The properties of polarized light emerging from turbid media in the exact backscattering direction are studied by modulating the incident light polarization state and isolating the synchronous signal with lock-in amplifier detection. The results are reported for polystyrene microsphere suspensions in distilled water, with and without glucose, and for both ex vivo and in vivo biological tissues. A new theoretical formulation based on Mueller calculus is developed to describe the observed behavior of the backscattered light in terms of two sample parameters: optical rotation and depolarization. This technique proved successful in modeling both phantom and tissue samples. Results showed the presence of a significant surviving polarization fraction in the backscattering direction even in extremely dense optical phantom media, an important finding that has not been observed at other detection angles. Substantial polarized light preservation in biological tissue samples is also demonstrated for this detection geometry. This illustrates the potential of using polarized light to investigate turbid biological materials in vivo in retroreflection geometry.

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An x-ray fluorescence measurement system has been developed with an 125I source to detect arsenic in superficial layers of phantoms and tissue. Based on in vivo measurements, in conjunction with Monte Carlo simulations, the detection limit for arsenic in skin ranges between 2.6+/-0.5 and 5.7+/-1.1 microg g(-1), depending on skin thickness and assuming that arsenic is uniformly distributed in the skin. The effect of skin arsenic distribution was also examined.

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Background Total-body irradiation (tbi) is used to condition patients before bone marrow transplant. A variety of