scanner (Signa HDx, GE Healthcare) with a 50mT/m, 150T/m/s gradient system and a custom 3 cm surface radiofrequency coil. Another group of mice (n = 3) were injected with an 8-fold lower dose of FeCo/GC (32 mg Fe/mouse) and imaged at 48 hours on a small-bore 7T system (30 cm bore magnet, Varian Inc. plus GE ‘‘Micro-Signa’’ environment), with a 9 cm gradient insert (770mT/m, and 2500T/m/s, Resonance Research, Inc.) and a custom 6-cm RF coil. To detect the T2* effects of FeCo/GC, bright-blood images were acquired using gradient echo sequences (3T: repetition time (TR) = 100 ms, echo time (TE) = 10 ms, matrix size = 2566256, slice thickness = 1.0 mm, field of view (FOV) = 3 cm, flip angle = 60u; 7T: same parameters except TR/ TE = 50 ms/4.2 ms, slice thickness = 0.5 mm). The slice position was matched using the aortic arch as a reference point. Image analysis For in situ carotid fluorescence imaging, regions-of-interest (ROIs) were placed on the left and right carotid regions and trachea. Average signal intensity divided by exposure time for left and right carotids was calculated and normalized to the trachea signal. For ex vivo carotid imaging, ROIs were placed around the entire left or right carotid artery and total signal intensity divided by exposure time was calculated. For in vivo MRI, FeCo/GC accumulation was assessed by measuring the extent of T2*- induced reduction in carotid lumen size, which was calculated as follows: % reduction of carotid lumen area = (1-[post-contrast carotid lumen area]/[pre-contrast carotid lumen area]) x 100% [15]. Histology After euthanasia, carotid arteries were cut into two 3 mm sections. These sections, as well as liver and heart, were embedded immediately in optimum cutting temperature (OCT) compound (Sakura Finetek USA, Inc., Torrance, CA) and flash frozen in liquid References 1. 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PLoS ONE | www.plosone.org 5 January 2011 | Volume 6 | Issue 1 | e14523