This PDF file contains the front matter associated with SPIE Proceedings Volume 12833, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

While pulse oximeters have traditionally been utilized for measuring arterial saturation (SpO2), the widespread adoption of pulse oximetry has led to its expanded applications, including diagnostic uses like detecting hypoxemia during the COVID-19 epidemic. Recent research has identified unexpected errors in off-label applications, with discrepancies in diagnostic efficacy based on race or skin pigmentation. The positive bias in SpO2 measurements, particularly in the critical SpO2 range of 85-90%, poses a significant concern for devices intended for SpO2 measurement. This study employs Monte Carlo simulations to model transmittance mode pulse oximetry to investigate whether documented racial and pigmentation-based biases can be attributed to epidermal melanin. The research aims to elucidate key mechanisms that may guide the improvement of technology. Specifically, the study explores sensitivity to the epidermal region under conditions with and without surface reflection, shedding light on pulse oximeter function in diverse device designs. Results demonstrate a 26% increase in the total detected signal from the epidermis when transitioning from low to high surface reflection at 660 nm, and a 22% increase in the total sensitivity of the system to the epidermis at 940 nm with surface reflection. These findings suggest that heightened sensitivity to the epidermis region leads to more pronounced spectral effects, especially with reflective sensors, potentially due to reflected photons re-entering the tissue through the epidermis.

Pulse oximeters are widely used in healthcare systems to estimate blood oxygen saturation level (SpO2) using red and infrared light. Recent clinical and simulation studies reported that in darkly pigmented subjects oximeter over-estimates SpO2 which could lead to higher rates of occult hypoxemia in highly pigmented subjects. The probable solutions to solve this over-estimation bias could be modification of the current oximeter design, calibration enrollment or modification of oximeter ratio (R). In this study, a modification of the current oximeter ratio (R) was presented by using different combinations of currently estimated oximeter parameters. Simulation results showed that modified oximeter ratio reduces over-estimation bias in highly pigmented subjects compared to the conventional oximeter ratio. In the regions near hypoxemia threshold (90% oxygenation level), the over-estimation bias in the simulated test cohort could reduce from 1.36% to -0.01% if modified oximeter ratio is used. Results show that modification of oximeter ratio could be used in future to improve oximeter accuracy and produce pigmentation independent outcomes.

Pulse oximeters’ varying performance based on skin tones has been highly publicised. Pulse oximeters tend to overestimate oxygen saturation values for people with darker skin (occult hypoxemia). The study aimed to construct a test bench to assess commercially available home based pulse oximeters. A laboratory simulator was used to mimic different oxygen saturation values (~70% to 100%). Four synthetic melanin filters were used to reproduce the effects of varying melanin attenuation levels. Three commercially available pulse oximeters (Biolight, N=13; ChoiceMMed, N = 18; MedLinket, N = 9) were reviewed and their response documented. All pulse oximeters’ responses under the effects of melanin attenuation did not change across various simulated oxygen saturation values. This does not match with the clinically observed data and one reason is that the light scattering due to tissue had not been fully replicated in the test bench. To investigate this further a Monte Carlo simulation of light propagation through the finger has been developed considering pulsatile flow and different skin tones. In reflection mode, the simulations highlight differences in measured R value and oxygen saturation with change in skin tone in the epidermal layer. However, in case of transmission mode, no change in the measured R value and oxygen saturation was observed. Further validation of these results from simulations is required to help us design pulse oximeters that are reliable and equitable for all users, regardless of skin tone.

Turbid phantoms play a crucial role in evaluating optical systems and estimating optical properties. Liquid phantoms offer precise tuning of optical properties, but accurately determining their scattering properties is challenging. By using aqueous suspensions of standardized polystyrene microspheres, their optical properties can be theoretically derived using Mie theory. The parameters involved in calculating the scattering coefficient and phase function of microspheres in a liquid medium include the refractive index, density, size probability distribution and solid content of the microspheres and refractive index of the medium. The accuracy of these parameters directly affects the accuracy of calculated optical properties. A lack of clear protocols for phantom preparation and conflicting data in the literature may lead to easily avoidable inaccuracies. We introduce an open-source software that offers a detailed mixing protocol and subsequent optical property calculations for turbid phantoms. The software allows users to input details of the microsphere suspension, target optical property values, and choose between individual or sequentially diluted phantom mixing. It also accommodates the introduction of non-scattering molecular dyes to achieve specific absorption coefficients. The software facilitates recalculations of optical properties based on the actual quantities used during phantom preparation, offering flexibility and increased accuracy. Error estimates are provided using Monte Carlo sampling and error propagation. The open-source software is established as a comprehensive tool for preparing liquid turbid phantoms using microsphere suspensions, accessible to non-experts with basic familiarity of pipetting and use of analytical scales.

MOTIVATION: Biological samples are not always available to validate performance during development of optical imaging devices for in vivo detection of potentially malignant lesions. Thus, to provide readily available testing, there is a need for phantoms with optical response similar to that of target tissue.

OBJECTIVES: 1) Fabricate lung tissue phantoms that mimic structural and optical properties of central and segmental airways for 1310 ± 50 nm endoscopic OCT. 2) Simulate vascular flow to characterize angiography. 3) Produce a robust and cost-effective alternative to ex vivo tissue.

METHODS: An agar matrix is mixed with intralipid and coconut oil to achieve tissue-like absorption and scattering properties. A partitioned 3D printed mould is used to mimic airway geometry and embedded tubing is used to simulate vasculature. Fluid-flow is visualized with inter-A-line speckle decorrelation methods. Phantom optical performance is qualitatively and quantitatively compared against segmental airways in previous in vivo human studies using the same imaging system.

RESULTS: Images of common bronchial structures (eg: ducts, airway branches) reproduced in the phantoms qualitatively resemble similar structures in vivo (lung airway LB9) in OCT. Airway epithelial thickening indicative of dysplastic progression in vivo is re-created in the phantoms. Depth resolved attenuation coefficients are calculated and plotted for images collected on the same system, quantitatively characterizing replication. Live vasculature is mimicked using intralipid flow and visualized.

Medical imaging is advancing rapidly through the development of novel laser sources and non-linear imaging methodologies. These developments are boosting deep tissue imaging allowing researchers to study diseases deep in the body enabling early diagnosis and better treatment. To help with the testing and optimization of these imaging systems and to aid in this process of deep tissue imaging, it's important to have robust, stable and reproducible standards and phantoms. Herein we present the design and fabrication of robust, multi-layered, hydrogel-based standards. The hydrogel used is a double network hydrogel consisting of two interpenetrating networks agarose and polyacrylamide. Thin layers of tough double network hydrogels are stacked to form multilayered depth standards having modality specific signaling markers embedded in between. Standard design and assembly ensured long term stability and easy transport. These proved useful in-depth imaging studies, utilizing multiple imaging modalities, including one photon fluorescence (1PEF), two photon fluorescence (2PEF), coherent anti-Stokes Raman imaging (CARS) and second harmonic generation imaging (SHG).