MRI T2-mapping And IDEAL Water Fat Separation Imaging Study Of Fat Infiltration Of Multifidus Muscle In Patients With Ankylosing Spondylitis

Purpose:The purpose of this study was to evaluate the fat infiltration of the multifidus muscle by T2-mapping and IDEAL imaging in patients with Ankylosing spondylitis(AS),and to stduy whether or not any clinical biomarkers could serve as a preditor of fat infiltration in AS.Materials and methods:Fourty AS patients and 41 matched subjects were all evaluated multifidus muscle at 1.5T MRI including conventional T1 WI,T2WI,T2-mapping with and without fat saturation and IDEAL.The fat content was grades semiquantitatively by the Goutallier classification system(GCS)(grades 0-4)on T2 WI imaging.We obtained fat fraction by IDEAL,and the T2 fat values was determined by T2-mapping without fat saturation subtracted T2-mapping with fat saturation.Kruskal-Wallis H test was used to analyze the difference of all subjects’ s T2 fat values and fat fraction of multifidus muscle between different Goutallier grades.The independent sample t test was used to analyze the difference in CSA,T2 fat values and fat fraction between AS group and control group.The independent sample t test was also used for analysis the difference in T2 fat values and fat fraction of multifidus muscle between different Goutallier grades in each group.The correlation of T2 fat values and fat fraction in AS group with ESR,CRP and BASDAI scores was assessed by Pearson correlation.Results:T2 fat values and fat fraction of multifidus muscle progressive increased in the Goutallier grades(r=0.671,r=0.715,P < 0.05),and multiple comparison between Goutallier grades were significantly different in T2 fat values and fat fraction of multifidus muscle(all P < 0.05).The values of T2 fat values and fat fraction of the multifidus muscle were expressed as mean ±standard deviation(SD),as 11.61±6.92 ms and 0.28±0.09 in AS group,8.11±2.87 ms and 0.24±0.05 in control group,respectively.And,there were statistically significant difference in T2 fat values and fat fraction between groups(both P < 0.05),while CSA between groups was not statistically significant(P=0.285).The T2 fat values and fat fraction of multifidus muscle differences were not significant between groups at grade 0(both P > 0.05),while significant difference were found at grade I(both P<0.05).The difference at grade II is unable to compare because of the small number of included trials in health group.Finally,we found a positive correlation existed between T2 fat values,fat fraction with disease duration(r=0.361,r=0.335,P < 0.05),but also with ESR(r=0.433,r=0.393,P < 0.01).No significant correlation was seen between T2 fat values or fat fraction between CRP and BASDAI score.(all P > 0.05).Conclusion:T2-mapping and IDEAL is of certain value in quantitative evaluation of the fat infiltration in multifidus muscle.The process of fat infiltration of multifidus muscle in AS patient was more significant than those in healthy peers,and fat infiltration was earlier than morphological changes.The fat infiltration of multifidus muscle in AS patient was positively correlated with the disease duration and ESR,but not significantly correlated with CRP and BASDAI score.