Abstract： Objective:To explore the feasibility of using magnetic resonance image compilation(MAGiC)parameters to quantitatively evaluate changes of sacroiliac joint in ankylosing spondylitis(AS),in order to provide a quantitative index for the evaluation of sacroiliac joint inflammatory activity in AS.And to evaluate the correlations of T1,T2 and proton density(PD)values with Bath Ankylosing Spondylitis Disease Activity Index(BASDAI)and Spondyloarthritis Research Consortium of Canada(SPARCC)scores.Materials and Methods:A total of 78 AS patients with sacroiliitis and 35 healthy controls were enrolled.All patients were scanned using a GE SIGNATM Architect 3.0 T MRI scanner by T1WI,fat-saturated T2-weighted imaging(FS-T2WI)and MAGiC sequence of the sacroiliac joints.According to Ankylosing Spondylitis Disease Activity Score(ASDAS)scores and C-reactive protein(CRP),the 78 patients were divided into an active group(40 cases)and an inactive group(38 cases).The T1,T2 and PD values of the subchondral bone marrow were measured in the active group,the inactive group,and the healthy control group using the MAGiC sequence.The T1,T2 and PD values of the active,inactive,and healthy groups were compared using one-way analysis of variance(ANOVA).Receiver operating characteristic(ROC)curves were used to analyze the diagnostic efficacy of T1、T2 and PD values for sacroiliitis.The correlations of the T1,T2 and PD values with the BASDAI and SPARCC scores were analyzed using Spearman's rho.Results:The T1 values[(531.04±60.28)ms]in the active group were lower than those in the inactive group[(691.50±72.44)ms],and lower than those in the healthy control group[(933.23±100.98)ms],t=-11.517,P＜0.001.T2 and PD values in the active group[(119.00±9.56)ms,(86.03±14.79)pu]were both higher than those in the inactive group[(96.61±8.86)ms,(68.12±7.77)pu],and higher than those in the healthy control group[(78.94±6.20)ms,(53.71±6.69)pu],t=-15.332,15.972,all P＜0.001;the area under the ROC curve(AUC)of T1,T2 and PD values between the active and inactive groups were 0.965(95%CI:0.949-0.991),0.981(95%CI:0.970-0.998),0.840(95%CI:0.842-0.923),respectively.The T1,T2 and PD values of the AS patients were positively correlated with BASDAI scores,and the correlation coefficients(r)were-0.771,0.914 and 0.846(all P＜0.001),respectively.And positively correlated with BASDAI scores,and the correlation coefficients(r)were-0.924,0.915 and 0.938(all P＜0.001),respectively.Conclusions:MAGiC parameters can be used to quantitatively assess the activity of AS,especially,T2 value can serve as a biological marker for the activity of sacroiliac arthritis,providing imaging basis for clinical diagnosis.