Scientists from the University of Warwick and The Chinese University of Hong Kong (CUHK) have developed a new method that uses a type of radiation known as T-rays to analyze skin structure. This original method is expected to improve the diagnosis and treatment of skin conditions such as eczema, psoriasis, and skin cancer.
The interesting fact about this method is that it can help scientists build a more detailed picture of the structure of an area of skin and how hydrated it is than current methods allow.
Its unique properties, imaging, and analysis with terahertz (THz) radiation have attracted much attention in recent years as T-rays can see through many common materials such as plastics, ceramics, and clothes. This makes them potentially useful in non-invasive inspections. Furthermore, these rays consist of non-ionizing low-energy photons. This property makes them very safe in biological settings, including security and medical screening.
Only the T-rays going through the external layers of skin before being reflected can be identified, as those traveling deeper are attenuated excessively. This makes T-ray imaging a possibly successful method of monitoring these outermost layers.
To test this, terahertz light is focused onto the skin through a prism to adjust the beam in a specific focal plane. Contingent upon the properties of the skin, that light will be reflected marginally in an unexpected way. Researchers would then be able to think about the properties of the light when it enters the skin.
There are restrictions in standard THz reflection spectroscopy. However, to overcome these, the scientists behind this new research instead utilized ellipsometry, which includes focusing T-rays at different angles on the same skin area.
They successfully demonstrated that using ellipsometry, they could accurately calculate the refractive index of skin measured in two directions at right angles. The difference between these refractive indices is termed birefringence—and this is the first time that the THz birefringence of human skin has been measured in vivo.
These properties can provide valuable information on how much water is in the skin and enable the skin thickness to be calculated.
Professor Emma Pickwell-MacPherson, from the Department of Physics at the University of Warwick and the Department of Electronic Engineering at CUHK, said: “We wanted to show that we could do in-vivo ellipsometry measurements in human skin and calculate the properties of skin accurately. In ordinary terahertz reflection imaging, you have thickness and refractive index combined as one parameter. By taking measurements at multiple angles, you can separate the two.”
“Hydrated skin will have a different refractive index from dehydrated skin. For people with skin disorders, we’ll be able to probe their skin’s hydration quantitatively, more so than existing techniques. If you’re trying to improve skincare products for people with conditions like eczema or psoriasis, we would be able to make quantitative assessments of how the skin is improving with different products or differentiate types of skin.”
“For skin cancer patients, you could also use THz imaging to probe the skin before surgery is started, to get a better idea of how far a tumor has spread. Skin cancer affects the properties of the skin, and some of those are unseen as they’re beneath the surface.”
Dr. Xuequan Chen, the study’s first author and a post-doctoral fellow from the Department of Electronic Engineering at CUHK, said: “T-rays have been known to be sensitive to the hydration level of the skin. However, we point out that the stratum corneum’s cellular structure also reacts to the terahertz reflections. Our technique enables this structure-property to be sensitively probed, which provides comprehensive information about the skin and is beneficial for skin diagnosis.”
Scientists tested their method on volunteers by asking them to place their arm on the imaging window of their T-ray equipment for 30 minutes. By holding their skin against the surface of the imaging window, they blocked water from escaping away from their skin as perspiration, a process referred to as occlusion.
They made four measurements at right angles to each other every two minutes over half an hour. Through this, they were able to monitor the effect of occlusion over time.
T-rays are particularly sensitive to water; hence they observed a noticeable difference as water accumulated in the skin, suggesting that the method could show how effective a product is at keeping skin hydrated.
Professor Pickwell-MacPherson said: “We don’t have anything accurate for measuring skin that clinicians can use. Dermatologists need better quantitative tools to use and use easily.”
“If this works well, you could go into a clinic, put your arm on a scanner, your occlusion curve would be plotted, and a suitable product for your skin could be recommended. We could get more tailored medicine and develop products for different skin responses. It could fit in with the current focus on tailored medicine.”
In further studies, scientists will improve the instrumentation of the process and how it might work as a practical device.
- Xuequan Chen et al. Exploiting Complementary Terahertz Ellipsometry Configurations to Probe the Hydration and Cellular Structure of Skin In Vivo, Advanced Photonics Research (2020). DOI: 10.1002/adpr.202000024