Simultaneous pro ton density f at‐fraction and R 2 ∗ i maging with water‐specific T 1 mapping (PROFIT 1 ): application in liver

Purpose To describe and validate a simultaneous proton density fat‐fraction (PDFF) imaging and water‐specific T 1 mapping (T 1(Water) ) approach for the liver (PROFIT 1 ) with R 2 ∗ mapping and low sensitivity to B 1 + calibration or inhomogeneity. Methods A multiecho gradient‐echo sequence, with and without saturation preparation, was designed for simultaneous imaging of liver PDFF, R 2 ∗ , and T 1(Water) (three slices in ~13 seconds). Chemical‐shift‐encoded MRI processing yielded fat‐water separated images and R 2 ∗ maps. T 1(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 T 1 weighting, to reduce the B 1 + dependence of T 1(Water)  and PDFF (reduced flip angle dependence). T 1(Water)  accuracy was validated in mixed fat‐water phantoms, with various PDFF and T 1 values (3T). In vivo application was illustrated in five volunteers and five patients with nonalcoholic fatty liver disease (PDFF, T 1(Water) , R 2 ∗ ). Results A sin 3 (θ) flip angle pattern (0 < θ < π/2 over k‐space) yielded the largest PROFIT 1 signal yield with negligible B 1 + dependence for both T 1(Water) and PDFF. Mixed fat‐water phantom experiments illustrated excellent agreement between PROFIT 1 and gold‐standard spectroscopic evaluation of PDFF and T 1(Water)  (<1% T 1 error). In vivo PDFF, T 1(Water) , and R 2 ∗ maps illustrated independence of the PROFIT 1 values from B 1 + inhomogeneity and significant differences between volunteers and patients with nonalcoholic fatty liver disease for T 1(Water) (927 ± 56 ms vs. 1033 ± 23 ms; P  < .05) and PDFF (2.0% ± 0.8% vs. 13.4% ± 5.0%, P  < .05).  R 2 ∗ was similar between groups. Conclusion The PROFIT 1 pulse sequence provides fast simultaneous quantification of PDFF, T 1(Water) , and R 2 ∗ with minimal sensitivity to B 1 + miscalibration or inhomogeneity.