Measurements from digital scanned projection radiographs: couch detail and detector artefact removal by simple image enhancement.

Abstract

Over the past few years several hundred patients who have undergone intracavitary radiotherapy by remote afterloading techniques have had CT scans and digital scan projection radiographs (DSPRs) taken after the insertion of the applicators (Wilkinson et al, 1983). The prime purpose of these investigations was to study the dose distributions achieved in the pelvis by these techniques. More recently a retrospective study of these data has been initiated to quantify variations in patient anatomy and variations in position of the applicators within the pelvis, and measurements are being made from the DSPRs which were taken in both antero-posterior (AP) and lateral directions. Whilst the AP image is usually of good quality, with both anatomical detail and applicator positioning easily appreciated, the lateral view is often very difficult for clinicians to interpret. Two major obstacles interfere with ready identification of selected anatomical points that can be used as references. First, because of varying thicknesses of patient tissue in the lateral view, there is a high degree of background variation in pixel gray level across the image. This makes it impossible to view much of the image at any one window level or width. Second, couch detail produces confusing vertical striping that seriously obscures spinal anatomy useful for reference locations (Fig. 1). These further compoundwith vertical detector artefacts produced by detector gain inconsistencies.