Fig. 2.

Refractive index $n$, amplitude absorption coefficient $\alpha$, and H&E-stained histology of gelatin-embedded human brain gliomas of different WHO grades ex vivo: (a)–(c) grade I; (d)–(f) grade II; (g)–(i) grade III; and (j)–(l) grade IV. The THz optical properties of gliomas are compared with equal data for the intact and edematous tissues, averages within the entire set of brain tissues specimens. The error bars represent a $\pm 2.0\sigma$ confidential interval of measurements, assuming fluctuation of optical properties within each tissue sample and each tissue class.