Assessment of intravoxel incoherent motion MRI with an artificial capillary network: analysis of biexponential and...

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.

IVIM-MRI was performed at 12 different flow rates ( $$ ) in a capillary phantom using 4 different DW-MRI sequences (2 with monopolar and 2 with flow-compensated diffusion-gradient schemes, with up to $$$$ values between $$ and $$ ). Resulting parameters from the assessed IVIM models were compared to results from optical microscopy.

The acquired data were best described by a static and a flowing compartment modeled by the phase-distribution approach. The estimated signal fraction $$ of the flowing compartment stayed approximately constant over the applied flow rates, with an average of $$ in excellent agreement with optical microscopy ( $$ ). The estimated average particle flow speeds $$ showed a highly significant linear correlation to the applied flow. The estimated capillary segment length of approximately $$ agreed well with optical microscopy measurements. Using the biexponential model, the signal fraction $$ was substantially underestimated and displayed a strong dependence on the applied flow rate.

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 $$ , showed a substantial bias because the model assumptions were not met by the underlying flow pattern.