JPH10160850A - Positron ECT device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the quantitativeness of data in a simultaneous emission data / transmission data collection method using a mask data collection method. SOLUTION: When an output is uniformly generated from all pairs of detectors 11, an address signal passed through a T mask processing circuit 14 and an E mask processing circuit 15 is transmitted to a TCD memory 23 and an E mask processing circuit.
The data is guided to a CD memory 25 to collect TCD data and ECD data.
Emission data Et corrected for mask sensitivity non-uniformity
And the T mask sensitivity correction circuit 26 corrects the T mask sensitivity non-uniformity and obtains the true transmission data Tt excluding the emission data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positron ECT apparatus having a large number of detectors arranged in a ring, and more particularly, to a positron EC of a simultaneous acquisition system of emission data and transmission data by a mask data acquisition technique.
It relates to a T device.

[0002]

2. Description of the Related Art A positron ECT apparatus uses a positron-emitting radionuclide, detects an annihilated gamma ray, and takes an image of the nuclide distribution. For example, when a drug labeled with a positron-emitting radionuclide is administered to the human body, it accumulates in specific organs. At that time, gamma rays emitted outside the human body are detected by a detector arranged outside the human body to collect data. Since the annihilation gamma ray is emitted in the direction opposite to 180 °, it is detected that the annihilation gamma ray is incident on a pair of detectors at the same time, and data that a nuclide exists on a line connecting the pair of detectors is obtained. By processing data collected by such coincidence counting according to a predetermined algorithm, a concentration distribution image of nuclides at a predetermined cross section is reconstructed. This reconstructed image is used for diagnosis of a specific organ.

[0003] A scintillation detector or the like is used as a detector for detecting gamma rays outside the subject, and these are arranged in a number of rings. Since the gamma rays emitted from the nuclides located in the plane of the ring array of this detector and emitted in parallel with the above plane enter one of the ring-arranged detectors and are detected. , The data of the subject in this plane (slice plane) will be collected,
The reconstructed image is a concentration distribution image of nuclides on this slice plane.

On the other hand, in this positron ECT apparatus, since radiation from nuclides inside the subject is detected outside, it is inevitable that the radiation is absorbed by the inside of the subject. For this reason, in the reconstructed image, there are problems such as an abnormally low density at the central portion of the subject and a low accuracy because quantitative measurement cannot be performed.

[0005] Therefore, there is an idea that the absorption distribution in the subject is obtained and the influence of the absorption in the emission data is corrected using the distribution. This absorption distribution is obtained by collecting transmission data. Here, the transmission data (transmission data) is for emission data (radiation data) which is data due to radiation radiated from inside the subject, and is data corresponding to radiation radiated from outside the subject and transmitted through the subject. Say.

Specifically, an object to which a radiopharmaceutical is not administered is arranged inside a ring-shaped array of detectors, and a positron-emitting source is arranged along the ring-shaped array of detectors. To rotate around the subject, and collect coincidence data for each rotation angle. Next, after the subject is taken out of the ring array of the detector, coincidence data is collected while the source is rotated in the same manner.
The former data is affected by absorption due to the passage of radiation through the subject, whereas the latter data is not. Therefore, the influence of absorption can be understood from the relationship between these data. Then, this time, the radiopharmaceutical is administered to the subject, and the radiopharmaceutical is arranged in the ring-shaped array of the detector to collect the emission data (at this time, the radiation source outside the subject has been removed). If the emission data is corrected according to the above relationship, the influence of absorption can be eliminated.

Conventionally, transmission data and emission data for a subject are separately collected in a state where a radiopharmaceutical is administered to the subject and in a state where the radiopharmaceutical is not administered. It took a long time to fix the specimen (patient). Therefore, in Japanese Patent Application Laid-Open No. 4-168392, transmission data and emission data are simultaneously collected in a state where a radiopharmaceutical is administered to a subject, thereby shortening the examination time and shortening the patient fixing time.

[0008] That is, it is noted that the position of the external radiation source to be rotated around the subject can be easily detected, and if the position is known, it is possible to determine in which area on the address the data due to the radiation from that position appears. It was done.
If the area is masked and data is not collected in that area, emission data can be obtained even if the external source is rotated while the radiopharmaceutical is being administered to the subject, and at the same time, By collecting data without any masking and subtracting the emission data from this data, transmission data can be obtained.

