The patients were scanned at standard-dose CT ( mean [ SD ] volumetric CT dose index , 6 [ 0.9 ] mGy ; mean [ SD ] dose-length product , 208 44 mGycm ; and mean [ SD ] effective dose , 3 [ 0.6 ] mSv ) and at SubmSv dose ( 1.8 [ 0.2 ] mGy , 67 [ 2 ] mGycm , 0.9 [ 0.03 ] mSv , respectively ) on a Philips 128-slice CT scanner with double z-sampling .