JPS62277943A - Ct apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention improves the spatial resolution of reconstructed images even when a relatively large radiation detector is used. Regarding CT equipment.

[Prior art]

Conventional CT devices include, for example, Iwai W rCT Scanner, Electronics Engineering Advance Series 9 (February 1978) pp. 1
As described in 2003, narrow detectors are made to have multiple channels in order to improve the spatial resolution of reconstructed images and to shorten inspection time. The reason for narrowing the width of the detector is that 58 the distance between the source and the object is Q, the distance between the source and the detector is D, the width per channel of the detector is W,
Assuming that the size and focus of the radiation source are sufficiently smaller than W, the spatial resolution of the reconstructed image will be W-Q/D.

Since Q and D are constants determined by the geometrical arrangement of the CT scanner, it is necessary to reduce the detector width W in order to improve the spatial resolution6.Therefore, the X-rays used in the In CT apparatuses that use high energy (200 keV or less) or higher as MAg, the solid scintillator itself is miniaturized, as described in Japanese Patent Application No. 76155/1983, for example.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into account the deterioration in radiation detection efficiency that accompanies the miniaturization of solid-state scintillators, and has the problem that detection efficiency is sacrificed in exchange for improving spatial resolution. Figure 6 shows an example of defining the detection efficiency (probability of photoelectric effect occurring within the scintillator for incident γ-rays) when 7Cs γ-rays (662 keV) are irradiated using bismuth germanate (Bi4Gs80tz) as a solid scintillator. When the detector width becomes less than 10 IIn, the efficiency deteriorates rapidly, and when the width becomes less than 3 ms, the photoelectric peak itself is hidden by scattered radiation (mainly Compton scattering), making it impossible to define the efficiency itself.

An object of the present invention is to realize a CT apparatus that uses a large-sized detector that does not cause deterioration in detection efficiency and improves spatial resolution in order to eliminate deterioration in detection efficiency due to downsizing of the detector. 6 [Means for solving the problem] For this purpose, the present invention uses a relatively large radiation detector, a narrow collimator installed in front of the detector, and a scanning collimator or the detector itself. By doing so, it is intended to obtain the same effect as that obtained by arranging narrow detectors whose width is equivalently determined by the collimator width. In addition to the above-described means, this effect can be achieved by using the detector, collimator, and object scanning, or by a collimator placed immediately after the radiation source and a mechanism for scanning the same.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to examples.

FIG. 7 is a diagram showing a CT scan situation to which the present invention is applied. This method is called Rotito Rotito (
It is a R-R) type scan and is composed of a wide-angle (fan beam) radiation l1A72 that looks at the line g74 and the entire subject 71, and a multi-channel detector 73 that receives this radiation. Line g74 is a source that emits high-energy radiation, for example, γ
It is a line.

Low-energy X-rays are not targeted. High-energy X-rays are targeted. In scanning, the radiation source 74 and the detector 73 are simultaneously rotated at predetermined pitch intervals, and at each pitch position, they are stopped facing each other, radiation is emitted from the radiation source 72, and transmitted radiation from the subject 71 is detected. is detected by the multi-channel detector 73. The detected values of the multi-channel detector 73 obtained for each pitch position are taken into a computer as data, and the computer reconstructs the data to obtain both CT images.

In addition to RR, there are also examples in which only the subject is rotated.

γ-ray CT equipment deals with high-energy radiation.

However, in order to increase the spatial resolution, the width of the detector including the scintillator must be narrowed.

If the width of the detector is narrowed, the detection efficiency will deteriorate and it will not be put to practical use. This embodiment can address these drawbacks.

FIG. 1 is a diagram illustrating the first embodiment of the present invention, showing only a part of the object and the detector. The structural requirements of this embodiment are: a solid scintillator made of bismuth germanate, etc.
0 and a photoelectric conversion element 11 (which receives scintillation light)
In the following explanation, a case will be described in which a photomultiplier tube is used) and a collimator 12 and a means for scanning the collimator in an arc shape with the radiation source as the center 6, that is, the radiation 1
4 (lead if the radiation is X-rays, γ
In the case of a wire or an accelerator wire, a collimator is made of lead, tungsten, or a tungsten alloy, etc.) and installed in the radiation incident direction of the fixed scintillator 10.6 When creating multiple channels, a rectangular shape as shown in Figure 1 is used. The collimator materials 12 which are cut are continuously arranged with an interval W between them.

