| Diameter stenosis category | Peak systolic velocity | End diastolic velocity | Systolic velocity ratio (ICA/CCA) | Diastolic velocity ratio (ICA/CCA) |
| 0% | 110 cm/s | 40 cm/s | 1.8 | 2.6 |
| 1%‐39% | 110 cm/s | 40 cm/s | 1.8 | 2.6 |
| 40%‐59% | 130 cm/s | 40 cm/s | 1.8 | 2.6 |
| 60%‐79% | 130 cm/s | 40 cm/s | 1.8 | 2.6 |
| 80%‐99% | 250 cm/s | 100 cm/s | 2.5 | 5.5 |
| 100% | N/A | N/A | N/A | N/A |
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