Transdermal optical imaging, or TOI, is a novel technology that puts preventive health care in the palm of your hand.
Instead of trekking to doctor’s offices for health data, TOI provides a non-invasive, contactless way to measure key vitals. And all it takes is access to a digital camera or smartphone.
This technology gives people the freedom and convenience to take charge of their health. But it also gives health and wellness providers an easy way to assess each client’s health based on key indicators.
This article will cover what TOI is, how it works, and what benefits it can offer health providers and their clients.
The origins of transdermal optical imaging
TOI technology was developed by Dr. Kang Lee, a developmental psychologist, and Dr. Paul Zheng, his post-doctoral fellow.1
It wasn’t originally intended as a preventative healthcare tool. That was just a happy accident. Initially, it was created as a lie-detection method for children. Dr. Lee even devoted an entire TED talk to the subject.
The basis of the technology is that the human face is rich in blood vessels. As different emotions arise, it changes blood flow in the face. The TOI software analyzed these changes to pinpoint what emotions subjects were feeling. This helped them detect when children were lying and when they were telling the truth.
While useful as a lie detector, they soon discovered it worked equally as well at measuring blood pressure. Today, TOI has a much broader use. This contactless tool can measure a variety of physiological and psychological states.
How transdermal optical imaging works
Since human skin is translucent, light penetrates the skin. As light crosses through the skin’s tissues, it’s reflected and captured by a digital camera.
The TOI technology extracts facial blood flow data from the image. It does this using chromophores, which are the parts of a molecule that give it its distinct color.
The main chromophores used in TOI are hemoglobin and melanin. These give reflected light a unique color signature, which the camera captures.
Blood flow changes underneath the surface of the face mirror changes in the cardiovascular system, such as heart rate. As you know, as your stress levels and mood change, so does your heart rate. This allows TOI to assess several physiological and psychological conditions.
TOI and artificial intelligence
Transdermal optical imaging uses AI machine learning to extract high-quality blood flow information from video capture of the face. This information can be used to accurately estimate cardiovascular patterns.2 With data gathered from facial blood flow, TOI apps such as ZYTO Link can be used in the process of assessing physical health, as well as stress and emotional health.
The machine-learning systems built into TOI apps utilize elements of affective computing, which is designed to sense the emotional state of a user based on information gathered from cameras, microphones, sensors, and software logic.3 In the case of TOI apps, information is gathered from a cell phone camera.
While TOI apps use a cell phone camera to scan the face, it doesn’t save the actual images from the phone—only the data from the facial blood-flow measurements is gathered and analyzed.
What Does TOI Measure?
TOI technology can be used to measure heart rate, heart rate variability, stress levels, and more. Let’s break down these key metrics and what they can tell you about your health.
Heart rate, (aka your pulse), is how many times your heart beats in one minute. Your resting heart rate is your pulse when you’re relaxed and not moving. Typical resting heart rates range between 60 to 100 beats per minute. Any values outside that range could suggest a deeper issue.
A high resting heart rate may be due to a sedentary lifestyle or certain medications, for example. On the other hand, a low resting heart rate may indicate an issue such as sleep apnea or hypothyroidism.
Heart rate variability
Heart rate variability (HRV) measures the difference in time between each heartbeat and how much it varies. HRV offers clues about the activity of the autonomic nervous system. This can help assess stress levels and mood.
Your autonomic nervous system has two divisions: the sympathetic and the parasympathetic. The sympathetic nervous system handles your body’s “fight or flight” response. It’s the branch that’s activated when you’re under stress.
The parasympathetic nervous system, also known as the “rest and digest” mode, is restorative and calming. This branch is activated when you feel safe and relaxed.
In general, a higher HRV means the parasympathetic nervous system is dominant. A lower HRV means fight-or-flight mode is active.4
Medical settings typically use an electrocardiogram (ECG) to measure HRV. This method involves attaching sensors to the skin to detect your heart’s electrical activity. Transdermal optical imaging provides a less invasive way to measure HRV.
Blood flows to different areas of your face depending on whether the sympathetic or parasympathetic branch is dominant. TOI uses those blood flow signatures to measure HRV and assess stress levels and psychological states.
Also known as respiratory rate, breathing rate is how many times you inhale or exhale per minute. Twelve to 20 breaths per minute is considered a normal resting breathing rate. Anything less than 12 or over 25 breaths may be a sign of a medical condition.
Similar to heart rate, breathing rate is controlled by the body’s autonomic nervous system. Issues like anxiety, illness, and allergies can cause a breathing rate that’s higher than normal, while things like sleep apnea and hypothyroidism can cause a lower-than-normal breathing rate.
As breathing rate is controlled by our autonomic nervous system, this rate can be accurately determined by measuring facial blood-flow signatures as well.
TOI analyzes the surface of the face to determine skin age using an artificial intelligence (AI) prediction model. If your skin age is older than your actual age, it may be due to factors such as genetics, spending too much time in the sun, smoking, poor diet, and more.
It should be noted that lighting can impact skin age readings as well. That’s why scanning in a well-lit area with even light distribution is recommended.
TOI research reveals that blood flow in the face happens in different regions of interest (ROI). Blood flow patterns in different facial regions often correlate with certain psychological and emotional states.
