Volume 29 Issue S3 | Journal of Biomedical Optics

Journal of Biomedical Optics

VOL. 29 · NO. S3 | June 2024

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Special Issue on Pulse Oximetry: 50 Years of Inventions and Discoveries in Biomedical Optics (12)

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Special Issue on Pulse Oximetry: 50 Years of Inventions and Discoveries in Biomedical Optics

Assessing changes in regional cerebral hemodynamics in adults with a high-density full-head coverage time-resolved near-infrared spectroscopy device

Farah Kamar, Leena Shoemaker, Rasa Eskandari, Daniel Milej, Darren Drosdowech, John Murkin, Keith St. Lawrence, Jason Chui, Mamadou Diop

Journal of Biomedical Optics, Vol. 29, Issue S3, S33302, (May 2024) https://doi.org/10.1117/1.JBO.29.S3.S33302

TOPICS: Surgery, Brain, Hemodynamics, Near infrared spectroscopy, Oxygenation, Tunable filters, Head, Skin, Bandpass filters, Wavelets

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Significance

Cerebral oximeters have the potential to detect abnormal cerebral blood oxygenation to allow for early intervention. However, current commercial systems have two major limitations: (1) spatial coverage of only the frontal region, assuming that surgery-related hemodynamic effects are global and (2) susceptibility to extracerebral signal contamination inherent to continuous-wave near-infrared spectroscopy (NIRS).

Aim

This work aimed to assess the feasibility of a high-density, time-resolved (tr) NIRS device (Kernel Flow) to monitor regional oxygenation changes across the cerebral cortex during surgery.

Approach

The Flow system was assessed using two protocols. First, digital carotid compression was applied to healthy volunteers to cause a rapid oxygenation decrease across the ipsilateral hemisphere without affecting the contralateral side. Next, the system was used on patients undergoing shoulder surgery to provide continuous monitoring of cerebral oxygenation. In both protocols, the improved depth sensitivity of trNIRS was investigated by applying moment analysis. A dynamic wavelet filtering approach was also developed to remove observed temperature-induced signal drifts.

Results

In the first protocol (28±5 years; five females, five males), hair significantly impacted regional sensitivity; however, the enhanced depth sensitivity of trNIRS was able to separate brain and scalp responses in the frontal region. Regional sensitivity was improved in the clinical study given the age-related reduction in hair density of the patients (65±15 years; 14 females, 13 males). In five patients who received phenylephrine to treat hypotension, different scalp and brain oxygenation responses were apparent, although no regional differences were observed.

Conclusions

The Kernel Flow has promise as an intraoperative neuromonitoring device. Although regional sensitivity was affected by hair color and density, enhanced depth sensitivity of trNIRS was able to resolve differences in scalp and brain oxygenation responses in both protocols.

Distribution-informed and wavelength-flexible data-driven photoacoustic oximetry

Janek Gröhl, Kylie Yeung, Kevin Gu, Thomas R. Else, Monika Golinska, Ellie V. Bunce, Lina Hacker, Sarah E. Bohndiek

Journal of Biomedical Optics, Vol. 29, Issue S3, S33303, (June 2024) https://doi.org/10.1117/1.JBO.29.S3.S33303

TOPICS: Education and training, Computer simulations, In vivo imaging, Blood, Tissues, Error analysis, Oximetry, Network architectures, Acoustics, Photoacoustic spectroscopy

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Artificial neural networks trained on simulated multispectral data for real-time imaging of skin microcirculatory blood oxygen saturation

Marcus Larsson, Maria Ewerlöf, E. Göran Salerud, Tomas Strömberg, Ingemar Fredriksson

Journal of Biomedical Optics, Vol. 29, Issue S3, S33304, (July 2024) https://doi.org/10.1117/1.JBO.29.S3.S33304

TOPICS: Artificial neural networks, Education and training, Spectral response, Data modeling, Tissues, Sensors, Skin, Blood, Cameras, Manufacturing

