Maximal safe resection is a key strategy for improving patient prognosis in the management of
brain tumors. Intraoperative fluorescence guidance has emerged as a standard in the surgery of high-grade
gliomas. The administration of 5-aminolevulinic
acid prior to surgery induces
tumor-specific accumulation of
protoporphyrin IX, which emits red fluorescence under blue-light illumination. The technology, however, is substantially limited for low-grade
gliomas and weakly
tumor-infiltrated brain, where low
protoporphyrin IX concentrations are outweighed by tissue autofluorescence. In this context, fluorescence lifetime imaging has shown promise to distinguish spectrally overlapping fluorophores. We integrated frequency-domain fluorescence lifetime imaging in a surgical microscope and combined it with spatially registered fluorescence spectroscopy, which can be considered a research benchmark for sensitive
protoporphyrin IX detection. Fluorescence lifetime maps and spectra were acquired for a representative set of fresh ex-vivo
brain tumor specimens (low-grade
gliomas n = 15, high-grade
gliomas n = 80,
meningiomas n = 41, and
metastases n = 35). Combining the fluorescence lifetime with fluorescence spectra unveiled how weak
protoporphyrin IX accumulations increased the lifetime respective to tissue autofluorescence. Infiltration zones (4.1ns ± 1.8ns, p = 0.017) and core
tumor areas (4.8ns ± 1.3ns, p = 0.040) of low-grade
gliomas were significantly distinguishable from non-pathologic tissue (1.6ns ± 0.
5ns). Similarly, fluorescence lifetimes for infiltrated and reactive tissue as well as necrotic and core
tumor areas were increased for high-grade
gliomas and
metastasis.
Meningioma tumor specimens showed strongly increased lifetimes (12.2ns ± 2.
5ns, p = 0.005). Our results emphasize the potential of fluorescence lifetime imaging to optimize maximal safe resection in
brain tumors in future and highlight its potential toward clinical translation.