Fluorescence lifetime imaging and spectroscopy for enhanced protoporphyrin IX guided brain tumor surgery

Protoporphyrin IX (PpIX) fluorescence-guided surgery has established as a standard for resecting malign glioma. However, low-grade glioma or sparsely infiltrated brain often emit weak PpIX fluorescence and are hard to distinguish from non-pathological tissue. Furthermore, spectrally overlapping autofluorescence inherently limits the sensitivity of fluorescence-intensity based PpIX detection. We therefore integrated frequency-domain fluorescence lifetime imaging together with a spectrometer in a surgical microscope. When analyzing human glioma samples ex vivo, weak PpIX fluorescence could be differentiated from the autofluorescence background through increased lifetimes. Characteristic peaks in the spectral measurements (635, 705nm) confirmed low concentrations of PpIX in the tissue.