Spectral principal axes system (SPAS) and tuning of tensor-valued encoding for time-dependent anisotropic diffusion

Tensor-valued diffusion encoding can be confounded by time-dependent diffusion (TDD). Matching sensitivity to TDD or tuning of b-tensors with different shapes is needed for unbiased microstructure assessment. We present a method for tuning linear tensor encoding (LTE) to spherical tensor encoding (STE), which could be optimized for different hardware constraints. Furthermore, we introduce the spectral principle axes system (SPAS), representing spectral anisotropy of STE. The SPAS LTEs could provide an alternative to tuning and enable disentangling effects of microscopic anisotropy and TDD, useful to correlate cell shape and size.