Abstract 3403: In vivo Imaging of Macrophage Infiltration with N1177-Enhanced Computed Tomography in Atherosclerotic Plaques of Hypercholesterolemic Rabbits

Introduction. Vulnerable atherosclerotic plaques are characterized by their high density in macrophages. N1177 (Nanoscan Imaging) is a new computed tomography (CT) contrast agent formed of a suspension of insoluble iodine molecules, which are taken up by macrophages. Hypothesis. Our hypothesis was to assess whether N1177-enhanced CT can be used to image in vivo macrophage infiltration in atherosclerotic plaques of hypercholesterolemic rabbits. Methods. Atherosclerotic plaques were induced in the aorta of 4 New-Zealand White rabbits by double balloon injury (4 weeks apart) and 4 months of hypercholesterolemic diet. Two non-injured rabbits fed a chow diet were used as controls. A 64-slice CT of the aorta (n=6) was acquired in each rabbit before and two hours after intravenous injection of N1177 (250 mg iodine/kg). The same protocol was repeated one week later using a conventional iodinated contrast agent (250 mg iodine/kg of iopamidol). On each CT acquisition, signal density was measured in the aortic wall. Changes in signal densities of the aortic wall on CT after injection of each contrast agent were compared to macrophage infiltration studied by immunohisto-chemistry (anti-RAM-11 antibody) on corresponding aortic cross-sections. Results. Increased signal densities were found on axial CT views two hours after the injection of N1177 in the aortic wall of all (4/4) atherosclerotic rabbits (mean increase of 11.2 ± 6.3 Hounsfield units; p = 0.05 vs. baseline), but not in control rabbits (2/2). No detectable change in aortic parietal signal density was observed after injection of iopamidol, neither in atherosclerotic nor in control rabbits (6/6). An intense macrophage infiltration was found on aortic cross-sections corresponding to atherosclerotic plaques with the highest increase in signal density on CT after injection of N1177. Conclusion. Macrophage-rich atherosclerotic plaques can be detected in vivo with N1177-enhanced CT in hypercholesterolemic rabbits. This technique is promising for the non invasive detection of vulnerable atherosclerotic plaques with CT.