Doppler Spectrum

Blood flow profile Width of ultrasound beam Sample volume size Intrinsic spectral broadening Blood flow profile - Blood flows through the vessel at many different velocities. Different velocity flow profiles are observed in arteries.

Laminar or parabolic flow describes flow in a vessel that is faster near the center of the vessel and slower near the vessel wall. Flow is slower at the vessel wall due to the viscosity of blood. Assuming that the entire vessel is completly insonated by the Doppler beam the velocities from all regions would be represented in the Doppler signal. The Doppler signal would display a wide range of frequencies. The spread of frequencies within the Doppler spectrum is known as spectral broadening.

A velocity profile for blunt flow describes flow that is all the same velocity. The Doppler signal will show that most of the blood cells are travelling at the same velocity and within a small range of frequencies.

Click on the thumbnail clinical image below to view the Doppler spectrum. Laminar flow is demonstrated with insonation of the entire vessel.