The Research On Estimation Of Doppler Blood Flow Velocity Distribution Based On Coherent Plane Wave Compounding

The arterial blood flow velocity distribution(BFVD)is one of the important parameters to evaluate human physiology and pathology,and it can reflect the human body’s metabolism,detect the morphology of the vascular lumen and calculate the arterial wall shear rate.Ultrasonic Doppler shift method is widely used in clinical BFVD due to its simple calculation and real-time performance.The traditional focus mode has some limitations,such as low frame rate in linear scan,poor detected accuracy outside the focus area and difficult estimation in a two-dimensional area.Those limitations are restrainedly used in clinic.Plane wave can improve those problems.The frame rate of plane wave can rea ch 20 kHz,plane wave can obtain the two-dimensional BFVD in the target area at one emission and reception,and the focus points penetrated by coherent plane wave compound is helpful to improve the estimation accuracy.Although the plane wave can improve the estimated accuracy and speediness in theory,its actual feasibility needs to be studied.Therefore,based on Field II ultrasonic simulation platform,focus and plane wave methods are used to estimate BFVD,respectively,the characteristics of the estimated results are analyzed.Then the effects of plane wave and element parameters on the estimation accuracy are studied,which have important significance to choose better parameters in clinic.Plane wave imaging mode,coherent multi-angle plane wave compound and autocorrelation estimation are described in detail in this thesis.Subsequently,a dynamic scatter point model of carotid artery blood flow is constructed.To calculate the BFVD in the simulation experiment,transducer emits plane waves of different inclination angle,delay and sum,coherent plane wave compound and autocorrelation estimation are used to deal with pulse-echo radio frequency signals.In order to analyze quantitatively the estimated results,the mean value of normalized root mean square errors(NRMSEs)between estimated results of velocity profiles at 40 different axial positions and theoretical values are calculated.The results show that,the NRMSEs of traditional focus mode are around 0.30.The plane wave can achieve the analogous effect to focus,its NRMSEs are also around 0.30(5 times compound and 5° inclination angle).What’s more,for the plane wave parameters,the NRMSEs are 0.23,0.28,0.31 and 0.33 when the inclination angle is set to 0.5°,3°,7° and 12°,respectively(the coherent composite numbers are fixed at 5).The NRMSEs are all around 0.23 when the coherent composite numbers are 3,5,7 and 9,respectively(the inclination angle is fixed at 0.5°).Moreover,for the element parameters,the estimation accuracy is within a reasonable range(with focus mode as a reference,NRMSEs is no more than 0.30)when the kerf is smaller than the width,otherwise,the NRMSEs is above 0.3.The NRMSEs hardly change when the element number is 32,64,128 and 196,respectively,but the number affects the size of the transducer.In summary,the plane wave method can substitute for focus method as a new way to estimate arterial BFVD.For the plane wave parameters,the estimation accuracy can be improved with a smaller inclination angle interval,and it has little to do with the compounding numbers.For the element parameters,the element kerf should be smaller than the element width,or the estimation accuracy is decreased;the element number does not affect the estimation accuracy,but it affects the estimated range.Therefore,choosing appropriate parameters in advance can improve the accuracy and speediness of the plane wave estimation.