JPH0711569B2 - PET device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a PET apparatus, that is, an ECT apparatus (emission type computer tomography apparatus) using RI (radioisotope) of a positron-emitting nuclide.

[Prior art]

In a PET apparatus, a radiation-detector is arranged in a ring shape, and a subject to which RI of a positron-emitting nuclide has been administered is placed in the radiation detector, and radiation from the RI in the body of the subject is detected. When the positron disappears, two γ-rays are emitted in the 180 ° direction so that they are incident on the ring-shaped detector at the same time. Therefore, if this simultaneous counting is performed, it can be determined that RI exists on the line connecting the two incident positions. Thus RI
The RI distribution image (tomographic image) in one slice can be reconstructed by collecting the position information of the above and processing it by the image reconstruction algorithm by the computer. In a typical PET device, as shown in FIG. 4, a detector 1 arranged in a ring shape is stacked in multiple layers in the direction of the central axis, and each layer is separated by a septa (collimator) 2 to form a large number of layers. I try to shoot slices at the same time. In addition to performing coincidence between the detectors 1 in the same layer (for example, the first layer), the detector 1 is also spread over the other layers (for example, between the detector 1 of the first layer and the second layer). It is common to perform simultaneous counting in. In the former case, data on a slice perpendicular to the central axis (this is called a direct slice) as shown by a dotted line can be obtained, and in the latter case, 2
It is possible to obtain data on slices that are inclined with respect to the central axis (this is called cross slice) as shown by the dotted line, and it is possible to simultaneously shoot direct slices and cross slices located between them, and slices that can be simultaneously shot. This is because the number can be increased. In order to increase the number of slices that can be taken simultaneously,
Slice thickness of detector 1 (width in the central axis direction) as shown
It is also practiced to make D thin and to arrange it in multiple layers. In this case, since the sensitivity per slice is proportional to 1 / D ² , there is a problem in that the width D of the detector 1 becomes narrow and the sensitivity is extremely lowered. Therefore, as shown in FIG. 6, when it is desired to obtain an image of the slice indicated by arrow a, the collected data of the direct slice (dotted line) regarding the second layer includes the first layer and the third layer.
It has been considered to add cross-slice (dashed-dotted line) collection data for layers to increase sensitivity and image reconstruction. Further, in the case of obtaining the slice image of arrow B in FIG. 6, the sensitivity is obtained by adding the cross-slice acquisition data regarding the fifth and sixth layers and the cross-slice acquisition data regarding the fourth and seventh layers. To increase.

[Problems to be Solved by the Invention]

However, when using the data collected on the cross slice in this way, there is a problem that the response (resolution) in the slice thickness direction (center axis direction) deteriorates particularly in the peripheral portion of the visual field. That is, when the slice indicated by the arrow A in FIG. 6 is taken as an example, the cross slices relating to the first layer and the third layer are:
In the vicinity of the central axis, the slice thicknesses agree with each other, but the distances increase with distance from the central axis. Therefore, the second
The first slice and the third are added to the data of the direct slice regarding the layers.
The response in the slice thickness direction when the cross-slice data regarding layers is added is as shown by A to C, which is good near the central axis, but deviates from the central axis, and deteriorates toward the peripheral part of the visual field. It will be. It is an object of the present invention to provide a PET device improved so as to cover poor resolution in the slice thickness direction of data acquired regarding cross slices.

[Means for solving problems]

The PET apparatus according to the present invention is a radiation detection means arranged in a ring shape and arranged so that the ring-shaped arrangement is laminated in a plurality of layers, and means for performing simultaneous counting between the detection means in each layer described above. , Means for collecting data on direct slices from now on, means for performing coincidence counting between the detecting means across the above layers, means for collecting data on cross slices from now on, and data collected on cross slices, It comprises means for applying a weighting coefficient that becomes smaller as the distance from the central axis increases, and means for processing the collected data to reconstruct the image.

[Action]

The field performance in the slice thickness direction of the data collected for the cross slice becomes worse toward the periphery of the visual field, but the data is multiplied by a weighting coefficient that becomes smaller as the distance from the central axis increases. . as a result,
Data with good resolution in the slice thickness direction near the central axis is effectively used for image reconstruction, and conversely, data in the peripheral part of the visual field with poor resolution in the slice thickness direction has a low contribution to the reconstructed image. Therefore, the image reconstructed using the data processed in this manner is an image in which the resolution in the slice thickness direction in the peripheral portion of the visual field is not significantly reduced.

