Diffuse photon probes of structural and dynamical properties of turbid media: Theory and biomedical applications

DIFFUSE PHOTON PROBES OF STRUCTURAL AND DYNAMICAL PROPERTIES OF TURBID MEDIA THEORY AND BIOMEDICAL APPLICATIONS David A Boas Arjun G Yodh Di using photons can be used to detect localize and characterize optical and dynamical spatial inhomogeneities embedded in turbid media Measurements of the intensity of di use photons reveal information about the optical properties of a system Speckle uctuations carry information about the dynamical and optical properties This dissertation shows that simple di usion theories accurately model the intensity and speckle correlation signals that di use through turbid media with spatially varying properties and discusses possible biomedical applications We rst look at the intensity of di use photons provided by a light source that is intensity modulated This generates di use photon density waves DPDW s which exhibit classical wave behavior We demonstrate experimentally and theoretically the refraction di raction and scattering of DPDW s Using accurate signal and noise models we then present a detailed analysis which shows that DPDW s can be used to detect and locate objects larger than mm and to characterize objects larger than cm which are embedded inside turbid media with biologically relevant parameters This di use photon probe should may nd applications in medicine as a bed side brain hematoma monitor or for screening breast cancer or other functional imaging applications We then consider the coherence properties of the di use photons as revealed by speckle intensity uctuations and show that the temporal autocorrelation function of these uctuations is accurately modeled by a correlation di usion equation Because the correlation di usion equation is analogous to the photon di usion equation all concepts and ideas developed for DPDW s can be directly applied to the di usion of correlation We show experimentally and with Monte Carlo simulations that the dif