Tumor imaging by terahertz spectroscopy of fresh tissue without dye is demonstrated using samples from a rat glioma model. The complex refractive index spectrum obtained by a reflection terahertz time-domain spectroscopy system can discriminate between normal and tumor tissues. Both the refractive index and absorption coefficient of tumor tissues are higher than those of normal tissues and can be attributed to the higher cell density and water content of the tumor region. The results of this study indicate that terahertz technology is useful for detecting brain tumor tissue.

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The origin of the differences in the refractive index observed between normal and tumor tissues using terahertz spectroscopy has been described quantitatively. To estimate water content differences in tissues, we prepared fresh and paraffin-embedded samples from rats. An approximately 5% increase of water content in tumor tissues was calculated from terahertz time domain spectroscopy measurements compared to normal tissues. A greater than 15% increase in percentage of cell nuclei per unit area in tumor tissues was observed by hematoxylin and eosin stained samples, which generates a higher refractive index of biological components other than water. Both high water content and high cell density resulted in higher refractive index by approximately 0.05 in tumor tissues. It is predicted that terahertz spectroscopy can also be used to detect brain tumors in human tissue due to the same underlying mechanism as in rats.

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