X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Patent
1987-04-21
1989-07-25
Fields, Carolyn E.
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
378901, G01N 2134
Patent
active
048521329
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a method of collecting data for an X-ray tomograph which uses continuous X-rays in the shape of fan beams.
2. Background Art
In a conventional X-ray tomograph, an which projects X-rays in the shape of fan beams and a multi-channel X-ray detector which opposes the X-ray source with an object to be examined (hereinunder referred to as "target") interposed therebetween are rotated around the target, so as to project the X-rays in the shape of fan beams along the section of the target, and the data which indicate the distribution of the transmission intensity of the X-rays in a plurality of directions in the section are measured, and the tomogram of the target is reconstructed on the basis of the data. In such a tomograph, the plurality of directions (hereinunder referred to as "view directions") in which the X-ray transmission data are collected are set at the directions obtained by dividing the trajectory of the rotation of the X-ray source and the X-ray detector around the target by an equal angle. These directions are determined by the timing of irradiation when the X-ray is a pulse X-ray, and by the timing for collection of X-ray transmission data when the X-ray is continuous X-rays.
The reconstruction of the tomogram of the target is carried out on the basis of the respective multi-channel data which have been collected in accordance with a predetermined number of views. The collected data are arranged in correspondence with the fan beam X-rays. The tomogram of the target may be reconstructed either directly from this arrangement of data, or after the arrangement is converted into the data arrangement which corresponds to parallel beam X-rays.
In order to enhance the resolution of the reconstructed image, the X-ray detector is sometimes disposed so that the central channel thereof is deviated from the X-ray which passes the center of rotation by 1/4 (such a detector will hereinunder be referred to as "offset detector"), and the data on the symmetrical channels of the right half and the left half of the X-ray detector, which have been obtained at angles at which the view directions are substantially opposite, (hereinunder these data will be referred to as "opposing view data") are combined for reconstruction.
The opposing view data are also utilized for positively utilizing the duplexity of the data eve in an X-ray detector which does not adopt the offset arrangement.
In such a conventional X-ray tomograph, since the X-ray transmission data obtained are the data arranged in correspondence with the fan beam X-rays, the exact opposing view data are not always obtained with respect to all channels, so that utilization of opposing view data becomes incomplete.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of collecting data which enables exact opposing view data to be obtained with respect to the data on any channel in an X-ray tomograph which uses fan beam X-rays.
The present invention is characterized in that the timing for collecting the output data of each detection channel is so selected that the relationship in which a pair of items of data based on a pair of X-ray beams which pass a substantially common route formed in a target in the opposite directions to each other are detected by a pair of channels which are situated at substantially symmetrical positions with respect to the center of an X-ray detector may be established with respect to all channels.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the structure of an embodiment of the present invention;
FIGS. 2, 3 and 6 show geometrical relationships among the X-ray source, the X-ray detector and the target in the embodiment of the present invention; and
FIGS. 4, 5 and 7 show the characteristics of the arrangement of channel data of the X-ray detector in the embodiment of the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
FIG. 1 is a schematic view of the structure of an embodiment of an X-ray
REFERENCES:
patent: 4075490 (1978-02-01), Kowalski
patent: 4168435 (1979-09-01), Duinker
patent: 4206359 (1980-06-01), Hounsfield
patent: 4266136 (1981-05-01), Duinker
patent: 4682290 (1987-07-01), Tan et al.
patent: 4736396 (1988-04-01), Boyd et al.
Fields Carolyn E.
Hynds Joseph A.
Kojima Moonray
Yokogawa Medical Systems
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