Fig. 1.

Diffusion-weighted and diffusion-calculated (ADC) images. The set of diffusion-weighted images is obtained using different b-values, by changing the intensity of the diffusion gradient pulses (gold trapezoids) in the MRI sequence. In diffusion-weighted images, the overall signal intensity in each voxel decreases with the b-value. Tissues with high diffusion (such as ventricles) get darker more rapidly when the b-value is increased and become black. Tissues with low diffusion remain with a higher signal. As diffusion-weighted images also contain T₁ and T₂ contrast, one may want to calculate pure diffusion (or ADC) images. To do so, the variation of the signal intensity, A(x, y, z), of each voxel (red boxes) with the b-value is fitted using Eq. (3) to estimate the ADC for each voxel (green box). In the resulting image, the contrast is inverted: bright corresponds to fast diffusion and dark to low diffusion.