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 >/=70% internal carotid artery (ICA) stenosis.

Material and methods: fifty-one patients with a previous diagnosis of 50-69% ICA stenosis (n =53) were re-evaluated by duplex scanning. Spectral Doppler velocity waveforms were obtained from common carotid (CCA), ICA and external (ECA) carotid arteries with the same Doppler angle of insonation as used 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 (mean+/-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 was 261+/-96 cm/s (mean+/-SD). In fifteen arteries the estimated degree 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 spectral Doppler velocity measurements. It is crucial that duplex criteria are standardised with a fixed angle of insonation and that this angle is consistently used during velocity estimations.