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Barium enema: use of increased copper filtration to optimize dose and image quality

Departments of ¹ Medical Physics and ² Radiology, Nottingham City Hospital, Hucknall Road, Nottingham NG5 1PB, UK

The purpose of this study was to determine and validate the optimum copper filtration for adult double contrast barium enema examinations. Entrance surface dose rates to polymethyl methacrylate slabs and corresponding image intensifier input kermas, were measured for various added copper filters. Image contrast was assessed using a Leeds TO.10 test object. Copper filter thickness of 0.3 mm was chosen, as this reduced entrance surface dose rate by 56%, without substantially degrading image contrast due to kV and mA saturation. 20 sets of clinical films taken with each of 0.3 mm copper, 0.1 mm copper and no copper were reviewed following randomization, by a specialist gastrointestinal radiologist. Each set of digital spot and conventional films was allocated a score for each of three regions of the bowel, on a scale of 0–3 for perceived barium coating. The Kruskal–Wallis test showed no significant difference in perceived coating between the three groups (Digital spot: sigmoid colon p=0.207, splenic flexure p=0.103, hepatic flexure p=0.894. Screen–film: left colon p=0.803, right colon p=0.487, transverse colon p=0.905). All examinations but one were classified as diagnostic. The remaining one was classified indeterminate, due to poor distension of the colon. On adding 0.3 mm copper filtration, the mean dose–area product per examination was reduced by 57%, from 17.7 Gy cm² to 7.6 Gy cm². The estimated reduction in effective dose was 11%, from 3.0 mSv to 2.7 mSv. X-ray tube loading increased by 30%, but this caused no overheating with our local examination protocol and schedule. Additional filtration of 0.3 mm copper for adult double contrast barium enemas has now been implemented in routine clinical use at our hospital.

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