<title>Rotating Aperture Devices In X-Ray Tomography</title>

Abstract

Rotating aperture wheel (RAW) devices can be used in conventional tomography. This represents the possibility for the first application of efficient scanning slit anti-scatter techniques to this area of radiology characterized by inherently low contrast images. 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 (with the ratios of the distances between the x-ray source, RAWs, patient, and image receptor kept constant throughout the motion) any RAW pattern may be used. Simple relations are given which describe the geometric constraints for various tomographic motions. As in any application of scanning slit techniques, it would be possible to use the excellent scatter elimination capabilities of a RAW device either to improve image contrast or to reduce patient dose. Applications of rotating apertures to computed tomography (CT) are also possible. Multiple, simultaneous coronal or sagittal sections might be obtained with incomplete sets of projections using a single RAW system or with complete sets of data using two orthogonal RAW systems. A new device involving three concentric cylindrical rotating apertures is introduced which appears to be applicable to simultaneous multi-plane CT using late generation CT scanner geometries.