Department of Fetal Medicine, Surgery and Imaging, Hôpital Universitaire Necker-Enfants Malades, AP-HP, Paris, France.
Plateforme LUMIERE, Hôpital Universitaire Necker-Enfants Malades, URP 7328 and PACT, affiliated to Imagine Institut, Université de Paris, Faculté de Médecine, Paris, France.
Ultrasound Obstet Gynecol. 2024 Aug;64(2):236-244. doi: 10.1002/uog.27609.
T2*-weighted magnetic resonance imaging (MRI) sequences have been identified as non-invasive tools with which to study placental oxygenation in vivo. This study aimed to use these to investigate both static and dynamic responses to hyperoxia of the normal placenta across gestation.
We conducted a single-center prospective study including 52 uncomplicated pregnancies. Two T2*-weighted sequences (T2* relaxometry) were performed, one before and one after maternal hyperoxia. The distribution of placental T2* values was modeled by fitting a gamma probability density function (T2* ), describing the structure of the histogram using the mean T2* value, the shape parameter (α) and the rate (β). A dynamic acquisition (blood-oxygen-level-dependent (BOLD) MRI) was also performed before and during maternal oxygen supply, until placental oxygen saturation had been achieved. The signal change over time was modeled using a sigmoid function, to determine the intensity of enhancement (ΔBOLD (% with respect to baseline)), a temporal variation coefficient (λ (min), controlling the slope of the curve) and the maximum steepness (Vmax (% of placental enhancement/min)).
The histogram analysis of the T2* values in normoxia showed a whole-placenta variation, with a decreasing linear trend in the mean T2* value (Pearson's correlation coefficient (R) = -0.83 (95% CI, -0.9 to -0.71), P < 0.001), along with an increasingly peaked and narrower distribution of T2* values with advancing gestation. After maternal hyperoxia, the mean T2* ratios (mean T2*/mean T2*) were positively correlated with gestational age, while the other histogram parameters remained stable, suggesting a translation of the histogram towards higher values with a similar appearance after maternal hyperoxia. ΔBOLD showed a non-linear increase across gestation. Conversely, λ showed an inverted trend across gestation, with a weaker correlation (R = -0.33 (95% CI, -0.58 to -0.02), P = 0.04, R = 0.1). As a combination of ΔBOLD and λ, the changes in Vmax throughout gestation were influenced mainly by the changes in ΔBOLD and showed a positive non-linear correlation with gestational age.
Our results suggest that the decrease in the T2* placental signal as gestation progresses does not reflect placental dysfunction. The BOLD dynamic signal change is representative of a free-diffusion model of oxygenation and highlights the increasing differences in oxygen saturation between mother and fetus as gestation progresses (ΔBOLD) and in the placental permeability to oxygen (λ). © 2024 International Society of Ultrasound in Obstetrics and Gynecology.
T2*-加权磁共振成像（MRI）序列已被确定为研究体内胎盘氧合的非侵入性工具。本研究旨在使用这些序列研究正常胎盘在妊娠过程中对高氧的静态和动态反应。
我们进行了一项单中心前瞻性研究，包括 52 例无并发症的妊娠。在母体高氧之前和之后进行了两次 T2*-加权序列（T2弛豫测量）。使用伽马概率密度函数（T2）拟合胎盘 T2值的分布，使用平均 T2值、形状参数（α）和速率（β）描述直方图的结构。在母体供氧之前和期间还进行了动态采集（血氧水平依赖 （BOLD）MRI），直到胎盘氧饱和度达到。使用 sigmoid 函数对信号随时间的变化进行建模，以确定增强的强度（相对于基线的 ΔBOLD（%））、时间变化系数（λ（min），控制曲线的斜率）和最大斜率（Vmax（% 胎盘增强/分钟））。
在正常氧合情况下，T2值的直方图分析显示出整个胎盘的变化，平均 T2值呈线性下降趋势（皮尔逊相关系数（R）= -0.83（95%CI，-0.9 至-0.71），P < 0.001），同时随着妊娠的进展，T2值的分布变得更加陡峭和狭窄。母体高氧后，平均 T2比值（平均 T2*/平均 T2*）与胎龄呈正相关，而其他直方图参数保持稳定，提示母体高氧后直方图向更高值平移，外观相似。ΔBOLD 在整个妊娠过程中呈非线性增加。相反，λ 在整个妊娠过程中呈反趋势，相关性较弱（R= -0.33（95%CI，-0.58 至-0.02），P = 0.04，R= 0.1）。作为 ΔBOLD 和 λ 的组合，整个妊娠过程中 Vmax 的变化主要受 ΔBOLD 的变化影响，并与胎龄呈正非线性相关。
我们的结果表明，随着妊娠的进展，T2*胎盘信号的降低并不反映胎盘功能障碍。BOLD 动态信号变化代表氧合的自由扩散模型，并突出了随着妊娠的进展，母体和胎儿之间的氧饱和度差异（ΔBOLD）以及胎盘对氧的通透性（λ）的增加。
Zotero 插件