JPH0240586A - Scanning method of positron ct - Google Patents

Abstract

PURPOSE:To expand a detection width of multilayer detector rings in the layer direction as required by shifting the multilayer detector rings in the layer direction until the whole of the necessary detection width can be covered in the layer direction. CONSTITUTION:In the case when detector rings 1 to 4 of four layers are provided and a gap between the adjacent ones of the detector rings 1 to 4 in the layer direction Z is D, the detector rings 1 to 4 are disposed at positions in the direction Z indicated by a solid line and the collection of data in slices positioned at Z1 to Z7 is executed by a scan on the occasion. When the detector rings 1 to 4 are shifted by D/4 as a whole in the direction Z, subsequently, the collection of data in seven slices at positions shifted by D/4 from Z1 to Z7 respectively can be executed. Data in slices at Z2 to Z8 are collected by making a shift further by D/4, and data in slices at positions shifted by D/4 from Z2 to Z8 are collected by making a shift by D/4 again. By this method, a detection width in the direction Z can be expanded to 3X3/4D.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a scanning method in the slice thickness direction in positron CT (emission-type computer tomography using positron-emitting nuclides).

[Conventional technology]

To perform positron CT, a detector link in which detectors for detecting radiation are arranged in a ring shape is required. Such a detector ring is placed around a subject to whom a positron-emitting nuclide has been administered, detects simultaneous incidence of radiation on two detectors in the detector ring, and records this coincidence data. By collecting and processing by computer, a concentration distribution image of positron-emitting nuclides is created.
It is an outline of positive 1-ron CT. Typically, such detector rings are arranged in multiple layers, allowing data to be collected on multiple slices at a time. For example, in a detector ring having four layers 1 to 4 as shown in Fig. 3, the layer direction (
When the slice thickness direction) is the Z direction, the detector ring 1
The coincidence data for ~4 is in two directions (17) Zl, Z3.
Z5. Data can be collected for the four slices located at Z7, or data can also be collected for slices located in between by collecting coincidence data between adjacent detector rings (for example, detector rings 1... 2
Data at the slice at position Z2 can be collected by coincidence data between Therefore, in a device having such four-layer detector rings 1 to 4, Zl, Z2 .・
..., data can be collected for seven slices located at Zl. The interval between these slices (the interval in the slice thickness direction, that is, the interval in the Z direction) is D/2, where D is the interval between detector rings, and the entire detection width in the Z direction is 3D. becomes. For example, when photographing the head of the subject 5 as shown in Fig. 4, within the entire detection width 3D in the slice thickness direction, 7
A tomographic image of two slices is obtained.

[Problem to be solved by the invention]

However, as shown in FIG. 4, if the entire detection width in the slice thickness direction does not cover the entire subject, there is a risk that lesions at the edges of the subject may be overlooked. In addition, especially when creating sagittal images or coronal images from a large number of transverse images (tomographic images in slices perpendicular to the Z direction),
As shown by the dotted lines in FIG. 5 (sagittal image) and FIG. 6 (coronal image), the edges are missing, resulting in a large loss of information and a poor appearance of the image. Interpolation scanning may be performed by shifting the multilayer detector ring in the layer direction by an integer fraction of the detector ring spacing in the layer direction, but even in this case, the total detection width in the layer direction does not change much. , the above problem remains. Of course, the total detection width in the layer direction (in the above example, 3D
) If the multilayer detector ring as a whole is shifted in the layer direction and scanned, there will be no missing information, but
In this case, unnecessary positions where no object is present will also be scanned, resulting in a large loss of time and the like. An object of the present invention is to provide a positron CT scanning method that can enlarge the detection width in the layer direction (slice thickness direction) of a multilayer detector ring as necessary.

[Means to solve the problem]

In order to achieve the above object, according to the present invention, a multilayer detector ring is scanned by shifting it in the layer direction by a width that is an integer fraction of the layer direction spacing, within a range where the data collection slices do not overlap. In the positron CT scanning method, the multilayer detector ring is further shifted in the layer direction until the data acquisition slices overlap, and the width described above covers the entire required detection width in the layer direction. The feature is that it can be scanned using

[For production]

