What this calculator does
Converts measured residual lumen and reference diameters into NASCET and ECST percentage estimates.
Enter the narrowest lumen, distal normal ICA, and estimated original bulb diameter.
Clinical scope
Use the calculator for extracranial internal carotid artery stenosis when the narrowest residual lumen and the method-specific reference diameter can be measured reliably on CTA or MRA.
Applicability and exclusions
- Near-occlusion and complete occlusion must be recognized morphologically; a simple percentage can be misleading.
- NASCET and ECST use different reference diameters, so their percentages are not interchangeable.
Method and calculation logic
NASCET compares the narrowest lumen with the normal distal ICA. ECST compares it with the estimated original diameter at the stenosis. Always state the method with the percentage.
NASCET stenosis = (1 - narrowest lumen / distal normal ICA) × 100ECST stenosis = (1 - narrowest lumen / estimated original bulb) × 100Interpretation table
| NASCET result | Common descriptor |
|---|---|
| <50% | Mild |
| 50-69% | Moderate |
| 70-99% | Severe; exclude near-occlusion |
| No patent lumen | Occlusion; assess directly, not by formula |
Worked example
Case: Fictional example: narrowest lumen 1.5 mm, distal normal ICA 5.0 mm, estimated original bulb 6.0 mm.
Calculation: NASCET = 70%; ECST = 75%.
Interpretation: Report both only when both reference measurements are defensible, label each method, and separately assess near-occlusion.
How to use this calculator
- Complete the visible imaging and measurement fields. Required inputs are marked in the workbench.
- Review the calculated category, score, measurements, and any recommendation or warning.
- Copy the report-ready text only after checking the result against the complete examination and source guideline.
Calculator-specific questions
Why are NASCET and ECST percentages different?
They use different reference diameters: distal normal ICA versus estimated original bulb diameter.
Can near-occlusion be calculated reliably as a percentage?
Often no. Distal collapse changes the reference diameter, so morphological criteria and guideline-specific reporting are required.
Are patient measurements sent to RadPhrases?
No. Calculator inputs and results are processed in the browser and are not submitted by this page.