Effect of gradient nonlinearity on spatial non-uniformity of diagonal (a–c) versus off-diagonal (d–f) elements of b-matrix over FOV = 300×300×300mm is illustrated for DWI gradients along “Z”-LAB (a,d), “Z”-OVP (b,e), and corrected “Z”-OVP (c,f). Spatial dependence is represented by color gradient at boundary planes (X=150mm, Y=150mm, Z=−150mm) and spherical slice through the FOV. Color-bars to the right of each 3D-map provide the scale for depicted b-values (s/mm2). The unbiased (uniform) b-value corresponds to 1010 (a), 755 (b) and 1510s/mm2 (c) at isocenter. The deviation from uniformity is visually estimated by the color gradient scale away from isocenter. The color gradient of the corrected map (c) preserves all spatial non-uniformity information of (b) to remove nonlinearity bias via Eqs.[4,5]. The residual non-uniformity error, Eq.[2], of b-matrix is represented by the spatial bias and relative scale of the off-diagonal b-elements (d–f).