Abstract
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.
Highlights
Introduction and theoretical backgroundIn the growing research field of Biomedical Photonics, the knowledge of the refractive index (RI) of biological tissues and fluids is highly necessary to understand and describe how light propagates and interacts with tissue components [1]
The authors of reference [5] have measured the RI of various mammalian animal and human tissues. Another method is designated by the total internal reflection method, which was proposed in 1996 by Li and Xie to measure the RI of biological tissues [6]
Considering that optical diagnostic and treatment procedures can operate at different wavelengths, we have studied the RI of colorectal healthy and pathological mucosa samples for visible and near-infrared (NIR) wavelength ranges
Summary
Introduction and theoretical backgroundIn the growing research field of Biomedical Photonics, the knowledge of the refractive index (RI) of biological tissues and fluids is highly necessary to understand and describe how light propagates and interacts with tissue components [1]. The authors of reference [5] have measured the RI of various mammalian animal and human tissues Another method is designated by the total internal reflection method, which was proposed in 1996 by Li and Xie to measure the RI of biological tissues [6]. It has been widely used since and several publications explain how this method works and present results for various wavelengths and tissues. Imaging methods like confocal microscopy [11], spatial light interference microscopy (SLIM) [12] or optical coherence tomography (OCT) [13,14] have been proposed to measure the RI of biological tissues
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