Researchers from the University of Zurich and the Technical University of Zurich in Switzerland have developed a new technique called Diffuse Optical Positioning Imaging (DOLI), which uses it to observe microvascular vessels deep in the brains of living mice at high resolution and without invasiveness. The technology has excellent resolution, can see deep tissue, provides a powerful optical tool for observing brain function, and has broad application prospects in the study of neural activity, microcirculation, neurovascular coupling, and neurodegeneration.
The study was published recently in the Journal of the American Optical Society.
This technique utilizes the second near-infrared (NIR-II) spectrum between 1000 and 1700 nanometers, which scatters less and can reach four times the depth limit of light diffusion depths for microfluorescence imaging.
Fluorescent microscopes are often used to image molecular and cellular details of the brain in animal models of various diseases. Previously, however, fluorescent microscopes were limited to small size and highly invasive operations due to the strong light scattering in the skin and skull. The study is the first to show that 3D fluorescent microscopes can help scientists observe the brains of adult mice in a non-invasive, high-resolution manner. The microscope effectively covers a field of view of about 1 cm.
The researchers first tested the technique in a tissue synthesis model that mimics the tissue characteristics of the average human brain, proving that they can obtain micro-resolution images up to 4 mm deep in optically opaque tissue. They then tested the technique on live mice. They injected fluorescent droplets into the veins of living mice, and tracking these flowing fluorescent droplets could reconstruct high-resolution maps of deep microvascular vessels in the brains of mice. Observations have found that the speed and direction of cerebrovascular vessels and blood flow can be observed completely invisibly with DOLI technology.
The researchers say this method eliminates background light scattering and can be done without damage to the scalp and skull. They also observed that the size of the spots recorded by the camera had a strong relationship with the depth of the droplets in the brain, which made it possible for the brain to identify the depth of imaging.
“In biomedical imaging, achieving high-resolution optical observations of deep living tissue is a long-term goal.” Daniel Razansky, head of the research team, said.
Now, researchers are working to optimize DOLI technology to improve its resolution. They are also developing improved fluorescent agents that are smaller, have higher fluorescence intensity, and are more stable in the body, which will greatly improve the technology’s performance in terms of clarity and imaging depth.
Credit: ETH Zurich, University of Zurich / Daniel Razansky