Evaluation Of The Levator Ani Injury In Primipara After Vaginal Delivery Using Diffusion Tensor Imaging And Fiber Tractography

Objective To compare the image quality of diffusion tensor imaging(DTI)of the pelvic floor muscles using different numbers of diffusion-encoding gradient directions(NDGD).In order to get the optimum DTI parameters of pelvic floor muscles which would balance the image acquisition time and a good image quality for clinical practice.To investigate the clinical application of diffusion tensor imaging(DTI)and fiber tractography in evaluating the levator ani muscle injury after first vaginal delivery.It can provide objective evidence for clinical rehabilitation treatment after delivery and prevention of pelvic floor dysfunction.Methods Part1: Thirty normal female volunteers without experience of pregnancy and delivery were prospectively studied.All women underwent FSE-T2 WI and diffusion tensor imaging sequences with unidirectional NDGD(6,15,32)at the pelvic floor.Offline fiber tractography of each major levator ani subdivision(pubovisceralis and iliococcygeus)and internal obturator muscle,and then quality assessment of fiber tracking were performed.Fractional anisotropy(FA),apparent diffusion coefficient(ADC),apparent signal to noise ratio(SNR)and contrast to noise ratio(CNR)of the muscles were calculated to furtherly evaluate the quality of DTI image by the same two radiologists.Inter-rater agreement for fiber tracking quality assessment was evaluated by using kappa(?)test.Inter-rater reliability of other indexes(such as FA,ADC etc.)was interpreted by using the intraclass correlation coefficient(ICC)analysis.The scores of fiber tracking quality assessment were compared by using Friedman test to find the differences among all the groups(NDGD=6,13,32).FA,ADC,SNR and CNR values of the three groups were compared by using ANOVA analysis.Part2: Sixty primiparous six weeks after vaginal delivery and thirty normal women without experience of pregnancy and delivery as control group were prospectively studied.All women underwent axial,coronal fast spin-echo T2-weighted sequences and diffusion tensor imaging sequences of the pelvic floor.Offline fiber tractography of each major levator ani subdivision(pubovisceralis and iliococcygeus)and quality assesssment of fiber tracking were performed.From accurate tracking results(scores ? 2)fractional anisotropy(FA)and apparent diffusion coefficient(ADC)were calculated.FSE-T2 WI imags were evaluated for levator ani muscle abnormalities.The scoring system of the levator ani muscle based on MRI was used for comparing the difference of the levator ani muscle injury.And on the basis of the levator ani muscle defects,the primiparous were divided into two groups.The pubovisceralis normal group and pubovisceralis injuried group,iliococcygeus normal group and iliococcygeus injuried group respectively.Inter-rater reliability for other results were interpreted using the intraclass correlation coefficient(ICC).FA,ADC values between the control group,levator ani muscle normal group and injuried group were compared using ANOVA.Results Part1: Inter-rater agreement for overall quality assessment of fiber tracking results were found(? 0.904).Inter-rater reliability for overall FA,ADC,SNR and CNR values were found(ICC 0.828).There were significant difference of muscles fiber tracking image quality among the three NDGD protocols(P < 0.001).With the increase of NDGD,muscles fiber tracking image quality were improved.There were significant difference of FA values between each two NDGD protocols(P < 0.05).With the increase of NDGD,FA values were decreased.But the decrease degree between15-NDGD and 32-NDGD protocols had a mild fluctuate compared with the 6-NDGD and15-NDGD protocols.For ADC values,SNR and CNR,there were no significant differences among three NDGD protocols(For pubovisceralis,F = 2.836,0.497,0.779.For iliococcygeus,F = 2.144,0.163,0.731.For internal obturator muscle,F = 0.716,1.428,0.140.P > 0.05).Part2: Inter-rater reliability for overall FA,ADC values were found(ICC 0.765~0.976).The quality of the 3D fiber tracking representation was judged as accurate(scores ? 2)for all of the pubovisceralis.For iliococcygeus,the quality of the 3D fiber tracking representation was judged as accurate(scores ?2)for77.5%(93/120)of the primiparous group,and 75.0%(45/60)of the contral group.Thirty-three sides of pubovisceralis injuries were detected in 24/60primiparous(40.0%).Sixteen sides show pubovisceralis edema,five sides show partial or complete loss of pubovisceralis combined with muscle edema,twelve sides show merely partial or complete loss of pubovisceralis.Four primiparous(6.7%,4/60)had injuries in their iliococcygeus,all of them shows unilateral defects.No levator ani defects were identified in nulliparous women.There were significant difference of FA and ADC values among the three groups(F=3.534,P=0.032;F=8.408,P<0.001).The FA value of primiparous pubovisceralis injured group was lower than the contral group and primiparous pubovisceralis normal group,the ADC value was higher than the contral group and primiparous pubovisceralis normal group,difference were statistically significant(P < 0.05).The FA values of iliococcygeus on contral group and primiparous iliococcygeus normal group were 0.37±0.10,0.35±0.08,respectively.The ADC values were(1.18±0.33)×10-3mm2/s,(1.14±0.33)×10-3mm2/s,respectively.There were no significant difference of FA and ADC values between the two groups(F=-1.885,P=0.062;F=-0.781,P=0.436).Conclusion Pelvic floor muscles have a very small size and are complex with many different kinds of tissue components.A higher NDGD(32)was advised to use in clinical practice to achieve a good quality of fiber tracking and an accurate quantitative parameters of DTI.Diffusion tensor imaging and fiber tractography offers new insights into levator ani muscle problems.DTI allows 3D visualisation of the levator ani muscle and provide a accurate quantified diagnostic evidence to differentiate normal and abnormal states of the levator ani muscle.