Time -resolved laser induced fluorescence spectroscopy for detection of brain tumors

Time-resolved laser induced fluorescence spectroscopy (TRLIFS) is a potential tool to detect various biochemical changes in the tissues. We demonstrate the potential of TRLIFS to delineate normal human brain tissue from the primary brain tumors. Ultra-violet light (337 nm) was used excite normal cortex, normal white matter, various grades of gliomas in both ex-vivo and in-vivo studies and spectral and temporal fluorescence characteristics noted. We have recognized two significant wavelength ranges at 390-400 nm and 440-460 nm, where peak fluorescence emission is observed. In order to explain the biochemical origin of these fluorescence characteristics of various tissues, we have tried to determine and explore various fluorophores which fluoresces at 460 nm (NADH) and 390 nm (Pyridoxamine-5-Phosphate (PMP), Glutamate Decarboxylase (GAD), Collagen I) of wavelength. Time-resolved fluorescence characteristics of pure form of PMP at various concentrations in water are examined and confirmed with peak emission at 390 nm with lifetime of 1.7 ns. By using various fluorescence features from these observations we show that the tissue can be statistically classified using discriminant function analysis, ex-vivo samples meningioma can be differentiated from normal cortex and normal dura with vary high sensitivity (100%) and specificity (>90%). Similarly, ex-vivo samples of gliomas were also classified with sensitivity (>80%) and specificity (>90%). Preliminary TRLIFS analysis of in-vivo samples of low grade glioma reveal an absence of fluorophore at 390 nm of wavelength which is observed in normal brain tissue. To complement our findings of longer lifetimes at 390 nm than 460 nm of wavelength, we have demonstrated, using Monte-Carlo simulation in conjunction with the experimental data that, there is no significant distortion of fluorescence pulse due to the effect of tissue optical properties. Additional Monte-Carlo simulations were performed to understand the spatial origin of fluorescence. Single medium simulations indicated the lowest penetration depth of excitation light (2.5 mm) was estimated in astrocytoma, while deepest penetration depth (4.8 mm) was estimated in normal cortex indicating the effect tissue optical properties. From these findings we demonstrate the potential of TRLIFS in delineation of brain tumors.