The influence of antiscatter grids on soft‐tissue detectability in cone‐beam computed tomography with flat‐panel detectors

TLDR

The study assessed antiscatter grids in cone‑beam CT with a flat‑panel imager across head and body sites, varying scatter ratios, dose, and resolution, and quantified soft‑tissue detectability by contrast, noise, CNR, and observer preference tests. Grids reduced scatter cupping and improved uniformity, yet offered limited CNR benefit and overall image quality gains except when high scatter, high dose, and low spatial resolution conditions apply.

Abstract

The influence of antiscatter x‐ray grids on image quality in cone‐beam computed tomography (CT) is evaluated through broad experimental investigation for various anatomical sites (head and body), scatter conditions (scatter‐to‐primary ratio (SPR) ranging from to 150%), patient dose, and spatial resolution in three‐dimensional reconstructions. Studies involved linear grids in combination with a flat‐panel imager on a system for kilovoltage cone‐beam CT imaging and guidance of radiation therapy. Grids were found to be effective in reducing x‐ray scatter “cupping” artifacts, with heavier grids providing increased image uniformity. The system was highly robust against ring artifacts that might arise in CT reconstructions as a result of gridline shadows in the projection data. The influence of grids on soft‐tissue detectability was evaluated quantitatively in terms of absolute contrast, voxel noise, and contrast‐to‐noise ratio (CNR) in cone‐beam CT reconstructions of “head” and “body” cylindrical phantoms. Imaging performance was investigated qualitatively in observer preference tests based on patient images (pelvis, abdomen, and head‐and‐neck sites) acquired with and without antiscatter grids. The results suggest that although grids reduce scatter artifacts and improve subject contrast, there is little strong motivation for the use of grids in cone‐beam CT in terms of CNR and overall image quality under most circumstances. The results highlight the tradeoffs in contrast and noise imparted by grids, showing improved image quality with grids only under specific conditions of high x‐ray scatter , high imaging dose , and low spatial resolution (voxel size ).