Living Brain Optical Imaging: Technology, Methods and Applications

Abstract

Within the last few decades, optical imaging methods have yielded revolutionary results when applied to all parts of the central nervous system. The purpose of this review is to analyze research possibilities and limitations of several novel imaging techniques and show some of the most interesting achievements obtained by these methods. Here we covered intrinsic optical imaging, voltage-sensitive dye, photoacoustic, optical coherence tomography, near-infrared spectroscopy and some other techniques. All of them are mainly applicable for experimental neuroscience but some of them also suitable for the clinical studies.

High-dynamic-range fluorescence laminar optical tomography (HDR-FLOT)

“…Hemodynamic response usually occurs in seconds; therefore, the LOT system with ∼40 frames/s imaging speed can be used to study hemodynamic responses [8,17]. Use of exogenous fluorescent dyes and transgenic animals can also aid in studying functional parameters, such as changes in membrane potential [voltage-sensitive dyes (VSD)] or ion concentrations (pH-, calcium-, chloride-, or potassium-sensitive dyes) [17,35]. The time-resolved acquisition protocol to record the fast neural dynamics, which requires the biological response to be repeatable for each stimulation trial [17], was investigated for FLOT [1,6,17].…”

“…Increasing the penetration depth would broaden the application of FLOT for neuroscience research. Since the optical properties of the living mouse brain are too complicated to mimic using a simple phantom, a 150-μm glass capillary filled with voltage-sensitive dye (commonly used for reporting neural activities [6, [32][33][34][35]) was inserted into a mouse brain in vivo to demonstrate the feasibility of HDR-FLOT to increase penetration depth.…”

Improving neurovascular outcomes with bilateral forepaw stimulation in a rat photothrombotic ischemic stroke model

“…Photoacoustic (PA) imaging is a hybrid nonionizing imaging technology that is based on the intrinsic optical absorption of laser pulses leading to ultrasonic emission due to transient thermoelastic expansion. 14,15 PA imaging exploits the combined advantage of weak ultrasonic scattering and high optical contrast. 16 By varying the optical wavelength of the excitation laser, PA imaging is able to extract certain physiological parameters for functional imaging.…”

Correlation between volumetric oxygenation responses and electrophysiology identifies deep thalamocortical activity during epileptic seizures

“…However, they lack the spatial and/or temporal resolution for accurate characterization of the seizure dynamics. Other optical methodologies have further been used to localize cerebral cortex activity in vivo, 6 yet it remains challenging to apply those methods to visualize subcortical brain structures involved into the epileptic process. Recently, miniature endoscopic probes have offered a potential alternative for imaging deep brain areas not accessible by intravital microscopy.…”

“…In contrast to optical microscopy and tomography techniques, whose penetration and resolution are severely hampered by strong light scattering in living tissues, optoacoustics is based on a direct transduction of light energy into ultrasonic waves, thus it enables mapping optical absorption with ultrasonic resolution not affected by light diffusion. The rich and spectrally distinctive hemoglobin-based optoacoustic contrast has resulted in a remarkable performance in label-free visualization of tissue hemodynamics, 6,8 stimulus-induced function, and brain metabolism. 9,10 Furthermore, by detecting spectroscopic changes in genetically encoded calcium indicators, functional optoacoustic neurotomography has shown promise for direct monitoring of fast neural activity.…”