Abstract
Functional photoacoustic imaging of the placenta could provide an innovative tool to diagnose preeclampsia, monitor fetal growth restriction, and determine the developmental impacts of gestational diabetes. However, transabdominal photoacoustic imaging is limited in imaging depth due to the tissue’s scattering and absorption of light. The aim of this paper was to investigate the impact of geometry and wavelength on transabdominal light delivery. Our methods included the development of a multilayer model of the abdominal tissue and simulation of the light propagation using Monte Carlo methods. A bifurcated light source with varying incident angle of light, distance between light beams, and beam area was simulated to analyze the effect of light delivery geometry on the fluence distribution at depth. The impact of wavelength and the effects of variable thicknesses of adipose tissue and muscle were also studied. Our results showed that the beam area plays a major role in improving the delivery of light to deep tissue, in comparison to light incidence angle or distance between the bifurcated fibers. Longer wavelengths, with incident fluence at the maximum permissible exposure limit, also increases fluence within deeper tissue. We validated our simulations using a commercially available light delivery system and ex vivo human placental tissue. Additionally, we compared our optimized light delivery to a commercially available light delivery system, and conclude that our optimized geometry could improve imaging depth more than 1.6×, bringing the imaging depth to within the needed range for transabdominal imaging of the human placenta.
Highlights
The placenta is a vital organ that develops during pregnancy to support fetal growth and viability, providing oxygen, transport, and metabolism of nutrients, as well as endocrine and immunity functions.[19]
We found that a 10 mm distance between the bifurcated light sources resulted in the highest fluence at the placental surface, 17 mm below the skin surface
We have investigated the impact of the light delivery geometry and wavelength on photoacoustic imaging depth, towards the goal of enabling transabdominal imaging of the placenta
Summary
The placenta is a vital organ that develops during pregnancy to support fetal growth and viability, providing oxygen, transport, and metabolism of nutrients, as well as endocrine and immunity functions.[19] Abnormal placental function can lead to fetal growth restriction,[8] and is a clinical presentation of both gestational diabetes,[10] and preeclampsia.[17] Abnormal placental function may be a result of either the improper remodeling of the uterine spiral arteries or insufficient decidual invasion, leading to abnormal uteroplacental circulation.[9] This abnormal uteroplacental circulation can lower oxygenation of the placenta due to reduced placental perfusion and blood volume.[38]. Doppler ultrasound provides measures of uterine spiral artery blood flow, which are secondary indicators of function, as demonstrated in patients with preeclampsia and fetal growth restriction.[33,35,42]. Since the maternal health and cardiovascular system physiology affect uterine artery spiral blood flow, measures of blood flow are limited in diagnostic capability.[15,46] BOLD MRI can measure changes in placental perfusion or oxygenation by exploiting the interference of deoxyhemoglobin on the magnetic field which results in re- Doppler ultrasound provides measures of uterine spiral artery blood flow, which are secondary indicators of function, as demonstrated in patients with preeclampsia and fetal growth restriction.[33,35,42] since the maternal health and cardiovascular system physiology affect uterine artery spiral blood flow, measures of blood flow are limited in diagnostic capability.[15,46] BOLD MRI can measure changes in placental perfusion or oxygenation by exploiting the interference of deoxyhemoglobin on the magnetic field which results in re-
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