Background: The half-life of [11 C] PiB is short while that of [18 F] flutemetamol is long. [11 C] PiB has been used widely as an amyloid imaging agent for brain PET. In recent years, [18 F] flutemetamol has been developed as a new PET amyloid imaging agent. In this study, PET images taken from the same patient using [18 F] flutemetamol and [11 C] PiB were compared so that the amyloid deposition in the brain could be visually and quantitatively evaluated.
      Methods: PET was conducted in three patients with amyloid-positive Alzheimer's disease (AD) and one patient with amyloid-positive mild cognitive impairment (MCI), using [18 F] flutemetamol and [11 C] PiB. Ninety minutes after intravenous administration of 185 MBq of [18 F] flutemetamol, dynamic PET imaging was performed for 30 minutes. For [11 C] PiB, dynamic PET imaging was performed for 70 minutes immediately after administration of 350 MBq of [11 C] PiB. The distribution of amyloid deposition in the region of interest in each cortex was quantitatively evaluated using the standard uptake value (SUV) sum images taken in the latter half of the PET session when a higher level of brain amyloid deposition was more readily detectable. The SUV ratio (SUVR) was calculated using the SUV in the cerebellum as the reference value. Moreover, the mean cortical SUVR (MSUVR) was calculated from the SUVR data in the cortex where a high level of amyloid deposition was detected.
      Results: When both [18 F] flutemetamol and [11 C] PiB PET images were evaluated, high levels of amyloid deposition were observed in the frontal lobe, posterior cingulate gyrus (PCG), precuneus, parietal lobe, and lateral temporal lobe. On the other hand, amyloid deposition was only weakly evident in the medial temporal lobe, occipital lobe, and the cerebellar cortex. In [18 F] flutemetamol PET, the MSUVR was 2.32, and the MSUVR in the PCG was 2.68. In [11 C] PiB PET, the MSUVR was 2.04, and the MSUVR in the PCG was 2.26. These data indicate that, although the dose of radioisotope was lower in [18 F] flutemetamol PET, the SUVR in each cortex were generally high in [18 F] flutemetamol PET.
      Conclusions: [18 F] flutemetamol has a longer half-life and can be delivered for a longer duration. The data indicate that, as an amyloid imaging agent, the performance of [18 F] flutemetamol is similar to that of [11 C] PiB in AD and AD-associated MCI.