Through-skull fluorescence imaging of the brain in a new near-infrared window

Abstract

To date, brain imaging has largely relied on X-ray computed tomography and magnetic resonance angiography with limited spatial resolution and long scanning times. Fluorescence-based brain imaging in the visible and traditional near-infrared regions (400–900 nm) is an alternative but currently requires craniotomy, cranial windows and skull thinning techniques, and the penetration depth is limited to 1–2 mm due to light scattering. Here, we report through-scalp and through-skull fluorescence imaging of mouse cerebral vasculature without craniotomy utilizing the intrinsic photoluminescence of single-walled carbon nanotubes in the 1.3–1.4 micrometre near-infrared window. Reduced photon scattering in this spectral region allows fluorescence imaging reaching a depth of >2 mm in mouse brain with sub-10 micrometre resolution. An imaging rate of ~5.3 frames/s allows for dynamic recording of blood perfusion in the cerebral vessels with sufficient temporal resolution, providing real-time assessment of blood flow anomaly in a mouse middle cerebral artery occlusion stroke model.

Use of labeled tomato lectin for imaging vasculature structures

“…Calculations of mouse blood circulation suggest that lectin in the serum would reach major organs within 10 s (Janssen et al 2002), a figure in line with a recent report that intravenously applied carbon nanotubes can be detected in brains of living mice within a few seconds (Hong et al 2014). Further, our observation that extensive labeling of capillary beds resulting from direct intracardiac injections of lectin followed within 1 m with vascular perfusion, also support the notion of rapid binding to endothelium.…”

Measurement of multispectral scattering properties in mouse brain tissue

“…Thus, based on these results, wavelengths longer than 900 nm wavelength can facilitate the visualization of deeper tissue regions, especially for the fiber tracts in the brain. This is in agreement with previous reports [25][26][27]. During our analysis, the absorption coefficient (µ a ) was ignored because µ s is typically much larger than µ a .…”

Graphene-Based Nanomaterials in Bioimaging

“…Their quantum yield (QY) is in the range of 0.02-70.3% (119)(120)(121). However, reduced GO shows a strong photoluminescence quenching effect with enhanced absorbance in the NIR region (12), unlike single-walled carbon nanotubes (SWNTs), which has unique photoluminescence in both NIR-I (700-900 nm) and NIR-II (1100-1400 nm) regions (122)(123)(124).…”