Advances in optical biopsy – correlation of malignancy and cell density of primary brain tumors using Raman microspectroscopic imaging

Abstract

Raman spectroscopy is a promising tool towards biopsy under vision as it provides label-free image contrast based on intrinsic vibrational spectroscopic fingerprints of the specimen. The current study applied the spectral unmixing algorithm vertex component analysis (VCA) to probe cell density and cell nuclei in Raman images of primary brain tumor tissue sections. Six Raman images were collected at 785 nm excitation that consisted of 61 by 61 spectra at a step size of 2 micrometers. After data acquisition the samples were stained with hematoxylin and eosin for comparison. VCA abundance plots coincided well with histopathological findings. Raman spectra of high grade tumor cells were found to contain more intense spectral contributions of nucleic acids than those of low grade tumor cells. Similarly, VCA endmember signatures of Raman images from high grade gliomas showed increased nucleic acid bands. Further abundance plots and endmember spectra were assigned to tissue containing proteins and lipids, and cholesterol microcrystals. Since no sample preparation is required, an important advantage of the Raman imaging methodology is that all tissue components can be observed - even those that may be lost in sample staining steps. The results demonstrate how morphology and chemical composition obtained by Raman imaging correlate with histopathology and provide complementary, diagnostically relevant information at the cellular level.

Improving the accuracy of brain tumor surgery via Raman-based technology

“…Other reports were able to further differentiate vital tumor from the invasive tumor margin and edematous white matter. 2,30,32 …”

Optical technologies for intraoperative neurosurgical guidance

“…5,21,28,35,53–55,59,64,67,77,117,143,173 Raman is based on the inelastic scattering of photons upon interaction with tissue. Tissue is interrogated with light, and a small amount of this incident light at a specific wavelength is scattered to different wavelengths.…”

Subcellular Raman Microspectroscopy Imaging of Nucleic Acids and Tryptophan for Distinction of Normal Human Skin Cells and Tumorigenic Keratinocytes

“…In order to circumvent labelling with exogenous marker molecules, the use of Raman microspectroscopy, which exploits the intrinsic vibrational contrast of endogenous biomolecular species, has been widely explored for label-free cancer diagnostics 1-5 . Like in conventional histology, the direct visualization of sub-cellular compartments has become important also for label-free tumour identification techniques. For example, in brain tissue sections, low-and highly-malignant tumour cells could be differentiated based on their respective nucleic acid concentrations in cell nuclei 6 . Equally informative for tumour diagnostics could be the quantitative study of concomitant changes in the concentration of the amino acid tryptophan inside the cell 7 .…”