Abstract
Reaching efficient, safe and painless medical diagnosis procedure is a very valued goal for many research areas. Despite the great advantages of using optical imaging techniques in medical diagnosis including high safety and relative simplicity, it still suffers from relatively low resolution and penetration depth in the multiple scattering mediums such as biological tissues. Therefore, researchers began to devise ways to reduce the scattering properties of the tissue, hence increasing the imaging contrast. Optical clearing concept is introduced to do this job. This technique can reduce tissues scattering properties by using high refractive index chemicals, thus making the tissue transparent by equalizing the refractive index through that medium. In this paper, theory and techniques of optical clearing method are illustrated utilizing its benefits for deep imaging of different body tissues and organs.
Highlights
The relatively low optical penetration as a result of the scattering properties of biological tissues is considered the main limitation of many optical imaging techniques
Recent studies have been aimed at altering turbid biological tissues in such a way that they become more optically transparent while keeping their internal structure intact using chemical compound with distinct osmotic properties such as glucose and glycerol [5]
In the physical optical clearing approach, the clearing is achieved by using refractive index matching solutions in order to reduce the optical inhomogeneity of the tissue sample, these solutions can be either organic or aqueous [4] [9]
Summary
The relatively low optical penetration as a result of the scattering properties of biological tissues is considered the main limitation of many optical imaging techniques. The principal reason of this multiple scattering characteristics is the difference in the refractive indices between the tissue cell components and its background [1] The tissue components such as cell nuclei, collagen, elastin fiber, mitochondria, organelles, cytoplasm and plasma membrane of the cell have refractive indices ranging from 1.47 to 1.51, while the surrounding medium has refractive index equals to 1.33, similar to that of water. This causes light diffusion and scattering inside biological tissues [2]. Determination of tissue optical parameters can be achieved using either integrating sphere measurements [6] or distant detector based configuration [7]
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