Abstract
The optical immersion clearing technique has been successfully applied through the last 30 years in the visible to near infrared spectral range, and has proven to be a promising method to promote the application of optical technologies in clinical practice. To investigate its potential in the ultraviolet range, collimated transmittance spectra from 200 to 1000 nm were measured from colorectal muscle samples under treatment with glycerol-water solutions. The treatments created two new optical windows with transmittance efficiency peaks at 230 and 300 nm, with magnitude increasing with glycerol concentration in the treating solution. Such discovery opens the opportunity to develop clinical procedures to perform diagnosis or treatments in the ultraviolet.

Abstract
A robust method is presented for evaluating the diffusion properties of chemicals in ex vivo biological tissues. Using this method that relies only on thickness and collimated transmittance measurements, the diffusion properties of glycerol, fructose, polypropylene glycol and water in muscle tissues were evaluated. Amongst other results, the diffusion coefficient of glycerol in colorectal muscle was estimated with a value of 3.3 x 10(-7) cm(2)/s. Due to the robustness and simplicity of the method, it can be used in other fields of biomedical engineering, namely in organ cryoprotection and food industry.

Abstract
In this paper, we describe a simple and indirect method to evaluate the kinetics of the optical properties for biological tissues under optical clearing treatments. We use the theoretical formalism in this method to process experimental data obtained from colorectal muscle samples to evaluate and characterize the dehydration and refractive index matching mechanisms.

Abstract
[No abstract available]

Abstract
The optical immersion clearing is an effective method to reduce light scattering in tissues, but to optimize each treatment, it is necessary to understand the mechanisms involved. Since these treatments are intended to be temporary, it is also important to know if the mechanisms involved are reversible. Various studies have been made to evaluate and characterize the mechanisms of optical clearing. In all cases studied, two major mechanisms were observed—the tissue dehydration and the refractive index matching mechanisms. Some particular studies have reported that the agents used in treatments also dissolve proteins and suggested that protein dissolution is also a clearing mechanism. All these mechanisms have been reported as reversible, both on ex vivo or on in vivo studies. We make an analysis on these studies and present a method based on ex vivo collimated transmittance and thickness measurements to characterize the major clearing mechanisms—tissue dehydration and refractive index matching. Although this method can only be made with ex vivo tissues, alternative measurements are suggested for in vivo characterization of the clearing mechanisms. © 2019, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Abstract
After making an overview on the most recent progresses regarding the optical immersion treatment technique, we use this chapter to look to the future and perspectives of the following developments and benefits that can be achieved. The increasing number of publications on OC in the last 30 years, which we present in Sect. 9.1, indicates that this is a promising method to aid in the application of optical techniques in clinical practice for diagnosis or treatment purposes. Since several spectroscopy, fluorescence, or imaging methods have recently been used to test and validate the OC effects in various human and animal tissues, a collection of OCAs and OC protocols have been developed. Section 9.2 shows that to get even better results in tissue OC, the discovery of new agents and establishment of new protocols is a work in progress. Section 9.3 indicates the future perspectives for tissue spectroscopy during OC treatment and that the potential of the refractive index matching mechanism can also be evaluated in the ultraviolet range. Section 9.4 discusses the future perspectives of tissue imaging and OC. The establishment of new and faster OC protocols for tissue imaging is suggested, and indication for the necessary efforts to adapt the light-sheet technique to image in vivo is also made. Finally, Sect. 9.5 presents other applications of tissue OC and suggests the cooperation between research fields to increase knowledge in the use of OCAs and their benefits for each field. © 2019, The Author(s), under exclusive license to Springer Nature Switzerland AG.