Refractive index of biological tissues: Review, measurement techniques, and applications

Khan, Rana Ejaz Ali; Gul, Banat; Khan, Shamim; Nisar, Hasan; Ahmad, Iftikhar

doi:10.1016/j.pdpdt.2021.102192

Cited by 65 publications

(38 citation statements)

References 117 publications

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“…These values are close to the refractive index of water because the mass of the phantoms is mostly made up of water. More importantly, the experimental results are in close accordance with human skin refractive indices found in scienti c literature, ranging from 1.34 to 1.56 (Khan et al, 2021) .…”

Section: Group Refractive Indexsupporting

confidence: 87%

“…For example, Yang et al have shown that tissue samples with oral squamous cell carcinoma, a type of cancerous lesion, has a lower extinction coe cient compared to that of normal tissue (Yang et al, 2020) . The increased cell density in cancerous tissue meanwhile increases the overall refractive index of the lesion (Khan et al, 2021) . Thus, by studying the cross-sectional image together with the extinction coe cients and the refractive indices, we can improve the accuracy of disease diagnosis.…”

Section: Working Principles Of Td-octmentioning

confidence: 99%

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Time-Domain Optical Coherence Tomography System for Determining The Extinction Coefficient and Group Refractive Index of Gelatin-based Skin Phantoms

Galvez

Vallar

Shiina

et al. 2021

Sci. Technol. Indones

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Optical Coherence Tomography (OCT) is a non-invasive, non-destructive optical imaging technique that uses a low coherence interferometer to obtain real-time cross-sectional images of samples. OCT is notably used in biomedical applications including ophthalmology and dermatology. Aside from generating cross-sectional images, axial scans can also provide additional information about its optical properties such as extinction coefficient and refractive index. This study determines the extinction coefficients and group refractive indices of gelatin-based skin phantoms using a portable time-domain (TD) – OCT system. The gelatin-based skin phantoms were fabricated with varying concentrations of titanium dioxide (TiO2), while keeping the amount of both gelatin and water constant. By changing the proportion of the gelatin powder and TiO2, skin phantoms can then be fabricated to mimic various skin conditions, both pathologic and non-pathologic. Results of the study found a positive correlation of extinction coefficient and refractive index with TiO2 concentration. Thus, increasing TiO2 concentration also increases both extinction coefficient and group refractive index. The median extinction coefficient values of the phantoms ranged from 4.29 mm−1 to 8.48 mm−1. Literature showed that the epidermis can have extinction coefficients of 1.64-7.3 mm−1. For refractive indices of the fabricated phantoms, values ranged from 1.32 to 1.48, while studies on human participants showed that human skin has refractive index values of 1.34-1.56. Based on these properties, it is feasible to fabricate phantoms simulating the optical properties of human skin.

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Section: Group Refractive Indexsupporting

confidence: 87%

Section: Working Principles Of Td-octmentioning

confidence: 99%

Time-Domain Optical Coherence Tomography System for Determining The Extinction Coefficient and Group Refractive Index of Gelatin-based Skin Phantoms

Galvez

Vallar

Shiina

et al. 2021

Sci. Technol. Indones

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show abstract

“…The inner sphere wall was then coated with BaSO 4 by Gigahertz-Optik, Germany. For the evaluation of the biological samples, we used the scattering phase function postulated by Henyey and Greenstein [16] with an asymmetry factor of g = 0.9 and a refractive index of 1.4 surrounded by water, given by Kedenburg et al [17], and glass (five layers), except for muscle, brain and adipose tissue, for which 1.4 [18] and 1.46 [19] surrounded by glass (three layers, i.e., it is assumed that there are no water layers) were applied, respectively, see Table 1 and Section 2.2.…”

Section: Experimental Setup and Evaluation Processmentioning

confidence: 99%

“…For the refractive index of the tissue layer we used n = 1.4. Varying sample refractive indices in the range of 1.3 to 1.5, which seems to be realistic in biological media [18], results in typical relative changes of the determined effective scattering and absorption coefficients of ∆µ s < 5% and ∆µ a < 13%, respectively, according to Monte Carlo simulations. In the case of adipose tissue, muscle and brain matter, the sodium chloride solution was repressed by the soft tissue.…”

Section: Sample Preparationmentioning

confidence: 99%

Ex Vivo Determination of Broadband Absorption and Effective Scattering Coefficients of Porcine Tissue

et al. 2021

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A novel approach for precise determination of the optical scattering and absorption properties of porcine tissue using an optimized integrating sphere setup was applied. Measurements on several sample types (skin, muscle, adipose tissue, bone, cartilage, brain) in the spectral range between 400 nm and 1400 nm were performed. Due to the heterogeneity of biological samples, measurements on different individual animals as well as on different sections for each sample type were carried out. For all samples, we used an index matching method to reduce surface roughness effects and to prevent dehydration. The derived absorption spectra were used to estimate the concentration of important tissue chromophores such as water, oxy- and deoxyhemoglobin, collagen and fat.

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“…While in the THz range, direct RI measurement of biological tissues and OCAs for a wide spectral range is possible [15,16], in the ultraviolet-near infrared (UV-NIR) range such methodology is not possible, and dispersion calculations must be made from discrete measurements [4,[17][18][19]. There are some distinct methods to measure the RI of biological samples at discrete wavelengths, such as the ones based on interferometer or ellipsometer setups [20], but the most commonly used nowadays are the ones that use multiwavelength refractometers [18] or the total internal reflection setup to be used with various lasers at different wavelengths [21]. Other techniques to measure the RI of biological tissues and the importance of these measurements for optical diagnosis have also been recently described [22].…”

Section: Introductionmentioning

confidence: 99%

Estimation of Rabbit Pancreas Dispersion Between 400 and 1000 nm

Martins

Silva

Tuchin

et al. 2021

J-BPE

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Current biophotonics methods cover the entire optical spectrum from the deep ultraviolet to the terahertz. To optimize such methods for diagnostic and therapeutic applications, the need to obtain the wideband dispersion of tissues is high. The pancreas is a very important organ in the human body, since it produces insulin and its malfunction may induce diabetes. A reduced number of biophotonics publications regarding the pancreas is available, meaning that studies to determine its optical properties and their variation during optical clearing treatments are necessary. Considering this fact, we used the total internal reflection method to measure the refractive index of the rabbit pancreas for wavelengths between 400 and 850 nm. The experimental results allowed to calculate the pancreas dispersion with the Cauchy, Conrady and Cornu equations. It was observed that all those equations provided good data fitting in the spectral range of the measurements, but differences were observed outside these limits. Considering the wavelength of 633 nm, the mean value from the three dispersions was 1.3521, while the one published for porcine pancreas is 1.3517. The dispersion calculated with the Conrady equation does not present a fast decreasing behavior for shorter wavelengths as the ones calculated with the Cauchy and Cornu equations, but comparing these curves with a dispersion for a tissue-like material, all seem to have good agreement.

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Refractive index of biological tissues: Review, measurement techniques, and applications

Cited by 65 publications

References 117 publications

Time-Domain Optical Coherence Tomography System for Determining The Extinction Coefficient and Group Refractive Index of Gelatin-based Skin Phantoms

Time-Domain Optical Coherence Tomography System for Determining The Extinction Coefficient and Group Refractive Index of Gelatin-based Skin Phantoms

Ex Vivo Determination of Broadband Absorption and Effective Scattering Coefficients of Porcine Tissue

Estimation of Rabbit Pancreas Dispersion Between 400 and 1000 nm

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