Richard Clothier

An imaging system has been developed based on pulses of Terahertz (THz) radiation generated and detected using all- optical effects accessed by irradiating semiconductors with ultrafast pulses of visible laser light. This technique, commonly referred to as T-Ray Imaging or THz Pulse Imaging (TPI), holds enormous promise for certain aspects of medical imaging. We have conducted an initial survey of possible medical applications of TPI and demonstrated that TPI images show good contrast between different animal tissue types. Moreover, the diagnostic power of TPI has been elicidated by the spectra available at each pixel in the image, which are markedly different for the different tissue types. This suggests that the spectral information inherent in TPI might be used to identify the type of soft and hard tissue at each pixel in an image and provide other diagnostic information not afforded by conventional imagin techniques. Preliminary TPI studies of pork skin show that 3D tomographic imaging of the skin surface and thickness is possible, and data from experiments on models of the human dermis are presented which demonstrate that different constituents of skin have different refractive indices. Lastly, we present the first THz image of human tissue, namely an extracted tooth. The time of flight of THz pulses through the tooth allows the thickness of the enamel to be determined, and is used to create an image showing the enamel and dentine regions. Absorption of THz pulses in the tooth allows the pulp cavity region to be identified. Initial evidence strongly suggests that TPI my be used to provide valuable diagnostic information pertaining to the enamel, dentine, and the pump cavity.

Results from tests of the first 30 MEIC reference chemicals in 68 different toxicity assays are presented as a prerequisite to subsequent in vitro/in vivo comparisons of acute toxicity data. A comparative cytotoxicity study was also carried out. Firstly, the variability of all of the results was analysed by using principal components analysis (PCA), analyses of variance (ANOVAs) and pairwise comparisons of means according to Tukey's method. The first PCA component described 80% of the variance of all of the cytotoxicity data. Tukey's ANOVA indicated a similar sensitivity for the assays, of approximately 80%. Secondly, the influence of five major methodological components on the general variability of the results was evaluated by linear regression and ANOVA linear contrast analyses. The findings were that: a) the toxicity of many chemicals increased with exposure time; b) in general, human cytotoxicity was predicted well by animal cytotoxicity tests; c) this prediction was poor for two chemicals; d) the prediction of human cytotoxicity by the ecotoxicological tests was only fairly good; e) one organotypic endpoint used, i.e. contractility of muscle cells, gave different results to those obtained according to viability/growth toxicity criteria; f) twelve comparisons of similar test systems involving different cell types (including highly differentiated cells) showed similar toxicities regardless of cell type; and g) nine out often comparisons of test systems with identical cell types and exposure times revealed similar toxicities, regardless of the viability or growth endpoint measurement used. Factors b, f and g must be the main causes of the remarkable similarity between the total results, while factors a, c, d and e, together with other minor factors that were not analysed, contributed to the 20% dissimilarity. The findings strongly support the basal cytotoxicity concept, and will facilitate future in vitro toxicity testing.