Department of Obstetrics and Gynecology, Aalborg University Hospital, Aalborg, Denmark.
Department of Clinical Engineering, Central Denmark Region, Aarhus, Denmark.
Ultrasound Obstet Gynecol. 2016 Jun;47(6):748-54. doi: 10.1002/uog.14917.
The magnetic resonance imaging (MRI) variable transverse relaxation time (T2*) depends on multiple factors, one important one being the presence of deoxyhemoglobin. We aimed to describe placental T2* measurements in normal pregnancies and in those with fetal growth restriction (FGR).
We included 24 normal pregnancies at 24-40 weeks' gestation and four FGR cases with an estimated fetal weight below the 1(st) centile. Prior to MRI, an ultrasound examination, including Doppler flow measurements, was performed. The T2* value was calculated using a gradient echo MRI sequence with readout at 16 different echo times. In normal pregnancies, repeat T2* measurements were performed and interobserver reproducibility was assessed in order to estimate the reproducibility of the method. Placental histological examination was performed in the FGR cases.
The method was robust regarding the technical and interobserver reproducibility. However, some slice-to-slice variation existed owing to the heterogeneous nature of the normal placenta. We therefore based T2* estimations on the average of two slices from each placenta. In normal pregnancies, the placental T2* value decreased significantly with increasing gestational age, with mean ± SD values of 120 ± 17 ms at 24 weeks' gestation, 84 ± 16 ms at 32 weeks and 47 ± 17 ms at 40 weeks. Three FGR cases had abnormal Doppler flow, histological signs of maternal hypoperfusion and a reduced T2* value (Z-score < -3.5). In the fourth FGR case, Doppler flow, placental histology and T2* value (Z-score, -0.34) were normal.
The established reference values for placental T2* may be clinically useful, as T2* values were significantly lower in FGR cases with histological signs of maternal hypoperfusion. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.
磁共振成像（MRI）的横向弛豫时间（T2*）变量取决于多个因素，其中一个重要因素是脱氧血红蛋白的存在。我们旨在描述正常妊娠和胎儿生长受限（FGR）的胎盘 T2*测量值。
我们纳入了 24 例妊娠 24-40 周的正常妊娠和 4 例估计胎儿体重低于第 1 百分位的 FGR 病例。在 MRI 之前，进行了超声检查，包括多普勒血流测量。使用梯度回波 MRI 序列测量 T2值，该序列具有 16 个不同的回波时间读取。在正常妊娠中，进行了重复 T2测量，并评估了观察者间的重现性，以估计该方法的重现性。在 FGR 病例中进行了胎盘组织学检查。
该方法在技术和观察者间的重现性方面具有稳健性。然而，由于正常胎盘的异质性，存在一些层间变化。因此，我们基于每个胎盘的两个切片的平均值来估计 T2值。在正常妊娠中，胎盘 T2值随着胎龄的增加而显著降低，妊娠 24 周时的平均值±标准差为 120±17ms，妊娠 32 周时为 84±16ms，妊娠 40 周时为 47±17ms。3 例 FGR 病例存在异常的多普勒血流、母体灌注不足的组织学征象和降低的 T2值（Z 评分<-3.5）。在第 4 例 FGR 病例中，多普勒血流、胎盘组织学和 T2值（Z 评分，-0.34）正常。
建立的胎盘 T2参考值可能具有临床意义，因为具有母体灌注不足组织学征象的 FGR 病例的 T2值显著降低。版权所有©2015ISUOG。由 John Wiley & Sons Ltd 出版。
