Multimodal Noninvasive Functional Neurophotonic Imaging of Murine Brain‐Wide Sensory Responses

Abstract

Modern optical neuroimaging approaches are expanding the ability to elucidate complex brain function. Diverse imaging contrasts enable direct observation of neural activity with functional sensors along with the induced hemodynamic responses. To date, decoupling the complex interplay of neurovascular coupling and dynamical physiological states has remained challenging when employing single-modality functional neuroimaging readings. A hybrid fluorescence optoacoustic tomography platform combined with a custom data processing pipeline based on statistical parametric mapping is devised, attaining the first noninvasive observation of simultaneous calcium and hemodynamic activation patterns using optical contrasts. Correlated changes in the oxy-and deoxygenated hemoglobin, total hemoglobin, oxygen saturation, and rapid GCaMP6f fluorescence signals are observed in response to peripheral sensory stimulation. While the concurrent epifluorescence serves to corroborate and complement the functional optoacoustic observations, the latter further aids in decoupling the rapid calcium responses from the slowly varying background in the fluorescence recordings mediated by hemodynamic changes. The hybrid imaging platform expands the capabilities of conventional neuroimaging methods to provide more comprehensive functional readings for studying neurovascular and neurometabolic coupling mechanisms and related diseases.

Hybrid magnetic resonance and optoacoustic tomography (MROT) for preclinical neuroimaging

“…6 ). For this, the OAT data acquired at multiple wavelengths (see Methods) was unmixed into separate oxygenated (HbO) and deoxygenated (HbR) hemoglobin components 18 (Fig. 6 a, b ) and coregistered to the MRI scans (Fig.…”

“…During reconstruction, OAT signals were normalized to the laser pulse energy at each wavelength. To reduce the spectral coloring effects, i.e., the spatially and wavelength-dependent light fluence distribution within the tissue, an exponential light attenuation model was applied to compensate for the depth-dependent signal decay 18 . Finally, linear spectral unmixing was performed to directly obtain the individual HbO and HbR components without additional processing 18 , 53 .…”

“…To reduce the spectral coloring effects, i.e., the spatially and wavelength-dependent light fluence distribution within the tissue, an exponential light attenuation model was applied to compensate for the depth-dependent signal decay 18 . Finally, linear spectral unmixing was performed to directly obtain the individual HbO and HbR components without additional processing 18 , 53 . The data processing, including OAT image reconstruction and spectral unmixing, was automated in a customized script written in Matlab (version 2021a, Mathworks Inc., Natick, MA, USA).…”

“…OAT benefits from the unique advantages of optical contrast to visualize endogenous chromophores as well as exogenous absorbers, such as nanoparticles, organic dyes, or fluorescent proteins 11 – 13 . The method’s versatility was demonstrated in the label-free mapping of angiogenesis 14 and blood oxygenation 15 – 18 , targeted molecular imaging studies 19 – 21 , or monitoring of therapies 22 , 23 , to name a few examples. Despite its important advantages, OAT often provides insufficient soft-tissue contrast, complicating anatomical interpretation of the data.…”

“…Despite its important advantages, OAT often provides insufficient soft-tissue contrast, complicating anatomical interpretation of the data. Due to the inherent hybrid optical and ultrasound nature of OAT, multi-modality efforts have thus far been focused on hybridization with ultrasound 24 – 26 , fluorescence imaging 18 , 27 – 29 , or optical coherence tomography (OCT) 30 – 32 . Registration of OAT images with stand-alone computerized tomography (CT), single-photon emission computerized tomography (SPECT), and MRI has also been reported 4 , 33 , 34 .…”