Shortwave infrared imaging is a rapidly expanding area of biomedical research that has emerged as a promising method to increase tissue penetration. This imaging technique requires a new class of bright, stable, and compatible with human tissue emitters.
The ability to image deep within the tissue of a living person would enable early detection of a variety of pathologies, including deep-seated tumours. However, one difficulty in optical imaging is that visible light does not penetrate far enough into the body.
Skin and the underlying connective tissue scatter visible photons and prevent them from getting through more than several millimetres. On the other hand, highly energetic X-ray imaging penetrates well through tissue, but can be damaging even after short periods of exposure.
A new and promising approach
Shortwave infrared light (SWIR) has longer wavelengths than visible light and thus, can penetrate much deeper within biological tissues. The use of SWIR to image abnormalities is a new, safe, and promising approach to biomedical imaging, particularly with the recent advances in cameras, sensors, and equipment that specifically detect this type of light.
The key challenge is to develop contrast agents consisting of molecules or small particles that efficiently emit SWIR light. These agents could be introduced into a patient by injection or ingestion and then used to locate tumours or other lesions that are normally difficult to detect. However, existing materials known to emit SWIR photons are not yet efficient enough for this type of imaging.
In their article published in Nanophotonics, experts in the synthesis of optical materials and optical imaging examine the deficiency behind current shortwave infrared emitters. The low efficiency of these emitters arises due to fundamental constraints that control the emission as well as the way the emitters interact with their environment. In particular, the efficiency of emitters is reduced when surrounded by hydrogen atoms from the protective shell or nearby water molecules from the biological tissue.
New generation of agents to pave the way
After reviewing the mechanisms by which the emission of shortwave infrared light is inhibited, the authors discuss possible strategies to increase the efficiency of light emission from these materials to be suitable for biological imaging. “A new generation of contrast agents emitting in shortwave infrared can change the way biomedical imaging is conducted today,” explains author Mikhail Berezin.
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