Abstract
Cerebrovascular imaging of rodents is one of the trending applications of optoacoustics aimed at studying brain activity and pathology. Imaging of deep brain structures is often hindered by sub-optimal arrangement of the light delivery and acoustic detection systems. In our work we revisit the physics behind opto-acoustic signal generation for theoretical evaluation of optimal laser wavelengths to perform cerebrovascular optoacoustic angiography of rodents beyond the penetration barriers imposed by light diffusion in highly scattering and absorbing brain tissues. A comprehensive model based on diffusion approximation was developed to simulate optoacoustic signal generation using optical and acoustic parameters closely mimicking a typical murine brain. The model revealed three characteristic wavelength ranges in the visible and near-infrared spectra optimally suited for imaging cerebral vasculature of different size and depth. The theoretical conclusions are confirmed by numerical simulations while in vivo imaging experiments further validated the ability to accurately resolve brain vasculature at depths ranging between 0.7 and 7 mm.
Highlights
Optoacoustic (OA) imaging is a hybrid technology based on wideband detection of ultrasonic waves generated due to absorption of laser pulses in optically heterogeneous media [1]
We calculated the dependence of the integrated optoacoustic pressure upon diameter d and depth D of the blood vessel based on Eq (4)
All the major blood vessels were attributed in accordance with the brain atlas (Fig.5a): while the sagittal (SS) and transverse (TS) sinuses were located on the dorsal side of the brain dura mater at the depths D < 1 mm, the basilar (BA) and posterior communicating (PCA) arteries, as well as the basal vein (BV) were located in the ventral side of the rodent brain at 5-6 mm depth. In this manuscript we report on a comprehensive theoretical analysis of the optimal wavelengths for in vivo OA angiography in whole rodent brains
Summary
Optoacoustic (OA) imaging is a hybrid technology based on wideband detection of ultrasonic waves generated due to absorption of laser pulses in optically heterogeneous media [1]. Hemoglobin is the major bio-chrome allowing for high-contrast OA angiography with optical contrast and ultrasonic spatial resolution. Recent OA studies attained functional neuroangiography of pial microvasculature at up to 500 μm depth under the skull of a rodent [7,8]. High resolution whole-brain OA neuroangiography through an intact skull and scalp remained challenging due to the strong light attenuation by the brain as well as frequency-dependent acoustic reflections and dispersion effects introduced by the skull [9,10,11,12]
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