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Magn Reson Med. 2019 Oct;82(4):1373-1384. doi: 10.1002/mrm.27816. Epub 2019 May 26.

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

Author information

1
Department of Radiology, University Hospital, LMU Munich, Munich, Germany.
2
Comprehensive Pneumology Center, German Center for Lung Research, Munich, Germany.

Abstract

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 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 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.

KEYWORDS:

DW-MRI; IVIM; capillary phantom; flow-compensated IVIM; intravoxel incoherent motion; perfusion

PMID:
31131482
DOI:
10.1002/mrm.27816

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