MRI AND NMR-SPECTROSCOPY OF THE LIPIDS OF ATHEROSCLEROTIC PLAQUE IN RABBITS AND HUMANS

The early stages of atherosclerosis are characterized by the depositio n of cholesteryl esters and triglycerides into the arterial wall. In t he excised human atherosclerotic plaque these lipids are in a liquid-l ike state at body temperature and observable via MRI and NMR spectrosc opy, To assess the ability of MRI to quantitatively image the lipids o f atherosclerotic plaque in vivo, we have investigated eight New Zeala nd White rabbits fed atherogenic diets (2 weight (wt)% cholesterol, 1 wt% cholesterol + 6 wt% peanut oil, and 1 wt% cholesterol + 6 wt% corn oil). Postmortem examination indicated that all rabbits developed ath erosclerosis in the aorta, Except for one animal, magnetic resonance a ngiography showed no noticeable obstruction in the aorta. MRI was carr ied out in an attempt to image atherosclerotic plaque lipids directly, but no signal was detected in vivo. However, a plaque lipid signal wa s observed from excised tissue using a small diameter RF coil, H-1 NMR spectroscopy of the atherosclerotic plaque from excised aortas indica ted that the major fraction of plaque lipids in rabbits is not in a li quid state at physiological temperature and are only marginally MRI-vi sible compared to human plaque lipid, The differences in the MRI chara cteristics of rabbit and human plaque are due to differences in the fa tty acid profile of the cholesteryl esters, chiefly a decrease of lino leic acid in rabbit lesions.