Research On Near-infrared Spectroscopy For Tissue Blood Flow Measurement Enhanced By Acoustic Radiation Force

Diffuse correlation spectroscopy(DCS)is an emerging technique for measuring blood flow in the microvascular system by using light field temporal autocorrelation data.In some situation,the flow contrast between healthy and pathological tissues may not be so evident.The purpose of this paper is to study a new blood flow measurement method combining ultrasound and DCS.In this study,the relationship between the ARF and the BFI under different ultrasonic modes was analyzed.Innovative work includes:(1)A finite element simulation model of ultrasonic emission and propagation in biological tissues was established.Firstly,using the finite element simulation software(COMSOL Multiphysics),the geometric model of ultrasound transducers arrays and transmission medium were built,adding the corresponding physical field and boundary conditions for multiphysics coupling.Then,we programed sinusoidal and rectangular pulses with controllable parameters in MATLAB,driving the transducer arrays in the finite element model to emit a plane beam or a focused beam.Finally,the software calculated the acoustic parameters during the propagation of sound waves through a medium,and the simulation results are presented in visually.The acoustic pressure curve in probe location was detected and the magnitude relation of ARF generated by different ultrasonic mode were derived.(2)A phantom experiment of DCS blood flow measurement under ARF enhancement was performed.Firstly,the ultrasonic sequence was programed in MATLAB software environment of ultrasonic research platform(Verasonics Vantage 64 LE),controlling the transducer arrays emitting ultrasonic sequence used in the simulation.Then,using the self-developed DCS flowmetry measured the temporal autocorrelation data of light field.Finally,using Monte Carlo simulation,the propagation path and weight of photons in the phantom were obtained to plug into N-th order algorithm for calculating BFI in different ultrasonic modes.The simulation results show that,the ARF generated by the focused beam is greater than the plane beam.In the same beam type,the ARF generated by the rectangular pulse is greater than the sinusoidal pulse.In the phantom experiments show that ultrasound could alter the temporal autocorrelation of light electric filed and result in BFI increases.The magnitude of the BFI measured by the phantom experiment in different ultrasound modes is exactly the same as the magnitude of the ARF derived in the simulation,and has a high correlation.The coefficient of variation(CV)was less than 2%,and it shows that the BFI enhanced by ARF is stable.Under the conditions of focused beam(sinusoidal and rectangular pulses),the BFI are relevant to the voltage(ultrasonic amplitude)of UST,but the relation between BFI and ultrasonic frequency is relevant to frequency spectrum characteristics of the UST.The result of this study indicate that there is a certain corresponding relation between ARF and enhanced BFI.This study will facilitate the development of ultrasonic enhanced blood flow measurement method.