Fig. 5: CT for quantitative coronary atherosclerosis imaging.

Example of plaque characterization using CT angiography, intravascular ultrasonography (IVUS), optical coherence tomography (OCT) and histology. a, A volume-rendered (left panel) and a curved multiplanar reconstruction (right panel) of CT taken from a male patient aged 62 years with atypical angina using a photon-counting detector scanner with 0.2-mm slice thickness (part a). Parts b–e show cross-sectional correlations showing fibroatheroma with sheet calcification and lipid pool (part b), fibrous plaque and a small side branch (SB) (part c), early fibroatheroma and a large SB (part d), and adaptive intimal thickening (part e); derived from CT, IVUS, OCT and histology. These images were acquired as part of an ex vivo investigation (courtesy of Cardiovascular Imaging Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA). High-risk plaque features related to major adverse cardiovascular events depicted on CT (part f). Spotty calcification is a marker of ongoing inflammation: the image shows a cross-section of a partially calcified plaque (spotty calcification diameter <3 mm in all directions). Napkin-ring sign: the central area of the plaque adjacent to the coronary lumen represents a lipid-rich core (low attenuation), which is surrounded by a peripheral rim of fibrous tissue in the vessel wall (higher CT attenuation). Positive remodelling of a non-calcified plaque: the dotted yellow lines indicate the vessel wall and show outward remodelling of the vessel wall at the location of highest plaque volume. Remodelling is calculated using vessel cross-sectional areas at the site of maximal stenosis or plaque divided by the average cross-sectional areas of proximal and distal reference segments, and an index of ≥1.1 is used to define positive remodelling. Low-attenuation plaque: a non-calcified plaque with an average attenuation of <30 Hounsfield units (HU). The napkin-ring sign, positive remodelling and low attenuation are associated with an increased risk of subsequent plaque rupture (Fig. 2). Pericoronary adipose tissue on CT has emerged as a strategy to detect and quantify coronary artery inflammation (part g). Pericoronary adipose tissue is shown using coloured attenuation maps around the right coronary, with a higher value (in terms of HU) indicating inflammation and a possible increased risk of disease in the future. Ao, aorta; L, lumen; LAD, left anterior descending coronary artery; LCx, left circumflex coronary artery.