1. A method of correcting diffusivity measurements of a medium of arbitrary anisotropy, the method comprising; (a.). generating three-dimensional spatial correction maps for an arbitrary set of no more than three orthogonal diffusion gradient waveforms using gradient coil non-linearity characteristics of a magnetic resonance imaging (MRI) scanner, (b.). performing a diffusion weighted MRI scan of the medium using the selected arbitrary set of no more than three orthogonal diffusion gradient waveform at any nominal b-value, and acquiring diffusion weighted images (DWIs), (c.). applying the three-dimensional spatial correction maps to correct intensity of each pixel of the acquired DWIs to compensate for MRI scanner-specific gradient non-linearity bias in diffusion weighting gradients, and (d.). determining corrected diffusivity images for a mean diffusivity of the medium from the corrected DWIs and nominal b-values.