MRM-GRE法を用いた肝臓の鉄含有量および脂肪含有率の同時測定

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We evaluated the R2* (iron content) and fat fraction of the liver tissue simultaneously using modulus and real multiple gradient-echo (MRM-GRE) sequence. On a 1.5-T MRI, modulus images of 7-9 gradient-echoes were obtained by MRM-GRE sequence at a time. A real part of the first echo image was also reconstructed to differentiate below and above the 50 percent fat fraction. The fat fraction and R2* were obtained from the parameters of a theoretically fitted formula with each echo signal. R2* and fat fraction were measured with MRM-GRE in the phantom and the liver in normal volunteers (n=6) and patients with fatty liver (n=4) . MRI-derived fat fraction of the phantom was in good agreement with the actual value, and R2* of the phantom showed a strongly positive correlation with the actual iron content. MRI-derived fat fraction in fatty liver was significantly higher than that in the normal volunteers. However, no significant difference in R2* was found between fatty liver and normal volunteers. These results show that the MRM-GRE enables to differentiate the causes of signal reduction whether increasing R2*or increasing fat fraction. The MRM-GRE method makes it possible to simply and accurately assess the fat content and the iron content.
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