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Monte Carlo simulation of the effect of melanin concentration on light–tissue interactions for transmittance pulse oximetry measurement

Raghda Al-Halawani, Meha Qassem, Panicos Kyriacou

Journal of Biomedical Optics, Vol. 29, Issue S3, S33305, (August 2024) https://doi.org/10.1117/1.JBO.29.S3.S33305

TOPICS: Skin, Monte Carlo methods, Calibration, Oximeters, Oxygen, Transmittance, Oximetry, Blood, Light absorption, Data modeling

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Significance

Questions about the accuracy of pulse oximeters in measuring arterial oxygen saturation (SpO2) in individuals with darker skin pigmentation have resurfaced since the COVID-19 pandemic. This requires investigation to improve patient safety, clinical decision making, and research.

Aim

We aim to use computational modeling to identify the potential causes of inaccuracy in SpO2 measurement in individuals with dark skin and suggest practical solutions to minimize bias.

Approach

An in silico model of the human finger was developed to explore how changing melanin concentration and arterial oxygen saturation (SaO2) affect pulse oximeter calibration algorithms using the Monte Carlo (MC) technique. The model generates calibration curves for Fitzpatrick skin types I, IV, and VI and an SaO2 range between 70% and 100% in transmittance mode. SpO2 was derived by inputting the computed ratio of ratios for light and dark skin into a widely used calibration algorithm equation to calculate bias (SpO2−SaO2). These were validated against an experimental study to suggest the validity of the Monte Carlo model. Further work included applying different multiplication factors to adjust the moderate and dark skin calibration curves relative to light skin.

Results

Moderate and dark skin calibration curve equations were different from light skin, suggesting that a single algorithm may not be suitable for all skin types due to the varying behavior of light in different epidermal melanin concentrations, especially at 660 nm. The ratio between the mean bias in White and Black subjects in the cohort study was 6.6 and 5.47 for light and dark skin, respectively, from the Monte Carlo model. A linear multiplication factor of 1.23 and exponential factor of 1.8 were applied to moderate and dark skin calibration curves, resulting in similar alignment.

Conclusions

This study underpins the careful re-assessment of pulse oximeter designs to minimize bias in SpO2 measurements across diverse populations.

Patient-specific arterial input function for accurate perfusion assessment in intraoperative fluorescence imaging

Yue Tang, Shudong Jiang, Joseph Sottosanti, Thomas Usherwood, Xu Cao, Logan Bateman, Lillian Fisher, Eric Henderson, Ida Leah Gitajn, Jonathan Thomas Elliott

Journal of Biomedical Optics, Vol. 29, Issue S3, S33306, (September 2024) https://doi.org/10.1117/1.JBO.29.S3.S33306

TOPICS: Tissues, Bone, Biological imaging, Targeting Task Performance metric, Fluorescence imaging, Skin, Modeling, Accuracy assessment, Blood, Perfusion imaging

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Ninety years of pulse oximetry: history, current status, and outlook

Valentina Quaresima, Marco Ferrari, Felix Scholkmann

Journal of Biomedical Optics, Vol. 29, Issue S3, S33307, (August 2024) https://doi.org/10.1117/1.JBO.29.S3.S33307

TOPICS: Oximeters, Oximetry, Blood, Ear, Skin, Calibration, Oxygenation, Tissues, Light absorption

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Significance

This year, 2024, marks the 50th anniversary of the invention of pulse oximetry (PO), which was first presented by Takuo Aoyagi, an engineer from the Nihon Kohden Company, at the 13th Conference of the Japanese Society of Medical Electronics and Biological Engineering in Osaka in 1974. His discovery and the development of PO for the non-invasive measurement of peripheral arterial oxygenation represents one of the most significant chapters in the history of medical technology. It resulted from research and development efforts conducted by biochemists, engineers, physicists, physiologists, and physicians since the 1930s.

Aim

The objective of this work was to provide a narrative review of the history, current status, and future prospects of PO.

