JP2001194459A - Positron ct equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively gather transmission data in a short time with a high counting rate by using an intensive external radiation source for transmission data gathering, and perform absorption correction of the emission data in real time. SOLUTION: A subject 50 to be inspected is moved with respect to a gantry 10. A ring-type detector 13 for transmission data is arranged on this side of the movement. A ring detector 11 for emission data is arranged in the rear side of the movement. After transmission data concerning a slice 52 are gathered, the slice 52 arrives at a position of the ring-type detector 11, and emission data concerning the slices 52 are gathered. While the above process is in progress, the transmission data are processed, absorption correction is obtained, and absorption correction is performed immediately after emission data gathering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a positron CT apparatus for capturing a distribution image of positron-emitting RI (radioisotope) distributed in a subject.

[0002]

2. Description of the Related Art In a positron CT apparatus, R
180 ° when the positron emitted from I disappears
Data (emission data) is collected by simultaneously counting two gamma rays radiating in opposite directions, and calculating this data to obtain a distribution image of RI.
Gamma rays are radiated out through the subject and are absorbed in the body. Therefore, it is necessary to correct this absorption. In order to obtain data for this absorption correction,
A positron emitting source is placed outside the subject to collect gamma ray data (transmission) passing through the subject.

Conventionally, transmission data is collected using a detector for collecting emission data, and a method of collecting these data at different times and a method of collecting the data at the same time (Japanese Patent Laid-Open No. Hei 9-184885). And had been taken. The former involves placing a radiation source around the subject before RI administration and collecting transmission data, then administering RI to the subject, and collecting emission data with the above radiation source removed. is there.
In the latter case, a radiation source is arranged around a subject to which RI has been administered, and transmission data collection and emission data collection are performed simultaneously.

As a detector, a ring-type detector in which radiation detectors are arranged in a ring-type is used, and a multi-ring-type detector in which the radiation detectors are stacked in multiple layers in the central axis direction is also used. When a multi-ring type detector is used, simultaneous counting data between all the ring detectors facing each other is collected to perform imaging of a subject in a wide volume in the body axis direction, that is, imaging of a three-dimensional image (3D positron CT imaging) ) Is possible, but in order to perform imaging of a larger volume in the body axis direction, the subject is moved relatively to the detector. Move the bed or the detector by the amount of movement as the width of the detector in the body axis direction or the width excluding the specified overlap width. The data is stored in the obtained data matrix, and the image is reconstructed for each position.

[0005]

However, the conventional positron CT apparatus has a problem. If the transmission data for absorption correction is collected at a different time from the collection of the emission data, there is a problem that the entire inspection time increases. Inspection time can be reduced if transmission data and emission data are collected at the same time.However, since gamma rays are detected simultaneously by a common detector, both data are easily affected by each other, and the external source intensity is increased. However, transmission data cannot be collected at a high counting rate. Furthermore, even if data is collected at the same time, absorption correction must be performed in post-processing, and cannot be corrected in real time.

In addition, the conventional 3D positron CT apparatus using a multi-ring type detector has a problem that, when a wide field of view is photographed in the body axis direction, sensitivity unevenness occurs in the body axis direction. In a multi-ring detector, the sensitivity distribution in the axial direction is higher at the center of the field of view and lower at the periphery, so simply arranging images reconstructed for each position in the body axis direction In particular, due to the influence of the sensitivity unevenness, image deterioration is remarkable particularly in a plane image parallel to the body axis such as a sagittal image or a coronal image, resulting in a decrease in diagnostic performance.
If the overlap width between the positions is increased to reduce this, wasteful data collection increases, and the memory utilization efficiency decreases. In addition, if the range of data used for image reconstruction is limited to a range from a ring type detector having a small number of layers, sensitivity unevenness is reduced, but overall sensitivity is reduced and the advantage of 3D acquisition cannot be used.

An object of the present invention is to provide a positron CT apparatus improved in view of the above.

Another object of the present invention is to enable transmission data to be collected in a short time at a high counting rate using a strong external radiation source for transmission data collection and to perform absorption correction in real time. It is an object to provide a positron CT apparatus improved as described above.

Still another object of the present invention is to perform 3D positron CT imaging using a multi-ring type detector by moving the detector with respect to the subject in a field of view larger than the axial field of view of the detector. It is an object of the present invention to provide a positron CT apparatus improved so as to eliminate sensitivity unevenness in the body axis direction when performing.

