目的：探讨胎盘植入产前MRI诊断的影像特征及诊断价值。材料和方法：回顾性分析72例凶险型前置胎盘患者的产前MRI影像表现和临床及术后病理资料，评价胎盘植入的产前MRI影像学表现及其诊断价值。结果：①MRI对粘连型、植入型、穿透型胎盘的敏感性和特异性分别为50.0%和91.7%、79.2%和91.7%、80.0%和100.0%。②用于评价胎盘植入的各种MRI征象的敏感性和特异性分别为胎盘-子宫肌层分界不清67.3%和85%、胎盘内信号不均65.4%和75%、胎盘内血管影增多50%和85%、T2WI上条带状低信号影40.4%和95%、子宫局部外凸17.3%和100%、膀胱“帐篷”状改变或结节状突起26.9%和95%。③随着胎盘植入深度的增加，T2WI上低信号带出现的概率及体积相应增大。结论：产前MRI检查对植入型和穿透型胎盘的诊断价值较高，而对粘连型胎盘的诊断敏感性较低；对胎盘植入诊断有较高价值的MRI征象为胎盘-子宫肌层分界不清、胎盘内血管影增多、T2WI条带状低信号影、子宫局部外凸以及膀胱“帐篷”状改变或结节状突起；T2WI上低信号带的总体积越大，发生胎盘植入可能性越高、植入程度越深。

Objective: To investigate the prenatal MRI features and diagnostic value of placenta accreta. Methods: The prenatal MRI findings and clinical and pathological data of 72 patients with pernicious placenta previa were retrospectively analyzed. The prenatal MRI imaging manifestations and its diagnostic value were evaluated. Results: ①The sensitivity and specificity of MRI in the diagnosis of placenta accreta, placenta increta and placenta percreta were 50% and 91.7%, 79.2% and 91.7%, 80% and 100%, respectively.②The sensitivity and specificity of MRI manifestations in the evaluation of placenta increta were 67.3% and 85%(loss of placental-myometrial interface), 65.4% and 75%(heterogeneous signal in placenta), 50% and 85%(abnormal placental vascularity), 40.4% and 95%(low signal bands on T2WI), 17.3% and 100%(abnormal uterine bulging), and 26.9% and 95%(“tents” shape change or nodular protuberance of the bladder wall). ③The depth of placenta increta was positively related with the volume and occurred probability of low signal bands on T2WI. Conclusion: MRI technique is of great value in diagnosis of placenta increta and percreta. But the sensitivity in diagnosis of placenta accreta is too low. The most useful signs of placental invasion are loss of placental-myometrial interface, abnormal placental vascularity, low signal bands on T2WI, abnormal uterine bulging, and “tents” shape change or nodular protuberance of the bladder wall. The larger size of low signal bands on T2WI, the deeper placental invasion would be.