On the use of Doppler bandwidth for more accurate blood flow estimation

If the range cell or measurement volume of a Doppler flow measurement system is small enough so that the flow through it is of uniform velocity, the resulting Doppler spectrum will be relatively narrow, with a mean frequency related to the velocity in the range cell by the Doppler equation. If the range cell is now enlarged so as to encompass a range of velocities, the resulting Doppler spectrum will broaden correspondingly. It is shown theoretically and confirmed by experiment, that this broadening of the Doppler spectrum which accompanies an increase in length of the range cell, does not affect the maximum frequency of the spectrum which remains constant, being a function only of the maximum velocity passing through the range cell. Applications of this phenomenon to blood flow estimation in narrow vessels is discussed