Nonlinear microscopy, infrared and Raman microspectroscopy for brain tumor analysis

Scope of the neurosurgical management of brain tumors is to remove pathological tissue, preserve normal tissue and brain functions, and collect material for neuropathological diagnosis. A prerequisite is to recognize the tumor margins as precise as possible. Scope of neuropathology is to determine the type and grade of the tumor that is an important indicator for the treatment and prognosis of the patient. In this contribution we present vibrational spectroscopic approaches to complement existing neurosurgical and neuropathological tools. First, Fourier transform infrared (FTIR) imaging is applied to obtain molecular contrast from dried, thin tissue sections. Second, Raman spectroscopic images were collected from the same specimens. Finally, coherent anti-Stokes Raman scattering (CARS) microscopic images were obtained. To demonstrate the complementary nature of the techniques results from a brain metastasis of a lung cancer are discussed. Whereas CARS images could be collected within seconds, exposure times were minutes for FTIR images and hours for Raman images. However, the CARS microscope just probed a single band near 2850 cm-1. FTIR and Raman system probed the full spectral range involving the fingerprint region below 1800 cm-1 and the stretch vibrations between 2800 and 3600 cm-1. Morphological features were resolved in the images such as solid tumor, tumor islets, necrosis and cell nuclei.