Quantification Of Glucose Metabolism In Rats With Hepatic Ischemia-reperfusion Injury Based On Glycogen Chemical Exchange Saturation Transfer Imaging

Purpose:The aim of this study was to optimize and verify the glycogen chemical exchange saturation transfer（GlycoCEST）method for detecting in vivo liver glucose metabolism through model and rat experiments;then,quantitative evaluation of liver glycogen concentration mapping before and after ischemia reperfusion.Materials and methods:Firstly,scan parameters of GlycoCEST were optimized on a 7T small animal MR scanner based on the tube model contained of glycogen and glucose with different concentrations and in different p H environments.Gluco CEST images,GlycoCEST images and CEST spectral lines were acquired using different saturation power（B₁）and saturation pulse durations to explore the optimized scan parameters of GlycoCEST mapping.Through animal experiments,the reliability of the GlycoCEST images of rat liver was verified.The GlycoCEST signals of rat liver before and after hypoxia and fasting were compared to verify the accuracy and reliability of the detection of changes in liver glycogen concentration.:（1）12 rats in the control group without fasting（maintained respiratory rate at 30-40 times/min during scanning）and 7 rats in the hypoxia group（maintained respiratory rate at 19-22 times/min during scanning）.The changes of GlycoCEST signals before and after hypoxia were compared to verify the feasibility of glycogen detection by GlycoCEST.（2）12 SD rats were scanned before fasting and 24h after fasting,and the changes of GlycoCEST signal before and after fasting were compared to further verify the feasibility of glycogen detection by GlycoCEST.Furthermore,a liver ischemia-reperfusion model was established on 12 fasted SD rats.The biochemical indexes（AST and ALT）before and 24h after ischemia were used to verify the success of the liver ischemia-reperfusion model.MR scans were performed before ischemia-reperfusion,1h,12h,and 24h after ischemia-reperfusion,respectively,to obtain the CEST map of rat liver glycogen at the above time points,and combine ATP,T1 mapping and T2mapping imaging to explore the changing in glucose metabolism before and after hepatic blood reperfusion injury.Results:In the test tube model of glucose and glycogen,both of CEST effect peak are around 1ppm,and the difference spectrum peaks of glucose are relatively wide.The effect of GlycoCEST is roughly as same as those of Gluco CEST with the change of solution concentration,solution p H,B₁power and B₁duration times.Saturation energy（B1）3.6ut,radio frequency duration 4s is the optimal saturation parameter.Since glycogen is much higher than glucose in the liver,it is considered that the CEST effect at 1 ppm in the liver is mainly glycogen effect.In hypoxia and fasting rat liver GlycoCEST in vivo experiments,,decreased GlycoCEST signal of the hypoxia group and the pre-fasting group were found compared with those of the control group（3.23±2.00%before hypoxia（n=12）vs.1.28±0.75%after hypoxia（n=7）;3.23±2.00%before fasting vs.1.61±0.89%after fasting,n=12）,which confirmed the feasibility of our glycogen results in liver in vivo.In the liver ischemia-reperfusion injury model experiment,serum AST and ALT at 24h after operation were significantly higher than the above indexes before operation.In the early postoperative period（within 12h）,the glycogen CEST signal gradually increased（1.61±0.89%before operation,3.11±1.94%at 1h after operation,4.09±2.01%at 12h after operation）,and after 24h after the operation,the glycogen CEST signal gradually decreased（from 4.09±2.01%to 2.12±1.10%）).At the above times points,ATP had no significant change before and after ischemia reperfusion injury;the T₁relaxation time and T₂relaxation time gradually elevated after injury.Compared with the T₁and T₁relaxation time before treatment,there is a significant difference of T₁time at 12h and 24h after surgery,and T₂time at 24h after surgery.Conclusion:GlycoCEST imaging technology can accurately reflect changes in liver glycogen in vivo and is a new method to explore liver glucose metabolism.In liver ischemia-reperfusion injury,liver GlycoCEST signal is more sensitive than liver ATP signal.combined with T₁mapping and T₂mapping imaging technology,it can better understand the hepatic ischemia-reperfusion injury,and is conducive to the clinician diagnosis and treatment.