Parametric maps. Parametric images from the [11C]Pittsburgh Compound B ([11C]PIB) scans of the two subjects shown in Figure 3: top images, control subject; bottom images, Alzheimer's disease (AD) patient. Images generated with spectral analysis; colour bars for each column indicate the image minimum and maximum values. The impulse response function (IRF) at 1 minute in the left column gives a reflection of tracer delivery. The cerebral blood flow in most grey matter areas of the AD subject's brain is lower than that in the elderly control subject. The IRF 75-minute images in the centre give an indication of [11C]PIB retention in tissue. In the control subject, [11C]PIB is retained predominantly in the white matter; whereas in the AD patient, widespread [11C]PIB retention in cortical grey matter occurred with association cortical areas, in particular, being targeted. Note that the cerebellar grey matter in both the control subject as well as the AD patient shows only very little [11C]PIB retention. The total volume of distribution (VD) parametric images in the right column also reflect [11C]PIB uptake in tissue, but with a slightly lower contrast between grey matter and white matter than the IRF 75-minute parametric images.