Good contrast is seen between normal tissue and regions of tumor in terahertz pulsed imaging of basal cell carcinoma (BCC). To date, the source of contrast at terahertz frequencies is not well understood. In this paper we present results of a spectroscopy study comparing the terahertz properties (absorption coefficient and refractive index) of excised normal human skin and BCC. Both the absorption coefficient and refractive index were higher for skin that contained BCC. The difference was statistically significant over the range 0.2 to 2.0 THz (6.6 cm<sup>−1</sup> to 66.6 cm<sup>−1</sup>) for absorption coefficient and 0.25 to 0.90 THz (8.3 cm<sup>−1</sup> to 30 cm<sup>−1</sup>) for refractive index. The maximum difference for absorption was at 0.5 THz(16.7 cm<sup>−1</sup>). These changes are consistent with higher water content. These results account for the contrast seen in terahertz images of BCC and explain why parameters relating to the reflected terahertz pulse provide information about the lateral spread of the tumor. Knowing the properties of the tissue over the terahertz frequency range will enable the use of mathematical models to improve understanding of the terahertz response of normal and diseased tissue.
Vincent P. Wallace, Anthony J. Fitzgerald, Emma Pickwell, Richard J. Pye, Philip F. Taday, Niamh Flanagan, and Thomas Ha, "Terahertz Pulsed Spectroscopy of Human Basal Cell Carcinoma," Appl. Spectrosc. 60, 1127-1133 (2006)