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

Design a b-value, first-order motion moment (M₁), and echo time (TE)-optimized data acquisition for simultaneous intravoxel incoherent motion (IVIM) and R₂ quantification in the liver.

The b-M₁-optimized (i.e., single TE) and b-M₁-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 [f₁ and f₂], 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 (f₁ and V_b1) and fast (f₂ and V_b2) microvascular flow. Six R₂-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).

The b-M₁-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, f₁, f₂, 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 f₁ and f₂ (rMD ≥ 37.7%). For the b-M₁-optimized acquisition, R₂ correction of f₁ and f₂ provided similar estimates as the b-M₁-TE-optimized acquisition (|MD| ≤ 1.98%).

The b-M₁-TE-optimized IVIM acquisition enabled simultaneous and repeatable IVIM and R₂ quantification in the liver. For single-TE IVIM data, R₂ correction of f estimates using fixed values of R_2t and R_2b may be acceptable.