## Abstract

Optical measurements of tissue can be performed in discrete,
time-averaged, and time-varying data collection modes. This
information can be evaluated to yield estimates of either absolute
optical coefficient values or some relative change in these values
compared with a defined state. In the case of time-varying data,
additional analysis can be applied to define various dynamic
features. Here we have explored the accuracy with which such
information can be recovered from dense scattering media using linear
perturbation theory, as a function of the accuracy of the reference
medium that serves as the initial guess. Within the framework of
diffusion theory and a first-order solution, we have observed the
following inequality regarding the sensitivity of computed measures to
inaccuracy in the reference medium: Absolute measures ≫ relative
measures > dynamic measures. In fact, the fidelity of derived
dynamic measures was striking; we observed that accurate measures of
dynamic behavior could be defined even if the quality of the image data
from which these measures were derived was comparatively modest. In
other studies we identified inaccuracy in the estimates of the
reference detector values, and *not* to corresponding errors
in the image operators, as the primary factor responsible for
instability of absolute measures. The significance of these
findings for practical imaging studies of tissue is
discussed.

© 2001 Optical Society of America

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