SCATTER REDUCTION IN CONVENTIONAL RADIOGRAPHIC TOMOGRAPHY USING ROTATING APERTURES.

Since images in conventional radiographic tomography are inherently low in subject contrast, it is essential that scattered radiation be prevented from reaching the image receptor. Scanning beam or slit radiographic techniques are known to be the most efficient scatter elimination methods, yet have been inapplicable to this area of radiography. It is shown that the scanning beam method using rotating aperture wheel (RAW) devices can be used in conventional tomography. One coder wheel between the x-ray tube and patient and two scatter discriminator wheels between the patient and image receptor form sections of the RAW ″projection cone″ with the lines of radiation from the x-ray source forming the ″flux pyramid.″ As long as the projection cone follows the motion of the x-ray flux pyramid any RAW pattern may be used. Relations are given which describe the geometric constraints for various tomographic motions. It is possible to use the scatter elimination capabilities of a RAW device either to improve image contrast or to reduce patient dose.