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 [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 (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 [11C]-PK11195 and CT angiography. [11C]-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 [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. 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 [11C]-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, [11C]-PK11195 enables noninvasive imaging of vascular inflammation. Alternative longer-lived radioligands for probing peripheral benzodiazepine receptors are being tested for wider clinical applications.