Wavelength dependence of the refractive index of human colorectal tissues: comparison between healthy mucosa and cancer

Sónia Carvalho
Department of Pathology and Cancer Biology and Epigenetics Group-Research Centre, Portuguese Oncology Institute of Porto, Portugal

Nuno Gueiral
School of Engineering, Physics Department, Polytechnic Institute of Porto, Portugal
Centre of Innovation in Engineering and Industrial Technology, ISEP, Porto, Portugal

Elisabete Nogueira
School of Engineering, Physics Department, Polytechnic Institute of Porto, Portugal,
Centre of Innovation in Engineering and Industrial Technology, ISEP, Porto, Portugal

Rui Henrique
Department of Pathology and Cancer Biology and Epigenetics Group-Research Centre, Portuguese Oncology Institute of Porto, Portugal
Department of Pathology and Molecular Immunology, Institute of Biomedical Sciences Abel Salazar – University of Porto (ICBAS-UP), Portugal

Luís Oliveira (Login required)
School of Engineering, Physics Department, Polytechnic Institute of Porto, Portugal,
Centre of Innovation in Engineering and Industrial Technology, ISEP, Porto, Portugal

Valery V. Tuchin
Research-Education Institute of Optics and Biophotonics, Saratov National Research State University, Russia
Laboratory of Laser Diagnostics of Technical and Living Systems, Precision Mechanics and Control Institute of the
Russian Academy of Sciences, Saratov, Russia
Interdisciplinary Laboratory of Biophotonics, National Research Tomsk State University, Russia

Paper #3130 received 2016.12.02; accepted for publication 2016.12.29; published online 2016.12.31.

DOI: 10.18287/JBPE16.02.040307


Biological tissues have individual optical properties that may be used as an identity card. The refractive index in particular, which can be measured directly, is very significant for the improvement or development of optical technologies in clinical practice. With the objective of verifying if healthy and pathological tissues can be discriminated from refractive index measurements, we have studied human colorectal mucosa. By using the total internal reflection method to measure the refractive index from healthy and pathological colorectal mucosa tissues at different wavelengths, it was possible to calculate the dispersion curves for both types of tissues. It was observed a decaying refractive index with wavelength, both for healthy and pathological tissues, which were fitted with curves described by Cornu’s equation for wavelengths between ultraviolet and near-infrared range. Experimental results show higher refractive index values for the pathological mucosa for all wavelengths. By performing measurements at wavelengths near 850 nm, we have detected non-monotonic behavior for the refractive index of both healthy and pathological tissues. Such abnormal wavelength dependence is evidence of lipids in both tissues. The acquired experimental data demonstrated that it is possible to discriminate between healthy and pathological tissues from refractive index measurements. Similar studies can be made for different biological tissues. By using lasers with different wavelengths it might be possible to identify other tissue components.


Colorectal tissue; Cancer; Refractive index; Total internal reflection; Tissue dispersion

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