Fetal cardio-vascular and functional Magnetic Resonance Imaging (MRI) using a MR-compatible Doppler-Ultrasound-Sensor

先天性心脏缺陷（CHD）和宫内生长受限（IUGR）是最常见的胎儿病理，与发病率和死亡率增加相关（Thompson 2012）。对于这些病理的产前诊断，胎儿（多普勒）超声是诊断的金标准。尽管产前诊断CHD是可能的，但胎儿超声检查经常会漏诊（Abu-Harb 1994，克兰1994，Abdul-Khaliq 2011）。此外，胎儿超声的诊断灵敏度受到几个因素的限制，例如母亲肥胖、羊水过少和胎位。胎儿慢性低氧血症也是IUGR的病因，通过多普勒超声检查发现母儿血流变化可间接诊断。需要反复进行超声检查，以检测血流变化，提示胎儿严重低氧血症，从而帮助确定分娩时间（Baschat 2004）。然而，这些测量只能间接估计胎儿低氧血症。血管MRI可以在成人进行形态和功能分析。为了避免由心脏收缩和血管搏动引起的运动伪影，通常的ECG被应用于心脏触发。然而，胎儿的宫内位置使得常规ECG触发不可能，因此阻碍了用于诊断成像的胎儿心血管MRI。本研究小组开发的新型MR兼容多普勒超声传感器（DUS）允许胎儿心脏触发，从而对胎儿心脏和血管进行形态和功能分析，并在动物模型中成功证实（Yamamura 2009，Yamamura 2012，Ueberle 2012）。此外，使用BOLD技术（MR血氧测定）的胎儿血管的无运动描绘甚至可以定量估计胎儿血氧饱和度。本项目的目的是进一步发展的DUS在人类胎儿的初步应用。因此，通过与胎儿超声的参考方法进行比较，将在疑似CHD的胎儿中评价胎儿心血管MRI。胎儿氧合的定量估计将通过用较大胎儿血管的体内MR血氧测定法校准胎儿血红蛋白氧饱和度（体外脐带血）来实现。因此，DUS允许胎儿心脏和血管的无运动描绘，具有改善CHD和IUGR的产前诊断和预后的潜力。

Congenital heart defects (CHD) and intrauterine growth restriction (IUGR) are the most common fetal pathologies and are associated with increased morbidity and mortality (Thompson 2012). For prenatal diagnosis of theses pathologies fetal (Doppler-) Ultrasound represents the diagnostic gold standard. Although prenatal diagnosis of CHD is possible, detection is often missed performing fetal ultrasound (Abu-Harb 1994, Clane 1994, Abdul-Khaliq 2011). Additionally, diagnostic sensitivity of fetal ultrasound is limited by several factors, e.g. maternal obesity, oligohydramnion, and fetal position. Also chronic fetal hypoxemia, as the cause of IUGR, can be indirectly diagnosed revealing variations of maternal and fetal blood flow patterns in Doppler Ultrasound examinations. Repeated ultrasound examinations are required for detection of blood flow variations indicating critical fetal hypoxemia, thus helping delivery timing (Baschat 2004). However, these measurements only allow indirect estimation of fetal hypoxemia.Cardio-vascular MRI allows morphological and functional analysis in adults. To avoid motion artefacts by cardiac contraction and vessel pulsation, a usual ECG is applied for cardiac triggering. However, the intrauterine position of the fetus makes conventional ECG triggering impossible, therefore preventing fetal cardio-vascular MRI for diagnostic imaging.The development of a novel MR-compatible Doppler-Ultrasound Sensor (DUS) by our study group allows fetal cardiac triggering and therefore the morphological and functional analysis of the fetal heart and vessels, which was successfully demonstrated in an animal model (Yamamura 2009, Yamamura 2012, Ueberle 2012). Additionally, using the BOLD-technique (MR-oxymetry) the motion-free delineation of fetal vessels would even allow quantitative estimation of fetal blood oxygen saturation.The aim of this project is further development of the DUS for initial application in human fetuses. Therefore, fetal cardio-vascular MRI will be evaluated in fetuses with suspected CHD by comparison with the reference method of fetal ultrasound. The quantitative estimation of fetal oxygenation will be realized by calibration of fetal haemoglobin-oxygen-saturation (in-vitro umbilical cord blood) with in-vivo MR-oxymetry of the greater fetal veesels. Thus, the DUS allowing motion-free depiction of the fetal heart and vessels, has the potential to improve the prenatal diagnosis and prognosis of CHD and IUGR.