Could Transdermal Optical Imaging change Healthcare Monitoring?

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Transdermal Optical Imaging (TOI) may well change how you will manage your health soon. 

In 2025, almost 43 million Americans will wear a smartwatch giving them the potential to monitor blood pressure, heart rhythm, calories burned, and even stress levels. Forty-three million seem like a lot but is pale compared to 290 million smartphones already in use as of 2021.

Transdermal Optical Imaging is still in its infancy. Still, it has the potential to transform any smartphone into an accurate and reliable medical device with the ability to detect most of the vital signs detected by health smartwatches.

Soon, a smartphone will be the only device needed always to carry your doctor in your pocket.

How does this new technology work? Is it reliable? Will TOI change the way we monitor our health in the future? These are just a few of the questions we will address in this article that may change how you look at your phone.

What are the applications of contactless vital signs monitoring

Non-contact cardiovascular monitoring relies on the same principles as Photoplethysmography (PPG) that constitutes the primary sensors found in smartwatches for assessing cardiovascular activity.

RemotePPG (rPPG) is not new. In 2012, Philips introduced the VitalSigns Camera Technology designed to detect the subtle skin color changes associated with facial blood flow during each heartbeat.

The technology developed by Philips was robust enough to work with any skin color and in subjects standing or even moving between 1 to 5 meters in front of the camera. 

The potential applications range from wellness, security, gaming, fitness up to detecting drivers’ heart rate and breathing patterns to ensure proper levels of vigilance while driving. 

Contactless remote monitoring is already used by Insurance companies, such as the Japanese Insurer Sompo, to monitor wellness, health, and early signs of depression.

What are the scientific bases of Transdermal Optical Imaging Technology?

Transdermal Optical Imaging refers to videos of the face to remotely measure the changes in facial blood flow, extracting meaningful physiological indicators such as the Heart rhythm, Heart Rate Variability, blood pressure, and even stress levels.

How does TOI work?

The face is rich in microvessels, making it ideal for detecting the superficial changes in blood flow during each heartbeat. 

The core principle is that skin is translucent, meaning that light will travel through the different skin layers before being re-emitted and captured by a video camera. 

The skin contains chromophores, principally hemoglobin, and melanin, which have different color signatures. Given the differences in color signatures, machine learning can differentiate photos of hemoglobin-rich regions from melanin-rich parts.

The video images of hemoglobin changes beneath the skin detect the facial blood flow patterns associated with cardiovascular activity.

Just as a smartwatch will rely on photoplethysmographic sensors to detect blood flow through the veins underneath the skin, TOI will extract the equivalent information by just detecting the color micro-changes at the surface of the epidermis.

Preliminary Scientific Validation

In 2018, researchers in China and Canada developed a Transdermal Optical Imaging experiment to detect heart rate and extract stress levels through analysis of the Heart Rate Variability (HRV.)

The HRV corresponds to the time difference between two consecutive heartbeats and is under the control of the Autonomic Nervous System that automatically regulates perspiration that will induce changes in skin electrical conductivity. HRV is extensively used to detect mental states and changes in stress levels. 

The study conducted in control settings on 136 participants compared the TOI technology to the FDA-approved BIOPAC system ECG100C for monitoring heart rate and HRV. The heart rate and stress level measures acquired with the TOI technology closely matched those obtained with the BIOPAC. Thus, this study demonstrated that TOI might accurately assess an individual’s heart rate, HRV, and stress level.

The following year, in 2019, the same multidisciplinary team published the first proof-of-concept study of the possibility to use a video camera and Transdermal Optical Imaging algorithm to assess blood pressure in a study including 1,328 adults. Still the largest one to date.

Using an advanced machine learning technique, the team developed computational models that estimate reference systolic, diastolic and pulse pressure from face blood flow data.

When using TOI image acquisition associated with the Artificial Intelligence model, the preliminary predicted blood pressure fell the clinically accepted accuracy threshold of 5±8 mm Hg.

Even though the experimental setting was controlled in terms of illumination, distance to the camera, and blood pressure among the participants, these results were the first to demonstrate the potential of such technology in a large set of participants.

