Intraoperative detection of IDH-mutant glioma subtype using fluorescence lifetime imaging

In-situ identification of glioma subtype can enable modifications of clinical and surgical strategies. Particularly, astrocytoma benefit from more aggressive resection than oligodendroglioma, which have a more favorable response to post-surgical chemotherapy. Preoperative MRI and intraoperative histology cannot accurately determine glioma subtype. There is a need for real-time identification of adult-type diffuse glioma subtypes to aid the neurosurgeon's decisionmaking during resection surgery. Fluorescence lifetime imaging (FLIm) where tissue autofluorescence can be used as an indicator to distinguish among brain tumor tissue types in real-time could aid this process. Here, we report the use of label-free FLIm in distinguishing IDH-mutant glioma subtypes (astrocytoma and oligodendroglioma). The FLIm system (excitation: 355 nm; emission bands: 390/40 nm, 470/28 nm, 542/50 nm) was used to scan brain tissue from the resection margins of glioma patients during tumor resection. Fluorescence lifetimes were extracted and analyzed by constrained least-squares deconvolution with the Laguerre expansion method. FLIm data was validated with histopathology of collected biopsies. Current results show that FLIm provides optical contrast between tumor and healthy white matter, and between IDH-mutant astrocytoma (N=7 patients) and oligodendroglioma (N=5 patients). Tumors showed shorter lifetime values (470-nm: 3.6 +/- 0.6ns; 542-nm: 3.3 +/- 0.7ns) than healthy white matter (470-nm: 4.6 +/- 0.4ns; 542-nm: 4.3 +/- 0.5ns, p<0.01). Oligodendroglioma had shorter lifetimes in the 470-nm (3.3 +/- 0.1ns) and 542-nm (2.8 +/- 0.2ns) channels, which are associated with NAD(P)H and FAD fluorescence respectively, when compared with IDH-mutant astrocytoma (470-nm: 4.1 +/- 0.1ns; 542-nm: 3.9 +/- 0.2ns, p<0.01). Together, these results demonstrate the feasibility of using FLIm as an intraoperative tool in glioma diagnosis.