Abstract-In vivo estimation of water diffusivity in occluded human skin using terahertz reflection spectroscopy

Qiushuo Sun  Rayko I. Stantchev  Jiarui Wang,   Edward P. J. Parrott,   Alan Cottenden,   Tor‐Wo Chiu,  Anil T. Ahuja,   Emma Pickwell‐MacPherson

https://onlinelibrary.wiley.com/doi/10.1002/jbio.201800145

Water diffusion and the concentration profile within the skin significantly affect the surrounding chemical absorption and molecular synthesis. Occluding the skin causes water to accumulate in the top layer of the skin (the stratum corneum [SC]) and also affects the water diffusivity. Scar treatments such as silicone gel and silicone sheets make use of occlusion to increase skin hydration. However with existing techniques, it is not possible to quantitatively measure the diffusivity of the water during occlusion: current methods determine water diffusivity by measuring the water evaporated through the skin and thus require the skin to breathe. In this work, we use the high sensitivity of terahertz light to water to study how the water content in the SC changes upon occlusion. From our measurements, we can solve the diffusion equations in the SC to deduce the water concentration profile in 
skin and subsequently to determine the diffusivity. To our knowledge, this is the first work showing how the diffusivity of human skin can be measured during occlusion and we envisage this paper as being used as a guide for non‐invasively determining the diffusivity of occluded human skin in vivo.

Abstract-THz in vivo measurements: the effects of pressure on skin reflectivity

Jiarui Wang, Rayko I. Stantchev, Qiushuo Sun, Tor-Wo Chiu, Anil T. Ahuja, and Emma Pickwell MacPherson

Fig. 1 Experimental setup and stratified media model illustration. (a) The THz beam is focused onto the top interface of the quartz window, and the reflected signal is collected and then detected by a photoconductive antenna. (b) Schematic illustration of the layers within human skin: each layer has a different permittivity. The hydration profile of skin is approximately linear in the SC and epidermis, and constant in the dermis.

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-12-6467

Terahertz (THz) light is non-ionizing and highly sensitive to subtle changes in water concentration which can be indicative of disease. The short THz penetration depth in bio-samples restricts in vivo measurements to be in a reflection geometry and the sample is often placed onto an imaging window. Upon contacting the imaging window, occlusion and compression of the skin affect the THz response. If not appropriately controlled, this could cause misleading results. In this work, we investigate and quantify how the applied pressure affects the THz response of skin and employ a stratified model to help understand the mechanisms at play. This work will enable future THz studies to have a more rigorous experimental protocol, which in turn will facilitate research in various potential biomedical applications under investigation.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Freeze-thaw hysteresis effects in terahertz imaging of biomedical tissues

Yuezhi He, Benjamin S.-Y. Ung, Edward P. J. Parrott, Anil T. Ahuja, and Emma Pickwell-MacPherson

Freeze-thaw hysteresis effects in terahertz imaging of biomedical tissues

There have recently been several studies published involving terahertz (THz) imaging of frozen biomedical samples. In this paper, we investigate the effects of the freeze-thaw cycle on THz properties of porcine muscle and fat samples. For ordinary freezing, there was a significant change in the THz properties after thawing for muscle tissue but not for fat tissue. However, if snap-freezing was combined with fast-thawing instead of ordinary freezing and ordinary thawing, then the freeze-thaw hysteresis was removed.

© 2016 Optical Society of America

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