For example, one study found that when subjects experienced a bitter taste, blood flow in the nose decreased.5 But pleasant, sweet tastes increased blood flow in the eyelids.
Facial blood flow patterns, heart rate, and HRV all offer clues about a person’s nervous system activity and mood. Since TOI captures all this data remotely, it shows promise as a tool to assess an individual’s stress levels.6
Blood pressure measures how much force your heart uses to push up against the walls of the artery. Blood pressure is given with two numbers: systolic and diastolic.
Systolic pressure, or the higher number, is your blood pressure while your heart is beating. Diastolic pressure, or the lower number, is your blood pressure between beats.
People with high blood pressure, or hypertension, are at an increased risk of developing other health problems.7 This includes heart disease, stroke, and heart attack.
Blood biomarkers are often used in medical settings to identify physiological and disease states. Some common blood markers include white blood cell count (WBC), lipids, and metabolic factors.
In the past, blood tests were needed to gauge these markers. However, new research is showing that TOI can be a helpful tool for predicting these blood biomarkers based on vital signs collected from facial blood flow.8
It should be noted that TOI doesn’t measure blood biomarkers directly and isn’t a substitute for blood tests. Rather, it can be used to predict the prevalence of certain biomarkers based on facial blood flow data combined with machine learning.
As mentioned above, certain blood biomarkers are assessed with health risks. But physiological characteristics such as age, body mass index (BMI), and body fat also offer insights into overall health.
New research is exploring how TOI may be used to assess disease risk. In one study, TOI collected facial blood flow patterns and analyzed them in combination with the person’s age, BMI, body fat, and vital signs.8
What they found is that TOI was a non-invasive and inexpensive way to identify the risk of abnormal blood markers. This can help pinpoint who should get follow-up blood testing. But it also helps identify imbalances early on before full-blown disease sets in.
How accurate is transdermal optical imaging?
Recent studies show that TOI rivals traditional methods of measuring heart health.
One 2018 study compared the accuracy of TOI data to ECG. They used TOI to measure the heart rate and HRV of 136 healthy adults.5 They found that TOI data strongly lined up with ECG measurements.
Another 2019 study from the American Heart Association assessed the accuracy of TOI for blood pressure.9 Researchers compared TOI to standard cuff-based blood pressure measurements. They found that on average, TOI measured pulse, systolic blood pressure, and diastolic blood pressure with an accuracy of 95%.
Along with the physical component of cardiovascular health, we know that stress creates chemical changes in the body that impact blood pressure and heart rate.4 10 Thus, we can conclude that these measurements combined with other blood flow data can give us accurate insight into mental stress levels as well.
Similarly, as blood biomarkers and health risk factors also have a strong correlation with cardiovascular health, we can see how these measurements can also be useful in these areas.
How can TOI benefit your health?
TOI provides a convenient way for people to track their vitals all from the comfort of home.
This helps people monitor health conditions between visits to their health and wellness providers. But it also empowers them to address any health concerns before they get too serious.
In addition, transdermal optical imaging serves as a powerful tool for healthcare providers. Due to the pandemic and technological advancements, telehealth has boomed in recent years. Many people prefer the safety and comfort of visiting their providers from home.
Previously, collecting health information such as vital signs required an office visit. Now with TOI, healthcare practitioners can measure heart rate, HRV, stress levels, and more remotely.
Plus, TOI is far less invasive than traditional medical tests such as blood pressure cuffs and ECGs. Its ease of use makes it more likely that people will stay diligent in tracking their health data.
And while further research is needed, TOI also shows promise as a way to identify risk factors for hypertension and other related conditions. This can help those with cardiovascular issues monitor their conditions and address problems before they become serious.
While TOI technology is in its infancy, it has the potential to change how healthcare is monitored in the future.
About Mindy Palmer
Mindy Palmer is a wellness writer and certified holistic health coach. She enjoys inspiring others to live healthier lives by creating informative content for leading-edge health and wellness brands.
1. “Kang Lee Lab.” Dr. Kang Lee’s Development Lab.
2. Barszczyk, A., W. Zhou, & K. Lee. “AIM and Transdermal Optical Imaging.” Artificial Intelligence in Medicine (2021): 1-14.
3. “What is Affective Computing?” OpenMind BBVA. Bbvaopenmind.com.
4. Kim, H.G., E.J. Cheon, et al. “Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature.” Psychiatry Investigation 15, no. 3 (2018): 235-245.
5. Liu, J., H. Luo, et al. “Transdermal optical imaging revealed different spatiotemporal patterns of facial cardiovascular activities.” Sci Rep 8, 10588 (2018).
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7. “Blood pressure symptoms and causes.” U.S. Department of Health and Human Services. Cdc.gov.
8. Zhou, W., Y. Wang, X. Gu, et al. “Importance of general adiposity, visceral adiposity and vital signs in predicting blood biomarkers using machine learning.” Int J Clin Pract. 2020; 75:e13664.
9. Luo, H., D. Yang, A. Barszczyk, et al. “Smartphone-Based Blood Pressure Measurement Using Transdermal Optical Imaging Technology.” Circulation: Cardiovascular Imaging 12 no. 8 (2019).
10. Mukkamala, R. “Blood Pressure With a Click of a Camera?” Circulation: Cardiovascular Imaging 12, no. 8 (2019).