Automatic bolus tracking program

All scans were performed using a 320 row multidetector CT scanner (Aquilion ONE PRISM; Canon Medical Systems, Otawara, Japan) with the following parameters: 80 row × 0.5 mm, pitch of 0.813, 0.6 s rotation time (fixed), 120 kVp tube voltage, and automatic exposure control with a noise index of 20. The standard care of abdominal CT in our hospital is the MBIR protocol (FIRST BODY Mild), which is designed for low exposure, with a mean volume CT dose index (CTDIvol) of 7.9 mGy. This value was obtained by retrospectively evaluating the doses of 125 consecutive patients prior to the start of this study. Iohexol (Omnipaque 300; Daiichi-Sankyo, Tokyo, Japan), iomeprol (Iomeron 350; Eisai, Tokyo, Japan), or iopamidol (Iopamiron 370; Nihon Schering, Osaka, Japan) was administered via an antecubital vein using a 20-gauge catheter at a dose of 600 mgI/kg; the injection procedure was standard across all patients. The scan delays for arterial and portal venous phase imaging were determined using an automatic bolus-tracking program (Canon Medical Systems). The region of interest (ROI) cursor was placed in the aorta at the level of the diaphragmatic dome, and scanning for the arterial and portal venous phases began automatically at 20 and 60 s, respectively, after the trigger threshold of 100 Hounsfield Units was reached.