Internal carotid artery stenosis criteria–Ultrasound (NASCET)
| % Stenosis | ICA PSV(cm/sec) | ICA/CCA PSV ratio | ICA EDV(cm/sec) |
| <15% | <125 with deceleration spectral broadening | ||
| 16-49% | <125 with pansystolic spectral broadening | ||
| 50-69% | >125 AND | 2 – 4 OR | <110 |
| 70-79% | >270 OR | >4 OR | >110 |
| 80-99% | >140 | ||
| Complete Occlusion | No flow | No flow | No flow |
Internal carotid artery stenosis criteria–Ultrasound (SRU)
| % Stenosis | ICA PSV(cm/sec) | ICA/CCA PSV ratio | ICA EDV(cm/sec) |
| Normal | <125 (no plaque) | <2.0 | <40 |
| <50% | <125 (visible plaque) | <2.0 | <40 |
| 50-69% | 125-230 | 2.0-4.0 | 40-100 |
| 70%-less than near occlusion | >230 | >4.0 | >100 |
| Near Occlusion with marked narrowed lumen | Variable | Variable | Variable |
| Total Occlusion | Undetectable | Undetectable | Undetectable |
PSV = peak systolic velocity; EDV = end diastolic velocity; ICA = internal carotid artery; CCA = common carotid artery