The importance of Doppler angle of insonation on differentiation between 50-69% and 70-99% carotid artery stenosis

Aim: to investigate the importance of Doppler angle differentiating between 50-69% and greater than or equal to 70% internal cartoid artery (ICA) sten osis. Material and methods: fifty-one patients with a previous diagnosis of 50-69 % ICA stenosis (n = 53) were re-evaluated by duplex scanning. Spectral Dopp ler velocity waveforms were obtained from common cartoid (CCA), ICA and ext ernal (ECA) cartoid arteries with the same Doppler angle of insonation as u sed at the initial duplex scanning, followed by repeated measurements with a fixed 60 degrees angle of insonation. Results: the peak systolic velocity (PSV) in the ICA was 181 +/- 55 cm/s (m ean +/- SD) at the second duplex scanning when the same angle of insonation (mean 46 degrees +/- 9) was used as during the initial investigation. When the examination was done with a 60 degrees angle of insonation, PSV ICA wa s 261 +/- 96 cm/s (mean +/- SD). In fifteen arteries of insonation at 60 de grees of ICA stenosis changed from 50-69% to 70-99% due to the application of a fixed Doppler angle of insonation at 60 degrees. Conclusion: the Doppler angle of insonation has a significant effect on spe ctral Doppler velocity measurements. It is crucial that duplex criteria are standardised with a fixed angle of insonation and that this angle is consi stently used during velocity estimations.