Imaging of Vascular Inflammation With [11C]-PK11195 and Positron Emission Tomography/Computed Tomography Angiography

Objectives We sought to investigate whether positron emission tomography/computed tomography (CT) angiography using [ 11 C]-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 (age 52 ± 16 years) with systemic inflammatory disorders (6 consecutive symptomatic patients with clinical suspicion of active vasculitis and 9 asymptomatic control patients) underwent positron emission tomography with [ 11 C]-PK11195 and CT angiography. [ 11 C]-PK11195 uptake was measured by calculating target-to-background ratios of activity normalized to venous blood. Results Coregistration of positron emission tomography with contrast-enhanced CT angiography facilitated localization of [ 11 C]-PK11195 arterial wall uptake. Visual analysis revealed focal [ 11 C]-PK11195 uptake in the arterial wall of all 6 symptomatic patients, but in none of the asymptomatic controls. Although serum inflammatory biomarkers (C-reactive protein, erythrocyte sedimentation rate, white cell count) did not differ significantly between the 2 groups, symptomatic patients had increased [ 11 C]-PK11195 vascular uptake (target-to-background ratio 2.41 ± 1.59 vs. 0.98 ± 0.10; p = 0.001). Conclusions By binding to activated macrophages in the vessel wall, [ 11 C]-PK11195 enables noninvasive imaging of vascular inflammation. Alternative longer-lived radioligands for probing peripheral benzodiazepine receptors are being tested for wider clinical applications.