Sonographic NASCET index

Notes

Original Sonographic NASCET index (SNI)
  • The highest measured angle-adjusted velocity in each segment should be used for calculating the SNI
  • SNI is calculated using the following formula:
    • SNI = [1 – (PSVd / PSVp)0.5] x 100
    • Where
      • PSVd = maximum angle-adjusted PSV in the normal distal internal carotid artery (ICA)
      • PSVp = maximum angle-adjusted PSV at the maximum narrowing of the ICA
  • SNI can be used to aid the identification of significant (>70%) ICA stenosis but is neither a standalone tool, nor the substitute for grading systems such as e.g. the SRU criteria
  • It has been shown that an SNI threshold value of 45.5 has a high specificity (94%) but modest sensitivity (80%) in identifying >70% ICA narrowing, while a threshold value of 33.3 has a greater sensitivity (93%) with an associated drop in sensitivity (82%)
  • Note that since flow velocity parameters become inaccurate in critical stenosis or near-occlusions SNI should not be relied upon in these cases

Hathout GM, Fink JR, El-Saden SM, Grant EG. Sonographic NASCET index: a new doppler parameter for assessment of internal carotid artery stenosis. AJNR Am J Neuroradiol. 2005 Jan;26(1):68-75. PMID: 15661704; PMCID: PMC7975044.

Last updated: 2022-02-19