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Regions of interest (ROIs) can be defined and compared to counts obtained at the same site in the contralateral limb or a separate defined region in the same patient. The relative uptake ratio is calculated by dividing the mean counts per pixel for the target ROI by the mean counts per pixel for a reference ROI on the same image to account for variability in absolute counts. Profile analysis can also be used if ROI analysis is equivocal. It has been reported that subtle differences or abnormal radiopharmaceutical uptake may be more readily identified by using ROI analysis [100]. However, information may be lost from the averaging effect, and subjective assessment has been reported as superior for focal areas of IRU [101].