limited imaging depth. Furthermore, more scattered 'quasi-ballistic' photons are often measured as well to increase the signal 'strength' (i.e., signal-to-noise ratio). Due to the exponential reduction (with respect to distance) of ballistic photons in a scattering medium, often image processing techniques are applied to the raw captured ballistic images, to reconstruct high quality ones. Ballistic imaging modalities aim to reject non-ballistic photons and retain ballistic photons that carry useful information. To perform this task, specific characteristics of ballistic photons vs. non-ballistic photons are used, such as time of flight through coherence gated imaging, collimation, wavefront propagation, and polarization. See also Ballistic photon Diffuse optical imaging Optical coherence tomography Optical tomography Photon diffusion Photon diffusion equation Laser Doppler imaging References External links Medical Optics Group at ICFO, Barcelona, Spain Understanding Near-Infrared Imaging – Resource to better understand the benefits of Near-Infrared imaging. Diffuse Optics Lab at University of Pennsylvania, Philadelphia DOI at Massachusetts General Hospital, Boston Biomedical Imaging Group at Dartmouth DOS/I Lab at the Beckman Laser Institute, University of California, Irvine A review article in the field by A.P. Gibson et al. An article on optical breast imaging Illinois ECE 460 Principles of Optical Imaging Course lecture notes MRRA Inc. fNIRS Systems Neuroimaging