view of the above, the present invention provides a uniformity correction without error as in the case of using a highly uniform surface source even if the uniformity of the actually used uniform surface source is not so high. It is an object of the present invention to provide a radiation camera improved so that data for use can be obtained and accurate uniformity correction can be performed.

[0008]

In order to achieve the above object, a radiation camera according to the present invention outputs a position signal indicating the position of incident radiation and an event generation signal indicating that an incident event has occurred. Detecting means, and the photographing position of the detecting means with respect to the correction source is changed to at least two positions at which the source density distribution of the correction source is more offset, at each of the photographing positions. Data collecting means for collecting correction data, calculating means for obtaining a correction value for each incident position from the correction data at the plurality of photographing positions, and each incident position in accordance with the correction value for each incident position thus obtained. Correction means for performing weighting correction of the count value for each.

[0009]

When collecting the correction data by directing the detection means to the correction radiation source, at least two photographing positions are set. These photographing positions are positions where the source density distribution of the correction source is more offset. For example, if the source density increases or decreases in a certain direction in the correction source,
Photographing is performed at two photographing positions where the density gradient is offset. Then, a correction value for each incident position is obtained using the correction data obtained at the two locations. Therefore, when the correction source itself has non-uniformity, it is possible to obtain a correction value that is less affected by the non-uniformity. When the source density is increased or decreased in a certain direction in the correction source as described above, the image is taken at two imaging positions where the density gradient is offset, and the correction data obtained at the two locations is used. By using this, a correction value that is not affected by the gradient of the source density can be obtained. Therefore, by performing weighting correction of the count value for each incident position using the correction value thus obtained, more accurate uniformity correction can be performed, and a radiation image with excellent image quality can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied to a scintillation camera. In this figure, detectors of the scintillation camera include a scintillator 12, a light guide 13, a photomultiplier (abbreviated as PMT) 14, It comprises a position and energy calculation circuit 15 and a housing 16 made of a radiation shielding material for accommodating them.

A radiation shielding material is removed from the front surface of the housing 16, and a collimator 11 having a large number of parallel radiation transmission holes, for example, for regulating the direction of radiation is mounted on the front surface. Scintillator 12
Is formed in a flat plate shape, and emits light when irradiated with radiation. The light is transmitted to a large number of PMTs
It is led to 14 light receiving surfaces. The closer the position of the PMT 14 is to the light emission position, the larger the amount of incident light and a large output can be obtained. Therefore, the output of each PMT 14 is weighted and added to the plane (XY plane) of the flat scintillator 12 in the X and Y directions. Thus, position signals X and Y are obtained. Also, the sum of the outputs of all the PMTs 14 corresponds to the total light emission amount,
Since this corresponds to the energy of the incident radiation, this sum is treated as an energy signal, and it is determined that this is within a predetermined energy window, indicating that there has been a radiation incident event from a predetermined nuclide. Obtain an unblank (UNB) signal. These calculations are performed by the position and energy calculation circuit 15, and X, Y signals and unblank signals are output.

When the collimator 11 is mounted as described above, the position corresponding to the radiation transmitting hole of the collimator 11 and the position corresponding to the radiation shielding member are different from each other.
The number of radiation that reaches 2 is naturally different. Also, since the position calculation is not always performed linearly,
This also makes the radiation incident count different depending on the position. Due to these, it is inevitable that non-uniformity in which the count differs for each position occurs.

Therefore, the weighting correction of the count is performed on the unblank signal through the correction circuit 18. The value for weight correction of the count differs for each position indicated by the X and Y signals.

A correction value for this uniformity correction is obtained by the data collection memory 17 and the correction operation circuit 19. That is, the correction source 30 is arranged in front of the scintillator 12 and the collimator 11, and the radiation from this is made incident on the scintillator 12. When the correction source 30 is photographed, the number of incident events for each position is counted in the data acquisition memory 17.

As the correction source 30, a source which is usually used most often is used as in the prior art. That is, the correction source 30 is prepared by putting a liquid source and water in a flat container 31. A solution such as Tc-99m and water are injected from the injection port 33 of the rectangular / flat closed container 31 and stirred. In this case, no matter how well agitated, the concentration distribution of the radiation source is generated in the direction from the injection port 33 to the air vent hole 32, as described above.