What are the benefits of TOI?

In a world that still suffers from the Covid-19 pandemics and strict social distancing rules, transdermal optical imaging is a cost-effective way to monitor vitals without the need for physical interaction remotely.

Circadia Health developed a radar-based technology to monitor ICU patients’ breathing patterns remotely. Thus reducing the risk of Covid-19 transmission. 

Transdermal Optical Imaging goes several steps further and relies on analyzing blood flow patterns and hemoglobin concentration to extract numerous medical information, both physiological and psychological.

  • Heart rhythm
  • Systolic blood pressure
  • Diastolic blood pressure
  • Autonomic Nervous Systems associated cues such as basal stress, cognitive load, or Heart Rate Variability

In 2018, Liu et al. published an article in the prestigious Nature journal showing that when dividing the face into ten regions of interest, the analysis of spatiotemporal patterns of facial blood flow could be associated with five independent components.

Digital optical sensors analyses offer more than pure vitals information but could also be a window open to psychological health.

Biometric data provide multiple measurements but require the intervention of trained technicians to set the electrodes correctly. Even smartwatches rely on the proper adjustment of the wristband. 

By its contactless nature, Transdermal Optical Imaging offers a non-intrusive way to detect blood flow changes and extract numerous meaningful vitals as far as the computational models have been adequately trained.

What are the limitations and concerns of TOI?

Even if Transdermal Optical Imaging appears as a promising technology, it does not come without technical and ethical drawbacks.

Privacy Concerns

As far as ethics is concerned, the main concern associated with TOI comes from its potential implication with privacy issues. When considering that any video camera could extract medical information, at least in theory, privacy could quickly become a significant concern.

The Covid pandemics has seen a dramatic increase in the number of automated cameras fitted with thermo-sensors. The possibility to link Artificial Intelligence-powered computer vision face recognition cameras to TOI vital monitoring poses a significant potential privacy risk.

In that sense, HIPAA and GDPR need to be constantly updated to reflect technology advances best. 

Robustness of the technology

 As with any technology relying on the acquisition of digital videos, the lighting conditions are critical to ensure proper analysis of the facial blood flow information.

The technology relies on detecting chromophores under the skin and needs to be validated in subjects with various skin colors.

Finally, the underlying models used to extract the vitals need to be trained extensively on substantial data sets to ensure their robustness and reproducibility.

What are the companies involved in TOI?

Considering the potential of such technology, startups aim to develop robust SDK that will make the most of it and bring it from a clinical setting to a broader environment.


Nuralogix, a Canada-based company, is probably the most advanced company when it comes to using Transdermal Optical Imaging. The validation articles presented were made in partnership with scientists from the company.

The company developed the ANURA app available for iOS and Android that allows to quickly, and for free, measure various vitals, including:

  • Heart rate
  • Irregular heartbeats
  • Breathing rate
  • Heart rate variability
  • Stress level
  • Skin Age

We tested it on my wife and, in just 30 seconds, received numerous data that appear as coherent compared to the Huawei Band 6 tracker she was wearing at the time. Respiration at 6 per minute was a bit weird, though. As for the skin age, no need to mention that, at 45, she was delighted to learn that her skin was estimated to be 30 years old. On the opposite side, mine was detected as looking like 61 years old! A 15-year increase. The computer vision algorithm may prefer shaved faces.

Overall, Nuralogix brings a complete set of SDKs backup up by robust science that can be used for various applications. Advanced Human Imaging partners with Nuralogix for the development of their comprehensive body analysis offer.

Israel based company Binah develop SDKs aiming at offering complete vitals analyses, including:

  • Heart Rate
  • Heart Rate Variability
  • Parasympathetic Activity
  • Sympathetic Stress
  • Blood Pressure
  • Blood Oxygen Saturation
  • Pulse Respiratory Quotient
  • Respiration Rate

The AI-based TOI solution is offered as SDK to Healthcare Providers, Insurers, and Wellness companies. Binah benefited from extensive press coverage following its partnership with Insurer Generali and was named of the best 10 AI-based Israeli companies for 2021.

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