【Example】

In FIG. 1, detectors 1 arranged in a ring shape are laminated so as to overlap seven layers in the central axis direction. A subject (not shown) is inserted into this ring. RI is administered to this subject, and the radiation emitted from the RI in the body is collimated by the septa 2 and enters the detector 1 of each layer. In this embodiment, it is assumed that an image is obtained for each slice indicated by arrow a. The coincidence counting between the detectors 1 in the second layer is detected by the coincidence counting circuit 3, and the data of the second layer direct slice is collected in the data memory 5. Further, the coincidence counting circuit 4 detects the simultaneous incidence of radiation between the detectors 1 of the first layer and the third layer, and the data memory 6 collects the cross slice data regarding the first layer and the third layer.
Thus, the data of the direct slice and the cross slice are stored in the memories 5 and 6 in the form of a sinogram (projection data is arranged for each projection angle) as shown in FIGS. 2A and 3A, for example. . These data are read from the memories 5 and 6 and multiplied by the weighting factors in the multipliers 7 and 8, respectively. The weighting coefficient is stored in advance in the weighting coefficient memory 9 according to the distinction between the direct slice and the cross slice and according to what kind of cross slice.
It is stored in. In the case of the direct slice, the resolution in the slice thickness direction does not decrease toward the peripheral portion, and therefore the weighting factor is uniformly set to "1" in the diameter direction as shown in FIG. 2B. On the other hand, in the case of the cross slice, the resolution in the slice thickness direction is good in the central part, but becomes worse as it goes to the peripheral part. Therefore, depending on the degree, as shown in FIG. ], The function gradually becomes “0” as the distance from the center increases. The sharpness of the curve of the weighting coefficient increases as the inclination with respect to the central axis increases, as in the cross slice of the first layer and the fourth layer. The data multiplied by the weighting coefficient in this way is added by the adder 10
Is added by and sent to the image reconstruction arithmetic unit 11,
Arithmetic processing for image reconstruction is performed. Therefore,
When the image is reconstructed, data having a good response in the slice thickness direction is effectively used, and conversely, bad data is less frequently used. Therefore, the resulting image has increased sensitivity near the center of the visual field due to the addition of the cross slice data to the direct slice data, and prevents deterioration of the resolution in the slice thickness direction at the peripheral part of the visual field as much as possible. It will be what you did. In this embodiment, the present invention is applied to the case where the cross slice data of two layers adjacent to the layer is added to a certain type of direct slice data, but the cross slice data of two layers next to the layer is further added. Can be similarly applied to the case of adding, and also applicable to the case of adding a plurality of cross slice data as in the case of photographing a slice shown by an arrow B in FIG. Further, the curve of the weighting factor may be changed for each case of photographing. Further, such operations on the collected data can be performed by hardware or software.

【The invention's effect】

According to the PET device of the present invention, the resolution in the slice thickness direction of the data collected regarding the cross slice is improved so as to cover the decrease in the periphery of the visual field, and thus such cross slice data is converted to direct slice data. Even if the sensitivity is increased by adding it, the poor response in the slice thickness direction can be minimized.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2A and 2B.
Also, FIGS. 3A and 3B are for explaining the relationship between the collected data and the weighting factors to be applied to them, and FIGS.
Fig. A is a diagram showing collected data, Fig. 2B, Fig. 3B
Is a graph showing a weighting coefficient, FIGS. 4 and 5 are schematic diagrams of a conventional example, and FIG. 6 is a schematic diagram for pointing out a problem. 1 ... Detector, 2 ... Septa, 3, 4 ... Simultaneous counting circuit, 5, 6 ... Data memory, 7, 8 ... Multiplier, 9 ...
… Weight coefficient memory, 10 …… Adder, 11 …… Image reconstruction arithmetic unit.

Claims (1)

[Claims] 1. Radiation detection means arranged in a ring shape and arranged so that the ring-shaped arrangement is laminated in a plurality of layers,
Means for performing coincidence counting between the detection means in each of the above layers, means for collecting data regarding direct slices from this, means for performing coincidence counting between the detection means across the above layers, and a cross slice from this A PET consisting of a means for collecting data concerning the cross slice, a means for applying a weighting factor to the data collected for the cross slice that becomes smaller as the distance from the central axis increases, and a means for processing the collected data to reconstruct an image. apparatus.