gms | German Medical Science

Objective: Raman spectroscopy reveals the molecular composition of tissues and proved to be suitable for intraoperative in situ diagnosis of glioma. Furthermore, the technique can provide prognostic information, for instance about the IDH1 genotype. Therefore, Raman spectroscopy is regarded as promising tool to early obtain an integrative diagnosis of brain tumors. However, studies have been performed on a small number of patients or on croysections until now. Therefore, we investigated fresh tissue biopsies to approximate the intraoperative setting with the aim to evaluate the potential and limitations of intraoperative Raman spectroscopy.

Methods: 208 biopsies were obtained during brain tumor surgery and subjected to Raman spectroscopy without any processing. Samples from surgeries for treatment of pharmaco resistant epilepsy served as non-tumor control tissue. Spectra were obtained with a RamanRxn1™ (Kaiser Optical Systems Inc) coupled to a microscope at five positions of each sample. Data analysis was performed using MATLAB functions

Results: Raman spectra of 51 meningioma, 53 glioblastoma multiforma, 19 recurrent glioblastoma, 11 astrocytoma, 8 oligodendroglioma, 6 oligoastrocytoma, 8 neurinoma, 24 metastases, and 16 other tumors were acquired. Furthermore, three samples of necrotic tissue and nine biopsies of non-tumor human brain tissue were analyzed. Raman bands related to hemoglobin at 754 cm^-1 and between 1540-1570 cm^-1 proved to be valuable markers to detect contamination with blood. Moreover, a sharp and intense Raman band at 959 cm^-1 indicated PO₄^3- groups of calcium hydroxyapatite. All tumor types showed a significant reduction in the spectral range 1050-1150 cm^-1 compared to non-tumor brain tissue according to the Fisher’s coefficient. Bands related to lipids (1297, 2850, 3011 cm^-1) were strongly reduced in glioblastoma. Furthermore, the band at 1660 cm^-1 (assigned to protein) was increased. These spectral changes were less pronounced in recurrent glioblastoma or low grade glioma. Neurinoma exhibited additional bands at 1158 und 1521 cm^-1 which are assigned to carotinoids. The band of cholesterol at 700 cm^-1 was largely missing in brain metastases and bands assigned to collagen (755, 856, 938, 1031, 1236, 1401 cm^-1) were more intense. Raman spectra of meningioma were characterized by higher intensities of bands assigned to (phospho)lipids (715, 1088, 1127, 1302, 1438, 1656 cm^-1) and DNA (830 and 1336 cm^-1) compared to dura. Furthermore, Raman bands of proteins and collagen were reduced.

Conclusion: The Raman spectra of fresh biopsies measured in the operating room were in accordance to previous data obtained from tissue sections, opening the possibility of in situ tissue classification with high sensitivity and specificity. Perspectively, this will assist neuropathologists and neurosurgeons to obtain early - intraoperative - integrated diagnosis and to consecutively apply personalized local therapies.