Significance: Gas in scattering media absorption spectroscopy (GASMAS) is a technique for gas sensing in cavities surrounded by scattering materials. GASMAS could be translated to the clinic to monitor lung function continuously and noninvasively in neonates. Accurate tissue phantoms are essential to assess the strengths and limitations of gas spectroscopy in gas-containing cavities in the human body.
Aim: The aim is to develop a detailed protocol to produce a long-lasting, multistructure tissue phantom of the thorax of a neonate. The phantom mimics the geometry and the optical properties of the main organs of the thorax and has an empty pulmonary cavity that facilitates GASMAS monitoring of gas content.
Approach: The anatomic geometry of heart, lungs, bones, muscle, fat, and skin was obtained from a neonatal computed tomography scan. Once segmented, organs were 3D printed and used to create negative rubber molds. The entire thorax was built in phantom material (silicone as matrix, black ink as absorber, and silica microspheres as scatters) by placing all phantom organs inside the muscle structure. Our phantom recipe was customized by mixing specific ratios of ink and spheres to match the optical properties of the different organs that were consider to be homogeneous.
Results: An anthropomorphic thorax phantom with the desired optical properties (μa and μs′) at 760 nm was built and used to obtain “transdermal” GASMAS measurements of oxygen content within the lung cavity.
Conclusion: A protocol to build a robust optical phantom of the thorax of a neonate was used to conduct benchtop studies. This recipe can be implemented to reproduce the geometry and optical properties of any human or animal tissue.
Pulmonary X-ray imaging together with pulse oximetry are harmful and invasive techniques used to monitor and diagnose the clinical course of lung dysfunction in preterm born infants which most of the cases suffer Respiratory Distress Syndrome (RDS) [1]. Biophotonics@Tyndall is exploring Gas in Scattering Media Absorption Spectroscopy (GASMAS) [2] as a novel non-invasive technique to measure continuously absolute lung oxygen volume and concentration. This could assist and improve the assessment of lung function in neonates [3].
In this paper, we present results of bench-top measurements carried out in the preclinical phase of GASMAS studies. We start with a detailed explanation of the manufacturing process of multi-structure thorax phantoms with realistic geometry based on organ segmentation from anonymized DICOM images of neonates. After segmentation, the organs are 3D printed and used to create negative rubber molds. The tissue optical properties of heart, bone and muscle are assigned by mixing the silicone matrix with different concentrations of absorbers and scatters, the lung is kept as a gas content cavity and the thorax phantom is build up by placing all organs inside out immersed in the muscle structure.
The phantoms are used for quality control and validation of the system performance [4]. Oxygen gas absorption imprints are measured for different light source-detector remittance configurations and the results are used to define the potential and limitations of the GASMAS technology in the development of a bed-side clinical device.
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