Multicolor CT is the popular name for spectral computed tomography. In spectral CT system, the incident x-rays are divided into multiple energy bins and is used for multicolour imaging. Gold high density nanoparticle contrast agent (Au-HDL) can be used for characterization of macrophage burden as they are taken up by the macrophages in the atherosclerotic plaques. A recent study published in Radiology. 2010 Sep;256(3):774-82 by Cormode DP et al evaluated the use of gold nanoparticles along with multicolour CT in animal studies of atherosclerotic plaques. Multi colour CT enabled differentiation of gold nanoparticles, iodine based contrast and calcium phosphate. Gold nanoparticles were located primarily in the macrophages in the aortic sections. This combined imaging enabled characterization of stenosis by the plaques, calcification and the macrophage burden. Macrophage rich plaques are considered as vulnerable plaques prone for rupture and producing vascular events like acute coronary syndrome.