Advances in Hyperspectral and Multispectral Optical Spectroscopy and Imaging of Tissue

1. Introduction

Optical imaging and characterization of tissue has become a huge applied field due to the advantages of the optical analysis methods, which include non-invasiveness, portability, high sensitivity, and high spectral specificity. This research field continues to grow and spread in many different directions due to the development of new light sources and detectors, such as, for example, the supercontinuum and tunable lasers, portable highly sensitive spectrometers, multiwavelength photoacoustic imagers, due to novel methods of data analysis, such as the machine-learning methods of spectral analysis, and due to novel applications, such as the imaging of embryogenesis or monitoring of the cerebral oxygen metabolism. Polarization analysis of the anisotropy of optical, mechanical, and electrical properties of materials is another active research direction in hyperspectral imaging from THz to IR spectral ranges.

The purpose of this Special Issue is to provide an overview of recent advances in the methods of tissue imaging and characterization, which benefit from using large numbers of optical wavelengths.

2. Review of Issue Contents

The human brain is an enchanting object of studies by near-infrared spectroscopy and imaging. In this Special Issue, Guerouah et al. [1] has contributed a profound study of the responses of adult human brain to breath-holding challenges by the hyperspectral near-infrared spectroscopy (hNIRS). This work examined brain signals across the entire near-infrared therapeutic spectral window and showed the critical role of the short-distance channel for the robust measurements of the hemodynamic and metabolic changes in the brain.

Hyperspectral spectroscopy and imaging requires broadband light sources. In the last 20 years, supercontinuum laser sources covering wide spectral bandwidths at high spectral power and fast switching have been developed. Lange et al. [2] contributed a timely and comprehensive review of the features and biomedical and clinical applications of supercontinuum laser sources.

Near-infrared spectroscopy is a quantitative tool that allows for the inspection and characterization of biological tissues and other turbid media such as wood, food and pharmaceutical products, soil, marble, etc. The quantitative accuracy of the medium characterization can be improved using hNIRS. In this Special Issue, Blaney et al. [3] reported a development of a calibration-free hNIRS system that can measure the absolute and broadband absorption and scattering spectra of turbid media.

The ability of the optical imaging techniques to provide real-time quantitative assessment of the biological tissue urges research on their use for tissue monitoring during surgeries. Slooter et al. [4] studied the utility of the measuring multiple tissue parameters simultaneously by four optical techniques operating at different wavelengths of light: optical coherence tomography (1300 nm), sidestream darkfield microscopy (530 nm), laser speckle contrast imaging (785 nm), and fluorescence angiography (~800 nm) of the gastric conduit during esophagectomy.

Neurosurgical procedures on the open human brain require localization of the functional cortical areas in real time. A Monte Carlo simulation study by Caredda et al. [5] showed feasibility to accurately quantify the oxy- and deoxy-hemoglobin and cytochrome-c-oxidase responses to neuronal activation and to obtain the spatial maps of these responses using a setup consisting of a while light source and a hyperspectral or a standard RGB camera.

3. Conclusions

This Special Issue is of interest for the developers and potential users of clinical brain and tissue optical monitors, and for the researchers studying brain physiology and functional brain activity.