ABSTRACT

There is a gap between pre-operative imaging techniques, such as magnetic resonance imaging, that provide a rough location and diagnosis of the disease (e.g. tumor, seizure focus), and the histopathology that provides an accurate diagnosis, but up to 24 hours after the surgery. Multi-photon microscopies, (combinations of) second harmonic generation (SHG) microscopy and third harmonic generation (THG) microscopy, two-and three-photon excited auto-fluorescence microscopy, and coherent Raman scattering microscopy, show great potential as clinical tool for the real time assessment of the pathological state of tissue during surgery: the relative speed of the imaging modalities approaches “real” time, and no preparation steps of the tissue are required. THG and SHG are nonlinear optical processes that may occur in tissue depending on nonlinear susceptibility coefficients χ(3) and χ(2) of the tissue and upon satisfying phase-matching conditions. THG and SHG modalities are intrinsically confocal and therefore provide direct depth sectioning.