FIGURE 5.  Effect of scan duration on quantification accuracy of VOI-based analysis (A and B) and voxelwise graphical analysis (C and D). Illustrated are mean relative deviations of DV_t estimates (ordinate) provided by the respective analyses with specified scan durations (abscissa), compared with reference analyses (i.e., 90-min VOI-based 2TCM analysis in A and B, 90-min VOI-based graphical analysis without blood-volume correction in C and D). Mean values (±SD) are given for representative anatomic regions. Times in minutes refer to total scan duration of the respective analyses. BVC = blood-volume correction; GA = graphical analysis; PI GA = parametric image generated by voxelwise graphical analysis without spatial smoothing; PI sGA = parametric image generated by voxelwise graphical analysis after spatial gaussian smoothing (filter kernel of 5 mm FWHM).