Slit design considerations for rotating aperture, scanning beam radiography

The rotating aperture wheel (RAW) scanning beam device is uniquely applicable for scatter elimination in short time, rapid sequence, and real time radiographic imaging because of the continuous rotary motion of its slit pattern. This rotary motion places special restrictions on the slit pattern design. Although simple sector shaped slits provide uniform primary transmission, they entail an unacceptable degree of slit widening on small diameter wheels. The use of multiple slit zones with slits of different angular width has reduced the extent of this widening on a prototype RAW; however, interzone boundary artifacts caused by differential primary x ray cutoff are apparent on some clinical images. This problem is eliminated with a unique spiral shaped aperture pattern which consists of slits of constant width and constant spacing. Each slit is radially continuous and provides uniform primary transmission without interzone artifacts. This spiral pattern satisfies all requirements and appears to be the pattern of choice for rotating aperture scanning beam radiography.