Research On Ultrasound Doppler Blood Flow Velocity Measurement Method Based On Linear Frequency Modulation Signal

Blood flow velocity is an important physiological parameters, it can reflect the physicalfunction of human health, so blood flow velocity measurement is an important part in clinicaldiagnosis. At present, Continuous Wave Doppler Method(CW) and Pulse Wave DopplerMethod(PW) are the two most used methods on quantitative measurement of the blood flowvelocity.Because of no pain, no radiation, non-invasive and low cost,these two methods arewidely used, but they also have some limitations.CW can get high SNR echo and it is good atmeasuring high-speed flow,however it can not measure blood flow in specified depth.PWslove this problem,but it has poor SNR, and it’s maximum measured depth and maximummeasured depth can not be gain together.In recent years, for solving the weakness of thesetwo methods,there are many new methods have been proposed. In this Article, we study fromfrom the perspective of the transmitted signal waveform and take the LFM signal,whichwidely used in the modern rada systems,as the study object,propose one quasi-continuousultrasound doppler method on flow velocity measurement. Theory and simulation show thatthe method has high speed measurement range, can estimate of the blood flow accurately inlow SNR environment and has a certain position measurement capability.The present paper firstly describes the basics of medical ultrasound, reviews the basicprinciples of CW and PW, then introduce the LFM signals, after their advantages anddisadvantages are fully introduced, we propose a new blood flow velocity measurementmethod, which can get the velocity value form the the demodulated signal’s modulationrate.As LFM signal is non-stationary, the traditional Fourier transform is not effective toanalyse it.Based on time-frequency property, we compare performance of the Short-TimeFourier Transform, Wavelet Transform, Wigner-Ville Transform and found that FractionalFourier Transform has optimal focusing property, besides that,it has no cross-interferenceterm. So we choose it to verify the validity of the new proposed method on Matlab.