Normal human and sheep fetal vessel oxygen saturations by T2 magnetic resonance imaging

Abstract

Human fetal Doppler ultrasound and invasive blood gas measurements obtained by cordocentesis or at the time of delivery reveal similarities with sheep (an extensively used model for human fetal cardiovascular physiology). r Oxygen saturation (SO 2) measurements in human fetuses have been limited to the umbilical and scalp vessels, providing little information about normal regional SO 2 differences in the fetus. r Blood T2 MRI relaxometry presents a non-invasive measure of SO 2 in the major fetal vessels. r This study presents the first in vivo validation of fetal vessel T2 oximetry against the in vitro T2-SO 2 relationship using catheterized sheep fetuses and compares the normal SO 2 in the major vessels between the human and sheep fetal circulations. r Human fetal vessel SO 2 by T2 MRI confirms many similarities with the sheep fetal circulation and is able to demonstrate regional differences in SO 2 ; in particular the significantly higher SO 2 in the left versus right heart.

Umbilical vein infusion of prostaglandin I2 increases ductus venosus shunting of oxygen‐rich blood but does not increase cerebral oxygen delivery in the fetal sheep

“…Oxygen saturation was then calculated from T 2 relaxation time using the T 2 ‐oxygen saturation relationship for sheep blood as previously described (Saini et al . 2020).…”

“…The regions-of-interest were manually adjusted for each image slice to cover the central 60% of the vessel of interest (UV, AAo, DAo and SVC) (Stainsby & Wright, 1998). Oxygen saturation was then calculated from T 2 relaxation time using the T 2 -oxygen saturation relationship for sheep blood as previously described (Saini et al 2020).…”

“…Previously, blood flow through the DV has been measured using techniques such as cineangiography, radioactively labelled microspheres, indicator dye dilution and ultrasound Doppler velocimetry (Tchirikov et al 2006). More recently, the use of an advanced magnetic resonance imaging (MRI) technique known as 4D flow in fetal applications has been established (Schrauben et al 2019;Sun et al 2020). 4D flow allows for the comprehensive quantification and visualization of blood flow for a volume of interest (Markl et al 2012).…”

“…In addition, we have validated the use of T 2 oximetry, an MRI technique that makes use of the differing magnetic properties of deoxy/oxy haemoglobin, to determine the oxygen saturation of blood within a given fetal vessel (Saini et al . 2020). Therefore, a combination of these two MRI techniques may be useful for the determination of oxygen delivery within the fetal circulation.…”

“…We have validated the use of 4D flow to accurately measure and track blood flow throughout the fetal circulation including flow through the fetal shunts (DV and FO); (Duan et al 2019;Schrauben et al 2019Schrauben et al , 2020. In addition, we have validated the use of T 2 oximetry, an MRI technique that makes use of the differing magnetic properties of deoxy/oxy haemoglobin, to determine the oxygen saturation of blood within a given fetal vessel (Saini et al 2020). Therefore, a combination of these two MRI techniques may be useful for the determination of oxygen delivery within the fetal circulation.…”