Further, the present inventors have proposed a method of improving the quantitativeness of data by developing a simultaneous emission data and transmission data collecting method using this mask data collecting method (Japanese Patent Application No. 7-353419). .
Since an external radiation source rotated around the subject is highly radioactive, scattered radiation is generated around the radiation source, and thus the collected data contains a large error. Therefore, the area of the shielding part (mask part) of the mask for collecting the emission data is set to be larger than the area where the data due to the radiation from the external radiation source appears, and the emission data is collected by removing the scattered noise appearing around the area. For transmission data collection, a mask is used, the passing portion of the mask (region not masked) is narrowed, scattered radiation noise is eliminated, and only data due to radiation from an external source is collected. With this proposal, it is possible to eliminate the influence of the scattered radiation noise of the external radiation source and to improve the quantitativeness of the data.

[0010]

However, the conventional simultaneous acquisition of emission data and transmission data by the mask data acquisition method has a problem that the quantitativeness is not perfect in any case. In other words, as long as data is collected while sorting using a mask,
The detection efficiency for each address is not uniform, and the problem of non-uniformity in sensitivity (non-uniformity) in mask data collection is inevitable, and there is a limit to improving quantitative performance due to this.

In view of the above, the present invention provides a positron ECT apparatus of a simultaneous emission data / transmission data acquisition system using a mask data acquisition technique, which corrects sensitivity nonuniformity in mask data acquisition and enhances data quantitativeness. The purpose is to provide.

[0012]

To achieve the above object, a positron ECT apparatus according to the present invention comprises:
A ring-shaped array of radiation detecting means in which a number of radiation detecting means are arranged in a ring shape; a simultaneous detecting means for detecting that outputs are simultaneously generated from two of the above-mentioned plurality of radiation detecting means; Address conversion means for converting a pair of the two detection means into a corresponding address signal; means for collecting data by counting at an address specified by the address signal when the address signal is generated; A positron-emitting radiation generating means which is arranged and rotated along the ring-shaped array, a means for obtaining its rotational position information, and a mask area on the address which is changed according to the rotational position information. It is assumed that the mask does not count at addresses within that area, and that the specimen containing the positron-emitting substance is Means for separately and simultaneously collecting transmission data and emission data in the data collection means when arranged in a mold arrangement; and sensitivity non-uniformity caused by mask data collection of the collected data. Mask sensitivity correction means for correcting, and absorption correction means for performing absorption correction of the emission data in accordance with the relationship between the transmission data and the transmission data when the subject is not arranged in the ring-shaped array. It is characterized by being able to.

Since the positron emitting radiation generating means is rotated along the ring-shaped array of detectors, it is easy to obtain information on its rotational position. Therefore, when the positron emitting radiation generating means is at a certain position, it is possible to know in which area the data by the radiation from that appears on the address, so if that area is masked and not counted in that area, Emission data is obtained, and transmission data can be obtained by subtracting this emission data from data collected without any masking at the same time. Alternatively, transmission data can be collected by masking the area other than the area where the data based on the radiation from the positron-emitting radiation generating means appears on the address. Then, if the emission data is subjected to absorption correction in accordance with the relationship between the transmission data and the transmission data when the subject is not arranged in the ring type array, the absorption by the subject is corrected. However, since the emission data is obtained by performing mask data collection, the collection efficiency varies depending on the address, so that the sensitivity non-uniformity is corrected. Therefore, since the correction of the sensitivity nonuniformity which is inevitable by collecting the mask data and the absorption correction are used together, the quantitativeness of the data is improved.

[0014]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In the positron ECT apparatus according to the present invention, as shown in FIG.
Many radiation detectors 11 are arranged in a ring shape,
A subject (patient) 30 is arranged in the ring-shaped array 10. Each output of these detectors 11 is guided to a coincidence circuit 12, and it is detected that radiation is incident on any two detectors 11 at the same time and outputs are simultaneously generated from these. Then, when outputs are simultaneously generated from the two detectors 11 and detected by the coincidence circuit 12, the output from the coincidence circuit 12 is sent to the address converter 13, and the combination of the two detectors 11 is output. Is performed in accordance with the address.

In the address conversion, when outputs are simultaneously generated from the two detectors 11, the addresses are converted into position information on a line connecting the two detectors 11. The information representing the position of the line connecting the two detectors 11 is represented by, for example, an angle θ and a distance d from the center, as shown in FIG. That is, when a detection signal is simultaneously generated by two certain detectors 11, conversion to an address consisting of θ and d representing a line connecting the two detectors 11 is performed.

The converted and output address signals are sent to the respective data collection memories 21 to 25 via the two mask processing circuits 14 and 15 and counted for each address. That is, in each of the data collection memories 21 to 25, when a certain address signal is input, “1” is added to the address, thereby indicating the number of gamma rays incident for each address represented by (d, θ). The count value is accumulated.

