Table 4.
Advantages and disadvantages of respective intravascular modalities.
| GS-IVUS | VH-IVUS | NIRS | OCT | |
|---|---|---|---|---|
| Fibroatheroma | Can identify lipid plaque—so-called “soft” plaque—which is described as the area with low echogenicity in contrast to the reference adventitia. | VH-IVUS cannot directly identify fibroatheroma. Fibroatheroma is described as the presence of 10% confluent necrotic core with an overlying layer of fibrous tissue on three consecutive frames (2). | Shows the probability of lipid as yellow pixels on the chemogram and lipid core burden index (LCBI). | Can identify lipid plaque described as signal-poor regions with diffuse borders (lipid pool) and overlying signal-rich bands (fibrous caps), accompanied by high signal attenuation. Due to this limitation, it is frequently not possible to assess the diameter of the artery with lipid plaque. |
| Calcification | Bright echo obstructing penetration of the ultrasound (casting acoustic shadow). Due to this limitation, the depth of calcification cannot be measured. | Visible as white pixels. | NA | Signal-poor regions with sharply delineated borders and limited shadowing. Due to good visualization of calcification, it is very easy to measure both the depth and angle of calcification. |
| Fibrocalcific plaque | Mixed plaque containing fibrous plaque and calcifications (1). | Presence of 10% confluent dense calcium without confluent necrotic core (2). | NA | NA |
| Calcific nodule | Calcification protruding to the lumen. | NA | NA | Calcification protruding to the lumen. |
| TCFA | GS-IVUS does not have a resolution high enough to visualize TCFA. | VH-IVUS cannot identify TCFA directly. TCFA is described as the presence of 10% confluent necrotic core in direct contact with the lumen on three consecutive frames (2). | NA | Lipid plaque with a minimum thickness of the fibrous cap of less than 65 μm or 80 μm and with lipid occupying >90° in circumference. |
| Erosion | NA | NA | NA | Presence of attached thrombus overlying an intact and visualized plaque (3). |
| Rupture | Plaque ulceration with possible remnants of the fibrous cap at the edges. Usually hard to identify. | NA | NA | Disruption of fibrous cap with visible cavity. |
| Thrombus | Intraluminal mass with layered or pedunculated appearance. Usually hard to distinguish from soft plaque. | Thrombus may be visible on VH-IVUS as plaque. | NA | Protruding mass either attached to the luminal surface or floating within the lumen (4). |
GS-IVUS, gray-scale intravascular ultrasound; NIRS, near-infrared spectroscopy; OCT, optical coherence tomography; TCFA, thin-cap fibroatheroma; VH-IVUS, virtual histology intravascular ultrasound. (1) Intermediate echogenicity between soft (hypoechoic) plaque and highly echogenic calcified plaques. (2) Necrotic core on VH-IVUS is visible as red pixels, calcium is visible as white pixels. (3) OCT does not have resolution high enough to visualize erosion. (4) Red thrombus is erythrocyte-rich and is highly backscattering and has high attenuation whereas white thrombus is platelet-rich and is less backscattering and has lower attenuation.