Catalogue of human tissue optical properties at terahertz frequencies

Recently published studies suggest that terahertz pulsed imaging will have applications in medicine and biology, but there is currently very little information about the optical properties of human tissue at terahertz frequencies. Such information would be useful for predicting the feasibility of proposed applications, optimising acquisition protocols, providing information about variability of healthy tissue and supplying data for studies of the interaction mechanisms. Research ethics committee approval was obtained, and measurements made from samples of freshly excised human tissue, using a broadband terahertz pulsed imaging system comprising frequencies approximately 0.5 to 2.5 THz. Refractive index and linear absorption coefficient were found. Reproducibility was determined using blood from one volunteer, which was drawn and measured on consecutive days. Skin, adipose tissue, striated muscle, vein and nerve were measured (to date, from one individual). Water had a higher refractive index (2.04 +/- 0.07) than any tissue. The linear absorption coefficient was higher for muscle than adipose tissue, as expected from the higher hydration of muscle. As these samples came from a single subject, there is currently insufficient statistical power to draw firm conclusions, but results suggest that in vivo clinical imaging will be feasible in certain applications.