The determination of maximum velocity from Doppler blood flow spectrum in the stenosed vessels

In this paper, the relationship between the blood flow velocity and Doppler power spectrum in stenosed vessel is investigated to determine the variation between the maximum velocities and their frequency locations at the spectra in the vessels with different degrees of stenosis, and then a new method is proposed to extract the maximum velocity of blood flow in narrowed vessels. Firstly, a geometric vessel-model with stenosis of bilateral symmetry axis is established to get the flow velocity distributions for different degrees of stenosis, and then the Doppler spectra from entire segment of the vessel covered by sound field are calculated. Finally, corresponding maximum frequency locations in the spectra are determined according to a comparison between the maximum values from blood flow velocity distributions and their calculated spectra. The theoretical analysis shows that the maximum frequencies, which correspond to the maximum velocities of blood flow for different degrees of stenosis, locate at different positions in the spectral falling-edge. For the normal vessel, the location is at the middle position of the falling-edge, and down shifts along the falling-edge with the increase of the stenosis degree approximately linearly. The proposed method could be helpful to extract the maximum velocities of blood flow in stenosed vessels.