Figure 4.

The approximate nature of the “single tensor” model. (A) “Restricted” diffusion processes such as those in white matter result in displacement probabilities that are no longer accurately described by a Gaussian “bell.” (B) Therefore, the assumption that the signal attenuation must have a linear relationship in a logarithmic scale with the b-value is no longer valid, resulting in tensor diffusivities that are “apparent” (i.e., model approximations) rather than “true” measures of restricted self-diffusion.