The Diagnostic Value Of The MRI-based Likert Scale's Scoring System For Invasive Placenta Previa

Obejective:To evaluate the interobserver agreement and diagnostic performance of the MRI-based Likert scale's scoring system for invasive placenta previa and to explore whether cumulative imaging score was useful for differentiating among degrees of placental invasion.Materials and Methods:From October 2011 to October 2016,a total of 104 pregnant women had performed placenta MRI imaging in our department.As a result,59 patients were diagnosed with invasive placenta previa(26 patients with accrete,28 patients with increta and 5 patients with precreta),while 45 patients with non-invasive placenta previa,all of whom were confirmed by surgery and pathology.The seven MRI features of invasive placenta previa were heterogeneous placenta,intaplacental T2 dark band,intraplacental abnormal vascularity,myometrial abnormal vascularity,placental bulge,indistinct myometrium and placental protrusion.The Likert scale's scoring system was defined as the sum of 5-point Likert scale scores for seven MRI features.Two experienced radiologists(A and B)retrospectively reviewed the MRI images and calculated the cumulative imaging score respectively.Interobserver agreement was evaluated by measuring the intraclass correlation coefficient(ICC).Diagnostic performance was evaluated by means of receiver operating characteristic(ROC)analysis.The differences in cumulative imaging score between the three types(placenta accreta,increta and percreta)were evaluated with Tukey's test.Results:Interobserver ageetment for the cumulative imaging score was excellent(ICC=0.796),and good(ICC?0.60)for the seven MRI features of invasive placenta,so the average imaging score of two radiologists was adapted into ROC analysis.The area under the ROC curve(Az)and accuracy(Acc)for the cumulative imaging score were higher than those of other MRI features(Az and Acc;cumulative imaging score,0.983,94.2%;heterogeneous placenta,0.888,P=0.003,82.7%,P=0.009;intraplacental T2 dark band,0.918,P=0.005,83.7%,P=0.015;intraplacental abnormal vascularity,0.850,P=0.000,76.0%,P=0.000;myometrial abnormal vascularity,0.850,P=0.000,76.9%,P=0.000;placental bulge,0.852,P=0.000,77.9%,P=0.001;indistinct myometrium,0.880,P=0.002,80.8%,P=0.003;placental protrusion,0.747,P=0.000,69.2%,P=0.000).The cumulative imaging score of placenta percreta,placenta increta and placenta accrete were 30.40±1.56,26.05±1.96 and 22.00±2.32,respectively.The cumulative imaging score for placenta accreta,placenta increta,and placenta.percreta showed differences(P<0.05).Conclusion:This MRI-based Likert scale's scoring system demonstrate good interobserver agreement and diagnostic performance for invasive placenta previa.The cumulative imaging score has great value in differentiation among the degree of placental invasion,the higher the score,the deeper the invasion and the greater the possibility of increta/percreta.Therefore,the MRI-based Likert scale's scoring system has high application value in the diagnosis of invasive placenta previa and can be used as a strong predictor for clinical treatment selection.