  Spatial Frequency Domain Imaging can map tissue scattering and absorption
properties over a wide field of view, making it useful for clinical
applications such as wound assessment and surgical guidance. This technique has
previously required the projection of fully-characterized illumination
patterns. Here, we show that random and unknown speckle illumination can be
used to sample the modulation transfer function of tissues at known spatial
frequencies, allowing the quantitative mapping of optical properties with
simple laser diode illumination. We compute low- and high-spatial frequency
response parameters from the local power spectral density for each pixel and
use a look-up-table to accurately estimate absorption and scattering
coefficients in tissue phantoms, in vivo human hand, and ex vivo swine
esophagus. Because speckle patterns can be generated over a large depth of
field and field of view with simple coherent illumination, this approach may
enable optical property mapping in new form-factors and applications, including
endoscopy.
