Pulse Sequence Optimization for Superparamagnetic Iron Oxide-enhanced MR Imaging in the Detection of Hepatic VX2 Tumors in Rabbits

Abstract

Purpose: The purpose of this experimental study was to determine the optimal pulse sequences for SPIO-enhanced MR imaging in the evaluation of multiple hepatic tumors. Materials and Methods: Twelve rabbits with multiple VX2 liver tumors underwent SPIO-enhanced MRI using the following nine pulse sequences: TSE T2-weighted imaging (T2WI), TSE proton density-weighted imaging (PDWI), and GRE -weighted imaging (WI) with seven different echo times (TE). Liver-lesion contrastto-noise ratios (CNRs) were calculated, and images were also assessed qualitatively by two radiologists, who reached a consensus as to lesion conspicuity and imaging artefacts using a four-level scale. By means of pathologic correlation, the sensitivity and positive predictive value of each sequence was calculated. Results: TSE T2WI and long-TE (35 msec) FLASH WI showed the highest liver-lesion CNR. The best lesion conspicuity was seen at TSE T2WI and medium-TE (12 msec) GRE WI. Short TE GRE T2*WI showed the least imaging artefacts. The four sequences which demonstrated the best sensitivity were medium-TE (12 msec), GRE WI (FLASH, 84%; FISP, 82%), TSE T2WI (79%), and TSE PDWI (76%). All nine sequences showed overall high positive predictive value (86-97%), with no statistically significant difference (p>0.05). Conclusion: In terms of image quality and the detection of sensitivity, TSE T2WI and medium TE (12 msec) GRE WI were the top two pulse sequences among the various sequences used for on SPIO-enhanced MRI. They are thus considered to be the optimal sequences for evaluating multiple malignant hepatic tumors.