An image processing device (1) comprises: an image data acquisition unit (10) for acquiring SPECT image data of a brain； a brain-region ROI definition unit (13) for defining a brain-region ROI in the SPECT image； a striatum ROI definition unit (14) for defining a striatum ROI in the SPECT image； a histogram generation unit (15) for generating a histogram whose horizontal axis represents the class of counts and whose vertical axis represents the frequency of unit region for each class； a threshold determination unit (16) for, based on counts in the SPECT image's background which is the brain-region ROI except the striatum ROI, determining a threshold for distinguishing ventricles and sulci in the SPECT image； a region distinction unit (17) for distinguishing between a region whose number of counts is smaller than or equal to the threshold and a region whose number of counts is larger than the threshold； and an SBR calculation unit (18) for calculating an SBR (Specific Binding Ratio) with the exception of the region whose number of counts is smaller than or equal to the threshold. This allows for using only nuclear medicine image data to eliminate the influence of ventricles and sulci in the calculation of the SBR.
