Assessment of intravoxel incoherent motion MRI with an artificial capillary network: analysis of biexponential and phase‐distribution models

PURPOSE: To systematically analyze intravoxel incoherent motion (IVIM) MRI in a perfusable capillary phantom closely matching the geometry of capillary beds in vivo and to compare the validity of the biexponential pseudo‐diffusion and the recently introduced phase‐distribution IVIM model. METHODS: IVIM‐MRI was performed at 12 different flow rates ([Formula: see text]) in a capillary phantom using 4 different DW‐MRI sequences (2 with monopolar and 2 with flow‐compensated diffusion‐gradient schemes, with up to [Formula: see text] [Formula: see text] values between [Formula: see text] and [Formula: see text]). Resulting parameters from the assessed IVIM models were compared to results from optical microscopy. RESULTS: The acquired data were best described by a static and a flowing compartment modeled by the phase‐distribution approach. The estimated signal fraction [Formula: see text] of the flowing compartment stayed approximately constant over the applied flow rates, with an average of [Formula: see text] in excellent agreement with optical microscopy ([Formula: see text]). The estimated average particle flow speeds [Formula: see text] showed a highly significant linear correlation to the applied flow. The estimated capillary segment length of approximately [Formula: see text] agreed well with optical microscopy measurements. Using the biexponential model, the signal fraction [Formula: see text] was substantially underestimated and displayed a strong dependence on the applied flow rate. CONCLUSION: The constructed phantom facilitated the detailed investigation of IVIM‐MRI methods. The results demonstrate that the phase‐distribution method is capable of accurately characterizing fluid flow inside a capillary network. Parameters estimated using the biexponential model, specifically the perfusion fraction [Formula: see text] , showed a substantial bias because the model assumptions were not met by the underlying flow pattern.