Mean values of fractional anisotropy (A) and mean diffusivity (B) for all 10 subjects (smaller points indicate standard deviations) in the left ventricle, colour coded by the Ndirs and plotted with the Ntot used in the tensor calculation. The horizontal lines indicate the mean values obtained from the reference data set which used every encoding direction and Nav=12. The lower subplots show the standard deviation in the left ventricle averaged over all 10 subjects to provide some indication of the variability of the parameters within a subject. For a given Ntot, the data acquired with Ndirs=10 directions appears to most commonly have the least variation and the FA closest to the reference value. For MD, Ndirs=12 appears to be optimal.