Optical properties of multicellular tumour spheroids.

Multicellular tumour spheroids grown in vitro have been widely used in cancer research as an experimental preparation with many of the characteristics of tumours. They provide a model system for understanding the optical behaviour of tumour tissue, which is of interest in novel diagnostic and therapeutic procedures. Optical measurements on fresh spheroids in the wavelength range of 600-1000 nm yielded scattering coefficients, absorption coefficients and g values (mean cosine of scatter) of 160-90 mm-1, 0.1-0.4 mm-1 and 0.99, respectively. Following fixation, considerably higher values of scattering and absorption coefficients were seen. The values are compared with those reported elsewhere for excised tumour tissue and interpretations of the optical behaviour are suggested.