Abstract 029: Photoacoustic Imaging - Novel In Vivo Quantification of Placental Hypoxia in a Mouse Model of Hypertensive Pregnancy

Abstract

Placental hypoxia/ischemia induces abnormal maternal and neonatal outcomes including preeclampsia and intrauterine growth restriction (IUGR). The ability to accurately determine placental oxygenation in a non-invasive way and in real-time is highly important during pregnancy as it may allow for the early diagnosis of IUGR and preeclampsia. Photoacoustic imaging (PA) is a novel preclinical and emerging clinical tool that combines optical contrast of photoacoustic laser technology with high spatial resolution of ultrasound. PA measures tissue oxygen saturation (sO2) that reflects differences in absorption spectra for oxygenated and deoxygenated hemoglobin. By using photoacoustic features of VEVO LAZR high resolution ultrasound system (VisualSonics) in a three-dimensional mode we investigated the sensitivity and accuracy of PA for placental oxygenation in C57Bl/6 mice at day 14 of gestation. Furthermore, since nitric oxide deficiency is associated with upregulation of circulatory hypoxia markers, C57Bl/6 mice were chronically treated with the nitric oxide inhibitor, L-NAME via osmotic minipumps (50 mg/kg/day; days 13 to 18 of gestation). The comparisons between scanned vs. not scanned uteroplacental units showed that PA had no effect on fetal (scanned: 0.028±0.001 vs. not scanned: 0.03±0.001 g/maternal body weight; p>0.05) or placental (scanned: 0.002±0.003 vs. not scanned: 0.002±0.002 g/maternal body weight; p>0.05) weights in C57Bl/6 mice. Changing inhaled O2 from 100- to 20% resulted on average in 12.5% reduction in total placental sO2. Systolic blood pressures were higher in L-NAME-treated vs. C57Bl/6 mice (215.8±0.8 vs. sham 99.3±4.4 mmHg; p<0.05). L-NAME infusion decreased sO2 in all areas of the placenta: labyrinth (73.6±0.97 vs. 58.6±3.4%, p<0.05), mesometrial triangle (63.0±2.0 vs. 48.9±1.0%, p<0.05), and total placenta (68.2±1.7 vs. 54.4±2.2%, p<0.05). Placental labyrinth had higher sO2 vs. mesometrial triangle area in both L-NAME infused (58.6±3.4 vs. 48.9±1.0%, p<0.05) and in C57Bl/6 (73.6±0.97 vs. 63.0±2.0%, p<0.05) mice reflecting elaborate branching morphology of the labyrinth. Our data suggest that PA imaging can detect regional differences in placental sO2 non-invasively and at different physiological states.