Optical Coherence Tomography to Optimize Stent Deployment: Seeing is Believing

Abstract

Optimal coherence tomography (OCT) is a new light-based intracoronary imaging modality with unprecedented spatial resolution. Currently, its axial resolution is only 15 mm, that is, 10 times higher than that of more classical techniques such as intravascular ultrasound (IVUS) based on ultrasounds (150 mm). Optimal coherence tomography therefore provides extremely high-quality images of the coronary wall, especially of the structures closest to the vessel lumen. Moreover, numerous studies with histological validation have confirmed its ability to adequately differentiate the distinct types of atheromatous plaque, including fibrous plaques (homogeneous, signal-rich regions), lipid plaque (progressively signal-poor regions) and calcified plaque (signal poor, sharp border lesions). For the first time, OCT allows precise measurement of the thickness of the fibrous cap covering the lipid cores and in vivo diagnosis of the presence of thin-cap fibroatheromas. Similarly, this technique can identify the characteristic signs produced by the accumulation of macrophages and cholesterol crystals in the vessel wall, as well as the presence of small ruptures of the intima and of intracoronary thrombi that could not be visualized with IVUS until now. All these properties explain the enormous attractiveness of this technique in the characterization of vulnerable plaques and in the study of the micromorphology of plaques that have already developed a complication. However, the penetration of OCT in the vessel wall is limited and consequently visualization of structures beyond the lumen (near the adventitia) is compromised when there is a substantial amount of atheromatous plaque. Equally, OCT cannot penetrate through red thrombi (fibrin-rich), which produce an intense posterior shadow. Therefore, OCT is not suitable for measuring the total volume of atheromatous plaque. To do this, IVUS remains the technique of choice when the aim is to study the progression or regression of coronary atherosclerosis. From a practical point of view, with the initial technology (time domain), image acquisition was relatively slow and, due to the need to completely eliminate blood from the interior of the