Research Of Quantitative Magnetic Resonance Imaging Methods In Evaluating Renal Function

Normal renal function plays an important role in maintaining a stable internal environment and an orderly metabolism in the body.Acute kidney injury(AKI)is a common clinical kidney disease characterized by rapid decline in renal function.Its typical pathological changes include renal tissue ischemia,hypoxia,and edema.The clinical diagnosis of AKI relies on the patient's blood and urine indicators.The blood and urine indicators only reflect the overall condition of the renal tissue,and have a lag,and are easily affected by external factors such as diuretics.Quantitative magnetic resonance imaging(qMRI),as a novel non-ionizing radiation imaging technique,can obtain the parameters that reflect the changes in physical and chemical environment of renal tissues,and therefore has the potential to assess changes in renal function during disease.For example,T2 mapping,blood oxygenation level-dependent magnetic resonance imaging(BOLD-MRI),and arterial spin labeling(ASL)can quantify the parameters that reflect changes in renal tissue water content,tissue oxygenation,and perfusion,respectively.At present,most of the related studies are based on a single qMRI technique to investigate the AKI,a study of panoramic observation of the development of AKI is lacking.Moreover,whether there is a correlation between the qMRI parameters that reflect different pathological changes in AKI is still unknown.Measuring the changes of renal BOLD-MRI signal after gas stimulus is helpful to assess the healthiness of the kidney,existing studies only simply compare the changes of the renal T2*before and after the gas stimulus,an in-depth study that analyzing the renal dynamic T2*response is lacking.This article focuses on the issues listed above and did three related work as follows:(1)Joint analysis of T2 mapping,BOLD-MRI and ASL in rat AKI model.The changes of renal T2,T2*,T2' and perfusion in AKI were jointly analyzed,and the relationships between renal perfusion and T2,T2*,T2' were investigated by using the correlation analysis.The results showed that during the AKI,the renal perfusion was significantly decreased.T2 in the renal cortex and outer stripe of outer medulla were increased,and were negatively related to the renal perfusion with a degree of weak to moderate(cortex r=-0.45,outer stripe of the outer medulla r=-0.40).T2*and T2' in the renal inner stripe of the outer medulla were decreased,and were positively related to the renal perfusion with a degree of moderate to strong(T2*,r=0.52,T2',r=0.63).(2)Dynamic measurement and modeling analysis of the renal T2*response to a step-like oxygenation stimulus.To measure the renal T2*response during step-like oxygenation stimulus,fast BOLD-MRI scan with a temporal resolution of 9 seconds was achieved by optimizing the pulse sequence parameters and experimental design.The step response model of the second-order linear constant-coefficient continuous time system was proposed to fit the measured dynamic T2*data,and quantified the model parameters that can be used to characterize the renal oxygenation system,include:the amplitude,the time delay,the damping constant,and the oscillation period.The preliminary results demonstrated the feasibility of modeling analysis of the renal T2*response.Compared to healthy rat kidneys,the damping constant substantially increased in the outer stripe of the outer medulla(3.7 times)and the inner stripe of the outer medulla(10 times)in AKI rat kidneys,which suggested its potential as a diagnostic biomarker for AKI.(3)Dynamic measurement and modeling analysis of changes in renal size during step-like oxygenation stimulus.The 2D UNet renal segmentation model was trained and applied to the fast BOLD-MRI data,to measure the dynamic changes of renal size during step-like oxygenation stimulus,and the measured dynamic renal size data was analyzed by modeling analysis.The results showed that the renal size attenuated by 10%after 10 minutes hypoxia.Compared with the results of modeling analysis on T2*data,renal size changed with a smaller amplitude and longer time delay than those for renal T2*,suggested that renal T2*was more sensitive to the step-like oxygenation stimulus than renal size.