JPH08313636A - Position ct apparatus - Google Patents

Abstract

PURPOSE: To make the sensitivity distribution in a body axis direction when a whole-body scanning is conducted by using a multilayer detector ring. CONSTITUTION: A bed 21 is controlled by a controller 34. Its top plate 22 is stepwisely moved at each shorter distance D than the laminar direction visual field width W of a multilayer detector ring 13 to scan the whole-body of a patient 20. Simultaneous counted data captured by a simultaneous counter 31 at each stationary position is acquired by a data acquisition memory 32, and an image is reconstructed by an image reconstructing unit 33 without using the data of the overlapped ends of the visual field width at each position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positron CT apparatus, and more particularly to a positron CT apparatus for moving a multi-layer detector ring with respect to a subject and imaging an area of a field width of the multi-layer detector ring or more.

[0002]

2. Description of the Related Art A positron CT apparatus uses a positron-emitting radionuclide and detects annihilation gamma rays to take a distribution image of the nuclide. For example, when a drug labeled with a positron-emitting radionuclide is administered to the human body, it accumulates in a specific organ. At that time, gamma rays emitted to the outside of the human body are detected by a detector placed outside the human body, data is collected, and the data is processed by a predetermined algorithm to determine the nuclide concentration distribution in a predetermined cross section. Reconstruct the statue. This reconstructed image is used for diagnosis of a specific organ.

A scintillation detector or the like is used as a detector for detecting gamma rays outside the subject, which is arranged in a multi-ring type. Of the gamma rays from the nuclides located on the array plane of this detector ring, those emitted parallel to the above plane enter the one of the ring array detectors and are detected. Data on this plane (slice plane) of the specimen will be collected, and the reconstructed image will be a concentration distribution image of nuclides on this slice plane. Usually, this detector ring is formed in a plurality of layers so that data acquisition and image reconstruction can be performed not only on one slice plane but also on a plurality of slice planes stacked in a certain range.

The data acquisition range in the direction (layer direction) perpendicular to the slice plane in this multilayer detector ring is called the visual field width. If this visual field width is moved with respect to the subject (multilayer detector). By moving the ring or the subject), it is possible to collect data in a wider range than the visual field width. Thus, for example, by moving the detector ring from the head of the human body to the feet, it is possible to perform data acquisition and image reconstruction of the whole body, so-called whole body scanning.

In the case of collecting data over a wide field of view such as a whole-body scan using such a multi-layer detector ring, conventionally, the object is moved for each field of view and then stopped, and Simultaneous counting data is collected during the stationary period. A tomographic image in each slice is reconstructed using the data collected in this way, and this is arranged in the slice thickness direction (layer direction) to obtain a three-dimensional image in the layer direction in a wider range than the visual field width. Alternatively, it is also possible to reconstruct layerwise images such as sagittal images and coronal images directly from the collected data.

[0006]

However, when performing a whole-body scan or the like by stepwise moving while matching the moving distance of the subject with the width of the field of view of the multi-layer detector ring as in the conventional case, the There is a problem that an artifact such as a striped pattern that is discontinuous in the layer direction occurs in the constituent image.

This is because the sensitivity distribution of the multilayer detector ring is not uniform in the layer direction. In fact, the sensitivity distribution in the layer direction of the multi-layer detector ring is as shown in FIGS. In FIG. 3, a ring-shaped collimator 14 is arranged in front of (inside) the multi-layer detector ring 13 to perform collimation between the layers, and only the radiation within the layer enters the detector ring of each layer of the multi-layer detector ring 13. Thus, two-dimensional data collection is performed by the detector ring of each layer. In this case, the sensitivity distribution in the layer direction is as shown by the polygonal line 15 within the field width W in the layer direction, and the sensitivity at the central portion is almost constant, but the sensitivity gradually decreases at the end portions.

Such a so-called two-dimensional data collection type has been used for a long time, but recently,
A collimator 14 for collimating each layer as shown in FIG.
It is also practiced to detect all of the radiation that is incident obliquely across the layers, without using. In this case, since the coincidence count data also includes position information in the layer direction,
It is called three-dimensional data collection. Here, the sensitivity distribution in the layer direction within the layer-direction visual field width W is as shown by a polygonal line 16, which is highest in the central portion in the layer direction and decreases toward the edges, and the difference is about 10 times.

As described above, since the sensitivity distribution of the multi-layer detector ring is nonuniform in the layer direction and becomes lower toward the edge in the layer direction, the statistical noise of the collected data becomes large in the low sensitivity portion. Therefore, when a sagittal image or a coronal image that is continuous in the layer direction is reconstructed, a portion with a small amount of statistical noise and a portion with a large amount of statistical noise appear in the layer direction, which causes a striped pattern and deteriorates the image quality.

In view of the above, the present invention does not cause a stripe pattern or other artifact in a reconstructed image when collecting data in a wide range of the field width of the multi-layer detector ring such as a whole-body scan. It is an object of the present invention to provide a positron CT device improved as described above.

[0011]

To achieve the above object, in a positron CT apparatus according to the present invention, a multi-layer detector ring in which detector rings in which radiation detectors are arranged in a ring shape are laminated in multiple layers, The subject is inserted into the hollow portion of the multi-layer detector ring, and the subject is moved relative to the multi-layer detector ring in steps at predetermined distances smaller than the width of the multi-layer detector ring in the layer direction. It is characterized in that a moving device and an image reconstructing device for carrying out an image reconstructing process using the coincidence counting data collected during the stationary period of the stepwise movement are provided.

