Tomoyuki Okuaki1,2, Kengo Yoshimitsu3, Ivan Zimine1, Shutaro Saiki1, Marc Van Cauteren4, Toshiaki Miyati5
1Philips Electronics Japan, Minato-ku, Tokoyo, Japan; 2Graduate School of Medical Science, Kanazawa University , Kanazawa, Ishikawa, Japan; 3Radiology,Faculty of Medicine,, Fukuoka University, Fukuoka, Japan; 4Philips Healthcare, Netherlands; 5Kanazawa University Graduate School of Medical Science, Kanazawa, Ishikawa, Japan
Estimation of fat fraction is affected by T2* decay. The aim of this study was to determine the accuracy of fat fraction estimation combined with T2* estimation depending on the number of echoes acquired with a multi-echo gradient echo sequence. 11 volunteers with fatty liver of various degrees were scanned on a 1.5T clinical system. Dual echo T1-weighted fast field echo and multi-echo fast field gradient echo, before and after SPIO administration. Fat fraction maps from dual echo data and mFFE data were compared before SPIO injection and for each acquired time point after injection. For each time point fat fraction ratio (FFr) maps were calculated as post-contrast data divided by pre-contrast data and average values across time points from manually placed ROIs was used for comparison. FFr by dual echo method was 0.32}0.28, by mFFE method using 3 echoes (1.03 } 0.11), 4echoes (1.00 } 0.07), 6 echoes (1.04 } 0.05), 8 echoes (1.12 } 0.08) and 10echoes (1.32 } 0.05). With Dual echo method, fat fraction is clearly underestimated because of unaccounted T2* decay, while with mFFE, the ratio stays close to expected 1.0. Accurate estimation of fat fraction accounting T2* decay is possible using mFFE method in the liver, even in patients with iron accumulation. Considering that abdominal imaging requires breath holding, and that the results for 3, 4, 6, and 8 echoes are not significantly different, the use of smallest number of echoes is justified.