[0010]

In order to achieve the above object, in a positron CT apparatus according to the present invention, a first ring type detector for collecting emission data of a subject and a transmission data of the subject are provided. A second detector for collection, an external radiation source arranged on the same plane as the second detector, and a method of detecting the object with respect to the first and second detectors and detecting the object with the second detection. A moving device that moves relatively so as to move from the instrument side to the first detector side, and a volume for which transmission data of the subject has been collected moves, and emission data collection for the volume is performed. During this time, the transmission data is processed to determine the absorption correction data on the coincidence line, and the absorption data is collected immediately after the collection of the emission data for the volume. It is the distinctive feature of a data processing device that performs correction is provided.

Since the subject is moved from the second detector side to the first detector side, transmission data is first collected by the second detector, and then the same volume of the subject is stored in the first detector. Emission data is collected by the detectors. In other words, when emission data is being collected for a certain volume, transmission data collection for that volume has been completed, and during the emission data collection, the transmission data for that volume is processed and the absorption correction data on the coincidence line is collected. It becomes possible to calculate. Then, when the collection of the emission data for the volume is completed, the absorption correction for the emission data can be immediately performed using the above-described absorption correction data, and the absorption correction can be performed in real time.

Further, in the positron CT apparatus according to the present invention, a multi-ring type detector in which ring-type detectors are stacked in a multilayer in the axial direction, and an object is detected by the multi-ring type detector with respect to the multi-ring type detector. A moving device for relatively moving the rings at intervals of each ring of the vessel, the coincidence data between the rings obtained at each position of the movement, and the coincidence data between the rings at the position of the immediately preceding movement; A data collection device that collects data while adding data may be provided between the rings adjacent to the ring.

The subject is relatively moved at intervals of each ring of the multi-ring type detector, and coincidence data between rings is collected for each position. Ring i and ring k at a certain position (first position)
And the coincidence count data between the ring i + 1 and the ring k + 1 is obtained at the next position (second position). Since the distance between the first position and the second position is the distance between the rings of the multi-ring detector, the line connecting the ring i and the ring k at the first position and the ring i + 1 at the second position The line connecting the ring and the ring k + 1 is the same line for the subject. Therefore, while adding the coincidence data between the rings obtained at each position of the movement as the coincidence data between the rings at the position of the immediately preceding movement and between the rings adjacent to each of the former rings, Collect data. Thereby, uniform sensitivity is obtained over a wide field of view in the body axis direction, and sensitivity unevenness in the body axis direction can be eliminated.

[0014]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, a ring-shaped detector 11 in which radiation detectors are arranged in a ring shape is stacked in a multilayer in a central axis direction in a cylindrical gantry 10. Among the ring detectors 11, the multilayer ring detector 11 excluding one layer (right end in the figure) closest to the entrance on the side where the subject 50 is inserted is:
A multi-ring detector 12 (see FIG. 3) is configured and used for collecting emission data. The ring type detector 13 at the right end in the figure is for collecting transmission data. That is, a ring-shaped positron-emitting external radiation source 14 is arranged on the plane of the ring-shaped detector 13, and is emitted from the radiation source 14 and positioned on the subject 50, that is, on the plane of the ring-shaped detector 13. The radiation passing through the slice 52 that is
3 is detected. Since the slice sceptor 15 constituted by a lead shield is disposed so as to sandwich the external source 14, the radiation emitted from the external source 14 is transmitted to the right end of the ring detector 13 for transmission data collection. Only to the other ring type detector 11, that is, the multi-ring type detector 12 for collecting emission data. In addition, the slice sceptor 15 prevents radiation from a volume other than the slice 52 from being incident on the transmission data acquisition ring detector 13 at the right end. The external source 14 may be a point-shaped source instead of a ring type. In this case, the external source 14 is rotated around the subject 50 with the body axis 51 as a rotation center axis. When the point source is rotated in this way, it is possible to use a single photon emitting source instead of a positron emitting source, in which case the ring detector 13 is used for single photon counting. Use a detector. When a detector for single photon counting is used, it is not necessary to use a ring type, but a partial ring type (part of an arc) may be used. Rotate with rotation.

A multi-ring type detector 12 for collecting emission data and a ring type detector 13 for collecting transmission data are placed at different positions.
In addition, since the data is partitioned by the slice septa 15 as described above, both data can be separately collected, and it is possible to prevent both data from affecting each other. Therefore, it is possible to efficiently collect transmission data in a short time at a high counting rate by using an external radiation source having a high radiation intensity.

The subject 50 is placed on the bed 20, and the bed 20 is moved by the bed moving device 21 in the direction of the arrow (to the left in the figure), whereby the cylindrical gantry 10 including the ring type detector 11 is moved. From the right to the left. The body axis 51 of the subject 50 is aligned with the center axis of the ring detector 11.

