Abstract
The hippocampus is associated with memory and navigation, and the rodent hippocampus provides a useful model system for studying neurophysiology such as neural plasticity. Vascular changes at this site are closely related to brain diseases, such as Alzheimer’s disease, dementia, and epilepsy. Vascular imaging around the hippocampus in mice may help to further elucidate the mechanisms underlying these diseases. Optical coherence tomography angiography (OCTA) is an emerging technology that can provide label-free blood flow information. As the hippocampus is a deep structure in the mouse brain, direct in vivo visualisation of the vascular network using OCTA and other microscopic imaging modalities has been challenging. Imaging of blood vessels in the hippocampus has been performed using multiphoton microscopy; however, labelling with fluorescence probes is necessary when using this technique. Here, we report the use of label-free and noninvasive microvascular imaging in the hippocampal formation of mice using a 1.7-μm swept-source OCT system. The imaging results demonstrate that the proposed system can visualise blood flow at different locations of the hippocampus corresponding with deep brain areas.
Highlights
The hippocampus is associated with memory and navigation, and the rodent hippocampus provides a useful model system for studying neurophysiology such as neural plasticity
We demonstrated the feasibility of label-free, noninvasive deep brain vascular imaging using en face maximum intensity projection (MIP) images acquired by Optical coherence tomography angiography (OCTA) with 1.7-μm swept laser source in mice
The proposed OCTA system used the wavelength swept laser with a long coherence length (>11 mm), which contributed to greater roll-off characteristics (2 dB falling-off at 4 mm) when compared with previous 1.7-μm SD-optical coherence tomography (OCT) systems[10]
Summary
The proposed OCTA system used the wavelength swept laser with a long coherence length (>11 mm), which contributed to greater roll-off characteristics (2 dB falling-off at 4 mm) when compared with previous 1.7-μm SD-OCT systems[10]. We have reported the high sensitivity and roll-off characteristics of the 1.7-μm SS-OCT system, achieving noninvasive, label-free, in vivo deep vascular imaging. We found that a lower optical scattering characteristic of 1.7-μm was useful for deep brain OCTA imaging due to lower background levels in the image when compared with the 1.3-μm wavelength light. The measured axial resolution was degraded to 25 μm This decrease could be due to the limited data that was acquired by performing a k-clock, and the limited operating wavelength of the circulator. Volumetric OCT data was acquired at a line rate of 90 kHz in a 4 × 3 mm field of view using raster scanning provided by 2D galvanometric scanners. The merged volumetric data sets provided clear OCTA images in deep brain areas with uniform resolution and intensity
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