Feasibility study of MR T2-mapping for evaluating birth-related levator ani muscle injury / 实用放射学杂志

ABSTRACT

Objective To investigate MR T2-mapping in evaluating birth-related levator ani muscle injury.Methods 25 primiparas at 6 weeks after first vaginal delivery as primiparous group and 12 nulliparous volunteers as control group were prospectively studied. All the subjects underwent pelvic MRI including T2-mapping,mDIXON-T2 WI sequences.Levator ani muscle were divided into two subgroupslevator ani muscle injury group and non-injury group according to if there were edema,avulsion,or rupture in each levator ani muscle subdivisions[puborectal muscle(PRM);iliococcygeal muscle(ICM)],which were showed on mDIXON-T2 WI images.Two radiologists evaluated T2 values of PRM,ICM and observed artificial color images respectively.The consistency between two observers for T2 values of PRM,ICM were evaluated using the intraclass correlation coefficient (ICC ),the difference of T2 values in each levator ani muscle subdivisions among control group,non-injury group and muscle injury group were analyzed using ANOVA .Results There were 26 PRM injury cases and 24 non-injury cases in primiparous group on mDIXON-T2 WI images,and no ICM injured cases in our study.Inter-rater reliability for T2 values between two observers were good(ICC >0.75).T2 values in PRM injury group,non-injury group and control group were(62.78±1.23)ms,(49.75±3.17)ms,(49.96±4.37)ms respectively and the difference was significant. There were significant difference between PRM injury group and non-injury group,control group respectively(P =0.000,P =0.000). The T2 values of ICM in PRM injury group,non-injury group and control group were(70.80±6.50)ms,(62.41±7.32)ms,(62.78±6.91)ms and there were significant difference(P =0.000),meanwhile the difference between PRM injury group and non-injury group,control group were significant respectively(P =0.000,P =0.000).The color gradation of PRM in PRM injury group were mixed with blue, green,and yellow,and tone were lightened on T2-mapping artificial color images;ICM color gradation were uneven with green and yellow, a d tone were higher than those of control group and non-injurygroup.Conclusion T2-mapping can quantitatively assess birth-related levator ani muscle injury and T2-mapping artificial color images show the range and degree of levator ani muscle injury visually.It is hopeful to find micro lesions that T2 WI images are difficult to find.