Image formation in turbid media under a microscope

Image formation in a turbid medium under a microscope is studied both theoretically and experimentally. In particular, the relationship of image resolution to scattered photons, which experience different numbers of scattering events, is explored in a scanning microscope. The effects of the numerical aperture of a microscope objective and the detector size on image resolution that is contributed by scattered photons are carefully investigated. The results show that for an object embedded in a turbid medium of a thickness of 12 scattering mean-free-path lengths, transverse resolution of an image contributed by scattered photons is much lower than the diffraction-limited resolution. A criterion for determining the efficiency of a gating method is proposed in terms of the relationship of resolution to signal strength. (C) 1998 Optical Society of America.