Integrated intravoxel incoherent motion tensor and diffusion tensor brain MRI in a single fast acquisition

Area of Science:

• Neuroimaging
• Medical Physics
• Radiology

Background:

• Intravoxel incoherent motion (IVIM) and diffusion tensor imaging (DTI) are established MRI techniques for brain analysis.
• Integrating IVIM and DTI allows for orientation-dependent perfusion parameter assessment.
• Current IVIM acquisitions typically use three diffusion gradient directions, limiting detailed analysis.

Purpose of the Study:

• To evaluate the feasibility of a combined IVIM-DTI protocol within a clinically practical scan time (<6 minutes).
• To identify the most suitable IVIM-DTI model for describing brain data using a model-selection approach.
• To explore the potential for advanced diffusion and perfusion parameter quantification.

Main Methods:

• Acquired brain diffusion-weighted images at 3T in 20 elderly participants with cerebral small vessel disease.
• Utilized a multiband echoplanar imaging sequence with 15 b-values (0-1000 s/mm²) and six non-collinear diffusion directions.
• Implemented and compared seven IVIM-DTI models (4-14 parameters) assessing diffusion and pseudo-diffusion as scalar or tensor quantities.

Main Results:

• Model fitting performance was evaluated using goodness of fit (chi²) and Akaike weights.
• A nine-parameter IVIM-DTI model (isotropic perfusion) was optimal for normal-appearing white matter (NAWM).
• An eleven-parameter model (including pseudo-diffusion anisotropy) best described white matter hyperintensities (WMH) and gray matter (GM).

Conclusions:

• A combined IVIM-DTI protocol is feasible within a 6-minute scan time for brain imaging.
• The optimal IVIM-DTI model varies by brain tissue type, with anisotropy parameters being crucial in WMH and GM.
• This integrated approach enables calculation of pseudo-diffusion tensor fractional anisotropy, offering insights beyond standard IVIM.