A so-called interpolation scan can be performed by scanning a multilayer detector ring by shifting it in the layer direction by a width that is an integer fraction of the layer spacing within a range where the data collection slices do not overlap. This interpolation scan cannot expand the total detection width in the layer direction by the multilayer detector ring. On the other hand, if the multilayer detector ring is scanned by shifting it in the layer direction by the above width even if the data collection slices overlap, the total detection width in the layer direction by the multilayer detector ring can be reduced. It can be expanded to cover the entire required detection width in the layer direction.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, as shown in FIG. 1, there are four layers of detector rings 1 to 4, and the distance between each detector ring in the layer direction (slice thickness direction, Z direction) is D. It was applied to As shown in FIG. 1(A), the detector rings 1 to 4 are placed at the positions indicated by the solid lines (positions in two directions), and during the scan at this time, as shown in FIG. Z3. Z4. Z5. Z6. , Zl, data collection is performed for seven slices located at Zl. Next, as shown by the dotted line in Figure 1 (a), detect the detector rings 1 to 4.
If the whole is shifted by D/4 in the Z direction, the same figure (c)
Like Zl, Z2. ...Data can be collected in seven slices, each located at a position shifted by D/4 from z7. This is conventionally called an interpolation scan,
If the data collection position is further shifted by D/4, the data collection positions overlap, so in the conventional scanning method, the interpolation scan is limited to this, but in this invention, the data collection position is further shifted by D/4 many times to collect data. I try to do that. In other words, in the embodiment shown in FIG.
Z2. Z3. Z
4. ..., data is collected for the slice at the Z8 position, shifted again by D/4, and then the Z
2. Z3゜Z4. ..., data is being collected for the slice at a position shifted by D/4 from Z8. As a result, the detection width in two directions is expanded from 3+D when performing conventional interpolation scanning to 3+D. However, depending on the slice, data may be collected twice, and the sensitivity is twice as high in the center as in the edges, as shown in the figure (see the figure), so the data is collected in the highly sensitive part. need to be multiplied by ten. In addition, high sensitivity in the central region means that the S/N ratio is high in the central region, which is preferable considering that the most necessary parts are usually located in this central region. be. In the embodiment shown in FIG. 2, the detection width in the Z direction is further expanded to 4-)D. That is, in the embodiment shown in FIG. 2, the detector rings 1 to 1 shown by solid lines in the first FIG.
(It was shifted 5 times by D/4 from the position of 4, but in the example of Fig. 1, it was shifted 3 times), respectively (B), (C), (D), (E), (He), ( We are collecting data regarding the slice at the position shown in (g). In this case, the sensitivity is in three stages as shown in the same figure (H), and the center part is high, so it is necessary to make the data uniform by setting it as + or old. Although the data collection slice interval D/2 is shifted by 10, that is, half of the data collection slice interval D/2, it is also possible to shift it by another integer fraction, such as D/6. Although not explained, the movement of the multilayer detector ring in the layer direction as a whole can be caused by movement of the bed on which the patient is lying or by movement of the gantry in which the multilayer detector ring is housed relative to the bed. ,
Or a combination of both may be used. [Effect of the invention] According to the positive 1 to long CT scanning method of this invention,
Even if the overall detection width of the multilayer detector ring in the layer direction is narrow, the width can be substantially expanded, making it possible to obtain a sagittal image or a coronal image without chipping. Furthermore, since the sensitivity of the data of the slice located in the center among the data of a large number of slices is increased, the 87/N ratio of the most needed region can be increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a method according to an embodiment of the present invention, in which (a) shows the position of the detector ring, (b), (c), (d), ( E) is a diagram showing the position of the data collection slice, FIG. 2 is a diagram showing the sensitivity distribution in the Z direction, and FIG. (a) is a diagram showing the position of the detector ring, (b), (c), (d), (e), (f) in the same diagram
, (1) is a diagram showing the position of the data collection slice, (H) is a diagram showing the sensitivity distribution in the Z direction, FIG. 3 is a diagram showing the data collection slice position relative to the position of the detector ring, and FIG. The figure shows a case where positron CT of the head is performed, FIG. 5 shows a sagittal image of the head, and FIG. 6 shows a coronal image of the head. 1 to 4...detector ring, 5...subject.

Claims (1)

[Claims] (1) In a positron CT scanning method in which a multilayer detector ring is scanned by shifting it in the layer direction by an integer width of an integer of the layer direction spacing, within a range where the data collection slices do not overlap, the above multilayer Positron CT characterized in that the detector ring is scanned by shifting the detector ring in the layer direction until the required overall detection width in the layer direction can be covered by the above-mentioned width even if the data collection slices overlap. How to scan.