T2* Mapping of Placental Oxygenation to Estimate Fetal Cortical and Subcortical Maturation

This cohort study investigates the association between T2* mapping of placental oxygenation and cortical and subcortical fetal brain volumes in typically developing fetuses scanned longitudinally in the third trimester.


Introduction
Placental dysfunction is associated with a decrease in nutrients and oxygen to the fetus; the gestational age at which this happens varies depending on severity but is an important factor in outcome as it relates to when and which brain structures are most at risk.Evidence from Doppler ultrasonography of fetuses affected by severe placental dysfunction leading to intrauterine growth restriction (IUGR) suggests blood flow distribution occurs in a hierarchical manner.In IUGR, oxygenated blood is directed toward the brain, away from other fetal organs (except the fetal heart), a process referred to as brain sparing.Further evidence suggests that subcortical regions critical for homeostasis receive more blood flow, at the cost of cortical regions involved in higher-order functions.Although Doppler findings suggest that cortical regions show more variability to placental oxygenation changes, a Cochrane review found that the evidence was of moderate to low quality, 1 indicating the need for more sensitive techniques to study how placental function affects the brain.
Recent work has demonstrated an association between a magnetic resonance imaging (MRI)-based measure of placental oxygenation, transverse relaxation time (T2*), and birth weight, 2 suggesting that T2* may similarly estimate variations in fetal brain development.
To determine whether placental MRI-based methods could provide a biomarker of fetal brain development, we investigated the association between placental T2* and cortical and subcortical fetal brain volumes in typically developing fetuses scanned longitudinally in the third trimester.We hypothesized that in fetuses with reduced placental oxygenation, cortical brain regions would show reduced volumes relative to subcortical regions.

Methods
This prospective cohort study followed the STROBE reporting guideline 3 and was approved by the research ethics board at Western University.Female participants were recruited from the community (December 2020 to August 2023) and provided written informed consent.Participants were imaged with MRI at 2 time points in the third trimester more than 2 weeks apart.2D multiecho Cortical and subcortical volumes were extracted using previously published methods 5,6 and converted to z scores (eMethods in Supplement 1).Volumes were submitted to linear mixed-effects

(
LME) analysis with an interaction between T2* values and region (cortical or subcortical), controlling for fetal sex, maternal age, socioeconomic status, and time point.Participant was included as a random effect.A significance threshold of P < .05 was used.Statistical analysis was performed using R statistical software version 4.0.3(R Project for Statistical Computing) in September 2023.

Figure
Figure.Placental T2* Values and Cortical and Subcortical Volumes 4nd single-shot fast spin echo anatomical brain images were acquired using a 3T GE Discovery MRI scanner and 32-channel torso coil at Western University (see eMethods in Supplement 1 for full scanning parameters).Placental masks were manually drawn using FSLeyes version 1.6.1 (FMRIB Centre), and T2* values were calculated by fitting the mean signal within each mask as a function of echo time.The T2* values were standardized to adjust for gestational age.4 a Barratt Simplified Measure of Social Status.Open Access.This is an open access article distributed under the terms of the CC-BY License.JAMA Network Open.2024;7(2):e240456.doi:10.1001/jamanetworkopen.2024.0456(Reprinted) February 27, 2024 1/4 Downloaded from jamanetwork.comby guest on 03/03/2024 stack placental images