JPS6146138B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses computerized tomography (CT), which obtains radiation projection data from multiple directions on the same tomographic plane of a subject and reconstructs a tomographic image of the subject based on the data. CT
(referred to as "device").

In a CT apparatus, a radiation source generates a radiation beam with a wide angle that is substantially fan-shaped and can cover a tomographic region of a subject, and a corresponding detector is provided, and the radiation source-detector is connected to the subject. On the other hand, the method that uses only rotation to obtain projection data from multiple directions (projection data) about the tomographic region is commonly referred to as the third generation.
It is called a CT device. An example of a general projection method used in such a CT apparatus is shown in FIG. 1st
In the figure, the imageable area is circle Q, and the center of circle Q is
Q ₀ , S is the subject enclosed in circle Q, B is the radiation source that generates a fan-shaped radiation beam (fan beam), α is the fan-shaped spread angle of the radiation beam, and D is the detector with one-dimensional position resolution. It is shown. Generally, the subject S is included in a circle Q indicating an imageable region, and this circle Q needs to be included in a radiation beam having a divergence angle α. When obtaining projection data, radiation source B and detector D face each other with circle Q in between, and both radiation source B and detector D are integrated on the circumference centered on point _Q0. and rotate. As a result, the detector D can obtain projection data regarding the subject S from multiple directions necessary for creating a tomographic image.

By the way, conventionally, the detector D has been constructed by arranging a plurality of radiation detection elements D ₁ , D ₂ , _. . .

However, in FIG. 2, for example, if the object is inside the circle _S1 , the point _P1 located at the center of the imaging area
The only sensing element that contributes to image reconstruction is the sensing element located at the central position D _a of the detector D. Furthermore, all the sensing elements included in the range D _b of the detector D are the sensing elements that contribute to the image reconstruction of any point on the diagram S ₂ , for example, the point P ₂ . The sensing elements that contribute to the image reconstruction of any point on the circle _S1 , for example, the point _P3 , are all the sensing elements included in the range _Dc of the detector D.

In addition, in Fig. 3, if the inside of the circle _S1 is the subject, the detection element located at the center position _Dd of the detector D reconstructs the image of all the parts inside the circle _S1 (the entire subject). Contribute to Further, the sensing element located at the illustrated position D _e of the detector D contributes to image reconstruction of the hatched area sandwiched between the circle S ₁ and the circle S ₂ . The sensing element located at the illustrated position D _f of the detector D contributes only to the image reconstruction of the portion on the outer periphery of the circle S ₁ .

From the above points, the overall image quality of the reconstructed image of the tomographic plane of the object is higher due to the projection data obtained by the detection element group in the center than the detection element group in the peripheral part of detector D. You can see that it depends.
That is, it can be said that the sensing element group in the central part of the detector D is more important than the peripheral part.

Therefore, in the present invention, the third generation
An object of the present invention is to provide a CT device configured to obtain projection data at smaller angular intervals for the central region of the spread angle of a fan-shaped radiation beam than for the peripheral regions, and to improve the image quality of reconstructed images. It is said that

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, B is a radiation source and D is a detector. For example, in this case, the detector D uses a detector cell C using a semiconductor element such as Si (silicon) or CdTe (cadmium telluride) that can convert the intensity of radiation into an electrical signal, and this detector cell C is shown in the figure. As shown in the figure, the width of the detector cells C in the central portion is made smaller and gradually increases toward the periphery, and a plurality of these are densely arranged one-dimensionally.
This detector D therefore detects radiation projection data at substantially smaller angular intervals with respect to the central region of the divergence of the fan-shaped radiation beam than in the peripheral region of the divergence.

With such a configuration, the following effects can be obtained.

Conventionally, since the detection elements were arranged at equal intervals, the path distribution of the projection radiation was substantially denser at the periphery than at the center of the imaging area. By narrowing the interval closer to the center of the beam divergence angle, the distribution of radiation paths can be made substantially uniform over the entire imaging area, resulting in an image with more homogeneous spatial resolution over the entire imaging area. It becomes possible to obtain.

Additionally, it is generally known that increasing the number of sensing elements in detector D is an effective means of improving the spatial resolution of reconstructed images, but if the number of sensing elements is too large, , which necessitates the complication of electronic circuits such as an increase in the number of amplifiers that must be prepared for each sensing element, and also requires an increase in imaging time or faster A/D conversion and data transfer.
This may lead to inconveniences such as requiring an increase in arithmetic processing capacity. In contrast, by configuring as described above and increasing the number of detector cells C in the central region, which has a large influence on the image quality of the reconstructed image, compared to the peripheral region, the number of detector cells C can be increased. In addition to improving the spatial resolution of the entire reconstructed image extremely efficiently without increasing the total number of images,
It is possible to substantially improve the image quality of reconstructed images, such as by making concentric ring artifacts that tend to occur due to non-uniform characteristics of detector cells less noticeable. Also,
It is also possible to further improve the spatial resolution of the central portion, which is particularly important in the imaging region, by further spacing the detector cells C in the central portion.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist thereof.

For example, in the above embodiment, the detector D is configured such that the interval between the detector cells C gradually increases from the center to the periphery, but in order to simplify the structure, Alternatively, the distance between the detectors D may be changed stepwise by a plurality of detectors, and the projection data may be changed by using means other than the density of the arrangement of the detecting elements, for example, by means of wiring to the detecting elements. The actual sampling angle intervals may be made different.

As described above, according to the present invention, in the third generation CT apparatus, projection data is obtained for the central region of the fan-shaped radiation beam spread angle at smaller angular intervals than for the peripheral region, and the projection data is reproduced. It is possible to provide a CT apparatus in which the image quality of constituent images is significantly improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the imaging method in the so-called 3rd generation CT device, and Figures 2 and 3 are diagrams showing the conventional imaging method.
FIG. 4 is a diagram for explaining problems in the CT apparatus, and is a diagram for explaining the configuration of an embodiment of the present invention. B... Radiation source, D... Detector, C... Detector cell.

Claims (1)

[Scope of Claims] 1. By rotating a fan-shaped radiation source that generates substantially fan-shaped radiation and a radiation detector for detecting radiation from this fan-shaped radiation source with respect to the subject, In a computerized tomography diagnostic apparatus that obtains radiation projection data from multiple directions on the same tomographic plane of a subject and reconstructs a tomographic image of the subject based on the radiation projection data, the width dimension of a central detector cell A computerized tomography diagnostic apparatus comprising a detector configured to have a width smaller than the width of a detector cell in a peripheral portion and a plurality of detector cells arranged one-dimensionally and densely. 2. A computer tomography diagnostic apparatus as set forth in claim 1, characterized in that the detector cells are formed in a continuous manner so as to become larger toward the periphery. 3. A computer tomography diagnostic apparatus according to claim 1, characterized in that the detector cells are formed to gradually become larger toward the periphery.