Optimization of b‐value schemes for estimation of the diffusion coefficient and the perfusion fraction with segmented intravoxel incoherent motion model fitting

PURPOSE: Intravoxel incoherent motion (IVIM) modeling for estimation of the diffusion coefficient (D) and perfusion fraction (f) is increasingly popular, but no consensus on standard protocols exists. This study provides a framework for optimization of b‐value schemes for reduced estimation uncertainty of D and f from segmented model fitting. THEORY: Analytical expressions for uncertainties of D and f from segmented model fitting were derived as Cramer‐Rao lower bounds (CRLBs). METHODS: Optimized b‐value schemes were obtained for 3 to 12 acquisitions and in the limit of infinitely many acquisitions through constrained minimization of the CRLBs, with b‐values constrained to be 0 or 200 to 800 s/mm(2). The optimized b‐value scheme with eight acquisitions was compared with b‐values linearly distributed in the allowed range using simulations and in vivo liver data from seven healthy volunteers. RESULTS: All optimized b‐value schemes contained exactly three unique b‐values regardless of the total number of acquisitions (0, 200, and 800 s/mm(2)) with repeated acquisitions distributed approximately as 1:2:2. Compared with linearly distributed b‐values, the variability of estimates of D and f was reduced by approximately 30% as seen both in simulations and in repeated in vivo measurements. CONCLUSION: The uncertainty of IVIM D and f estimates can be reduced by the use of optimized b‐value schemes.