On the other hand, the line source 18 is moved to the detector ring type array 1 as shown by a dotted line by a mechanism not shown in the figure.
It is rotationally moved stepwise within 0 at predetermined small angles. The line source 18 is a radiation source formed in a line shape, and is disposed so as to be orthogonal to a slice plane (a plane including the detector ring type array 10) (in the figure, disposed at right angles to the paper). . The line source 18 is formed of a positron emitting nuclide.

Therefore, the subject 30 to which the drug labeled with the positron-emitting nuclide is administered is arranged in the ring-shaped array 10 of the detector 11 and the memory 21 is rotated when the line source 18 is rotated around it. If the data collected by .about.25 are not considered in the processing by the mask processing circuits 14 and 15, they should be as shown in FIG. Note that FIG.
The data obtained by accumulating the count values for each address (d, θ) is called a sinogram.

The sinograms in FIGS. 3A to 3D are as follows:
2 shows the data collected when the line source 18 is located as shown in FIGS. 2 (a) to 2 (d). Actually, since the address signals obtained during the period in which the line source 18 makes one rotation are all added to the corresponding addresses, sinograms such as those shown in FIGS. They are not obtained, but are added (overlapping). When the line source 18 is located upward as shown in FIG. 2A, the data from the line source 18 is concentrated at the center (center of d) at an angle of 0 ° as in the sinogram of FIG. 3A. And at the right end at an angle of 90 °
It is centrally located at an angle of 180 °. Therefore, in FIG. 3A, the data obtained by the line source 18 becomes a curve 42. On the other hand, since the subject 30 is flat in the left-right direction, data by gamma rays from nuclides in the subject 30 are wide in the d direction at angles of 0 ° and 180 °, and at 90 ° in the d direction. Collected in a small area.
Therefore, the data from the subject 30 is
become that way.

Similarly, when the line source 18 is on the left side as shown in FIG. 2B, data from the line source 18 is collected at the position of the curve 42 in FIG. When the line source 18 is at a lower position as shown in FIG. 2C, data from the line source 18 is collected at the position of a curve 42 in FIG. Line source 18
Is to the right, data from line source 18 is collected at the location of curve 42 in FIG. 3 (d). On the other hand, the data from the subject 30 is invariable regardless of the position of the line source 18,
Collected in a grain pattern portion 41 having a similar shape.

The mask generator 16 moves with the position of the line source 18 and has a passage corresponding to the data collection area 42 from the line source 18.
The mask generator 17 generates a mask having a shielding portion (mask portion) corresponding to the data collection area 42 from the line source 18. The mask generator 16 generates a mask as shown in FIG. 4, and the mask generator 17 generates a mask as shown in FIG. With such a mask, the mask processing circuit 1
The processing performed by 4 and 15 is a processing in which a specific address is passed, and other specific addresses are shielded (masked) and not passed, and the mask here is an address section (passing section) through which the address is passed. And an address portion (shielding portion) to be shielded. 4 and 5,
The part of the grain pattern is the shielding part, and the white part is the passing part.

In order to generate these masks corresponding to the position of the line source 18, position information of the line source 18 is input to the mask generators 16 and 17. This location information
The rotation position of the line source 18 is obtained by a rotation position reading device 19. This rotational position reading device 19 is composed of, for example, a pulse encoder, a counter and the like.

When the line source 18 is at each of the positions shown in FIGS. 2A to 2D, masks such as those shown in FIGS. Since only the blank portion is passed through the mask processing circuit 14, only the data in the area 42 in FIG. 3 is passed. That is, Tm data (transmission data) due to radiation from the line source 18 is extracted. The Tm data is sent to the data collection memory 22 where the data is collected. The memory 22 is called a Tm memory, the mask generator 16 is a T mask generator, and the mask processing circuit 14 is a Tm memory.
It is referred to as a mask processing circuit. As the line source 18 rotates, the mask changes accordingly as shown in FIGS. 4A to 4D, and the Tm memory 2 is rotated during one rotation (360 °).
Data collection is performed by performing addition at each address of 2.

On the other hand, the line radiation source 18 is shown in FIG.
5 (a) to 5 (d) are generated by the mask generator 17 and only the white portions are passed through the mask processing circuit 15. The shielding portion (grain pattern portion) corresponds to the region 42 in FIG. 3, but has an increased width. Therefore, the data due to the radiation from the line source 18 and the data around it are shielded, and the data in other areas are
That is, only Em data (emission data) from the nuclide in the subject 30 is extracted. This Em data is
The data is sent to the data collection memory 24 to perform data collection. The memory 24 is called Em memory, the mask generator 17 is called an E mask generator, and the mask processing circuit 15 is called an E mask processing circuit. The Em memory 24 adds, for each address, data passing through a mask passing portion that changes as shown in FIGS. 5A to 5D as the line source 18 rotates.

