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For decades, near-infrared (NIR) spectroscopy has been used as an in vivo method of studying human tissue. Importantly, it has provided healthcare professionals and researchers with a reliable technique of looking at biological tissue non-invasively, gathering information from living subjects so that tissue functions can be explored within their natural context.
Here, we discuss the importance of NIR spectroscopy in exploring biological tissues, its current developments, and how it may be used in the future.
What is NIR Spectroscopy?
NIR spectroscopy's roots trace back as far as the early 1800s when Fredrick William Herschel discovered the first non-visible region of the absorption spectrum. However, it was not until the 1950s that Karl Norris and his colleagues leveraged this non-visible region's potential. NIR spectroscopy has been adapted for applications in various industries, including agricultural, food, chemical, pharmaceutical, and medical. It can be used to analyze the compositional, functional, and sensory nature of a sample.
The technique of NIR spectroscopy is based on electromagnetic (EM) radiation absorption, specifically between the wavelengths of 780 and 2500 nm. During NIR spectroscopy, a sample is exposed to light and a detector is used to measure the level of light absorbed by the sample. This data can be analyzed to review the key characteristics and behavior of the sample.
Introduction to NIR Technology
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The Success of NIR Spectroscopy in Biological Applications
In healthcare, NIR spectroscopy is used to investigate biological tissue by using light absorption to detect hemoglobin and myoglobin in a sample, usually skeletal muscle. The methodology has achieved success in this field due to numerous factors. Firstly, human tissue allows a sufficient amount of non-visible light through it. Second, light in the NIR range is scattered in tissues or absorbed by pigmented compounds. Additionally, NIR light's high attenuation that enters a human tissue sample is mainly caused by a specific chromophore, such as hemoglobin.
NIR spectroscopy allows for real-time, non-invasive measurements of hemoglobin as it can easily be detected in capillary vessels, which are sufficiently transparent enough to be illuminated via NIR spectroscopy. This real-time, non-invasive measurement is also possible in any other tissues that are transparent enough to let NIR light through. Often, NIR spectroscopy is used to measure hemoglobin oxygenation, an application of the technology that has been commonplace in functional brain imaging since the early 1990s.
Advancements in NIR Spectroscopy Technology
Recent years have seen significant advancements in technology that have benefited NIR spectroscopy applications. Particularly, they have allowed for device miniaturization, which has led to the technique being portable and applicable in a broader range of settings. The technology has also become cheaper, making it more accessible and cost-effective. Finally, technological advancements have simplified and increased the speed of NIR spectroscopy.
As a result, scientists can obtain “fingerprints” of studied samples quickly and efficiently, which has given rise to methodologies that use spectra as markers of complicated organic structures. These markers can be analyzed using specially designed software without the need for detailed chemical information.
NIR spectroscopy currently provides healthcare professionals with a cost-effective, reliable, and efficient technique for conducting in vivo analysis of human muscles. Until recently, a non-invasive method was not widely available for this application, but technological advances have allowed NIR spectroscopy to be adopted by the medical industry for this purpose.
The Future of NIR Spectroscopy in the Medical Industry
A paper published in 2019 in the journal Scientific Reports indicates how NIR spectroscopy may continue to evolve to benefit its medical industry applications. The research team presented an exploratory approach to obtaining chemometric data from NIR spectra acquired from human muscles.
The team outlined how they sought to establish an objective indicator of the organ’s present state, allowing NIR spectroscopy to measure the organ's health non-invasively and accurately.
The paper demonstrated how the scientists investigated the use of both visible and NIRS applications in identifying different muscle groups without chemical information. They were able to obtain spectra that revealed the “fingerprints” of the muscle.
Overall, the team’s findings reveal NIR spectroscopy's feasibility to investigate human tissues in vivo. The technique successfully obtained “fingerprints” from human tissue, opening the door to a wide range of medical applications.
The research will likely be significant in the future of biomedical optics, demonstrating the capabilities of techniques that analyze biological tissues using NIR light. Future research is predicted to continue to develop NIR spectroscopy, enhancing its capabilities and expanding its uses in medicine. The development of devices such as detectors and fiberoptic probes will help advance this technology, which is likely to remain commonplace in medical labs and research labs worldwide.
References and Further Reading
Afara, I., Shaikh, R., Nippolainen, E., Querido, W., Torniainen, J., Sarin, J., Kandel, S., Pleshko, N. and Töyräs, J., 2021. Characterization of connective tissues using near-infrared spectroscopy and imaging. Nature Protocols, 16(2), pp.1297-1329. https://www.nature.com/articles/s41596-020-00468-z
Currà, A., Gasbarrone, R., Cardillo, A., Trompetto, C., Fattapposta, F., Pierelli, F., Missori, P., Bonifazi, G. and Serranti, S., 2019. Near-infrared spectroscopy as a tool for in vivo analysis of human muscles. Scientific Reports, 9(1). https://www.nature.com/articles/s41598-019-44896-8
Miller, L. and Dumas, P., 2006. Chemical imaging of biological tissue with synchrotron infrared light. Biochimica et Biophysica Acta (BBA) - Biomembranes, 1758(7), pp.846-857. https://www.sciencedirect.com/science/article/pii/S0005273606001441