Abstract
Recent advances in materials and fabrication techniques provided portable, performant, sensing optical spectrometers readily operated by user-friendly cabled or wireless systems. Such systems allow rapid, non-invasive, and not destructive quantitative analysis of human tissues. This proof-of-principle investigation tested whether infrared spectroscopy techniques, currently utilized in a variety of areas, could be applied in living humans to categorize muscles. Using an ASD FieldSpec® 4 Standard-Res Spectroradiometer with a spectral sampling capability of 1.4 nm at 350–1000 nm and 1.1 nm at 1001–2500 nm, we acquired reflectance spectra in visible short-wave infra-red regions (350–2500 nm) from the upper limb muscles (flexors and extensors) of 20 healthy subjects (age 25–89 years, 9 women). Spectra off-line analysis included preliminary preprocessing, Principal Component Analysis, and Partial Least-Squares Discriminant Analysis. Near-infrared (NIR) spectroscopy proved valuable for noninvasive assessment of tissue optical properties in vivo. In addition to the non-invasive detection of tissue oxygenation, NIR spectroscopy provided the spectral signatures (ie, “fingerprints”) of upper limb flexors and extensors, which represent specific, accurate, and reproducible measures of the overall biological status of these muscles. Thus, non-invasive NIR spectroscopy enables more thorough evaluation of the muscular system and optimal monitoring of the effectiveness of therapeutic or rehabilitative interventions.
Highlights
Since the invention of the muscle oximeter by Glenn Millikan in the 1940s1, the application of optical methods has contributed extensively and significantly to the study of human tissues in vivo
Near Infrared Reflectance Spectroscopy (NIRS) applications in food industry revealed that muscle tissue has optical properties suitable for spectral analysis and classification; we reasoned that living human muscles might profit from undergoing optical spectroscopy[27]
We are currently unaware of any a priori knowledge about chemometrics applied to NIR spectra acquired in vivo from human muscles; this study essentially provided an exploratory approach
Summary
Since the invention of the muscle oximeter by Glenn Millikan in the 1940s1, the application of optical methods has contributed extensively and significantly to the study of human tissues in vivo. Dramatic advancements in technology and device miniaturization have further boosted NIRS applications; at present, they can be applied using devices that are cost-effective, small-sized, portable, simple and quick to use to build characteristic spectra that represent the “fingerprint” of examined samples[8] This ability has opened the way of using spectra as surrogate markers of complex attributes of organic structures, which can be studied and classified with the application of specific statistical packages, without the need for chemical information from the analysis of molecular bonds in the NIR spectrum. A cheap, reliable, and widely applicable technique for non-invasive in vivo analysis of human muscles is lacking, and we wished to determine whether NIRS of muscles can be adopted in clinical investigation without significant cost and time penalties
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