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In non‐stented lesions there are two strong acoustic interfaces that are well visualized by ultrasound: the leading edge of the intima and the outer border of the media (or media–adventitia junction). Therefore, two cross‐sectional area (CSA) measurements can be defined by IVUS: the lumen CSA and the media–adventitia CSA (or EEM CSA). The atheroma or plaque&media (P&M) complex is calculated as EEM minus lumen; the media cannot be measured as a distinct structure. Thus, complete quantification of a non‐stented lesion is possible by tracing the EEM and lumen areas of the proximal reference, lesion, and distal reference; calculating derived measures (minimum and maximum EEM and lumen diameters, P&M area and thickness, and plaque burden; P&M divided by EEM); and measuring lesion length (distance between the proximal and distal reference) (Figure 8.3).

Figure 8.3 IVUS measurements pre‐intervention in a non‐stented artery. The proximal and distal reference and minimum lumen area (MLA) of the lesion are shown. The IVUS study is shown in duplicate: one unlabeled and one highlighted with lines to illustrate quantitative analysis. The dashed line highlights each external elastic membrane cross‐sectional area (EEM CSA), and the solid line indicates each lumen interface (lumen CSA). The minimal lumen cross‐sectional area (lumen CSA) at the lesion site is 2.1 mm². Between the EEM CSA and lumen CSA, the atheroma or plaque&media (P&M) complex is calculated.

In stented vessels, the stent forms a third measurable structure (stent CSA). It appears as bright points along the circumference of the vessel. Complete quantification of a stented lesion is possible by tracing the EEM and lumen areas of the proximal and distal reference and the EEM, lumen, and stent areas of the stented lesion; calculating derived measures (minimum and maximum EEM, stent, and lumen diameters; peri‐stent P&M area and thickness; and intra‐stent intimal hyperplasia [IH, area and %IH); and measuring stent length. With the use of motorized pullback, area measurements can be added to calculate volumes using Simpson’s formula.