Raman spectroscopy of biological tissue for application in optical diagnosis of malignancy
The utilisation of near-infrared Raman spectroscopy for the discrimination of cancers and pre-cancers from normal tissue in the acro-digestive tract has been evaluated. A commercially available Raman microspectrometer has been modified to provide optimum throughput, sensitivity and fluorescence suppression for epithelial tissue measurements. Laser excitation at 830nm was demonstrated to be optimum. High quality (SN ratio 15-20) NIR-Raman spectra have been acquired from oesophageal and laryngeal tissues in time scales under 30 seconds. Pathological groupings covering the full range of normal and neoplastic tissues in the organs of interest have been studied. Both fresh (snap frozen) and formalin fixed tissue samples were investigated, firstly to indicate whether tissue-types can be distinguished in vivo and secondly to demonstrate the use of Raman spectroscopy as a tool for classification in the pathology lab. Results using multivariate statistical techniques to distinguish between spectra from specimens exhibiting different tissue pathologies have been extremely promising. Cross-validation of the spectral predictive models has shown that three groups of larynx tissue can be separated with sensitivities and specificities of between 86 and 90% and 87 and 95% respectively. Oesophageal prediction models have demonstrated sensitivities and specificities of 84 to 97% and 93 to 98% respectively for a three-group consensus model and 73 to 100% and 92 to 100% for an eight-group consensus model. Epithelial tissues including stomach, tonsil, endometrium, bladder and prostate have been studied to identify further tissues where Raman spectroscopy may be employed for detection of disease. Spectra were similar to those obtained from oesophagus and larynx, although sufficiently different for distinct discriminant models to be required. This work has demonstrated the generic nature of Raman spectroscopy for the detection and classification of cancers and pre-cancerous lesions in many tissues. The evidence provided by this study indicates that utilisation of Raman spectroscopy for non-invasive detection and classification of disease is a distinct possibility. Potential difficulties in the transferability from in vitro to in vivo have been evaluated and no significant barriers have been observed. However, further in vivo probe development and optimisation will be required before 'optical biopsy' with Raman spectroscopy can become a reality.