Effects of percent thresholding on the extraction of [18F]fluorodeoxyglucose positron emission tomographic region-of-interest data.

Although we and others have employed a thresholding strategy to extract "peak" values from positron emission tomographic (PET) regions of interest (ROIs), the effects of peak picking on fitted fluorodeoxyglucose rate constants, regional metabolic rate for glucose (rCMRglc) profiles, patterns of regional metabolic covariation, and PET-neurobehavioral correlations have not been systematically investigated. Our results suggest that under some commonly encountered imaging conditions percent thresholding may increase sensitivity to regional activation; however, the effect of thresholding is determined by a number of factors, including the relative magnitude of regional activation, ROI size, and the specific threshold selected. The difference-annulus concept is proposed as a means to study the effects of different region drawing and thresholding strategies, and to determine if a given ROI contains one and only one source of covarying metabolic activity.