Advancements in broadband near-infrared spectroscopy instrumentation for the assessment of in vivo mitochondrial function: a comparative review and outlook.

Significance: Broadband near-infrared spectroscopy (bNIRS) provides a noninvasive, nonionizing method for measuring oxidative metabolism through monitoring of cytochrome- c -oxidase oxidation changes. Despite its clinical potential, bNIRS adoption is limited by the complexity, cost, and size of instrumentation. We address the need for a comprehensive overview of bNIRS hardware developments to inform on gaps and propose future device design. Aim: We catalog and compare bNIRS systems developed over the past 37 years, focusing on hardware configurations, component choices, and trends toward miniaturization and multichannel measurements. Approach: A systematic literature review was conducted using Web of Science and citation mapping tools. Inclusion criteria targeted systems utilizing broadband light sources and spectrometers, covering a spectral range of 600 to 1000 nm, and capable of measuring CCO concentration changes. A total of 72 articles were reviewed. Results: The quartz tungsten halogen lamp and commercial bench-top spectrometers remain dominant in bNIRS developments. Recent advancements include fiber-optic innovations and compact charge-coupled device (CCD) based sensors, facilitating multichannel configurations. However, no fully commercial portable bNIRS device exists. The recent addition of micro form factor spectrometers drives the emerging trend toward wearable designs. Conclusions: Future bNIRS devices must prioritize miniaturization, ease of use, and cost reduction to support clinical translation. Emerging photonic technologies offer promising pathways for compact, wearable bNIRS systems.