[0012]

The object is moved stepwise with respect to the multilayer detector ring at a predetermined distance smaller than the width of the multilayer detector ring in the layer direction. Then, data is collected during the stationary period of the stepwise movement. Therefore, the coincidence count data is collected so that the field width of the multilayer detector ring in the layer direction partially overlaps near the end. Data is not lost in the layer direction without using the data of the overlapped portion. This overlapped portion corresponds to the edge of the width of the field of view of the multi-layer detector ring and has a low sensitivity,
If this is not used, it means that the image can be reconstructed without using the data whose sensitivity is lowered, and the artifact of the reconstructed image can be reduced. Even if the data of the overlapping portions are added together to increase the data amount of the portions, it is possible to compensate for the decrease in sensitivity in the vicinity of the end of the field width of the multilayer detector ring in the layer direction.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, a gantry 11 is provided with a tunnel portion 12, and a multi-layer detector ring 13 is arranged so as to surround the tunnel portion 12. A bed 21 is arranged beside the gantry 11, and a top plate 22 thereof is inserted into the tunnel portion 12 of the gantry 11. The bed top plate 22 is configured to move in a direction that penetrates the tunnel portion 12, and the subject 20 is laid on the bed top plate 22.

The signals from the respective detectors of the multi-layer detector ring 13 are input to the coincidence counting circuit 31, and it is detected that these two signals are simultaneously incident, and for each set of detectors that have simultaneously emitted signals. A count is made in the data collection memory 32. The bed 21 is controlled by the controller 34 to move the top plate 22. Information regarding the position of the top plate 22 is also stored in the data collection memory 32.
The image reconstruction device 33 performs image reconstruction using the data collected in the data collection memory 32.

A so-called whole body scan is usually performed by moving the bed top plate 22 from the maximum position as shown in FIG. 1 and moving it in the pulling direction as shown by the arrow. At that time, a stepwise movement is performed, and the movement amount D of one step is shorter than the layer-direction visual field width W of the multilayer detector ring 13. Then, at each position, as shown in (a), (b), (c), and (d) of FIG. 2, data is collected on the region of the range W in the layer direction, that is, the body axis direction of the subject 20. However, the range W overlaps at the end.

Therefore, when reconstructing an image using the collected data at these four positions, the data in the overlapping range is not used. Then, the data of the low sensitivity portion at both ends of the layer-direction visual field width W is not used, and only the data of the central high sensitivity portion is used. Therefore, the sensitivity distribution in the body axis direction of the subject 20 is as shown in (e) of FIG. 2, and there is no portion with extremely low sensitivity. As a result, when a sagittal image or a coronal image in the body axis direction is reconstructed, no striped pattern artifacts occur.

Alternatively, if the data of the overlapped portion is added and used without being discarded, the subject 20
The sensitivity distribution in the body axis direction is as shown in FIG. 2F, and the uniformity of the sensitivity distribution in the body axis direction is improved. In this case, it is desirable to perform weighted addition in consideration of the sensitivity of each position (each slice) in the layer direction within the field width W in the layer direction. As a result, theoretically, in the central portion except for both ends of the scan in the body axis direction, the sensitivities are almost the same, and images having almost the same S / N ratio can be obtained.

In the example of FIG. 2, so-called three-dimensional data collection is performed, but it is of course applicable to so-called two-dimensional data collection. The stepwise movement distance D can be arbitrarily set as long as a certain degree of overlap of the layer-direction visual field width W can be obtained. If it is applied at the time of collecting two-dimensional data, striped pattern artifacts may be removed only by setting the step moving distance D so as to overlap only one or two slices at the end and collecting the data. In the above description, the gantry 11 in which the multi-layer detector ring 13 is housed is fixed, the bed top plate 22 is moved, and the subject 20 is moved with respect to the multi-layer detector ring 13. Ring 13
Since the movement of the subject 20 with respect to may be relative,
It is needless to say that the subject 20 can be fixed and the gantry 11 side in which the multilayer detector ring 13 is housed can be moved.

[0019]

As described in the above embodiments, according to the positron CT apparatus of the present invention, a multi-layer detector ring is used, and a wide range of the multi-layer detector ring, such as a whole-body scan, which is equal to or larger than the layer-direction visual field width. S / S of data in the layer direction (scan direction) when collecting data in
It is possible to suppress the change of the N ratio and reduce the artifact of the reconstructed image due to the data of the low-sensitivity portion within the viewing width in the layer direction.

[Brief description of drawings]

FIG. 1 is a block diagram of a positron CT apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a sensitivity distribution at each position of a subject.

FIG. 3 is a diagram showing a layer-direction sensitivity distribution of a multi-layer detector ring when collecting two-dimensional data.

FIG. 4 is a diagram showing a layer-direction sensitivity distribution of a multi-layer detector ring when collecting three-dimensional data.

[Explanation of symbols]

 11 Gantry 12 Tunnel part 13 Multilayer detector ring 14 Collimator 20 Subject 21 Bed 22 Bed top 31 Simultaneous counting circuit 32 Data acquisition memory 33 Image reconstruction device 34 Control device

Claims (1)

[Claims] 1. A multilayer detector ring in which detector rings in which radiation detectors are arranged in a ring shape are laminated in multiple layers, and a subject is inserted into a hollow portion in the multilayer detector ring,
The object was collected relative to the multi-layer detector ring in a stepwise relative movement at a predetermined distance smaller than the layer-direction visual field width of the multi-layer detector ring, and collected during the stationary period of the step-like movement. A positron CT apparatus comprising: an image reconstructing device that performs image reconstructing processing using coincidence count data.