Molecular imaging of macrophages in atherosclerotic plaques using bimodal PEG-micelles

incubating for 45 minutes on a roller-bench at room temperature. The SATA-derivatized antibody was deacetylated by incubation with a hydroxylamine solution for 1 hour at room temperature. The activated antibody was added to the micelles. This preparation was stored at 4 °C under N2 overnight. Uncoupled antibody was separated from immunomicelles by washing twice. The size of this contrast agent was below 20 nm as determined with dynamic light scattering. Twelve thirteen-month-old apoE-KO mice were used for this study. The apoE-KO animals were fed a Western diet for 20 weeks. MSR-targeted micelles or untargeted micelles were administered at a dose of 0.075 mmol Gd/kg via intravenous injection into the tail vein. High resolution T1weighted images (pixel size: 0.109×0.109×0.5 mm 3 , TR: 800 ms and TE 9ms) of the abdominal aorta were acquired before, and 24 hours post injection at a Bruker 9.4 T, 89 mm-bore system. Images were analyzed using Mathematica (Wolfram Research, Inc.). The contrast to noise was defined as CNR = (I wall – I muscle)/I noise, which is a measure for how well the vessel wall can be discriminated from the surrounding tissue. Immediately after the imaging at 24 hours post micelle injection, the animals were sacrificed. The presence of MSR-targeted micelles containing rhodamine was compared to the location of macrophages studied by immunohistochemistry (anti-CD68 antibody) on fluorescence microscopy of aortic cross-sections corresponding to MRI slices.