An important usage of the VOI analysis is the generation of time-activity curves (TAC) from dynamic PET series for subsequent kinetic modeling. Naturally, the first step is to outline an appropriate set of VOIs, for instance by:
•loading the dynamic series, averaging a frame range so that the result shows enough anatomical information, and outline the VOIs on the average;
•trying to normalize an atlas to the average image and use the resulting atlas VOIs; or
•matching the PET series to an anatomical MR series which is used for the VOI outlining
Once the VOIs are defined in the space of the dynamic PET image, the TAC can be calculated as the VOI average for each frame.
Note: The dynamic image data needs to be loaded with the correct acquisition times and the correct input units. This is important, because otherwise the acquisition start/end times in kinetic modeling will be wrong, and the TACs may be different in magnitude with respect to the blood data. Such problems result in erroneous model parameters.