Research On Pressure Gradient Of A Vascular Stenosis Model Based On Four-dimensional Magnetic Resonance Blood Flow Acceleration Imaging

Background and Objective:Hemodynamic parameters are important indexes reflecting the state of blood flow,among which pressure is a commonly used index to evaluate the stability of cardiovas-cular diseases.In clinical examination,two methods are commonly used to measure cardiovascular pressure in vivo,including invasive catheter pressure measurement and Doppler echocardiography pressure measurement.However,catheter pressure meas-urement is not only invasive but also has certain radiation damage,and Doppler ultra-sound has the disadvantages of low accuracy and strong subjectivity.Compared with them,4D Flow MRI technology has the advantages of non-invasive,objective and re-liable.Therefore,based on 4D Flow MRI technology,this paper discusses the reliability and accuracy of using four-dimensional magnetic resonance blood flow acceleration imaging technology to reconstruct pressure gradient at different spatial resolutions.This will provide a new idea for 4D Flow MRI technology in reconstructing pressure.Methods:In this paper,a fluid model of vascular stenosis is constructed,with being driving by a pulsating pump to generate pulsating flow（simulate vascular pulsation）.The fluid model is scanned by four-dimensional magnetic resonance velocity imaging sequence and self-developed four-dimensional acceleration imaging sequence in the magnetic resonance environment.The velocity image and acceleration image are scanned at two spatial resolutions（0.63 mm×0.63 mm×0.63 mm and 0.89 mm×0.89 mm×0.89 mm）.The three-dimensional spatial velocity data and acceleration data of the fluid model are obtained by image processing and segmentation and formula calculation.According to the Navier-Stokes equation,the central finite difference method is used to calculate the pressure gradient at both ends of the narrow of the fluid model for the velocity calcula-tion,and the acceleration is added to replace the inertial term,and the rest is also cal-culated using the finite difference method.After the magnetic resonance data acquisi-tion is completed,the same experimental conditions are set up in the magnetic reso-nance outdoor to collect the data of the pressure sensor,and the data are collected at the far and near ends of the stenosis.The collected data are synchronized by the signal to obtain the pressure difference between the two ends of the stenosis.The pressure dif-ference is used as the standard to calculate the Fréchet distance and the maximum rel-ative error and perform regression analysis to evaluate the accuracy and correlation of the results.Results:Under two kinds of spatial resolution,the pressure gradient calculated by direct acceleration has smaller error and higher accuracy than that calculated by velocity de-rivative:at dx=0.63 mm d_f=0.84 and 1.32,ε_max=13.9%and 21.2%for acceleration calculating and velocity derivative calculating,respectively;at dx=0.89 mm d_f=1.33and 1.60,ε_max=29.4%and 33.2%for acceleration calculating and velocity derivative calculating,respectively.Spatial resolution has significant influence on the calculation of pressure gradient:linear regression analysis from acceleration calculating,k=0.72and 0.51,R²=0.97 and 0.91 at dx=0.63 mm and 0.89 mm,respectively;for velocity calculating,k=0.62 and 0.44,R²=0.91 and 0.72 at dx=0.63 mm and 0.89 mm,respec-tively.Conclusions:According to the experimental results,this study concludes that the pressure gra-dient reconstructed by four-dimensional magnetic resonance blood flow acceleration imaging technology is more accurate and stabler than that obtained by velocity imaging technology under appropriate spatial resolution,indicating that acceleration imaging technology has a good development prospect in reconstructing pressure,which pro-vides a new idea for the research and development of pressure reconstruction by 4D Flow MRI technology.