Here, since the width of the masking portion of the mask in FIG. 5 is wide, not only the data from the line source 18 but also the data of the peripheral addresses are not collected in the Em memory 24. Become. Therefore, noise due to scattered radiation generated around the line radiation source 18 having strong radioactivity is not collected. Although the width of the shielding portion is wide, the shielding portion moves along with the rotation of the line source 18 as shown in FIGS. 5A to 5D. In this case, there is no area that is always shielded, and data is collected almost equally.

However, strictly speaking, data is not collected with equal efficiency at each address. The same can be said for the Tm data collection by the T mask generator 16, the T mask processing circuit 14, and the Tm memory 22. This is because the time shielded by the mask shown in FIGS. 4 and 5 (or the time passing through) during one rotation of the line source 18 is not the same at all addresses, but depends on the address. There are differences. Therefore, if a detection output is uniformly generated from each pair of the detectors 11, a uniform count should normally be obtained at any address of the sinogram. As shown in FIG. 7, a sinogram in which a high count portion and a low count portion exist (a dark portion has a high count and a light portion has a low count) is obtained. FIG. 6 shows sinograms collected by mask processing using the E mask of FIG. 5, and a low count region appears in a region near both ends in the d direction. FIG. 7 shows sinograms collected by masking with the T mask of FIG.
A high count area appears at both end areas in the d direction.

Therefore, the sensitivity non-uniformity on the address of the sinogram due to such mask processing is corrected to improve the quantitativeness. Therefore, prior to data collection in a state where the subject 30 and the line source 18 are arranged as described above, detection output is uniformly generated from each pair of the detectors 11 and the TCD memory 23 and the ECD memory 25 are generated. Collect data using. That is, at this time, the T mask generator 1
6. The E mask generator 17 sequentially generates a T mask and an E mask that change by one rotation, and in the period that changes by one rotation, converts the address signal passed through the T mask processing circuit 14 and the E mask processing circuit 15 , TCD memory 23, E
The data is guided to the CD memory 25 and collected. As a result, data (TCD data) as shown in FIG. 7 is collected in the TCD memory 23, and data (ECD data) as shown in FIG.

After the TCD data 23 and the ECD data 25 have been collected by the TCD memory 23 and the ECD memory 25, data is collected with the subject 30 and the line source 18 arranged as described above, and the Tm memory 22, the Em memory 24, when the Tm data and Em data are obtained, the E mask sensitivity correction circuit 27 first normalizes them so that the average value of the ECD data becomes 1, and then performs E
Find CDN data. Specifically, an average value of ECD data different for each address of the sinogram is obtained, and the ECD value of each address is divided by this average value to obtain each value of ECDN for each address. Next, the following calculation is performed in the E mask sensitivity correction circuit 27. Et = Em / ECDN This is performed for each address Em of the sinogram to obtain true emission data Et in which the sensitivity non-uniformity caused by the E mask processing is corrected.

In the T mask sensitivity correction circuit 26, the following operation is performed for each address. Tt = Tm− (Em / ECD) · TCD Here, (Em / ECD) is created by reading from the Em memory 24 and the ECD memory 25. The Tm data includes the source 18
, The emission data from the subject 30 that has passed through the T mask (FIG. 4) is superimposed. This emission data is affected by sensitivity non-uniformity due to the action of the T mask.
It is proportional to the CD. On the other hand, Em memory 24
Since the Em data collected in step (1) was obtained by measuring the same object at the same time, it should be basically the same as the emission data included in the above Tm data. Value. Therefore, by multiplying Em by the collection efficiency ratio (TCD / ECD) between the T mask and the E mask, a true value of the emission data included in the Tm data can be obtained. However, since all data due to the radiation from the radiation source 18 passes through the T mask, the data is not affected by variations in the collection efficiency due to the T mask. Therefore, in the above calculation, the true value of the emission data included in the Tm data is subtracted from Tm, and the true transmission data Tt is subtracted.
Can be obtained.

