Simultaneous R₂^* and Liver Fat-fraction Measurement Using Modulus and Real Multiple Gradient-echo with Low-field MRI

抄録

We evaluated the R₂^* (iron content)and fat-fraction of liver tissue simultaneously using the modulus and real multiple gradient-echo(MRM-GRE)sequence at low-field MRI. Using a 0.4-Tesla open MRI, modulus images of 4 gradient-echoes(typically 8.9, 17.8, 26.7, and 35.6ms)were obtained by MRM-GRE. The real part of the first echo image was also reconstructed to differentiate below and above the 50percent fat-fraction. R₂^* and the fat-fraction were obtained from the parameters of a theoretically fitted formula for each echo signal. R₂^* and fat-fraction were measured with MRM-GRE from phantom data, liver of healthy volunteers(n=12)and from patients with fatty liver(n=3). The phantom MRI-derived fat-fraction was in good agreement with the actual value, with R₂^* showing a strongly positive correlation to actual iron content. MRI-derived fat-fraction in fatty liver was higher than that in the volunteer. However, no significant difference in R₂^* was found between fatty liver and volunteers. These results show that MRM-GRE enables a method to differentiate causes of signal reduction whether due to an increasing R₂^* or increasing fat-fraction. MRM-GRE enables a simple and accurate assessment of fat and iron content at low-fields.