A microscope the size of a matchbox can image blood vessels lying 1 millimeter below the surface of the brains of mice, with a resolution of 1 micrometer.

A pin-like probe, 1 mm in diameter, protrudes from the bottom of the device and punches a tiny hole in the head of the anesthetized mouse. The probe does not enter the brain, but sits on top of the hippocampus. There it images blood vessels directly below it, which are inside the brain, by illuminating tiny sections of the hippocampus one at a time with near- infrared light.