Keywords: Microstructure, Microstructure, Brain, Multidimensional diffusion MRI, Oscillating gradients
Motivation: Tensor-valued diffusion MRI allows estimation of microscopic fractional anisotropy (μFA) independent of orientation dispersion. However, diffusion time/frequency-dependence of μFA in the brain is not well understood.
Goal(s): To investigate the frequency dependence of diffusional variances and μFA in the rat brain using oscillating-gradient spherical (STE) and linear (LTE) b-tensor encoding waveforms.
Approach: Oscillating-gradient STE and LTE waveforms were implemented at frequencies of 65, 117, and 169 Hz. Tensor-valued dMRI data were acquired from fixed rat brains using the spectrally-matched STE and LTE gradients.
Results: Spectrally-modulated STE and LTE gradients revealed significant time/frequency-dependence of isotropic diffusivity, diffusional variances, and μFA in the rat brain.
Impact: We demonstrate that oscillating spherical and linear b-tensor encoding waveforms allow mapping of frequency-dependent isotropic diffusivity, diffusional variances, and μFA in the brain. The results are important to understand the effects of spectral content of the waveforms in tensor-valued dMRI.
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