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Optical coherence tomography revisited: imaging and imagination.

Optical coherence tomography (OCT) was introduced into cardiovascular imaging in 19971, emerging as a spin-off from an original scientific invention within the field of ophthalmology to enable imaging of retinal microstructures including arterioles and to facilitate detection of early degenerative changes of retinopathies. Consequently, OCT was praised as being a ground-breaking imaging technology which provides a far superior resolution as compared to the already established ultrasound-based imaging system (intravascular ultrasound [IVUS]). As such, it provides high-resolution tomographic images (10-20 μm), which enable recognition of atherosclerotic plaque patterns2,3, and can be used to identify high-risk lesions including their thrombotic complications. More specifically, it allows measurement of fibrous cap thickness and is used to identify high-risk coronary plaques that are prone to disruption. However, limited penetration of light, especially in diseased vessel wall segments, has been the Achilles’ heel of OCT imaging in coronary arteries. Distribution of light when passed through a tissue is predicated on its intrinsic optical properties. Lipid-rich tissue displays a high level of attenuation and has a low penetration depth, making it difficult to identify underlying plaque morphology correctly. This fact makes OCT penetration depth in arteries dependent on tissue type and limits correct classification of lesions where lipid content is high. Against this background, in this issue of EuroIntervention, Poulsen et al report the findings of a preclinical study comparing plaque morphology in the coronary arteries of five transgenic hypercholesterolaemic mini-pigs using OCT with co-registered histology4.