Approach

A comprehensive review of the literature on oximetry and PO was conducted.

Results and Conclusions

Our historical review examines the development of oximetry in general and PO in particular, tracing the key stages of a long and fascinating story that has unfolded from the first half of the twentieth century to the present day—an exciting journey in which serendipity has intersected with the hard work of key pioneers. This work has been made possible by the contributions of numerous key pioneers, including Kurt Kramer, Karl Matthes, Glenn Millikan, Evgenii M. Kreps, Earl H. Wood, Robert F. Show, Scott A. Wilber, William New, and, above all, Takuo Aoyagi. PO has become an integral part of modern medical care and has proven to be an important tool for physiological monitoring. The COVID-19 pandemic not only highlighted the clinical utility of PO but also revealed some of the problems with the technology. Current research in biomedical optics should address these issues to make the technology even more reliable and accurate. We discuss the necessary innovations in PO and present our thoughts on what the next generation of PO might look like.

Exploring the bias: how skin color influences oxygen saturation readings via Monte Carlo simulations

Suvvi Narayanaswamy, Chong Liu, Ricardo Correia, Barrie Hayes-Gill, Stephen Morgan

Journal of Biomedical Optics, Vol. 29, Issue S3, S33308, (August 2024) https://doi.org/10.1117/1.JBO.29.S3.S33308

TOPICS: Skin, Tissues, Reflection, Oxygen, Signal attenuation, Simulations, Monte Carlo methods, Photons, Signal to noise ratio, Light scattering

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Significance

Our goal is to understand the root cause of reported oxygen saturation (SpO2) overestimation in heavily pigmented skin types to devise solutions toward enabling equity in pulse oximeter designs.

Aim

We aim to gain theoretical insights into the effect of skin tone on SpO2-R curves using a three-dimensional, four-layer tissue model representing a finger.

Approach

A finger tissue model, comprising the epidermis, dermis, two arteries, and a bone, was developed using a Monte Carlo-based approach in the MCmatlab software. Two skin tones—light and dark—were simulated by adjusting the absorption and scattering properties within the epidermal layer. Following this, SpO2-R curves were generated in various tissue configurations, including transmission and reflection modes using red and infrared wavelengths. In addition, the influence of source–detector (SD) separation distances on both light and dark skin tissue models was studied.

Results

In transmission mode, SpO2-R curves did not deviate with changes in skin tones because both pulsatile and non-pulsatile terms experienced equal attenuation at red and infrared wavelengths. However, in reflection mode, measurable variations in SpO2-R curves were evident. This was due to differential attenuation of the red components, which resulted in a lower perfusion index at the red wavelength in darker skin. As the SD separation increased, the effect of skin tone on SpO2-R curves in reflection mode became less pronounced, with the largest SD separation exhibiting effects similar to those observed in transmission mode.

Conclusions

Monte Carlo simulations have demonstrated that different light pathlengths within the tissue contribute to the overestimation of SpO2 in people with darker skin in reflection mode pulse oximetry. Increasing the SD separation may mitigate the effect of skin tone on SpO2 readings. These trends were not observed in transmission mode; however, further planned research using more complex models of the tissue is essential.

Leveraging 3D convolutional neural network and 3D visible-near-infrared multimodal imaging for enhanced contactless oximetry

Wang Liao, Chen Zhang, Belmin Alić, Alina Wildenauer, Sarah Dietz-Terjung, Jose Guillermo Ortiz Sucre, Sivagurunathan Sutharsan, Christoph Schöbel, Karsten Seidl, Gunther Notni

Journal of Biomedical Optics, Vol. 29, Issue S3, S33309, (August 2024) https://doi.org/10.1117/1.JBO.29.S3.S33309

TOPICS: Video, 3D image processing, Cameras, Feature extraction, 3D metrology, RGB color model, Near infrared, Oxygen, Convolutional neural networks, 3D modeling

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Significance

Monitoring oxygen saturation (SpO2) is important in healthcare, especially for diagnosing and managing pulmonary diseases. Non-contact approaches broaden the potential applications of SpO2 measurement by better hygiene, comfort, and capability for long-term monitoring. However, existing studies often encounter challenges such as lower signal-to-noise ratios and stringent environmental conditions.

