OPTICAL CLEARING SUMMARY
The article highlights the dehydration mechanisms used in optical tissue clearing. Results obtained outline that dehydration is a vital aspect in the optical clearance of cellular and collagenous tissues. As such, optical tissue clearing is highlighted as the tissue response to chemical agents such as glycerol with, in turn, increases optical clarity (Rylander et al., 2006). There are three hypothesized mechanisms used in light scatterings, such as tissue constituent’s dehydration, interstitial replacement, and structural modification of collagens that are used in the optical clearing. In other cases, the authors show that the refractive index and dehydration can be coupled but only for intrinsic structures. Hence, the refractive index is characterized in terms of the matching native and passive species. The motivation of the paper is based on the need to provide evidence that dehydration is an important optical aspect. So, the article utilizes two methods in comparing optical clearance in tissues.
Moreover, the paper utilizes materials and methods to depict the properties of tissues immersed in water. As a result, the article used the evaporative process to exhibit the dehydration mechanism as developed in the optical clearing. Chemical agents used include anhydrous glycerol and used at approximately 250c (Rylander et al., 2006). In addition, photographic imaging is developed through dorsal sections having a full-thickness skin, which is separated by glass vials having anhydrous glycerol. Moreover, the OCT imaging with individual tendons fascicles placed at an 820-nm wavelength and imaged at 2.5 hours. As such, the OCT images are then allowed to measure dynamic parameters. Also, the article shows that TEM imaging is a tissue ultrastructure and used to detect the dehydration mechanism in an optical clearing. The TEM is, therefore, capable of making ultrastructural changes.
The evidence obtained from the results shows that photographic imaging is capable of assessing optical clearing with half of the testing tissue placed in overlying glass. Therefore, tissue transmittance can be calculated by deducting the reflectance intensity from the total. As such, the transmittance reflectance intensity ratio indicates the scattering strength. In a similar case, the fascicle immersion of the tail tendon causes similar observations relative to the phase microscopy (Rylander et al., 2006). Thus, stained tissues can only be imaged having HR digital cameras. In addition, the results for the OCT imaging shows that glycerol and air-immersions result in similar responses as those of scattering the fascicle size. Also, the TEM imaging in the case for tissue ultrastructure shows their distribution in terms of native and anhydrous state. The fascicle optical thickness is seen to exponentially reduce by 25% from its original size.
The discussion part shows that tissue dehydration correlates to mass loss in the event of evaporation. Hence, the primary components of the skin are water comprising of over 70% with proteins constituting 30% in mass (Rylander et al., 2006). Water is volatile and evaporates, leaving the tissue but only at standard temperature and pressure. As such, dehydration results in the reduction of light scattering due to the concentration of proteoglycan in the ground substance. Hence, tissue optical clarity is inversely proportional to its dehydration state. Also, it can be seen that the refractive index matching greatly contributes to the optical clearing. Consequently, optical clearing mechanisms of DMSO and glycerol are diverse due to the differences in mass transport. As such, the refractive index occurs due to the replacement of structural modifications.
Reference
Rylander, C. G., Stumpp, O. F., Milner, T. E., Kemp, N. J., Mendenhall, J. M., Diller, K. R., & Welch, A. J. (2006). Dehydration mechanism of optical clearing in tissue. Journal of biomedical optics, 11(4), 041117.