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This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions.

CMOS cameras are very appealing for fluorescence microscopy but they suffer from high readout noise and fixed-pattern noise. We propose a non-iterative, fast, and unsupervised algorithm that erases camera-related noise without losing the quantitative information of fluorescence signal. Finally, we demonstrate the performance of the algorithm using different sensors, from low-cost CMOS chips to high-end sCMOS cameras.

Endoscopic observation of biological tissues with quantitative depth perception, effective volumetric recognition of anatomical features, and efficient 3D navigation is critical for optical diagnostics and minimally invasive surgery for various target diseases. Light-field techniques have recently emerged as a promising approach to 3D photography and microscopy due to their scanning-free, highly scalable, and volumetric imaging capabilities. These advantages hold great potential for application to optical endoscopy, as the existing clinical endoscopy systems rely primarily on a 2D projection or use polarized glasses to provide visual parallax of complex 3D structures. Here, we report a light-field endoscopy prototype using a GRIN lens array (GLA). The GLA-based system maintains consistent spatial measurements with clinical endoscopic systems, a compact size in comparison with compound objective lenses, as well as the ability to maximally capture the angular information necessary for 3D imaging. We also present a computational strategy combining a wave-optics model and a hybrid point-spread function for high-resolution volumetric reconstruction. The system achieves spatial resolutions of 20–60 μm and 100–200 μm in the lateral and axial dimensions, respectively, across an imaging volume of ∼5 mm × 5 mm × 10 mm. We anticipate the prototype to offer a promising paradigm for glasses-free, high-resolution 3D medical endoscopy.