Effect of physiological factors on the biochemical properties of colon tissue – an in vivo Raman spectroscopy study

Raman spectroscopy provides diagnostic information by detecting disease-associated subtle biochemical changes in the tissue. Yet the physiological variations among normal subjects could confound data interpretation and thus compromise the sensitivity in disease discrimination. We analyzed Raman spectra acquired from colon tissue in vivo through an endoscopic Raman system and evaluated potential physiological factors affecting tissue biochemistry. Fifty-six healthy patients scheduled for colonoscopy screening were enrolled in the study. Intra-subject variability was evaluated via univariate analysis by comparing the intensities of major Raman bands from different anatomical locations. Inter-subject variability was investigated based on various physiological variables, such as age, gender, ethnicity (White/Caucasian, African American, and Hispanic), and body mass index (BMI). Both univariate analysis and principal component analysis-based multivariate analysis were implemented for the investigation of inter-subject variability. The differences among certain physiological variables were further analyzed after accounting for intra-subject variation by generalized estimating equation method due to its advantage in handling repeated measurements. The results showed that physiological factors including gender, ethnicity, age, BMI, and anatomical locations along the colon were significant sources of variability, resulting from different abundance in lipids and proteins. Further correlation analysis revealed that the variability from gender, ethnicity, and age is significantly associated with that from BMI, indicating that BMI might be the key contributor to the inter-subject variability in the spectra. This study suggested the importance of including normal variability, especially BMI and anatomical locations, into the interpretation of Raman spectra for in vivo application.