Fluorescence of normal and cancerous brain tissues: The excitation/emission matrix

This project investigates the use of fluorescence to discriminate cancerous margins from surrounding normal tissues during neurosurgery. This paper presents a study of the excitation/emission matrix for in vivo rat brain tissue and ex vivo human brain tissue. Measurements were made with an optical fiber fluorimeter, consisting of excitation with a nitrogen/dye laser and detection with a spectrograph and optical multichannel analyzer. The ex/em pair of wavelengths (nm) for excitation and emission of fluorescence are summarized for three types of fluorophores: (1) fluorophores similar to NADH at 470/520, (2) fluorophores similar to flavins at 440/520, and (3) porphyrins at 630/490. These peaks represent the experimentally observed peaks and do not yet consider the corrections for tissue optical properties and the geometry of fluorescence collection. Measurements of these fluorophores types were measured in ex vivo human normal and cancerous tissues, in vivo rat normal brain and glioma, and cell culture aggregates (GBM cells). In general, the magnitude of fluorescence decreases in cancerous tissues. The ratio of F"flavin"/F"NH" is an indicator of metabolic activity and a potential assay for normal vs cancerous tissues. Pilot studies with in vivo rat glioma model and with ex vivo human samples tested the use of this ratio for discriminating tissue types. The results did not show obvious trends but more work is still needed.