Calculation of measured ADC maps

The apparent diffusion coefficient (ADC) for a given direction is calculated on a pixel-by-pixel basis by fitting signal intensities to the Stejskal-Tanner equation

using a least-squares approach.

Here is shown a non-diffusion weighted image (b=0), an averaged, isotropically diffusion weighted image (b=900s/mm²) and the resulting trace image.

When a number of repeated measurements are done at each b-value, for example two b=0 measurements and four b=900 measurements, there are basically two approaches to take:

Do a least-square fit to all (6) points
Average all measurements at each b-value (for a given direction) and calculated ADC based on the averaged values.

We have decided to use the first approach because it applies equally well to the general case of any number of repetitions at any number of different b-values. Simulations (data not published) show that the two approaches are basically equivalent. See also DTI acquisition - repetitions.

Go to the next step: Calculation of Tensor elements.