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

PURPOSE

Design a b-value, first-order motion moment (M), and echo time (TE)-optimized data acquisition for simultaneous intravoxel incoherent motion (IVIM) and R quantification in the liver.

METHODS

The b-M-optimized (i.e., single TE) and b-M-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 and f], blood velocity standard deviations [SDs] [V and V], and/or relaxation rates of tissue and blood [R and R]) were obtained in the right and left liver lobes within distinct spatial locations associated with slow (f and V) and fast (f and V) microvascular flow. Six R-correction methods using combinations of estimated and/or fixed values of R and R were performed. Test-retest repeatability and interlobar agreement were evaluated using coefficients of variation (CVs) and relative mean differences (rMDs).

RESULTS

The b-M-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, V, f, f, R, and R, respectively) and interlobar agreement (|rMD| = 8.82%, 1.84%, 8.72%, 3.08%, and 0.20% for D, V, V, R, and R, respectively), except for interlobar agreement of f and f (rMD ≥ 37.7%). For the b-M-optimized acquisition, R correction of f and f provided similar estimates as the b-M-TE-optimized acquisition (|MD| ≤ 1.98%).

CONCLUSION

The b-M-TE-optimized IVIM acquisition enabled simultaneous and repeatable IVIM and R quantification in the liver. For single-TE IVIM data, R correction of f estimates using fixed values of R and R may be acceptable.