Spectral broadening (ultrasound)

Last revised by Yuranga Weerakkody on 17 Aug 2021

Spectral broadening is an important artifact in pulsed wave Doppler ultrasound imaging, due to its clinical relevance as a sign of vessel stenosis. 


Spectral broadening is caused by turbulence in blood flow as the normally homogeneous velocity of reflective red blood cells becomes more diverse, resulting in the apparent broadening of the spectral Doppler waveform. Typically this results in a "fill-in" of the area between a curve and the baseline due to varying velocity of reflectors in the sampling area. This is hallmark feature of poststenotic flow, which is increasingly turbulent with the progression of the narrowing. However, improper acquisition technique can also result in spurious spectral broadening via a variety of ways 1

Practical points

Spectral broadening is a valuable sign in arterial Doppler imaging, e.g. in the assessment of the carotids. It can signal the development of significant stenosis in difficult situations where e.g. direct measurement in the most stenotic areas is not possible due to circumferential atherosclerotic plaques resulting in complete acoustic shadowing. Observing spectral waveform broadening distal to this "black box" segment indirectly indicates significant narrowing. 

However, care must be taken to use a proper measurement technique in order to avoid spurious broadening of the spectrum. Artifactual spectral broadening is dependent on the angle of insonation and will increase as the angle approaches 90°. Maintaining a proper orientation (<60°) of the ultrasound beam can minimize this artifact 2. Care must be taken to use an appropriately sized sample volume within the interrogated blood vessel. If the sampling area is too wide, or too close to the vessel wall, the inclusion of slower velocity flow along the vessel walls will result in spectral broadening, which can be mistaken for poststenotic turbulence. A high pulsed wave Doppler gain setting can also result in spectral broadening 1,3


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