Guidelines for anti-scatter grid use in pediatric digital radiography

Abstract

Pediatric radiography presents unique challenges in balancing image quality and patient dose. Removing the anti-scatter grid reduces patient dose but also reduces image contrast. The benefit of using an anti-scatter grid decreases with decreasing patient size. To determine patient thickness thresholds for anti-scatter grid use by comparing scatter-to-primary ratio for progressively thinner patients without a grid to the scatter-to-primary ratio for a standard adult patient with a grid. We used Solid Water™ phantoms ranging in thickness from 7cm to 16cm to simulate pediatric abdomens. The scatter-to-primary ratio without a grid was measured for each thickness at 60kVp, 70kVp and 80kVp for X-ray fields of view (FOV) of 378cm(2), 690cm(2) and 1,175cm(2) using indirect digital radiography (iDR) and computed radiography (CR). We determined thresholds for anti-scatter grid use by comparing the intersection of a fit of scatter-to-primary ratio versus patient thickness with a standard adult scatter-to-primary ratio measured for a 23-cm phantom thickness at 80kVp with an anti-scatter grid. Dose area product (DAP) was also calculated. The scatter-to-primary ratio depended strongly on FOV and weakly on kVp; however DAP increased with decreasing kVp. Threshold thicknesses for grid use varied from 5cm for a 14 × 17-cm FOV using iDR to 12cm for an 8 × 10-cm FOV using computed radiography. Removing the anti-scatter grid for small patients reduces patient dose without a substantial increase in scatter-to-primary ratio when the FOV is restricted appropriately. Radiologic technologists should base anti-scatter grid use on patient thickness and FOV rather than age.