Their method is reported in Advanced Photonics Research and could provide a new tool for scientists and clinicians for characterising the properties of skin in individuals, to assist in managing and treating skin conditions.
Terahertz (THz) radiation, or T-rays, sit in-between infrared and WiFi on the electromagnetic spectrum. T-rays can see through many common materials such as plastics, ceramics and clothes, making them potentially useful in non-invasive inspections. The low-energy photons of T-rays are also non-ionizing, making them very safe in biological settings including security and medical screening.
There are limitations in standard THz reflection spectroscopy however, and to overcome these the scientists behind this new research instead used ellipsometry, which involves focusing T-rays at multiple angles on the same area of skin.
They successfully demonstrated that using ellipsometry they could accurately calculate the refractive index of skin (which determines how fast the ray travels through it) measured in two directions at right angles to each other. 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.
Prof. 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 the hydration of their skin 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 potentially be able to make quantitative assessments of how the skin is improving with different products or to 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 tumour 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 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 skin. However, we point out that the cellular structure of the stratum corneum also reacts to the terahertz reflections. Our technique enables this structure property to be sensitively probed, which provides comprehensive information about the skin and it is highly useful for skin diagnosis."
Professor Pickwell-MacPherson said: "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 really fit in with the current focus on tailored medicine."
MEDICA-tradefair.com; Source: University of Warwick