FIG. 2 shows a signal system of this embodiment. A detection signal from the emission data multi-ring type detector 12 is input to a coincidence counting data collection device 31. Multi-ring detector for emission data 12
Consists of the ring-type detectors 11 stacked as described above, and the coincidence count in each ring and the coincidence count between the rings are performed.

For example, the multi-ring detector 12
As shown in FIG. 3, if it is configured by the ring-type detector 11 of five layers (first to fifth layers), the first
Simultaneous counting is performed between the detectors arranged in the circumferential direction in each of the layers to the fifth layer, and between the detectors between the layers. First
When the coincidence is counted by the detector of the ring 1 and the detector of the ring 1, the coincidence is counted by the ring 1 and the ring 2, the coincidence is counted by the ring 1 and the ring 3, etc.
Simultaneous counting is performed for each combination as indicated by the line connecting the detectors in FIG. That is, since coincidence data is collected not only within the ring but also between detectors across the ring, the coincidence line exists for each ring combination. Therefore, counting on each coincidence line is performed in each of the matrices corresponding to the ring combinations as shown in FIG.

In each of these matrices, position data in a plane crossing the body axis 51 is collected as a sinogram. The sinogram is represented by the distance from the center axis and the inclination angle in the circumferential direction of a line (coincidence line) connecting two detectors that have simultaneously detected radiation. As described above, in the case of five rings, sinogram data is collected in each of the 5 × 5 matrices.

Here, considering the state where the bed 20 is stationary, the sensitivity distribution in the body axis direction within the entire field width D (= 4d) in the body axis direction of the multi-ring detector 12 is shown in FIG. Thus, the shape of the triangle becomes higher toward the center of the visual field and lower toward the periphery. This can be intuitively understood from the fact that, as shown in FIG. 3, the number of lines passing through the subject 50 and connecting the rings is large toward the center and only one at the end.

The bed 20 is successively moved by the bed moving device 21 at intervals d of the ring type detector 11. Each stationary position at that time is referred to as a first position P
1, the second position P2, the third position P3,..., For example, the line connecting the rings 2 and 4 at the first position P1 passes through the subject 50, and the ring 3 and 5 at the next second position P2. Is the same as the position passing through the subject 50. This is the same for other ring combinations. Therefore, as shown in FIG. 6, the matrix collected at P2 can be added to the matrix collected at P1 while being shifted by one in the vertical and horizontal directions.

In general terms, the coincidence data between the rings i and k at a certain position Pj and the coincidence data between the rings i + 1 and k + 1 at a position Pj + 1 after the same are the same as those of the subject 50. , And can be added. Therefore, as shown in FIG. 6, data obtained each time the position is moved is sequentially added while shifting the matrix, and this is repeated for the m position. Thus, assuming that the number of rings is n (n is 5 in the above), (2n−1) × (m−
1) + n × n sinogram data can be collected.

This is a ring-type detector 1 having (m-1) + n number of rings covering the entire travel of (m-1) .times.d.
Assuming that 1 is provided, this is the same as the data collected when the range of simultaneous counting is limited to only n rings. Then, the sensitivity distribution in the body axis direction becomes a trapezoid flat in the body axis direction as shown in FIG. 7, and the sensitivity becomes uniform except for both ends. This can be seen from FIG. That is, in FIG. 3, there is only one line connecting the rings 1 and 1 (this alone has low sensitivity), but after two positions, that part of the subject 50 is on the line connecting the rings 3 and 3. In this case, five lines pass, and these are added (the image is reconstructed after the addition), so that the sensitivity is the same everywhere. On the other hand, if an image is reconstructed using only data collected at a certain position as in the related art, an image having a sensitivity distribution as shown in FIG. 5 can be obtained for each position. Thus, a non-uniform sensitivity distribution in which a peak appears at each position is obtained. If the position interval is narrowed and the width of the overlap is widened, the sensitivity approaches uniformity, but the data collected by the overlap and overlap is wasted, the collection time is wasted, and the memory use efficiency is reduced.

