Premium
Normal human and sheep fetal vessel oxygen saturations by T2 magnetic resonance imaging
Author(s) -
Saini Brahmdeep S.,
Darby Jack R. T.,
Portnoy Sharon,
Sun Liqun,
Amerom Joshua,
Lock Mitchell C.,
Soo Jia Yin,
Holman Stacey L.,
Perumal Sunthara R.,
Kingdom John C.,
Sled John G.,
Macgowan Christopher K.,
Morrison Janna L.,
Seed Mike
Publication year - 2020
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jp279725
Subject(s) - fetus , fetal circulation , relaxometry , in vivo , magnetic resonance imaging , medicine , oxygen saturation , hypoxia (environmental) , blood flow , biomedical engineering , pathology , biology , radiology , oxygen , chemistry , pregnancy , placenta , genetics , microbiology and biotechnology , spin echo , organic chemistry
Key points 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). 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. Blood T2 MRI relaxometry presents a non‐invasive measure of SO 2 in the major fetal vessels. 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. 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.Abstract Blood T2 magnetic resonance imaging (MRI) relaxometry non‐invasively measures oxygen saturation (SO 2 ) in major vessels but has not been validated in fetuses in vivo . We compared the blood T2–SO 2 relationship in vitro (tubes) and in vivo (vessels) in sheep, and measured SO 2 across the normal human and sheep fetal circulations by T2. Singleton pregnant ewes underwent surgery to implant vascular catheters. In vitro and in vivo sheep blood T2 measurements were related to corresponding SO 2 measured using a blood gas analyser, as well as relating T2 and SO 2 of human fetal blood in vitro . MRI oximetry was performed in the major vessels of 30 human fetuses at 36 weeks (term, 40 weeks) and 10 fetal sheep (125 days; term, 150 days). The fidelity of in vivo fetal T2 oximetry was confirmed through comparison of in vitro and in vivo sheep blood T2–SO 2 relationships ( P = 0.1). SO 2 was similar between human and sheep fetuses, as was the fetal oxygen extraction fraction (human, 33 ± 11%; sheep, 34 ± 7%; P = 0.798). The presence of streaming in the human fetal circulation was demonstrated by the SO 2 gradient between the ascending aorta (68 ± 10%) and the main pulmonary artery (49 ± 9%; P < 0.001). Human and sheep fetal vessel MRI oximetry based on T2 is a validated approach that confirms the presence of streaming of umbilical venous blood towards the heart and brain. Streaming is important in ensuring oxygen delivery to these organs and its disruption may have important implications for organ development, especially in conditions such as congenital heart disease and fetal growth restriction.