Figure 6.

Fluorescence spectra induced by a photon beam. The intensity (I) as a function of wavelength (λ) collected from the scattering phantom with increasing levels of protoporphyrin IX, induced by a photon beam (a) 6 MV and (b) 18 MV. The PpIX concentrations are specified in the legend of Fig. 5 (a)–(b). In (c) the incremental intensity (ΔI) at 635 nm is seen as a function of protoporhyrin IX concentration, where (•) is photon energy 6 MV (R² =  0.94) and (▪) 18 MV (R² =  0.95). In (d) the spectra from chicken muscle tissue is seen where the photon energies are 6 MV and 18 MV.