Intense interest in the pathology of vulnerable plaques has lead to the recognition that plaque composition, more than degree of vessel occlusion, is the primary determinant of stability. Plaques prone to rupture are generally characterized by thin fibrous caps, large, lipid-rich cores, with high macrophage content. Macrophages present in the developing plaque release cytokines and other factors that can weaken the fibrous cap, eventually leading to plaque instability and rupture. In the coronary arteries, numerous reports have observed that high macrophage density is characteristic of lesions vulnerable to rupture. Furthermore, it has been observed that the pattern of distribution of macrophages in the plaque correlates with degree of instability. An ex vivo study of human coronary artery plaque specimens showed that the extent of inflammation at the plaque shoulders appears to correlate with degree of vulnerability slightly unstable plaques have little or no inflammation at the plaque shoulders, while highly unstable plaques have extensive inflammation at the plaque shoulders. Therefore, the ability to image plaques at high resolution to determine macrophage content and distribution could provide a means to noninvasively assess plaque vulnerability and degree of risk to rupture in inflamed arteries. There is currently no clinical method to assess plaque vulnerability in vivo; the ability to do so could provide a critical diagnostic to guide management of patients with vascular disease. The gold standard for imaging atherosclerotic disease is angiography. Angiographic images provide information on decreasing of vessel lumen as plaques invade the luminal space. Highly stenotic plaques may be revealed by this technique; however angiography cannot provide direct assessment of the extent of disease in the vessel wall, nor can it detect disease in vessels that have positive remodeling to enlarge vessel diameter in response to plaque growth. The recognition that the majority of clots leading to acute coronary events occur in plaques that are not highly stenotic highlighted the need for alternative imaging methods that can directly image the vessel wall. There are a number of alternative techniques to image plaques including invasive modalities such as intravascular ultrasound, angioscopy, thermography, optical coherence tomography, raman spectroscopy, near infra-red spectroscopy and intravascular MRI. These invasive techniques involve intravascular transceivers that must be threaded into the vessel being examined and therefore are unsuitable for exploratory imaging to assess overall plaque LDN-193189 burden in the patient. Noninvasive methods are better suited for examining larger regions; ultrasound, computed tomography and magnetic resonance imaging have received the most attention. Ultrasound and computed tomography can provide information about cap thickness and plaque calcification but MRI shows the most promise for assessing both structure and lipid composition to evaluate plaque stability.