Aim

We aim to develop and validate a contactless SpO2 measurement approach using 3D convolutional neural networks (3D CNN) and 3D visible-near-infrared (VIS-NIR) multimodal imaging, to offer a convenient, accurate, and robust alternative for SpO2 monitoring.

Approach

We propose an approach that utilizes a 3D VIS-NIR multimodal camera system to capture facial videos, in which SpO2 is estimated through 3D CNN by simultaneously extracting spatial and temporal features. Our approach includes registration of multimodal images, tracking of the 3D region of interest, spatial and temporal preprocessing, and 3D CNN-based feature extraction and SpO2 regression.

Results

In a breath-holding experiment involving 23 healthy participants, we obtained multimodal video data with reference SpO2 values ranging from 80% to 99% measured by pulse oximeter on the fingertip. The approach achieved a mean absolute error (MAE) of 2.31% and a Pearson correlation coefficient of 0.64 in the experiment, demonstrating good agreement with traditional pulse oximetry. The discrepancy of estimated SpO2 values was within 3% of the reference SpO2 for ∼80% of all 1-s time points. Besides, in clinical trials involving patients with sleep apnea syndrome, our approach demonstrated robust performance, with an MAE of less than 2% in SpO2 estimations compared to gold-standard polysomnography.

Conclusions

The proposed approach offers a promising alternative for non-contact oxygen saturation measurement with good sensitivity to desaturation, showing potential for applications in clinical settings.

Exploring the impact and influence of melanin on frequency-domain near-infrared spectroscopy measurements

Shidhartho Roy, Jingyi Wu, Jiaming Cao, Joel Disu, Sharadhi Bharadwaj, Elizabeth Meinert-Spyker, Pulkit Grover, Jana Kainerstorfer, Sossena Wood

Journal of Biomedical Optics, Vol. 29, Issue S3, S33310, (September 2024) https://doi.org/10.1117/1.JBO.29.S3.S33310

TOPICS: Near infrared spectroscopy, Signal to noise ratio, Skin, Oxygen, Optical properties, Absorption, Statistical analysis, Oxygenation, Photon counting, Optical testing

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Dual-ratio approach to pulse oximetry and the effect of skin tone

Giles Blaney, Jodee Frias, Fatemeh Tavakoli, Angelo Sassaroli, Sergio Fantini

Journal of Biomedical Optics, Vol. 29, Issue S3, S33311, (October 2024) https://doi.org/10.1117/1.JBO.29.S3.S33311

TOPICS: Tissues, Skin, Oximetry, Hemodynamics, In vivo imaging, Sensors, Muscles, Monte Carlo methods, Tissue optics, Data modeling

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Light-guided dynamic phantom to mimic microvasculature for biomedical applications: an exploration for pulse oximeter

Hui Ma, Dario Angelone, Claudia Nunzia Guadagno, Stefan Andersson-Engels, Sanathana Konugolu Venkata Sekar

Journal of Biomedical Optics, Vol. 29, Issue S3, S33312, (December 2024) https://doi.org/10.1117/1.JBO.29.S3.S33312

TOPICS: Liquid crystal displays, Modulation, Oxygen, Oximeters, Heart, Signal generators, Imaging spectroscopy, Biomedical optics, Blood, Optical properties

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Critical analysis of the relationship between arterial saturation and the ratio-of-ratios used in pulse oximetry

Giles Blaney, Angelo Sassaroli, Sergio Fantini

Journal of Biomedical Optics, Vol. 29, Issue S3, S33313, (November 2024) https://doi.org/10.1117/1.JBO.29.S3.S33313

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