Simultaneous proton density fat‐fraction and R2∗ imaging with water‐specific T1 mapping (PROFIT1): application in liver

Purpose To describe and validate a simultaneous proton density fat‐fraction (PDFF) imaging and water‐specific T1 mapping (T1(Water)) approach for the liver (PROFIT1) with R2∗ mapping and low sensitivity to B1+ calibration or inhomogeneity. Methods A multiecho gradient‐echo sequence, with and without saturation preparation, was designed for simultaneous imaging of liver PDFF, R2∗, and T1(Water) (three slices in ~13 seconds). Chemical‐shift‐encoded MRI processing yielded fat‐water separated images and R2∗ maps. T1(Water) calculation utilized saturation and nonsaturation‐recovery water‐separated images. Several variable flip angle schemes across k‐space (increasing flip angles in sequential RF pulses) were evaluated for minimization of T1 weighting, to reduce the B1+ dependence of T1(Water) and PDFF (reduced flip angle dependence). T1(Water) accuracy was validated in mixed fat‐water phantoms, with various PDFF and T1 values (3T). In vivo application was illustrated in five volunteers and five patients with nonalcoholic fatty liver disease (PDFF, T1(Water), R2∗). Results A sin3(θ) flip angle pattern (0