Quantitative fluorescence imaging enabled by spatial frequency domain optical-property mapping in the sub-diffusive regime for surgical guidance

Abstract

Intraoperative fluorescence guidance enables maximum safe resection of, for example, glioblastomas by providing surgeons with real-time tumor optical contrast. Specifically, 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence guided resection can improve surgical outcomes by better defining tumor margins and identifying satellite tumor foci. However, visual assessment of PpIX fluorescence is subjective and limited by the distorting effects of light attenuation (absorption and scattering) by tissue and background tissue autofluorescence. We have previously shown, using a point fluorescence-reflectance fiberoptic probe, that non-invasive measurement of the absolute PpIX concentration, [PpIX], further improves sensitivity and specificity, leading to the demonstration that the technique can also detect low-grade gliomas as well as otherwise undetectable residual tumor foci in high-grade disease. Here, we extend this approach to wide-field quantitative fluorescence imaging (qFI) by implementing spatial frequency domain imaging (SFDI) to recover the tissue optical absorption and transport scattering coefficients across the field of view. We report on the performance of this approach to determine the intrinsic fluorescence intensity in tissue-simulating phantoms in both the fully diffusive (i.e. scatter-dominated) and sub-diffusive (low transport albedo) regimes, for which higher spatial frequencies are used. The performance of qFI is compared to a Born- normalization correction scheme, as well as to the values obtained using the fiberoptic probe on homogeneous tissue phantoms containing PpIX.