Abstract 2610: In vivo Carotid Plaque Characterization Using T2*-Based Magnetic Resonance Analysis and the Role of Iron in Atherosclerosis
Background. Iron catalyzes lipid oxidation, is present in elevated concentrations in atherosclerotic plaque, and may contribute to plaque formation and destabilization; however, direct studies relating clinical history and iron in humans have not been performed to date. The magnetic resonance (MR) relaxation parameter T2* has been shown to accurately quantify myocardial and hepatic iron content in vivo. We investigated T2*-based characterization of carotid plaque in conjunction with ex vivo analyses.
Methods and Results. 25 patients referred for carotid endarterectomy completed clinical assessment to document events attributable to their carotid disease and preoperative MRI. The MR protocol performed on a standard 1.5 Tesla scanner used a variable echo gradient echo sequence with blood suppression to quantify T2* within the carotid plaque. The spatial resolution was 0.5mm x 0.5mm x 3mm. Analysis of explanted carotid plaques included electron paramagnetic resonance (EPR), inductively-coupled plasma mass spectroscopy (ICPMS), and histopathology. Symptomatic patients compared to asymptomatic patients had lower plaque T2* values in vivo (19.4±16.0 vs. 34.1±27.0 ms, p<0.02), and more iron (61.9±44.5 vs. 21.38±24.5 μg/g, p<0.01), more copper (1.03±0.68 vs. 0.42±0.27 μg/g, p<0.01), and less calcium (10.6±7.6 vs. 63.5±32.6 μg/g, p<0.05) by ex vivo analysis. EPR demonstrated a strong rhombic iron signal in plaques but not control vessels.
Conclusion. Measurement of plaque T2* is feasible at 1.5 Tesla, and may be useful in distinguishing plaques that produce clinical events. Further studies of iron and other factors producing this T2*-shortening effect are warranted.