|Category||Diameter Reduction (%)||Velocity Criteria||Flow Characteristics|
|A||0||PSV <125 cm/s||Minimal or no spectral broadening; flow separation within bulb often detected; no plaque visualized on B-mode|
|B||1–15||PSV <125 cm/s||Minimal spectral broadening; plaque visualized on B-mode image|
|C||16–49||PSV <125 cm/s||Spectral broadening fills the systolic window; plaque visualized on B-mode|
|D||50–79||PSV ≥125 cm/s||Marked spectral broadening often detected|
|D+||80–99||EDV ≥140 cm/s||Marked spectral broadening|
|E||Occlusion||NA||No flow detected in ICA; occlusive signal with low or reversed diastolic flow in CCA|
Doppler signals acquired 60° angle to vessel axis with 5-MHz probe and small sample volume. Diameter reduction used the diameter of the carotid bulb as denominator. Data from Roederer et al. (18).
CCA = common carotid artery; EDV = end diastolic velocity; ICA = internal carotid artery; PSV = peak systolic velocity.