Table III.
Types of plaques in OCT images.
| Type of plaque | Feature | OCT image performance | Sensitivity and specificity (%) |
|---|---|---|---|
| Fibrous plaque | The pathological feature is the pathological thickening of the intima, and an intimal thickness of 600 µm is regarded as the limit value between normal and pathological intimal thickening. In OCT, it is characterized by low attenuation, homogeneity and fine texture | It has a relatively uniform and highly reflective optical signal. If the inner elastic membrane and outer elastic membrane cannot be seen in the lesion, the lesion should be carefully considered as a fibrous plaque | 79, 97 |
| Calcified plaquea | The pathological feature is that calcium salt is deposited in the necrosis and the fibrous cap, and the arterial wall becomes hard and brittle. In OCT, it is characterized by low back reflection and low attenuation, with sharp edges | It is manifested as a sharp-edged low signal or uneven signal area. This definition is suitable for large calcifications. It has not been determined whether the above OCT definition is suitable for micro-calcification | 95-96, 97 |
| Lipid plaque | Pathological characteristics: Lipid deposition in the fat streak, smooth muscle cells in the middle membrane migrate into the inner membrane, part of the proliferation forms a fibrous cap, part of the phagocytosis of lipids forms smooth muscle-derived foam cells, which evolve into lipid plaques. In OCT, the edges are blurred or features are illegible | The edge contour is blurred in the weak optical signal area and there is a high signal fiber cap on the surface of the low signal area. When diagnosing lipid plaques deep in tissues, caution is warranted, as the attenuation of OCT signal may also lead to the appearance of weak signal areas. Therefore, OCT is more accurate at identifying lipid plaques and lipid pools near the surface of the lumen. It is generally thought that when the external elastic membrane cannot be identified, OCT cannot measure the thickness, area or volume of the lipid pool. In OCT images, the angle of the lipid pool is frequently used to evaluate the size of the lipid pool | 90-94, 90-92 |
| Microstructure within plaque | |||
| Macrophage infiltration | The rich lipid components in macrophages may cause significant attenuation or blocking of OCT signals | Highly reflective, strongly attenuated dot or stripe structure, frequently forming radial shadows behind high-signal dotted areas. At present, OCT images mainly evaluate macrophages in fibrous plaques and lipid plaques | - |
| Microchannel | From the adventitia of the blood vessel to the intima, it communicates with the blood vessels around the adventitia and finally extends to the coronary artery lumen | A hole with a diameter of 50-300 µm, weak signal and sharp edges, and may usually be tracked in multiple consecutive frames. It has not yet been determined whether these blood vessels are connected to the surface of the lumen or originate from nourishing blood vessels | - |
| Cholesterol crystals | It is usually located in the fibrous cap and the core of lipid. necrosis | Thin linear regions with higher signal strength and lower. attenuation | - |
aIncludes four categories: Annular calcification (angle of calcification spots exceeding 270˚), spotty calcification (refers to calcification with an angle of calcification <90˚ and a length <10 mm), deep calcification (refers to the calcified plaque being >100 µm away from the lumen) and superficial calcification (refers to a distance between the calcified plaque and the lumen of 65-100 µm). OCT, optical coherence tomography.