Analysis of radiolabelled metabolites in a plasma sample. Data from the 15-minute sample of a human subject injected with 370 MBq [11C]Pittsburgh Compound B ([11C]PIB), a marker of amyloid deposition in the brain. The plot shows the HPLC trace with three identifiable peaks. The peak of the unmetabolised parent compound with about a 9-minute retention time follows two more hydrophylic metabolites that partly overlap. Insert: measurements of the fractions of radioactivity in plasma belonging to metabolite 1, metabolite 2 and [11C]PIB, respectively. Eight plasma samples were analysed for this 90-minute positron emission tomography scan. The plot illustrates that the parent [11C]PIB (red line) is rapidly metabolised in humans. Modified with permission from .