Standard duplex		Stenosis %	Colour Doppler
Systolic velocity cm/s	Spectral analysis
> 250	± Negative low frequencies of high energy	70‐100	Marked colour fading. Severe lumen narrowing. ± post‐stenosis flow reversal. ± mosaic pattern
> 130	± Low frequency of high energy	50‐69	Moderate color fading. Moderate lumen narrowing. ± mosaic pattern
110‐130	± Minimal spectral broadening	30‐49	Laminar flow or color fading during systole
< 110	Normal spectrum	0‐29	Laminar flow. Red flow in systole and diastole