The Study Of T1-mapping And Extracellular Volume(ECV) Quantification Of Myocardial Fibrosis Caused By Iron Overload In A Pig Modle

Objective:To explore the quantitatively detect the diffuse myocardial fibrosis caused by iron overload by using the T1-mapping sequence and extracellular volume(ECV)on 3.0t magnetic resonance imaging,and investigate the effect of cardiac magnetic resonance on myocardial fibrosis with iron deposition.Materials and methods:1.Thirty one pigs were randomly divided into control group(4 pigs),experimental group(22 pigs)and verification group(5 pigs)by random number table method.Dextran iron injection was injected into the posterior buttocks of both sides in turn weekly with a weekly dose of 400mg/kg for the first time and200mg/kg for the next week.The control group was injected with the same dose of normal saline as the experimental group,and the maximum feeding cycle was15 weeks.2.Two pigs were selected for MRI scanning every week.One of the control group was feeding to 15 weeks for examination.After the scan fresh myocardial ventricular septal tissue was using for pathology analysis,measurement of Collagen volume fraction(Collagen volume fraction,CVF)and iron deposition.Cardiac iron content(CIC)of dried tissue was obtained by atomic emission spectrometry.MRI post-processing software was used to measure the T1 and T2~*values of the ventricular septum and blood pool,and calculated Extracellular volume(ECV).3.Statistical analysis was performed by IBM SPSS 24.0 software.The difference of ECV in different delay time was analysis by Rank sum test.We using the Spearman correlation analysis evaluation the cardiac ventricular septal ECV between injected iron dose,myocardial iron content,collagen volume fraction(CVF),Native T1,T2~*values.ECV and CVF are matching by linear regression.The difference was considered statistically significant when P<0.05.Results:1.CVF and EVC began to increase when the iron injection reached1200mg/kg and the feeding cycle was more than 5 weeks.There werehighly positive correlation among CIC,CVF,EVC and iron dose(P<0.001)in the Bama pig model of myocardial fibrosis caused by iron overload2.The myocardial histopathological results showed that collagen fibers surrounded the myocardial cells,and the myocardial cells walked in a variety of ways,with different proportion in different sections.There are more collagen fibers around the vessels.3.There are highly negative correlation among Native T1,T2~*and CIC.There was no statistically significant difference in ECV between different periods of enhanced scanning(X~2=4.47,v=10,P=0.923).4.There was a high correlation between ECV and CVF.The established regression equation Y(CVF)=0.015+0.399X(ECV)could be used to predict the CVF by measuring ECV.The equation was statistically significant(F=222.90,P<0.001)and the fitting degree R~2=0.903.Conclusion:1.Animal models of myocardial fibrosis induced by iron overload were obtained by intramuscular injection of iron dextran,and the higher the iron deposition,the more severe the myocardial fibrosis.2.The distribution of collagen fibers in myocardial fibrosis is uneven,and actual clinical samples may not be able to accurately assess the degree of myocardial fibrosis,while MRI can obtain complete myocardial information.3.When MRI is used to evaluate myocardial fibrosis,t1-mapping should not be used alone,but T2~*should be combined to evaluate whether there is iron deposition in myocardium,or ECV should be combined to more accurately evaluate myocardial fibrosis.4.The collagen volume fraction of pathological examination can be calculated by MRI determination of ECV.It is positive significance to provide important help for clinical treatment,evaluation and research.