The Tt data is sent to the absorption calculation circuit 28 and compared with the T data read from the T memory 21. This T data is data collected by the T memory 21 when only the line source 18 is rotated in a state where the subject 30 is not arranged. Since the subject 30 does not exist, the T data is completely absorbed by the subject 30. Not something. Therefore, their ratio (T
t / T) represents the absorption ratio in the subject 30 for each address (d, θ). Since the collection of the T data in the T memory 21 is to collect only the data based on the radiation from the radiation source 18, the T data is not affected by the variation in the collection efficiency due to the T mask as described above. The mask processing by the processing circuit 14 may be omitted and the data may be passed unconditionally, or the mask processing by the T mask processing circuit 14 may be performed similarly to the Tm data.

Therefore, in the absorption correction circuit 29, Et for each address obtained from the E mask sensitivity correction circuit 27 is obtained.
By applying the (Tt / T) ratio of the corresponding address to the data, emission data in which the influence of absorption is corrected can be obtained. The emission data is subjected to an image reconstruction operation by the image reconstruction device 31, and the reconstructed image is displayed on the display device 32 or recorded by a recording device (not shown).

In the above description, the memories 21 to 25 are represented as individual memories. However, any of these memories is merely required to be an addition memory for data collection having an address corresponding to the address of the sinogram. May be configured to use a part of each memory. The masking circuits 14 and 15 which are a kind of gate circuit perform the masking of a predetermined area of the address. However, since it is not necessary to add the addresses included in the masked area, mask generation is performed. Vessels 16, 1
The memory may be directly controlled by the information on the mask generated in step 7, or the address converter 13 may be configured not to perform the address conversion of the area to be masked. In the latter case, the address converter 13
May be provided in two systems, each having the functions of a T mask generator 16 and an E mask generator 17.

Further, since the TCD data and the ECD data are data to be collected by mask processing when outputs are uniformly generated from all pairs of the detectors 11, the patterns of the T mask and the E mask can be obtained. It may be obtained by computer simulation using the fact that In this case, the ECDN and (TCD / ECD)
Alternatively, the data may be obtained for each address and stored in a data memory or the like, and the E-mask sensitivity correction circuit 27 and the T-mask sensitivity correction circuit 26 may read out and correct the data.

[0034]

As described above, according to the positron ECT apparatus of the present invention, a state in which a radiopharmaceutical is administered to a subject by mask data collection while correcting sensitivity inhomogeneity inevitable in mask data collection. The emission data and the transmission data can be simultaneously collected by rotating the external radiation source and the absorption correction can be performed, thereby improving the quantitativeness of the data.

[Brief description of the drawings]

FIG. 1 is a block diagram of a positron ECT apparatus according to the present invention.

FIG. 2 is a schematic diagram showing each position of a line source 18;

FIG. 3 is a diagram showing sinograms at each position of a line source 18;

FIG. 4 is a view showing a T mask at each position of a line source 18;

FIG. 5 is a diagram showing an E mask at each position of a line source 18;

FIG. 6 is a diagram showing a sinogram obtained by performing E-mask processing on a uniform detection output.

FIG. 7 is a diagram showing a sinogram obtained by performing a T mask process on a uniform detection output.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Detector ring type arrangement 11 Detector 12 Coincidence circuit 13 Address converter 14 T mask processing circuit 15 E mask processing circuit 16 T mask generator 17 E mask generator 18 Line source 19 Rotational position reading device 21 For T data collection Memory 22 Tm Data Collection Memory 23 TCD Data Collection Memory 24 Em Data Collection Memory 25 ECD Data Collection Memory 26 T Mask Sensitivity Correction Circuit 27 E Mask Sensitivity Correction Circuit 28 Absorption Calculation Circuit 29 Absorption Correction Circuit 30 Subject 31 Image Reconstruction device 32 Display device 41 Data from subject 30 Data from line source 18

Claims (1)

[Claims] 1. Simultaneous detection for detecting that a plurality of radiation detection means are arranged in a ring shape and that a ring-shaped arrangement of radiation detection means and two of the plurality of radiation detection means simultaneously produce outputs. Means, an address conversion means for converting the pair of the two detection means into a corresponding address signal, and means for collecting data by counting at an address specified by the address signal when the address signal is generated; A positron-emitting radiation generating means disposed in the ring-shaped array and rotated along the ring-shaped array; a means for obtaining the rotational position information; and the address changed in accordance with the rotational position information. By masking the upper mask area, it is not possible to count at addresses within that area, Means for separately and simultaneously collecting transmission data and emission data in the data collection means when the body is placed in the ring-shaped array; and sensitivity caused by the mask data collection of the collected data. Mask sensitivity correction means for correcting the non-uniformity, and absorption correction for performing the above-described emission data absorption correction in accordance with the relationship between the transmission data and the transmission data when the subject is not arranged in the ring type array. And a positron ECT device.