As a result, slits having a width W (for example, W=1 mm) can be formed continuously. Furthermore, it is desirable that the coupling surface 15 between the collimator 12 and the photomultiplier tube 11 (width d is, for example, about 10 mm) be in close contact with each other, but in this embodiment, it is necessary to scan the collimator 12 as will be described later. For this reason, the bonding surfaces 15 are spaced apart by about 0.1 to 0.5 mm. If this interval is increased, crosstalk from adjacent channels will become a problem, so it is better to make it as small as possible without interfering with the driving of the collimator 12.Scintillator 1
Comrade 0 also uses a piece of opaque heavy metal such as lead or tungsten to shield scintillation light from adjacent channels and minimize the effects of scattering (mainly Compton scattering).
6 is inserted. The scintillator 10 used is one with a width of 10 m to 20 mm, which does not deteriorate the detection efficiency from the results shown in FIG. The scintillator 10 and the photomultiplier tube 11 are joined and integrated with an optical adhesive (grease, etc.).

Now, in this embodiment, the collimator 12 is scanned, but
To describe when the collimator 12 is not scanning, from FIG. 1, the width of the slit is W.

Assuming that the pitch between the collimators is p, the detector arrangement viewed from the sg side looks as if detectors with a width W are arranged at a distance p. However, since the collimator does not allow radiation to pass through to areas other than the slit 17, the detectors are arranged discretely.

As a data collection method for the CT method, it is possible to collect the most transmission data when detectors with a width W are closely connected, so the detectors are arranged discretely as shown above. In this case, there will be a shortage of (P/W)-1 pieces of transparent data. In the CT method, this insufficient collection of data appears as noise in reconstructed images (tomograms), causing blurring of a single image, deterioration of spatial resolution, or, in some cases, artifacts (pseudo images). . For example p = 20 m.

When W = 2 on, the number of missing data reaches 9.

Therefore, the present invention attempts to compensate for this insufficient transmission data by scanning the collimator 12 in an arc. That is, the collimator 12 is scanned in the direction of the arrow 13 centering on the radiation source.

This scanning is carried out through the slit 17 at the front face 18 of the collimator.
It may be moved discretely by the width W of , or it may be moved continuously.

One method for realizing the above scanning will be explained based on the structural diagram of FIG. 2. A pedestal 21 with a radius R centered on the radiation source is fixed to a CT scanner main body 22, and collimator groups 23 successively arranged at a pitch p are mounted on this pedestal 21 with sliding surfaces 24 in between.

The sliding surface 24 may be a thrust bearing, or may be a flat surface coated with oil or the like to reduce the coefficient of friction. The collimator group 23 is driven by a scanning motor 25,
For example, as shown in the figure, this structure includes a ball screw 26 and a connector 2.
7 can be used. Also,
Since the collimator group 23 must be accurately scanned on an arc having a radius R, for example, the collimator group 23 is scanned by a distance corresponding to the maximum detector pitch p while pressing the pedestal 21 with a cam follower 8 or the like fixed to the collimator group 23.

As explained above, according to the present embodiment, for example, if the collimator group 23 is scanned stepwise by W at a distance on the arc in front of the collimator, p/W pieces of data are collected. In other words, this is the same as when detectors having a detector width W are closely arranged, and a reconstructed image with less noise and high spatial resolution can be obtained. moreover,
Since it is also possible to scan with a step width of W or less, the number of transmission data increases even more than when detectors of 1 width W are closely arranged, making it possible to obtain a good reconstructed image with less noise. becomes.

FIG. 3 is a diagram showing a second embodiment of the present invention.

The difference between this embodiment and the first embodiment described above is that in the first embodiment (FIG. 1) only the collimator 12 is scanned on an arc with the radiation source as the center;
2, a scintillator 10, and a photomultiplier tube 11 are integrated to perform arcuate scanning 13. Therefore, unlike the first embodiment, there is no need to provide a gap between the coupling surfaces 31 of the collimator 12 and the scintillator 10 for sliding, and this makes them less susceptible to crosstalk from adjacent channels. Therefore, in this embodiment, the collimator 12 and scintillator 10 are semi-permanently bonded using an epoxy resin adhesive. The scanning driving method is as shown in FIG. scintillator 10
．． The photomultiplier tube 11 may be used instead.

As described above, this embodiment is superior to the first embodiment in reducing crosstalk from adjacent channels. However, on the other hand, since the photomultiplier tube is also scanned, there are drawbacks such as increased noise due to winding of cables from the photomultiplier tube 11 and mechanical vibration of the electric j@ (dynode) inside the photomultiplier tube. There is also.

FIG. 4 is a diagram showing a third embodiment of the present invention.

