Photoacoustic imaging for in vivo quantification of placental oxygenation in mice

Accurate analysis of placental and fetal oxygenation is critical during pregnancy. Photoacoustic imaging (PAI) combines laser technology with ultrasound in real time. We tested the sensitivity and accuracy of PAI for analysis of placental and fetal O2 saturation (sO2) in mice. The placental labyrinth (L) had a higher sO2 than the junctionalzoneplusdecidua region(JZ+D) inC57Bl/6mice.ChangingmaternalO2 from100 to20%inC57Bl/6mice lowered sO2 in these regions.C57Bl/6 mice were treatedwith theNOsynthase inhibitorL-NG-nitroargininemethyl ester (L-NAME) from gestational day (GD) 11 to GD18 to induce hypertension. L-NAME decreased sO2 in L and JZ+DatGD14 andGD18 in associationwith fetal growth restriction and higherblood pressure.Hypoxia-inducible factor 1a immunostaining was higher in L-NAMEvs. control mice at GD14. Fetal sO2 levelswere similar between L-NAME and controlmice atGD14 andGD18. In contrast to untreatedC57Bl/6, L-NAMEdecreased placentalsO2 at GD14andGD18 vs.GD10 orGD12.Placental sO2was lower infetalgrowthrestrictioninanangiotensin-converting enzyme 2 knockout mouse model characterized by placental hypoxia. On phantom studies, patterns of sO2 mea- sured directly correlatedwith thosemeasured by PAI. In summary, PAI enables the detection of placental and fetal oxygenation duringnormal andpathologic pregnancies inmice.