On Accurate Evaluation of Flow Rate by Ultrasonic Pulsed Doppler Method.

Abstract

Accurate evaluation method of flow rate using medical ultrasonic diagnostic equipment is presented and the factors of the error are discussed. The method takes B-mode ultrasonotomography with pulsed Doppler method and utilizes the video displayed power spectrum. In the method it is assumed that the velocity profile in the blood vessel is axisymmetric and that the power contribution at any Doppler frequency is proportional to the number of red cells with the velocities. The normalized power spectrum is distributed as the velocity profile on the vessel diameter and the profile is rotated. Then the velocity profile in the sectional area of the vessel is integrated and the flow rate is obtained. Experimental data show that the method is accurate compared with the conventional methods using the mean or maximum Doppler frequency. Furthermore, we construct the simplified simulation model and estimate the flow rate using the power spectrum of reflected ultrasound by fast Fourier trnsforms (FFT). It is found that the spectral broadening by FFT using finite discrete data is the major factor of the error. As the maximum velocity increases, the error decreases. Therefore, the error of the flow rate in the blood vessels at diastole is larger than systole.