Effect of patient size on radiation dose for abdominal MDCT with automatic tube current modulation: phantom study

OBJECTIVE. The purpose of this study was to evaluate in a phantom study the effect of patient size on radiation dose for abdominal MDCT with automatic tube current modulation.MATERIALS AND METHODS. One or two 4-cm-thick circumferential layers of fatequivalent material were added to the abdomen of an anthropomorphic phantom to simulate patients of three sizes: small (cross-sectional dimensions, 18 × 22 cm), average size (26 × 30 cm), and oversize (34 × 38 cm). Imaging was performed with a 64-MDCT scanner with combined z-axis and xy-axis tube current modulation according to two protocols: protocol A had a noise index of 12.5 H, and protocol B, 15.0 H. Radiation doses to three abdominal organs and the skin were assessed. Image noise also was measured.RESULTS. Despite increasing patient size, the image noise measured was similar for protocol A (range, 11.7–12.2 H) and protocol B (range, 13.9–14.8 H) (p > 0.05). With the two protocols, in comparison with the dose of the small patient, the abdominal organ doses...