MRI protocol

All MRI examinations were performed on all patients using a 1.5-T superconducting magnet (Magnetom Aera, Siemens Medical solutions, Erlangen, Germany) 8-equipped with phased-array coils. Dynamic contrast-enhanced MRI (DCE-MRI) was performed after the administration of the contrast agent, either gadopentetate dimeglumine or gadoxetic acid, by using a 3-D T1-weighted gradient echo sequence (volumetric interpolated breath-hold examination, VIBE) with the fat suppression technique covering the whole liver and part of each kidney. Baseline MRI parameters were as follows: 3.47 msec/1.36 msec (repetition time/echo time), 10° flip angle, 320 × 195 matrix, 380–400 × 300–324 mm field of view, 21.6 mm slab thickness with an interpolated 3-mm section thickness, and 400 Hz/pixel bandwidth. A parallel imaging technique (R factor of 2) was performed with generalized autocalibrating partially parallel acquisition (GRAPPA). The dose of contrast media was 0.1 mmol/kg for gadopentetate dimeglumine and 0.025 mmol/kg for gadoxetic acid. The contrast was rapidly administered manually (at a rate of nearly 1.5 ml/sec) by one investigator through a 20-gauge intravenous catheter placed in a cubital or cephalic vein. Immediately afterward, a 20-ml saline flush was administered at the same injection rate. The arterial phase acquisition was triggered automatically when the contrast media reached the ascending aorta. For subsequent acquisition, dynamic T1-weighted MRI at approximately 60 s (the portal venous phase, PVP) and approximately 90 s (the delayed phase) were performed. In addition, HBP acquisition (20 min after the administration of contrast media) was acquired when gadoxetic acid was used. Both transverse images and coronal images were obtained.