Fig. 1.

Global microglial activation following TBI as detected using PK11195-PET imaging. The mitochondrial 18 kDa translocator protein (TSPO) is expressed at high levels in activated microglia, macrophages, and, to a lesser extent, astrocytes; PK11195, a ligand for TSPO, is labeled with the ¹¹C isotope and has frequently been used as a contrast agent in positron emission tomography (PET) imaging of neuroinflammation both in the clinic and in animal models. The signals are mainly related to microglial activation. PK11195-PET images are merged with T1 magnetic resonance images (MRI) of 10 patients with traumatic brain injury (TBI) who underwent imaging at different time points after injury, as well as a healthy control subject. Numbers below the images captured from subjects with TBI indicate months elapsed from injury to image scanning. Compared to the control subject, the signal for bound PK11195 apparently increased globally in patients with TBI, indicating a global distribution of activated microglia. Images are reproduced from Ramlackhansingh et al.²⁹ with permission