22 February 2010 THz imaging of skin hydration: motivation for the frequency band
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A reflective terahertz (THz) system has been under development for imaging and monitoring of skin hydration, and through consideration of attenuation, scattering, spatial resolution and measurement of sensitivity, the frequency band 0.4 - 0.7 THz has been determined optimal for operation. THz, typically defined as the frequency range between 0.1-10 THz, has been proposed for skin hydration imaging and monitoring primarily due to being non-ionizing radiation and highly sensitivity to water concentrations. While it is important to maximize measurement sensitivity to changes in water concentration, the optimal operational frequency band must simultaneously minimize the scattering from the targets (i.e. skin) and attenuation, as well as maximize the spatial resolution. In terms of atmospheric attenuation, from 0.4 to 1 THz, there are broad absorption lines at 556 GHz and 750 GHz, and large transmission windows centered at 500, 650, and 870 GHz. Scattering of the energy reflected from skin was show, using modeling, that as the frequency increased there was a considerable decrease in the power fraction reflected in the specular direction. For measurement sensitivity, it was shown that a change in reflectivity per change in water volume at 100 GHz was nearly an order of magnitude higher at 1 THz. Finally, as should be expected, higher frequencies were better for spatial resolution. In consideration of the above criteria, the motivation for using the 0.4-0.7 THz band will be presented as well as an overview the developed THz pulse reflective imaging system for imaging of skin hydration.
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Rahul S. Singh, Zachary D. Taylor, Priyamvada Tewari, David Bennett, Martin O. Culjat, Hua Lee, Elliott R. Brown, Warren S. Grundfest, "THz imaging of skin hydration: motivation for the frequency band", Proc. SPIE 7555, Advanced Biomedical and Clinical Diagnostic Systems VIII, 755513 (22 February 2010); doi: 10.1117/12.845820; https://doi.org/10.1117/12.845820

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