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

先天性心脏病(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有关(Thompson 2012)。对于这些疾病的产前诊断，胎儿(多普勒)超声是诊断的金标准。虽然产前诊断CHD是可能的，但使用胎儿超声经常会漏诊(Abu-Harb 1994，Clane 1994，Abdul-Khaliq 2011)。此外，胎儿超声的诊断敏感性受到几个因素的限制，如母亲肥胖、羊水过少和胎儿体位。此外，作为IUGR的原因，慢性胎儿低氧血症也可以间接诊断，在多普勒超声检查中显示出母体和胎儿血流模式的变化。需要重复的超声检查来检测血流变化，以表明胎儿严重的低氧血症，从而帮助选择分娩时间(Baschat 2004)。然而，这些测量只能间接估计胎儿的低氧血症。心血管磁共振成像可以对成人进行形态和功能分析。为了避免心脏收缩和血管搏动引起的运动伪影，采用常规的心电来触发心脏。然而，胎儿在宫内的位置使得常规的心电触发是不可能的，因此阻碍了胎儿心血管MRI的诊断成像。我们的研究小组开发了一种新型的MR兼容的多普勒超声传感器(DUS)，可以触发胎儿心脏，从而可以分析胎儿心脏和血管的形态和功能，这在动物模型中得到了成功的演示(Yamamura 2009，Yamamura 2012，Ueberle 2012)。此外，使用BOLD技术(MR血氧测量法)，胎儿血管的自由描绘甚至可以定量估计胎儿的血氧饱和度。该项目的目的是进一步开发DUS，以便在人类胎儿中初步应用。因此，对疑似冠心病的胎儿进行胎儿心血管MRI检查时，应与胎儿超声检查的参考方法进行比较。胎儿血氧饱和度(体外脐带血)的定标和大血管的体内磁共振血氧测定仪将实现对胎儿氧合的定量评估。因此，DUS可以自由地显示胎儿心脏和血管，有可能改善CHD和IUGR的产前诊断和预后。

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.