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 ( 0.2 cdots, three dots, centered 2.4 m L / min ) in a capillary phantom using 4 different DW-MRI sequences (2 with monopolar and 2 with flow-compensated diffusion-gradient schemes, with up to 16 b values between 0 and 800 s / mm 2 ). 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 f of the flowing compartment stayed approximately constant over the applied flow rates, with an average of f = 0.451 +/- 0.023 in excellent agreement with optical microscopy ( f = 0.454 +/- 0.002 ). The estimated average particle flow speeds v = 0.25 cdots, three dots, centered 2.7 mm / s showed a highly significant linear correlation to the applied flow. The estimated capillary segment length of approximately 189 u m agreed well with optical microscopy measurements. Using the biexponential model, the signal fraction f 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 f , showed a substantial bias because the model assumptions were not met by the underlying flow pattern.
- Schneider, M. J.
- Gaass, T.
- Ricke, J.
- Dinkel, J.
- Dietrich, O.
Keywords
- *dw-mri
- *ivim
- *capillary phantom
- *flow-compensated IVIM
- *intravoxel incoherent motion
- *perfusion