ABSTRACT
Over the last two decades, optical-based imaging techniques have seen robust development in the field of biomedical research. Despite all of the technique’s advantages, such as high resolution and significant sensitivity, there are two dramatic drawbacks: low penetration ability and low contrast. For example, the latter is quite an important factor in one of the major tasks of the modern biomedical era: the definition of tumor margins or the determination of normal and pathological tissue. The specific substances – contrast agents, both endogenous and exogenous – are widely utilized to enhance imaging contrast from a methodological point of view. One of the latest trends in the field of biomedical imaging is the development of multimodal contrast agents that can be simultaneously used in photoacoustic, fluorescence, and magnetic resonance imaging to validate one imaging method by another with only one kind of contrast substance. Among the above-mentioned imaging techniques, photoacoustic and fluorescent imaging are very successful in terms of resolution and sensitivity. Still, a common disadvantage is insufficient penetration depth. This issue can be readily solved by using a combination of contrast agents and optical clearing methods: chemical (immersion) methods and physical methods such as ultrasound-based methods. This chapter provides an overview of global research on the development of approaches based on the usage of contrast and optical clearing agents to improve the contrast of optical images.
