Implications of laser light characteristics on the Raman signal-to-noise ratio in diagnostic analysis of glioblastoma multiforme

The presented work is part of a study investigating the surgical diagnostic potential of Raman spectroscopy for the malignant brain tumor, glioblastoma multiforme (GBM). This work examines the trade-off of increased Raman signal observed using excitation at lower wavelengths (1/X4 signal dependence) versus the fluorescence caused by endogenous tissue fluorophores at those wavelengths. Within the VISIR regions, this fluorescence is known to increase with decreasing wavelength. Our previous results, demonstrating spectral differences between normal and malignant tissues in scid mice, were obtained using a pulsed alexandrite laser. These results are compared to those obtained similarly using pulsed 632.7 nm excitation, the second harmonic of Nd:YAG shifted by 2991 cm which is generated by means of stimulated Raman scattering of high pressure deuterium. This trade-off in signal versus fluorescence is discussed further, in relation to investigations using continuous wave excitation. A range of wavelengths between 632.8 and 799.3 nm of cw excitation are compared for signal magnitude and for background and fluorescence masking.