Simultaneous Analysis of Marrow Fat Fraction and Bone Mineral Density with Modulus and Real Multiple Gradient-echo MRI

Abstract

To evaluate bone status, we developed a method for analyzing fat fraction (FF) of the bone marrow and bone mineral density (BMD) simultaneously using modulus and real multiple gradient-echo (MRM-GRE) sequence. Modulus images of seven gradient-echoes were simultaneously obtained by the MRM-GRE sequence. Real image of the first echo was also reconstructed to differentiate the areas below and above 50 percent FF. T₂ ^∗ and the initial signal intensities of water and fat were obtained from the parameters of a theoretically fitted formula applied to each echo signal. FF was calculated from the initial signal intensities of water and fat, and BMD was calculated from T₂ ^∗. FF and BMD were measured in the lumbar vertebral body and tibia of seventeen normal subjects. BMD findings on MRI were compared with those measured by dual-energy X-ray absorptiometry (DXA) . FF on MRI was in good agreement with subject age. A positive correlation was found between BMD of the lumbar vertebrae and age under twenty-five years, but a negative correlation was found over twenty-five years of age. There was a positive correlation between BMD findings on MRI and DXA. The MRM-GRE method allows FF and BMD to be assessed simply, accurately and simultaneously.