Towards Transabdominal Functional Photoacoustic Imaging of the Placenta: Improvement in Imaging Depth Through Optimization of Light Delivery

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.

Ultrasound-guided Photoacoustic image Annotation Toolkit in MATLAB (PHANTOM) for preclinical applications

“…The placenta shown in this work was relatively superficial and unobstructed, and yet fluence compensation still significantly changed the measured StO 2 and HbT of the placental volume. These results agree with similar results in the field [60, 107]. Fluence compensation can allow more accurate access to information across the entire placenta in utero and at earlier time points when the placentas may be more hidden under vital maternal organs.…”

“…The diffusion approximation is the most common computational approach used to solve the radiative transfer equation (RTE) [52][53][54]. The MC toolkit used in this work, MCX, has been rigorously validated against the diffusion approximation [55] and has been used in fluence compensation and optical property calculation in various techniques [56][57][58][59][60].…”

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“…Regardless, in PIH, there is impedance in the placenta improvement, which along these lines antagonistically influences the PT and, in the same manner, the fetal turn of events and pregnancy results. The consequence of uncontrolled PIH is from the get go, the diminishing of the placental size and its thickness under the steady predictable value [13,14]. Ultrasonography (US) occupies the assessment of the placental thickness and capacity or exact methodology like three-dimensional Doppler [15,16].…”

Special Issue on the Advances in Engineering for Women’s Health

“…Computational in silico and cellular in vitro techniques for studying the placenta and placenta-related preterm birth were discussed in an extensive review by Wheeler and Oyen 18 .This transient organ, which connects the mother and the developing fetus during pregnancy, can only be studied with complementary bioengineering approaches. Improved transabdominal photoacoustic imaging methods for the placenta were proposed by Huda et al 12 The new imaging methods provide increased imaging depth through optimization of light delivery.…”