Imaging of Vascular Inflammation with [11C]-PK11195 and PET/CT Angiography

Objectives We sought to investigate whether positron emission tomography/CT angiography using [11C]-PK11195, a selective ligand for peripheral benzodiazepine receptors expressed in activated macrophages, can be used to image vascular inflammation.Background Activated macrophages and T lymphocytes are fundamental elements in the pathogenesis of large vessel vasculitides.Methods Fifteen patients (aged 52±16 years) with systemic inflammatory disorders (6 consecutive symptomatic patients with clinical suspicion of active vasculitis and 9 asymptomatic control patients) underwent PET with [11C]-PK11195 and CT angiography. [11C]-PK11195 uptake was measured by calculating target-to-background ratios (TBR) of activity normalized to venous blood. Results Co-registration of PET with contrast-enhanced CT angiography facilitated localization of [11C]-PK11195 arterial wall uptake. Visual analysis revealed focal [11C]-PK11195 uptake in the arterial wall of all 6 symptomatic patients, but in none of the asymptomatic controls. Whilst serum inflammatory biomarkers (C-reactive protein, erythrocyte sedimentation rate, white cell count) did not differ significantly between the 2 groups, symptomatic patients had increased [11C]-PK11195 vascular uptake (TBR 2.41±1.59 versus 0.98±0.10; p=0.001). Conclusions By binding to activated macrophages in the vessel wall, [11C]-PK11195 enables noninvasive imaging of vascular inflammation. Alternative longer lived radioligands for probing peripheral benzodiazepine receptors are being tested for wider clinical applications.