Assessing Inflammation in Acute Intracerebral Hemorrhage with PK11195 PET and Dynamic Contrast-Enhanced MRI

BACKGROUND AND PURPOSE: Studies in animal models suggest that inflammation is a major contributor to secondary injury after intracerebral hemorrhage (ICH). Direct, noninvasive monitoring of inflammation in the human brain after ICH will facilitate early-phase development of anti-inflammatory treatments. We sought to investigate the feasibility of multimodality brain imaging in subacute ICH. METHODS: Acute ICH patients were recruited to undergo multiparametric MRI (including dynamic contrast-enhanced measurement of blood-brain barrier transfer constant (Ktrans ) and PET with [11 C]-(R)-PK11195). [11 C]-(R)-PK11195 binds to the translocator protein 18 kDa (TSPO), which is rapidly upregulated in activated microglia. Circulating inflammatory markers were measured at the time of PET. RESULTS: Five patients were recruited to this feasibility study with imaging between 5 and 16 days after onset. Etiologies included hypertension-related small vessel disease, cerebral amyloid angiopathy (CAA), cavernoma, and arteriovenous malformation (AVM). [11 C]-(R)-PK11195 binding was low in all hematomas and 2 (patient 2 [probable CAA] and 4 [AVM]) cases showed widespread increase in binding in the perihematomal region versus contralateral. All had increased Ktrans in the perihematomal region (mean difference = 2.2 × 10-3 minute-1 ; SD = 1.6 × 10-3 minute-1 ) versus contralateral. Two cases (patients 1 [cavernoma] and 4 [AVM]) had delayed surgery (3 and 12 months post-onset, respectively) with biopsies showing intense microglial activation in perilesional tissue. CONCLUSIONS: Our study demonstrates for the first time the feasibility of performing complex multimodality brain imaging for noninvasive monitoring of neuroinflammation for this severe stroke subtype