JPH1033542A - Reconstituting method for optical computed tomography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the resolution of tomography by applying weight, which gradually increases toward the downstream side along the optical path of light to be transmitted through a subject, to the respective pixels of the tomograph and executing inverse projective operation for reconstitution. SOLUTION: A light beam 21a emitted from a light source 21 is made incident to a subject 10 arranged between the light source 21 and a detector 22, and one- dimensional intensity distribution 40 of emitted light 21b from the subject 10 inside a tomographic plane is detected. Rotation is performed in arrow direction with a rotational center O as a center and this operation is repeated so that the intensity distribution 40 in all the directions can be provided. The gap between the light source 21 and the detector 22 is equally divided into 10 areas, for example, the weight which gradually decreases toward the side of the light source 21 and gradually increases toward the side of the detector 22 is applied to the respective pixels on memories inside a reconstitution area 30, and inverse projection in the arrow direction is executed concerning all the data. The tomograph is reconstituted while changing the weight for each angle. Thus, the tomograph, of which the resolution is improved rather than the case of performing reconstitution without applying weight, can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computed tomography method using light (optical CT; optical Computed Tom).
a reconstruction method for obtaining a tomographic image representing a light absorption distribution in a tomographic plane including an optical path of light of the subject based on a light reception signal obtained by receiving light transmitted through the subject in the method of FIG. .

[0002]

2. Description of the Related Art Conventionally, X-ray CT using X-rays has been realized in the field of medical treatment and the like. In recent years, research has been conducted on applying tomography using light (optical CT) to living bodies. It is being actively conducted. Since the living body is a high scatterer, the light applied to the living body is absorbed while repeating multiple scattering, and comes out of the living body. As a method of obtaining an absorption profile of a living body by detecting only light that is emitted in the forward direction without being scattered in the living body among the light emitted outside the living body in this way, the time width is extremely narrow. A so-called time-gate method in which only the earliest outgoing light of the outgoing light from the subject is irradiated with the pulsed light and the outgoing light of the subject and a predetermined reference light are superimposed. A heterodyne detection method or the like that obtains an interference signal of only a component that travels straight in a subject is known. However, if only light that has traveled straight inside the living body is to be detected using these methods, it is necessary to detect extremely weak light.In the case of a practically sized subject, the attenuation of light is too large. This makes measurement impossible. In order to measure a practically sized subject, forward scattering information in a region slightly away from the incident axis, that is, not only perfectly straight light, but also scattered within the subject and emitted forward It is necessary to include the light to be detected.

However, in this case, since the emitted light to be detected includes light scattered in the object, the quality of the object information carried by the emitted light is degraded. There is a possibility that even if a tomographic image is obtained in such a manner, only an image with reduced resolution can be obtained.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a reconstruction method for obtaining a tomographic image having excellent resolution in optical CT.

[0005]

According to the present invention, there is provided a method of reconstructing an optical CT, which achieves the above-mentioned object, based on a light-receiving signal obtained by receiving light transmitted through a subject. In the reconstruction method of the optical CT for obtaining the tomographic image representing the absorption distribution of the tomographic image, a greater weight is given to each pixel of the tomographic image on the downstream side along the optical path of the light transmitted through the subject, and the inverse for the reconstruction is performed. Executing a projection operation.

Here, in the optical CT reconstruction method of the present invention, the contour of the subject appearing in the tomographic image is extracted,
It is preferable to execute a back projection operation for reconstruction by giving a weight to an inner region of the contour. Forward scattered light emitted forward (detector side) from the subject is more likely to have traveled straight without being scattered on the side closer to the detector, and is more likely to be scattered toward the incident side of the light on the subject. . In other words, of the object information included in the forward scattered light, the information of the portion of the object closer to the detector has high reliability, and the information of the portion farther from the detector (the portion closer to the incident side) has more information. The reliability of the device decreases.

Therefore, in the present invention, when performing back projection (back projection), a greater weight is given to each pixel of the tomographic image toward the downstream side along the optical path of light transmitted through the subject. Thereby, the tomographic image obtained by the reconstruction can obtain a tomographic image having a uniform weight and higher resolution than the tomographic image obtained by the previous reconstruction.

When the weight is given, since scattering occurs inside the subject, if the contour of the subject is determined and the weight is given only to the region inside the subject, a more accurate weight can be given, and a higher-quality tomographic image can be given. An image can be obtained. The present invention can be used in combination with the above-described time gate method or optical heterodyne method. The time-gate method and the optical heterodyne method are excellent in that they can extract straight-ahead light.However, the time-gate method can be used to lengthen the gate time, that is, the light emitted from the subject for a certain long time. , Or by giving a width to the reference optical axis in the optical hetero-gain method, it is possible to recover information deterioration due to an increase in the detected light amount and obtain a high-quality tomographic image.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is an explanatory diagram of one embodiment of the present invention. The subject 10 is arranged between the light source 21 and the detector 22, and the light beam 21 a emitted from the light source 21 is
And a one-dimensional intensity distribution (profile) 40 of the emitted light 21b from the subject 10 in the tomographic plane (in the paper plane of FIG. 1) is detected. After obtaining one profile, it is rotated about the rotation center O in the direction of the arrow shown in the figure. This operation is repeated to obtain profiles in all directions.

In back projection, the light source 21 and the detector 2
When the light source 21 is connected to the light source 21 by a straight line
And the detector 22 are divided into, for example, 10 equal parts, and a smaller weight on the light source 21 side and a larger weight on the detector 22 side are given to each pixel on the memory in the reconstruction area 30, and Back projection in the direction of the arrow indicated by the broken line in FIG. 1 toward the light source 21 is executed for all data. This is sequentially performed while changing the weight for each angle to reconstruct a tomographic image.

By doing so, a high-resolution tomographic image can be obtained as compared with the case where back projection is performed without giving a weight. FIG. 2 is an explanatory diagram of another embodiment of the present invention. here,
For example, the method of giving weights by giving equal weight between the light source and the detector ignoring the cross-sectional shape of the subject 10 without giving weights or with reference to FIG. Reconstruction is performed to obtain a tomographic image. Thereafter, the contour 10a of the subject 10 is extracted from the tomographic image,
The distance x from the emission point p on the contour 10a to the light source side
Define the weight as a function of

That is, the weight w is set to w = f (x) (1), and reconstruction is performed again. By doing so, a more accurate weight can be given, and a higher quality tomographic image can be obtained. However, if weights are given as in equation (1), the sum of the weights at each angle of the pixels inside the contour 10a will be different for each pixel. Therefore, in this case, the reciprocal of the weight is multiplied for each pixel after reconstruction so that the sum of the weights for each pixel becomes equal. By doing so, the difference in the sum of the weights is corrected.

It is to be noted that back projection after correcting the profile by multiplying the profile by an appropriate convolution function is the same as the conventional method.

[0014]

As described above, according to the present invention,
It is possible to reconstruct a high-quality tomographic image as compared with the related art.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 subject 21 light source 21a light beam 21b emission light 22 detector 30 reconstruction area 40 profile

Claims (2)

[Claims] 1. A method of reconstructing an optical CT for obtaining a tomographic image representing an absorption distribution of light in a tomographic plane of a subject based on a light reception signal obtained by receiving light transmitted through the subject. A method of reconstructing an optical CT, wherein each pixel of the image is given a larger weight toward the downstream side along the optical path of light transmitted through the subject, and a back projection operation for reconstruction is performed. . 2. Extracting a contour of a subject appearing in the tomographic image, giving a weight to an inner region of the contour,
2. The method for reconstructing optical CT according to claim 1, wherein a back projection operation for reconstruction is performed.