Hyperspectral imaging (HSI) technologies have been used extensively in medical research, targeting various biological phenomena and multiple tissue types. Their high spectral resolution over a wide range of wavelengths enables acquisition of spatial information corresponding to different light-interacting biological compounds. This review focuses on the application of HSI to monitor brain tissue metabolism and hemodynamics in life sciences. Different approaches involving HSI have been investigated to assess and quantify cerebral activity, mainly focusing on: (1) mapping tissue oxygen delivery through measurement of changes in oxygenated (HbO2) and deoxygenated (HHb) hemoglobin; and (2) the assessment of the cerebral metabolic rate of oxygen (CMRO2) to estimate oxygen consumption by brain tissue. Finally, we introduce future perspectives of HSI of brain metabolism, including its potential use for imaging optical signals from molecules directly involved in cellular energy production. HSI solutions can provide remarkable insight in understanding cerebral tissue metabolism and oxygenation, aiding investigation on brain tissue physiological processes.

We present a novel hyperspectral imaging (HSI) system using visible and near-infrared (NIR) light on the exposed cerebral cortex of animals, to monitor and quantify in vivo changes in the oxygenation of haemoglobin and in cellular metabolism via measurement of the redox states of cytochrome-c-oxidase (CCO). The system, named hNIR, is based on spectral scanning illumination at 11 bands (600, 630, 665, 784, 800, 818, 835, 851, 868, 881 and 894 nm), using a supercontinuum laser coupled with a rotating Pellin-Broca prism. Image reconstruction is performed with the aid of a Monte Carlo framework for photon pathlength estimation and post-processing correction of partial volume effects. The system is validated on liquid optical phantoms mimicking brain tissue haemodynamics and metabolism, and finally applied in vivo on the exposed cortex of mice undergoing alternating oxygenation challenges. The results of the study demonstrate the capacity of hNIR to map and quantify the haemodynamic and metabolic states of the exposed cortex at microvascular levels. This represents (to the best of our knowledge) the first example of simultaneous mapping and quantification of cerebral haemoglobin and CCO in vivo using visible and NIR HSI, which can potentially become a powerful tool for better understanding brain physiology.

Hyperspectral imaging (HSI) is an emerging optical technique for biomedical applications that can be potentially used to quantitatively monitor in vivo changes in the metabolic and hemodynamic states of the brain, specifically on the exposed cortex. HSI provides extensive spectral information, in addition to spatial data, by acquiring images over a broad range of the light spectrum at numerous and contiguous wavelength bands.^1,2 Changes in the concentrations of relevant biomarkers, such as oxyhemoglobin (${\mathrm{HbO}}_2$) and deoxyhemoglobin (HHb), can be retrieved by measuring the intensity changes of multiple different wavelengths of reflected light after having interacted with the cerebral tissue. These light intensity changes originate from variations in the optical properties of brain tissue during physiological processes, e.g., changes in brain oxygenation and perfusion.^3,4 HSI can also be used to target the changes of the redox state of cytochrome-c-oxidase (CCO), which is a chromophore directly involved in the production of adenosine triphosphate in the mitochondria.⁵ CCO has a high specificity as a biomarker for monitoring brain metabolism, due to its high concentration in the cortical tissue.^5,6

Various biomedical applications such as histopathology or neurosurgery require access to rapid monitoring of intrinsic tissue properties. In particular, neuronavigation would benefit by having structural and functional information on brain tissue in real time.^{1 – 3} Spatially resolved maps of the tissue characteristics would allow bypassing invasive disease diagnostics, e.g., biopsy, which halts the operation. Instead, a surgical decision could be made during the operation, reducing its time and preserving a healthy brain.

Histopathological screening of excised tissue is the current “gold standard” in post-surgical oncological practice,¹ for clinical and molecular evaluation of critical parameters such as type, grading, and classification of tumors, e.g., in glioma and glioblastoma (GBM) resection. ^{2 – 4} Normal routine involves the dispatch of fresh surgical biopsies after resection to the histopathology laboratory: therefore, the samples are typically fixed for preservation, sectioned, stained—various staining techniques are used, with hematoxylin and eosin (H&E) staining being the most prominent— and then imaged with a microscope to determine their structural and molecular composition.³ However, modern histopathological analysis presents several limitations, the most severe one being the lengthy preparation of the samples that lead to long duration of the procedures to obtain the final results, which can vary from several days to even weeks after the surgery. Extemporaneous and intraoperative analyses can be much faster (minutes to hours), but the number of biopsy samples is limited due to operational logistics and costs of the procedures, and the breadth of information they can provide is very limited for diagnostic purposes.⁵ Furthermore, diagnosis and classification can be affected by variability in the subjective interpretation of the results by histopathologists, with the screening essentially lacking a more quantitative and objective way to systematically process the imaging outcomes.⁶ Overall, postoperative prognosis and planning would enormously benefit from a different approach to histopathology that could provide much faster and more reliable information on the tissue biopsies, ideally by having a screening in situ right after the surgery that could lead to quantitative results in a matter of minutes to hours.

Optical techniques based on diffuse optics have been around for decades now and are making their way into the day-to-day medical applications. Even though the physics foundations of these techniques have been known for many years, practical implementation of these technique were hindered by technological limitations, mainly from the light sources and/or detection electronics. In the past 20 years, the developments of supercontinuum laser (SCL) enabled to unlock some of these limitations, enabling the development of system and methodologies relevant for medical use, notably in terms of spectral monitoring. In this review, we focus on the use of SCL in biomedical diffuse optics, from instrumentation and methods developments to their use for medical applications. A total of 95 publications were identified, from 1993 to 2021. We discuss the advantages of the SCL to cover a large spectral bandwidth with a high spectral power and fast switching against the disadvantages of cost, bulkiness, and long warm up times. Finally, we summarize the utility of using such light sources in the development and application of diffuse optics in biomedical sciences and clinical applications.