Scott B. Reeder1,2, Catherine DG Hines1,3, Huanzhou Yu4, Charles A. McKenzie5, Jean H. Brittain6
1Radiology, University of Wisconsin, Madison, WI, USA; 2Medical Physics, University of Wisconsin, Madison, WI, USA; 3Biomedical Engineering, University of Wisconsin, Madison, WI, USA; 4Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA; 5Medical Biophysics, University of Western Ontario, London, Ontario, Canada; 6Applied Science Laboratory, GE Healthcare, Madison, WI, USA
The most commonly used metric for fat quantification with MRI is fat-signal-fraction. After correction for confounding factors (eg. T2*-decay, etc) fat-signal-fraction is synonymous with fat-proton-density-fraction. Unfortunately, gold standard assays used to validate MRI provide estimates of fat-volume-fraction or fat-mass-fraction. The purpose of this work is to clarify fat-fraction definitions, and to estimate fat-volume-fraction and fat-mass-fraction from separated fat/water signals. Theory and experiment demonstrate that for fat, signal-fraction is equivalent to volume-fraction and mass-fraction. The same is not true, however, for other combinations of chemical species such as acetone and water, which require correction factors to determine volume or mass fraction.