**2.6 Measurement of neuroinflammation**

Microglial activation is the body's natural response to brain injury and associated neuroinflammation. In addition, microglial activation is also thought to play a significant role in the immune response to AD-related neuronal degeneration and, in AD patients, activated microglia can be found at sites associated with the deposition of aggregated Aβ (Kadir and Nordberg, 2010). There is consequently significant interest in developing radiopharmaceuticals that allow exploration of microglial activation using PET imaging, and the most common are ligands that target the peripheral benzodiazepine receptor including [11C]PK11195 and [11C]PBR28. Cagnin and co-workers reported increased levels of [11C]PK11195 in the entorhinal, temporoparietal, and cingulate cortices in patients with mild AD (when compared to normal controls) (A. Cagnin, et al., 2001). In related work, Edison and colleagues imaged AD patients with both [11C]PK11195 and [11C]PiB. They found a negative correlation between cortical microglial activation and cognition in AD patients, but there was no observable correlation between [11C]PK11195 uptake and [11C]PiB binding (Edison, et al., 2008).