Then, in the state as shown in FIG. 1, imaging of the correction radiation source 30 (collection of event count data at each position) is performed for a predetermined time to obtain a predetermined amount of data. By rotating the detector as shown, the same correction source 30 is now imaged from below. In this state, the event count data at each position is collected for the same time.

In the state of FIG. 1, a certain position (the scintillator 1
Assuming that the count value of (the position on the second position) is Ca, the calculated count value at that position should be Ck, the correction value (correction coefficient) Ka is obtained by Ka = Ck / Ca. Similarly, if the count value at the same position (position on the scintillator 12) is Cb in the state of FIG. 2, if the calculated count value at that position should be Ck, the correction value (correction coefficient ) Kb is Kb = Ck / C
b. Average these correction values, that is, K
From f = (Ka + Kb) / 2, a final correction value Kf is obtained. These calculations are performed by the correction operation circuit 19.
This is performed for each position.

Then, the correction coefficient Kf thus obtained for each position is set in the correction circuit 18. Each time an unblank signal is input together with the signals X and Y, the correction circuit 18 outputs an unblank signal weighted by a correction coefficient Kf relating to the position. In other words, an unblank signal with a small count of one count is output at a position with a high count value, and an unblank signal with a large weight of one count is output at a position with a low count value. However, correction is made so that the count value becomes the same.

Instead of rotating the detector and photographing the front and back surfaces of the correction source 30 as described above, the correction source 30 is rotated while the detector is fixed. You may make it image | photograph the front surface and the back surface of 30. The positional relationship (imaging position) between the correction source 30 and the detector of the scintillation camera when collecting the correction data may be at least two. Therefore, the correction source 30
(Or the detector) may be rotated 180 ° in that plane. Alternatively, the correction source 30 having a large area may be used, and the position of the detector may be shifted in the surface direction. In any case, it is desirable to select two photographing positions such that the density distribution of the source in the correction source 30 is more offset by the averaging process as described above. Further, the calculation for obtaining the correction value is not limited to the averaging process. The correction source 30 is photographed at three or more photographing positions, and the density of the correction source 30 itself is used by using the data obtained therefrom. It is also possible to obtain a correction coefficient that reduces the influence of the distribution.

Further, the specific configuration can be variously changed. For example, in the above description, the weighting correction of the unblank signal output for each event is performed by the correction circuit 18, but the count value itself collected for each position may be corrected later. In this case, the correction data can be collected using a memory that performs normal data collection without providing a memory 17 for collecting the correction data. Further, the present invention can be applied to other types of radiation cameras, for example, a semiconductor radiation position detector may be used instead of the combination of the scintillator 12 and the PMT 14.

[0021]

As described above, according to the radiation camera of the present invention, even if the correction source itself has non-uniformity, it is not affected by the non-uniformity. It is possible to obtain more accurate correction values, eliminate variations in correction values due to the performance of the correction source itself, and perform better uniformity correction to produce radiation images with excellent image quality. You can shoot.

[Brief description of the drawings]

FIG. 1 is a block diagram of a scintillation camera according to one embodiment of the present invention.

FIG. 2 is a block diagram showing another photographing position of the embodiment.

FIG. 3 is a front view showing the surface of a correction radiation source.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 collimator 12 scintillator 13 light guide 14 photomultiplier 15 position and energy calculation circuit 16 housing 17 data collection memory 18 correction circuit 19 correction calculation circuit 30 correction source 31 container 32 air vent 33 injection port

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01T 1/164

Claims (1)

(57) [Claims] A detecting means for outputting a position signal indicating the position of the incident radiation and an event occurrence signal indicating that an incident event has occurred; A data collection unit that collects correction data at each of the imaging positions when the source concentration distribution is changed to at least two locations where the source concentration distribution is more offset, and from the correction data at the plurality of imaging positions. Calculating means for determining a correction value for each incident position;
A radiation camera comprising correction means for weighting and correcting the count value for each incident position in accordance with the correction value for each incident position thus obtained.