The difference from the first embodiment (FIG. 1) and the second embodiment (FIG. 2) is that both include the collimator 12 or the collimator 12. Scintillator 10. While the components on the detector side such as the photomultiplier Igll were scanned in an arc shape, these components remained fixed and the object 71 was scanned in IIA@4.
According to this embodiment, the drawbacks mentioned in the first and second embodiments can be solved by performing an arc scan 13 with the object 71 as the center. 13, it cannot be used for a fixed subject 71. Furthermore, it cannot be used for a fixed subject 71.
In a type of CT equipment in which 1 itself is rotated and scanned, 1
Since the subject is placed on a rotary table, if the subject 71 is heavy, it will be disadvantageous in terms of the scanning accuracy of the 5-arc scan.

FIG. 5 is a diagram showing a fourth embodiment of the present invention.

The difference from the other embodiments is that the collimator 12 is not placed in front of the scintillator 10, and instead, a slit shielding material 50 is placed between the radiation source 40 and the subject 71, and this is centered around the radiation source. The point is that the lining is scanned. At this time, the subject 71 shown in Examples 1 to 3. Collimator 21. Collimator 21 and scintillator 10. The photomultiplier tube 11 does not need to perform arcuate scanning, that is, all these relationships are relative. All the slits 51 are processed so as to face the radiation source S40. A radiation beam 52 (
For example, it is necessary to perform scanning so that the radiation beam (for example, the radiation beam shown in the figure) is incident on a certain scintillator (for example, the scintillator 53 shown in the figure) and never to be incident on other scintillators. Rather, this is common to other embodiments.

The problems of this embodiment are that the machining accuracy of the slit shielding material 50 must be higher than that of the collimator of Embodiments 1 and 2, and that the scanning accuracy of the circular arc scan must be increased. be. The reason for this is that the beam width of the radiation 52 is narrower closer to the line gS. For example, the distance between the line [S40 and the slit shielding material 50 is d]
,! [If the distance between S40 and the scintillator 10 is D, the slit shielding material 50 corresponding to the detector width of width W]
The slit width is W. (d/D). Therefore, when d/D is 1/10, the slit width is 1/1 of W.
It needs to be 1o. The same thing can be said about the manufacturing accuracy of the slit width. For example, Examples 1 and 2.
If the manufacturing accuracy of the collimator is about 100 μm,
In order to obtain the same effect in this embodiment, the slit shielding material must be manufactured with a thickness of 10 μm, and the same applies to the scanning accuracy of circular arc scanning.3 However, the advantage of this embodiment is that the slit shielding material must be manufactured with a thickness of 10 μm. This means that the arcuate scanning range of 5° can be made d/D times shorter than in Example 1.2, which is advantageous for manufacturing a CT scanner.

The contents of the present invention have been explained in detail in the embodiments in Section 4 above. In any of the embodiments, according to the present invention, it is possible to use a relatively large scintillator with a width of 10 to 20 nm without deteriorating the detection efficiency as shown in FIG. 6, and radiation measurement with a good S/N ratio is possible. can. moreover,
In order to scan a collimator, a scintillator, a photomultiplier tube, a subject or a slit-covering material provided between a radiation source and a subject in an arc shape with the radiation source as the center, a collimator or a slit-covering material is used. The shunted radiation beam can be measured. As a result, it is possible to obtain an effect similar to that obtained by arranging equivalently narrow detectors closely, and it is possible to dramatically improve the spatial resolution of images reconstructed by CT method using radiation.

It should be noted that with conventional scintillators, it was impossible to realize a detector of 3 m or less as shown in Figure 6, but according to the present invention, the collimator width or slit width can be arbitrarily selected (possible to be 3 nvo or less) and manufactured. 0.
5 un~1! It becomes easy to manufacture the ff11 detector. According to the invention, therefore, C
The spatial resolution of reconstructed images using the T method can be dramatically improved compared to conventional ones.

〔Effect of the invention〕

According to the present invention, spatial resolution could be improved.

[Brief explanation of the drawing]

FIG. 1 shows the first embodiment of the present invention, FIG. 2 shows the movement mechanism for moving the collimator, FIG. 7 shows the detection efficiency of bismuth germanate, and FIG. 7 shows the first embodiment of the present invention. FIG. 2 is a diagram illustrating a CT scanning method to be applied.

Claims (1)

[Scope of Claims] 1. A radiation source, a multi-channel radiation detector placed in a position facing the radiation source with the subject in between, and a circle between the radiation detector and the subject. collimators arranged at intervals of a predetermined pitch width in the circumferential direction, and the collimator (or the collimator and the radiation detector) and the radiation source are configured to scan relative to each other in an arc shape. CT device. 2. A radiation source, a multi-channel radiation detector placed in a position facing the radiation source while sandwiching the subject, and a slit-shaped thin body provided between the radiation source and the subject. What is claimed is: 1. A CT apparatus comprising: a CT apparatus configured to scan a human body in an arc with a radiation source at the center;