One of the early promises of PET was that it would be quantitative (1), as opposed to imaging modalities such as x-ray CT, MRI, or SPECT, in which quantification is more of a challenge than in PET. By quantitative is meant that a raw PET signal can be transferred into absolute activity concentrations of the radiopharmaceutical in all tissues in units of, for example, kBq/cm3. In this sense, PET...
