X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Patent
1984-04-02
1988-05-31
Howell, Janice A.
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
378 99, 358111, A61B 600, H05G 164
Patent
active
047486457
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE PRIOR ART
The present invention relates to a device for producing X-ray pictures of bodies or objects that are moved in a test channel, relative to an X-ray generator.
Devices of this general type are known, wherein rows of detectors are linear and are disposed along a wall of a rectangular testing chamber. Such detector rows result in nonlinear distortion of the distances which become larger with increasing distance from the perpendicular, from the X-ray source to the detector row.
The object underlying the present invention consists of compensating the nonlinear distortions in a device of this type, wherein conventional components and equipment are to be employed to the greatest possible degree.
SUMMARY OF THE INVENTION
The invention is based on the knowledge that the change of the angle of the incident X-ray to the perpendicular from the X-ray generator to the straight line going through the two adjacent measurement points governs the degree of the nonlinear distortion. This relationship applies to straight detector rows as well as to detector rows which are curved in any manner and deviate from the shape of a circular arc, the center of which is located in the X-ray generator. Discontinuities in the profile of the detector rows also do not disturb this relationship.
Using the change of the distance between the measuring points in this way, has the further advantage of permitting all other components and equipment, especially also the picture monitor, to be commercially available components.
It follows that the distance between two adjacent measuring points is proportional to the reciprocal value of the cosine of the angle of the incident X-ray beam to the perpendicular from the X-ray generator to the straight line through two adjacent measuring points and this insight makes it possible to determine the distances between adjacent measuring points independently of the shape of the row of the detectors. The profile of the detector row may also include discontinuities.
The design rule to be used can be written in the form of a formula as follows: ##EQU1## wherein A.sub.i is the distance between adjacent measuring points having the numbers i and i+1. The distance A.sub.0 can be chosen according to the desired resolution or, in the case of a given number of picture elements per line on the picture monitor, according to the dimensions of the equipment. For r.sub.i =1, it indicates the spacing of two measuring points if the perpendicular from the X-ray generator to the connecting line through the two measuring points intersects the connecting line.
Advantageously, detector rows are arranged along all walls of the test channel accessible to the X-rays after transversing the test space, and are adapted to the shape thereof.
Advantageously, the device includes detector rows or arrays, which include detectors at regular spacings, not all the detectors are employed as measuring points for generating picture elements and their mutual spacing is determined by an appropriate selection of the type of detectors employed. This embodiment has the advantage of permitting detector arrays prefabricated in quantity with constant detector spacings to be used. Several prefabricated detector arrays can be arranged in tandem and used for displaying one line for reproduction on the monitor.
In summary, the device for producing X-ray pictures of bodies, in which the bodies can be moved in a test channel relative to an X-ray generator, includes a linear detector array disposed opposite the X-ray generator. The detector measures the intensity of the incoming X-radiation and feeds the measured values to a device for generating a picture composed of individual picture elements, wherein the brightness of every picture element of the visible picture is adjusted in accordance with a measured value of the linear detector array. At least one measuring point has a distance from the X-ray generator which is different from the distance of the adjacent measuring points in the detector array; and the picture elements of the
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Donges Gerhard
Koch Cornelius
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