Imaging the structure of the striatum: a fractal approach to SPECT image interpretation

The spatial pattern of striatal dopamine transporter density in the living human brain was tested by duplicate SPECT scans with [123I]PE2I, [123I]beta-CIT or [123I]beta-CIT-FP and striatal phantom measurements. The resolution-dependent spatial variation was calculated by the fractal analysis of SPECT images. This variation, which depends on the size of the region of interest, was described by the spatial dispersion i.e. the standard deviation of the count densities divided by the mean density. In each sub-region, the observed and methodological dispersions were computed, and the resulting spatial dispersion was calculated. The methodological dispersion is caused by the imaging resolution, flood field non-uniformity, count density, scatter, reconstruction errors and partial volume effects, whereas the spatial dispersion is based on the cerebral heterogeneity of the dopamine transporter density. Recognition of the normal variation in heterogeneity is important in evaluation of the striatal dopamine transporter density between controls and patients suffering from various neuropsychiatric disorders.