Microscopic imaging through a turbid medium by use of annular objectives for angle gating

We report a new method for microscopic imaging of an object embedded in a turbid medium. The new method is based on the angle-gating mechanism achieved by the use of polarized annular objectives in the illumination and collection paths of a microscopic imaging system. A detailed experimental study is presented of the effects of the size of annular obstructions on image quality when turbid media, including polystyrene microspheres and milk suspensions, are imaged. Images of 22-mum polystyrene microspheres embedded in the turbid media show that misinterpretation can occur when circular objectives are used, because of the detection of mainly multiply scattered photons (i.e., diffusing photons). However, when annular objectives are employed, diffusing photons from a turbid medium can be efficiently suppressed; thus image contrast appears correctly, and image resolution is increased.