'Optical biopsy' of gastrointestinal tumors

Indian scientist C.V. Raman firstly discovered the Raman scattering effect in 1928. The incident light is scattered in the medium because of inelastic collision between that and medium molecular. The energy level of molecular vibration and rotation is transformed, thus the frequency of the scattered light appears to change. Raman shift is the frequency difference between incident light and the scattered light. For the same material, Raman shift has nothing to do with the wavelength of incident light, but with the internal molecular vibration and rotation of the samples.
   Each material has its unique "Raman fingerprint spectrum". Functional groups within molecules, such as C=C,N-H,C-H,C=O,C-N,C≡C, benzene, each have specific Raman characteristic peaks. Raman spectroscopy can be used for the qualitative and quantitative analysis of matter. The sharp peaks of Raman spectra are suitable for qualitative analysis and independent Raman interval strength and the number of functional groups, make it applicable to quantitative analysis. Raman spectroscopy can also be used for molecular analysis of the structure because of the rule of molecular vibration and rotation. This technology is fast, simple, trace, repeatable, nondestructive and almost not interfered by water, so that it is especially suitable for the research in the field of medicine. Cells canceration originates from a series of physiological and biochemical changes, such as nucleic acid synthesis, the fracture of side chain, the change of the cell structure and the relative content of protein and the increased liquidity of cell membrane, etc. The molecular changes within cancer cells can generate changes in characteristic Raman spectra. Spectral differences including displacement, the intensity and the number of peak show that the vibration of the cancer molecular chemical bond, functional group within the organization changed, so as to explore the changes of molecular configuration conformation in the cancer tissue, the relative content and existing state.
   Professor Peng Guiyong’ group from Institute of Digestive Disease of Army Medical University committed to the study of Raman spectra of the gastrointestinal tumors and built a optical fiber Raman system equipped with an endoscopic examination as shown in figure1.

Optical fiber Raman endoscopy system

We used the system to detect the Raman spectrum of gastric mucosa and gastric adenocarcinoma and compared the ratio of integral energy of continuous band (1500 cm-1-1700 cm-1) and non -continuous band (1100 cm-1-1200 cm-1). The results showed that the intensities of Raman peak of gastric adenocarcinoma at 1002 cm-1、1073 cm-1、1450 cm-1、1655 cm-1 belonging to phenylalanine and proteins were higher than those of normal mucosal relatively. From continuous band (1500 cm-1-1700 cm-1) and non- continuous band (1100 cm-1-1200 cm-1), the ratios of the spectral integral energy of gastric adenocarcinoma were different with normal mucosa markedly (independent samples t test, P<0.05), and with the ratio of the integral energy for use as a diagnostic index, obtained the higher accuracy (97.5%~98.5%), sensitivity (91.7%) and specific degrees (100.0%). In addition, we applied this system to collect the Raman spectrum of normal tissue, poorly differentiated carcinoma and squamous cell carcinoma of esophagus, and found that there were significant differences between cancer tissue and normal tissue. Compared with the normal tissue spectra, esophageal cancer tissue spectra in the range 1100-1400 cm-1 had a wider spectrum peak HHW (Half - height width, HHW). From 1500 cm-1 to 1600 cm-1 ,  cancerous tissue spectral integral energy was higher than that in normal tissue. Within the scope of the 1200-1400 cm-1, each cancer spectrum HHW was almost twice the normal tissue. The ratio of spectral integral energy between 1600-1700 cm-1 and 1500 -1600 cm-1, the ratio of cancer tissue specimens was about 1, and the ratio of normal tissue samples was about 2. Compared with the traditional pathology diagnosis method, Fiber Raman spectroscopy system provided a new method for clinical diagnosis research on the gastrointestinal tumors. This method could be called 'optical biopsy' to some extent.

About team
Professor Peng Guiyong team devoted to Raman spectroscopy study of the digestive tract tumor diagnosis. We applied micro Raman spectroscopy spectrum to analysis characteristics of cancerous gastric mucosa tissues and related proteins, RNA, etc. Fingerprint region and high wave number region were combined with partial least squares method to establish model for diagnosis of gastric cancer. Fiber Raman spectroscopy system was formed to diagnose gastric cancer and esophageal cancer, introducing the integral spectrum energy ratio and peak half high width as a diagnostic index, and obtain high diagnostic performance. We won the national natural science funds and special funds to support our research and published many articles in professional journals at home and abroad.

Yin L J, Rao Y J, Dai J H, et al. A feasibility study of using fiber-optic Raman spectrum system for fast diagnosis of gastric cancer[J]. Opto-Electronic Engineering, 2019, 46(4): 180645
DOI: 10.12086/oee.2019.180645