Optical coherence tomography
Every year over one million people in the United State suffer an acute myocardial infarction. Spontaneous rupture or erosion of atherosclerotic plaques with subsequent thrombosis is the most frequent underlying cause of acute coronary syndromes. Autopsy studies have identified several histologic characteristics of plaques that are prone to disruption, so-called vulnerable plaques. Pathologic characteristics of these vulnerable plaques are (1) a thin fibrous cap (<65 µm); (2) a large lipid pool; and (3) activated inflammatory cells, such as monocytes, macrophages, form cells, lymphocytes, and neutrophils, near the fibrous cap.1-4 To date, a variety of diagnostic tools to detect structural abnormalities in vulnerable plaques have been developed. Intravascular optical coherence tomography (OCT) is a recently developed optical imaging technique that provides highresolution, cross-sectional images of tissue in situ.5 OCT originates from early work on white-light interferometry and optical coherence-domain reflectometry (OCDR). OCDR is a one-dimensional optical ranging technique that uses short coherence length light and interferometric detection6 that was evolved for finding faults in fiberoptic cables and network components.7 Its potential for medical application was soon recognized.8,9 Researchers at the Massachusetts Institute of Technology extended the technique of OCDR and developed optical coherence tomography in the early 1990s as a two-dimensional, tomographic imaging modality in biologic systems.10 The second dimension of the two-dimensional image was created by a physical translation or rotation of a fiberoptic probe. Since then, improvements of the light source, the interferometer, and beam scanning optics have been continuously pursued.11-13 Today - similar to intravascular ultrasound (IVUS) - intracoronary OCT allows for real-time imaging of the arterial wall but offers 10 times higher resolution and, thus, the possibility of detecting thin fibrous caps. An overview on image resolution of different diagnostic techniques is given in Table 17.1.14 This chapter gives an overview on currently available OCT technology for intracoronary application and summarizes the line of investigation with respect to vascular plaque characterization.