| Abstract: | 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 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 T1(Water) (three slices in ~13 seconds). Chemical-shift-encoded MRI processing yielded fat-water separated images and R 2 ∗ 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 B 1 + 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) , R 2 ∗ ). RESULTS: A sin3 (θ) flip angle pattern (0 < θ < π/2 over k-space) yielded the largest PROFIT1 signal yield with negligible B 1 + dependence for both T1(Water) and PDFF. Mixed fat-water phantom experiments illustrated excellent agreement between PROFIT1 and gold-standard spectroscopic evaluation of PDFF and T1(Water)  (<1% T1 error). In vivo PDFF, T1(Water) , and R 2 ∗ maps illustrated independence of the PROFIT1 values from B 1 + inhomogeneity and significant differences between volunteers and patients with nonalcoholic fatty liver disease for T1(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 PROFIT1 pulse sequence provides fast simultaneous quantification of PDFF, T1(Water) , and R 2 ∗ with minimal sensitivity to B 1 + miscalibration or inhomogeneity. |
