Interventional imaging in neurosurgery of gliomas: use of several fluorescence emission spectra of 5-ALA induced protoporphyrin IX to guide neurosurgeons

Gliomas are infiltrative tumors of the central nervous system that account for more than 50 % of primitive brain tumors [1]. Their current treatment is based on surgery when possible but a tradeoff needs to be found by neurosurgeons between removing the maximum amount of tumor cells and preserving functionality of the brain. To help removing the maximum amount of tumor cells, a clear definition of tumor margins is required and yet the identification of infiltrative parts is still a challenge [2]. To assist neurosurgeons, fluorescence technics provide high expectations since aminolevulinic acid (5-ALA) induced protoporphyrin IX (PpIX) accumulates in tumor cells and emits a reddish fluorescence when excited with UV/blue light. Intraoperative fluorescence microscopy enables therefore neurosurgeons to visualize some tumor cells [3] but its sensitivity is limited, particularly in tumor margins or in low grade gliomas. Moreover, this is a qualitative technic. In parallel, the relevance of 5-ALA induced PpIX fluorescence spectroscopy to increase the sensitivity has been shown [4,5] and allows quantification of PpIX concentration. Previous studies on human beings concentrated on the fluorescence emission spectrum of PpIX with a main peak at 634 nm. However, we demonstrated the presence of second fluorescence emission spectrum of PpIX with a main peak at 620 nm. We showed that the use of the two spectra of fluorescence enables to discriminate solid part of the tumor against tumor margins ex-vivo [6]. We now want to see how the two spectra can help disciminate tumor margins against healthy tissue during neurosurgery.