Detection of reduced oxygenation in 3D placental volumes by magnetic resonance imaging (MRI) in a rat model of fetal growth restriction (FGR) Yutthapong Tongpob1,2, Alexander Joos3, Caitlin Wyrwoll1, and Kirk Feindel3,4 1 School of Human Sciences, The University of Western Australia, Perth, Australia, 2 Faculty of Medical Sciences, Naresuan University, Thailand, 3 Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, Australia, 4 School of Biomedical Sciences, The University of Western Australia, Perth, WA 6009, Australia A key driver of FGR is placental insufficiency, including inadequate development of placental vasculature. However, there are currently limitations in assessing placental function in-vivo. MRI can measure relaxation time (T2*), which correlates with oxygenation via alterations in blood haemoglobin saturation. Results of previous placental T2* studies have been conflicting, due to technical and analytical challenges, including consideration of only 2D regions of interest (ROI). This study utilised a 3D-MRI approach in a rat model of FGR. Time-mated rats were treated with either vehicle (Veh) or dexamethasone (Dex; 0.5μg/ml) in drinking water from embryonic day (E)13 onwards. Serial scans at E15, E18, and E21 were conducted using a 9.4T MRI in-vivo: a 3D-multi-gradient-echo sequence with oxygen challenge (oxygen vs medical-air) to obtain 3D-maps of the T2* signal. E21 dams were euthanised, feto-placental units dissected, and weighed. E21 T2*-values were calculated for manually defined 3D-ROIs with custom-Matlab software using the SQEXP algorithm, which is better suited for low signal to noise data than standard algorithms. In a separate cohort of rats, feto-placental vascular casts were generated, scanned using micro-CT and quantified with custom-Matlab software. E21 fetal and placental weights decreased in Dex rats by 15.6% and 35.2% respectively in comparison to Veh (p<0.0002). MRI scans revealed that when shifting from oxygen to medical-air, mean whole-placental T2* decreased in Veh and Dex by 35.2% and 20.9% respectively (p<0.05). Importantly, the relative shift in whole-placental T2* differed significantly between Veh and Dex (3.1+0.4 vs 2.0+0.5 msec; p<0.05), indicating reduced blood oxygenation in Dex placentas. Furthermore, the MRI measures aligned with a marked decline in feto-placental vascular complexity in Dex. Ongoing analyses are determining whether these changes are dynamic across gestation. The results of this proof-of-concept study demonstrate that T2*-based measurements of the placental blood oxygenation can provide non-invasive assessments of in-vivo placental health.
|Publication status||Published - 19 Aug 2019|
|Event||2019 Annual Scientific Meeting of the Endocrine Society of Australia (ESA), the Society for Reproductive Biology (SRB), and the Asia and Oceania Thyroid Association (AOTA) - International Convention Centre, Sydney, Sydney, Australia|
Duration: 18 Aug 2019 → 21 Aug 2019
|Conference||2019 Annual Scientific Meeting of the Endocrine Society of Australia (ESA), the Society for Reproductive Biology (SRB), and the Asia and Oceania Thyroid Association (AOTA)|
|Abbreviated title||ESA-SRB-AOTA 2019|
|Period||18/08/19 → 21/08/19|