Optimized acquisition for simultaneous intravoxel incoherent motion and R2 quantification in the liver

Abstract Purpose Design a b ‐value, first‐order motion moment ( M 1 ), and echo time (TE)–optimized data acquisition for simultaneous intravoxel incoherent motion (IVIM) and R 2 quantification in the liver. Methods The b ‐ M 1 ‐optimized (i.e., single TE) and b ‐ M 1 ‐ TE ‐optimized (i.e., multi‐TE) IVIM acquisitions were determined using Cramer‐Rao lower‐bound optimization. Eleven healthy volunteers underwent MRI of the liver where each optimized acquisition was acquired twice (test–retest). For each data set, IVIM estimates (diffusion coefficient D , perfusion signal fractions f 1 and f 2 , blood velocity standard deviations SDs V b1 and V b2 , and/or relaxation rates of tissue and blood R 2t and R 2b ) were obtained in the right and left liver lobes within distinct spatial locations associated with slow ( f 1 and V b1 ) and fast ( f 2 and V b2 ) microvascular flow. Six R 2 ‐correction methods using combinations of estimated and/or fixed values of R 2t and R 2b were performed. Test–retest repeatability and interlobar agreement were evaluated using coefficients of variation (CVs) and relative mean differences (rMDs). Results The b ‐ M 1 ‐ TE ‐optimized acquisition demonstrated acceptable to excellent right‐lobe test–retest repeatability (CV = 4.58%, 8.94%, 8.62%, 27.5%, 18.8%, 2.85%, and 17.7% for D , V b1 , V b2 , f 1 , f 2 , R 2t , and R 2b , respectively) and interlobar agreement (|rMD| = 8.82%, 1.84%, 8.72%, 3.08%, and 0.20% for D , V b1 , V b2 , R 2t , and R 2b , respectively), except for interlobar agreement of f 1 and f 2 (rMD ≥ 37.7%). For the b‐M 1 ‐optimized acquisition, R 2 correction of f 1 and f 2 provided similar estimates as the b ‐ M 1 ‐ TE ‐optimized acquisition (|MD| ≤ 1.98%). Conclusion The b ‐ M 1 ‐ TE ‐optimized IVIM acquisition enabled simultaneous and repeatable IVIM and R 2 quantification in the liver. For single‐TE IVIM data, R 2 correction of f estimates using fixed values of R 2t and R 2b may be acceptable.