Development of brain tumor demarcation technique using two-color laser-induced fluorescence

In the field of neurosurgery for brain tumor, it is crucially important to remove almost totally certain brain tumors because of patients' quality of life. However, there has been few effective means of determining the boundaries between tumor tissue and surrounding normal brain parenchyma, making tumor resection totally dependent on the experiencing judgment of surgeons. Therefore, it is quite desirable to construct a real-time and highly sensitive monitoring system to detect tumor margins during surgery. In this study, proposed is the novel photo-dynamic diagnosis method for glioma-surgery. Using excited fluorescence from an oncotropic luminophore dye generally used in PDT and auto-fluorescence from some intracellular enzymes, e.g. NADH (Reduced Nicotinamide Adenine Dinucleotide), the ratio-metric technique in two-color laser-induced fluorescence was experimentally applied to brain tumor detection. The experiment was conducted using brain tumor rat models. An oncotoropic fluorescent dye, NPe6 (mono-L-aspartyl chlorin e6), was injected intravenously and then two fluorescence images were taken with irradiation of violet light, The fluorescence intensities of intracellular enzymes and NPe6 were found to decrease and increase in tumor lesions, respectively. Fluorescence intensity ratio could quantitatively identify tumor margins. Undesirable fluorescence variation could be reduced, which was dependent on inhomogeneous irradiation intensity distribution due to brain surface shape and illuminating light source itself. Thus, the ratio image could achieve higher contrast enhancement in tumor boundaries than single-color PDD. Furthermore, the histological examination provided correlation with ratio-image enhanced area. Consequently, the present method was clarified to be effective to brain tumor monitoring and quantitative tumor boundary demarcation.