ABSTRACT
This chapter discusses the optical clearing (OC) of adipose tissue ex vivo and in vivo, which has not yet been described but can be useful in optical diagnostics, therapy, and surgery when the site where it is necessary to carry out light exposure is covered by adipose tissue, which is typical in the case of many important internal organs. The chapter combines the review of adipose tissue structure and its optical properties and focuses on studies aimed at designing technology for in vivo optical clearing of abdominal adipose tissue using different optical clearing agents (OCAs), such as polyethylene glycol 200, dimethyl sulfoxide, metrizoic acid in low concentration, diatrizoic acid in high concentration, Omnipaque,™ and aqueous solutions of glucose, fructose, sucrose, altrose, erythrose, fucose, maltose, mannose, ribitol, tagatose, and trehalose. OC efficiency in the topical application of OCAs in combination with ultrasound action and/or laser fractional microablation was evaluated. To monitor possible tissue damage, histological studies were performed. All optical measurements in the study were carried out using an Olympus setup made to provide spatially resolved backreflectance measurements and the reconstruction of tissue optical properties – absorption and reduced scattering coefficients. The kinetics of the reduced scattering coefficient of adipose tissue during OC was measured. Prior to in vivo studies, ex vivo measurements were taken. The maximal optical clearing effect (77%) was observed for the ex vivo samples subjected to the fructose action during 40 min. For in vivo tissue, the maximal OC effect (65%) was observed when the diatrizoic acid was applied during 120 min. After tissue OC, an histological analysis was done for each sample to reveal a possible tissue injury. At the in vivo application of some OCAs (sucrose, diatrizoic, and metrizoic acids), adipocyte necrosis was observed. When using fructose solution, a low level of tissue destruction was found. The efficiency of OC correlated with local tissue damage through cell necrosis.
