[New method of determining regional fat fraction with modulus and real multiple gradient-echo (MRM-GRE)]

We devised a method of analyzing a regional fat fraction using a modulus and real multiple gradient-echo (MRM-GRE) 4-7 echo Dixon sequence. The regional fat fraction was calculated with a theoretically fitted signal-intensity curve for multiple GRE images at each echo time (i.e., 4-7 echoes.) on a 1.5 Tesla MRI to correct T2* decay and phase cycling. Then the real image of the first echo was used to differentiate between the areas above and below the 50 percent fat fraction. To eliminate the T1-effect, the flip angle was set at 12 degrees. Fat fractions of the phantom with MRM-GRE were compared with those using conventional double-GRE and other MRI techniques. Fat fractions of liver and spinal bone marrow in healthy volunteers were determined during a breath-hold. The fat fraction of the phantom obtained by the MRM-GRE method tended to agree with the actual fat fraction. On the other hand, in both the phantom and in healthy volunteers, the double-GRE was underestimated owing to T2* decay. The MRM-GRE method enables simple, accurate analysis of the regional fat fraction.