Separating fetal and maternal placenta circulations using multiparametric MRI

Abstract

Purpose: The placenta is a vital organ for the exchange of oxygen, nutrients, and waste products between fetus and mother. The placenta may suffer from several pathologies, which affect this fetal-maternal exchange, thus the flow properties of the placenta are of interest in determining the course of pregnancy. In this work, we propose a new multiparametric model for placental tissue signal in MRI.

Methods: We describe a method that separates fetal and maternal flow characteristics of the placenta using a 3-compartment model comprising fast and slowly circulating fluid pools, and a tissue pool is fitted to overlapping multiecho T2 relaxometry and diffusion MRI with low b-values. We implemented the combined model and acquisition on a standard 1.5 Tesla clinical system with acquisition taking less than 20 minutes.

Results: We apply this combined acquisition in 6 control singleton placentas. Mean myometrial T2 relaxation time was 123.63 (±6.71) ms. Mean T2 relaxation time of maternal blood was 202.17 (±92.98) ms. In the placenta, mean T2 relaxation time of the fetal blood component was 144.89 (±54.42) ms. Mean ratio of maternal to fetal blood volume was 1.16 (±0.6), and mean fetal blood saturation was 72.93 (±20.11)% across all 6 cases.

Conclusion: The novel acquisition in this work allows the measurement of histologically relevant physical parameters, such as the relative proportions of vascular spaces. In the placenta, this may help us to better understand the physiological properties of the tissue in disease.

Keywords: DECIDE; chorion; diffusion; flow-matching; relaxometry.

Figure 1

Whole‐placenta curve fitting results for fixed echo‐time IVIM imaging (case 2) for signal (A) and log‐signal (D) (curve fitting for b > 100 s.mm^–2). For zero b‐value, monoexponential relaxometry for signal (B) and log‐signal (E). For DECIDE fitting (Equation ((3))), a single model‐fitting procedure to all acquired images for signal (C) and log‐signal (F)

Figure 2

Example parametric maps for the T2‐IVIM fit for 1 case where myometrial analysis was feasible. Panels show parameter maps, from left to right, $f$, d*, d, T2 maternal blood, and T2 myometrium. Example figures for all cases are shown in the Supporting Information

Figure 3

Histograms for the voxel‐wise fit, for the 4 myometrial data sets. Row 1 shows f, d*, and d for the standard IVIM fit. Rows 2 and 3 show $f$, d*, d, and T2 relaxation time of maternal blood and myometrium for the combined myometrium fit

Figure 4

Parametric maps for the DECIDE fit (Equation ((2))) for 1 control singleton pregnancy. Panels show parameter maps, from left to right, $f$, d*, d, $v$, and T2 fetal blood. Example figures for all cases are shown in the Supporting Information

Figure 5

Voxel‐wise whole‐placenta parameter histograms for the 6 placenta data sets. Row 1 shows $f$, d*, and d for the standard IVIM fit. Rows 2 and 3 show $f$, d*, d, $v$, and T2 relaxation time of fetal blood for the DECIDE fit (Equation ((2)))

Figure 6

Histograms of voxel‐wise fit of the maternal‐fetal blood volume ratio for the 6 placenta data sets

Figure 7

Parametric maps for the voxel‐wise fit of fetal blood oxygen saturation, derived from fetal blood T2 relaxation time. A histogram showing the voxel‐wise fit for the whole‐placenta data is shown in Figure 8. Mean fetal blood saturation over the whole data set (s < 100%) was 72.93 (±20.11)%

Figure 8

Histogram showing the voxel‐wise fit of fetal blood oxygen saturation over the whole placenta for the 6 cases (Equation ((3))). There are few voxels with saturation less than 45%. Mean fetal blood saturation (s < 100%) over the whole data set was 72.93 (±20.11)%