Purpose or Case Report: Global mAs reduction is accepted as being superior to bismuth breast shields in reducing breast organ dose for children undergoing CT of the chest. However, in imaging of chest, abdomen, and pelvis (CAP), globally reducing mAs degrades image quality in the abdomen and pelvis. This study compares bismuth shields to global mAs reduction including a region-specific boost feature to maintain abdominal image quality.
Methods & Materials: CT CAP was performed on three phantoms of varying sizes, using three different techniques. First, each phantom was scanned with a bismuth breast shield. To establish dose savings, a control scan was performed with the same technique as the shielded scan but with the breast shield removed. Each phantom was scanned a third time without a shield but with global mAs reduction enabled to match image quality at the heart established during the shielded scan. Parameters for the third scan included a liver region boost feature to improve image quality in the abdomen. Entrance skin exposure was measured at the anterior and posterior chest, with the anterior measurement representing breast organ dose. Image quality was assessed using standard deviation measurements in the heart and liver regions.
Results: In the smallest phantom (water-equivalent diameter, WED 16.6 cm), the breast shield provided greater breast dose savings (14%) than global mAs reduction (7.6%) at the same image quality. In the larger two phantoms (WED 23.5 and 28.9 cm, respectively), breast dose savings with the breast shield (20.6% and 18.7%) were comparable to those when using global mAs reduction with the liver boost enabled (18.6% and 18.9%), with similar image quality in the heart and liver.
Conclusions: For small patients and for scanners without region-specific boost features, breast shields provide the best dose savings while maintaining abdominal image quality and therefore should be used for all CT CAP protocols. In larger patients with access to scanners with these advanced dose modulation methods, global mAs reduction can be used to achieve similar results to breast shields.