Laser speckle imaging of the hippocampus

Abstract

Research on hippocampal blood flow is essential for gaining insight into its involvement in learning and memory and its role in age-related cognitive impairment and dementia. In this study, we applied laser speckle contrast imaging (LSCI) and dynamic light scattering imaging (DLSI) to monitor perfusion in mouse hippocampus via a chronic, optically transparent window. LSCI scans showed hippocampal blood vessels appear more out of focus than similar caliber vessels in the mouse cortex. We hypothesize that it is caused by the inverse vascular topology and increased contribution of multiply-scattered photons detected from the upper layers of the hippocampus. We support the hypothesis with DLSI, showing a 1300% increased contribution of multiple-scattering unordered dynamics regime in large hippocampal vessels.

Fig. 1.

A,B - Examples of laser speckle contrast images of the cortex and hippocampus, respectively. C,D - Two-photon maximum intensity projection of z-stack angiograms of cortex and hippocampus . E,F - 3D rendering of z-stacks ( $\text{cortex}=190\mathrm{\mu }\mathrm{m}$ , $\text{hippocampus}=300\mathrm{\mu }\mathrm{m}$ )

Fig. 2.

Dynamic Light Scattering measurements. A,B - Example of decorrelation progression (based on normalised g2) at 0.066 ms time lag value for cortex and hippocampus, respectively. C,D - decorrelation progression at 3.3 ms. E,F - normalized g2 curves from vessels of comparable sizes and parenchymal regions with similar contrast values from cortex (n=1) and hippocampus (n=3). All subplots show that normalized g2 in the hippocampus decreases faster than in the cortex for early time lags but then slows, eventually resulting in more decorrelation of the cortex intensity at later time lags.

Fig. 3.

Example of Dynamic Light Scattering Imaging fitting results for cortex (A,C,E) and hippocampus (B,D,F). A,B - decorrelation time ${\tau }_c$ in microseconds. C,D - dynamics regime, represented by the parameter $d$ ranging from MU (d=0) to SU/MO regime (d=1). E,F - static scattering contribution.