Method and apparatus for imaging tissue by upstream illumination and downstream dual filtering of the exiting light for separation of ballistic photons rays from stray rays. Dual filtering includes spatial filtering via a pinhole and spatial filtering operated by a fast gate. A processor synchronizes flashes of illumination with the fast gate to command opening for passage of the ballistic photons rays and closure to exclude the stray rays. An image detector downstream of the fast gate collects the ballistic photons rays for processing by the processor and display on a monitor as a shadowgram. Illumination flashes have one or more wavelengths and the image detector is adapted to match the selected wavelengths of the illuminating flashes.