目的:T2*加权序列已被确定为研究体内胎盘氧合的非侵入性工具。这项研究旨在调查整个妊娠期正常胎盘对高氧的静态和动态响应。
方法:我们进行了一项单中心前瞻性研究,包括52例无并发症妊娠。进行了两个T2*加权序列:在母体高氧之前和之后进行T2*弛豫测量。通过将γ分布拟合为T2*〜Γ(αβ)来评估T2*值的直方图分布。在氧气供应之前和期间还进行了动态采集(BOLD协议),直到胎盘氧饱和度.使用sigmoid函数对信号随时间的变化进行建模,用于确定增强强度(ΔBOLD,%),时间变化系数(λ,min-1,控制曲线的斜率),和最大陡度(Vmax,ΔBOLD.胎盘强化min-1)。
结果:常氧中T2*值的直方图分析显示了整个胎盘的变化,平均T2*值呈线性下降趋势(R=-0.83,95%CI[-0.9,-0.71],p<0.001)以及整个妊娠期T2*值的峰值和较窄分布。母体高氧后,平均T2*比率(平均T2*高氧/平均T2*基线)与胎龄呈正相关,而其他直方图参数保持稳定,建议将直方图平移到具有类似方面的更高值。ΔBOLD在整个妊娠期显示出非线性增加。相反,λ(min-1)参数,在整个妊娠期显示出倒置的趋势,相关性明显较弱(R=-0.33,95%CI[-0.58,-0.02],p=0.04,R2=0.1)。作为ΔBOLD和λ的组合,整个妊娠期间Vmax的变化主要受ΔBOLD变化的影响,并与孕龄呈正非线性相关.
结论:我们的结果表明,在妊娠期间,T2*胎盘信号的降低并不反映功能障碍。BOLD效应,代表氧合的自由扩散模型,强调了母亲和胎儿在整个妊娠期间氧饱和度的不断增长的差异(ΔBOLD),和胎盘对氧气的渗透性(λ)。本文受版权保护。保留所有权利。
OBJECTIVE: 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.
METHODS: 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* ~ Γ α β ), 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-1), controlling the slope of the curve) and the maximum steepness (Vmax (% of placental enhancement/min)).
RESULTS: 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*hyperoxia/mean T2*baseline) 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, R2 = 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.
CONCLUSIONS: 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.