Estimation Of Doppler Ultrasound Blood Flow Velocity Profile Based On EEMD

Cardiac cerebral vascular disease（CCVD）has become one of the largest threats to human health.Many clinical studies show that atherosclerosis is the main cause of CCVD.Atherosclerosis will cause the change of blood flow velocity profiles（BFVPs）.Doppler ultrasound technology is widely used to explore the BFVP because of its advantages of non-invasive,safety and reliability.It is significance for the measurement accuracy of BFVPs to improve the formation,treatment and diagnosis of CCVD caused by carotid atherosclerosis.The accuracy of time-frequency analysis of Doppler blood flow signals（DBFSs）is helpful to BFVP’s measurement.The most important features of the DBFSs are its nonstationary nature and randomness.Short-time Fourier transform（STFT）is a common method to estimate the frequency of DBFSs.The STFT method has low accuracy in BFVP’s measurement becase it used a fixed window function and could not consider both time and frequency resolution.Therefore,a new approach based on the optimization of effective blood components using the EEMD and normalized fluctuation index（EEMD＿N）is proposed to overcome the limitations of STFT in processing non-stationary blood flow signals.DBFSs are decomposed by EEMD to get a group of intrinsic mode functions（IMFs）.From this group,normalized fluctuation indexs（NFIs）of IMFs are calculated.Then,the normalized root mean square errors（NRMSEs）of blood flow velocities,which are measured by IMFs with different NFI thresholds,are fitted by the Fourier function to determine the optimal threshold of NFI.Then,using the optimal threshold,the effective components in blood flow signals are chosen.Finally,blood flow velocities are computed by the Doppler frequency shift formula.In this paper,simulation and clinical experiments are operated to verify the effectiveness of EEMD＿N method.Firstly,DBFSs are obtained by use Field II ultrasound simulation software to scan the carotid artery blood flow model in the simulation experiment.The optimization of effective blood components are chosen by the optimal NFI-threshold.BFVPs are computed based on the effective blood components.Simulations show that the NRMSEs of blood flow velocity profiles estimated by the EEMD＿N method were reduced by 9.04 % in comparison with these by the traditional STFT method.In the clinical experiment,the carotid DBFS of 10 humans were obtained by using Sonix Touch ultrasound system.Then,BFVPs are calculated by using the optimal judged region and NFI-threshold determined by simulation experiment.Finally,the clinical experiment of human carotid artery further proved the effectiveness of EEMD＿N.In summary,The EEMD＿N method based on EEMD method can overcome the limitations of traditional methods in dealing with non-stationary blood flow signals.It could effectively improve the measurement accuracy of BFVPs,especially low velocities close to vessel walls,which is potential to provide more accurate diagnostic information for cardiovascular diseases.