In vivo imaging of activated microglia using [11C]PK11195 and positron emission tomography in patients after ischemic stroke.

Neuroprotective strategies are currently being developed for stroke patients. Although the focus is on the development of early treatment the importance of late pathogenetic events is increasingly recognized. To investigate the microglial reaction in stroke we used a marker for activated microglia, [11C]PK11195, and PET in five patients with ischemic stroke 5-53 days after infarction. In one patient serial measurements were made. We demonstrated in each individual and at each point in time that a microglial reaction takes place in the area where T1 weighted MRI (magnetic resonance imaging) shows intensity changes. We consider this PET method as a promising tool to study the late pathogenetic consequences of cerebral infarction and to evaluate neuroprotective strategies with respect to the consequences of the microglial activation.