The addition of such data with the matrix positions shifted is performed in the data collection memory 32 based on the movement information from the bed moving device 21. On the other hand,
The detection signal from the transmission data ring-type detector 13 is input to the coincidence counting data collection device 33, where the coincidence is counted, and the data is collected in the data collection memory 34. This data is transmission data for a slice 52 in the subject 50 on the plane where the ring-type detector 13 is located. This ring type detector 13
However, since the transmission data is first collected since the multi-ring type detector 12 for collecting the emission data is closer to the insertion side of the subject 50, the position is moved and the collection of the emission data is stopped. Done.
That is, when the emission data of a certain volume is being collected, the transmission data for that volume has already been collected in the data collection memory 34. The absorption correction data for the line can be calculated, and the absorption correction data can be stored in the table memory 36 as an absorption correction table. That is, the transmission data for the slice 52 stored in the memory 34 is read out, and the image is reconstructed to obtain an absorption coefficient map (absorption coefficient distribution image) for the slice 52. By performing this for a large number of slices based on the position information from the bed moving device 21, an absorption coefficient map (a three-dimensional distribution image of the absorption coefficient) in the volume is obtained, and the three-dimensional image is forward-projected. , Obtain absorption correction data for all coincidence lines at that volume. Thus, the absorption correction data for all coincidence lines in the volume can be sequentially stored in the table memory 36 as an absorption correction table.

As a result, the addition of the data whose positions of the matrices are shifted as described above is performed in the data collection memory 32. For the matrix for which the addition has been completed, the corresponding absorption correction table is read out from the memory 36, and all the simultaneous correction tables are read out. The processor 35 can perform emission data absorption correction for the counting line. Such absorption correction is sequentially performed in real time for each matrix for which addition has been completed. The processor 35 performs a three-dimensional image reconstruction operation from the corrected emission data, that is, the sinogram data of the entire matrix, so that the volume in the body axis direction is larger than the whole body axis direction view width D of the multi-ring detector 12. 3D positron CT images can be reconstructed.

In this example, the multi-ring type detector and the transmission data ring type detector located in front of the multi-ring type detector are connected. However, one emission data ring type detector and the transmission data ring type detector are combined. It may be combined with a detector, or it may be said that only a configuration in which data is collected by adding a matrix shifted as described above using a multi-ring detector, and a transmission data ring detector is not used. Configurations are also possible. In addition, the specific configuration and the like can be variously changed without departing from the spirit of the present invention.

[0027]

As described above, according to the positron CT apparatus of the present invention, transmission data can be collected in a short time at a high counting rate using a strong external radiation source for transmission data collection. , Real-time absorption correction can be performed. 3D positron CT using a multi-ring detector
When imaging is performed while moving the detector with respect to the subject in a field of view larger than the field of view in the body axis direction of the detector, the sensitivity can be improved so as to eliminate unevenness in the body axis direction.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an embodiment of the present invention.

FIG. 2 is an exemplary block diagram showing a signal system of the embodiment;

FIG. 3 is an explanatory diagram illustrating a positional relationship between a moving subject and a multi-ring detector.

FIG. 4 is a diagram showing a matrix for collecting sinograms at one position.

FIG. 5 is a graph showing a sensitivity distribution in the body axis direction of data collected at one position.

FIG. 6 is an explanatory diagram for explaining that data collected at each of multiple positions is added if a matrix is shifted.

FIG. 7 is a graph showing a sensitivity distribution in the body axis direction of data collected by adding a matrix if it is shifted.

FIG. 8 is a graph showing a sensitivity distribution in the body axis direction when an image is reconstructed using data collected for each position in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Gantry 11 Ring type detector 12 Multi ring type detector 13 Ring type detector for transmission data 14 Ring type external radiation source 15 Slice septa 20 Bed 21 Bed moving device 31 Simultaneous counting data collection device for emission 32 Data collection memory for emission 33 Transmission coincidence counting data collection device 34 Transmission data collection memory 35 Processor 36 Table memory 50 Subject 51 Body axis 52 Slice

Claims (2)

[Claims] 1. A first ring-shaped detector for collecting emission data of a subject, a second detector for collecting transmission data of a subject, and a plane arranged with the second detector. And moving the subject relative to the first and second detectors such that the subject moves from the second detector side to the first detector side. While the mobile device and the volume of the subject whose transmission data has been collected have been moved and the emission data has been collected for that volume, the transmission data is processed to determine the absorption correction data on the coincidence line. A positron CT apparatus comprising: a data processing device that performs absorption correction immediately after the collection of emission data for the volume is completed. 2. A multi-ring detector in which ring-type detectors are stacked in layers in the axial direction, and an object is positioned relative to the multi-ring detector at intervals of each ring of the multi-ring detector. And the coincidence data between the rings obtained at each position of the movement, the coincidence data between the rings at the position of the immediately preceding movement, and the data between the rings adjacent to the former. And a data collection device for collecting data while adding.