Practical Limits for the Detection and Characterization of Optical Inhomogeneities using Diffuse Photon Density Waves

Abstract

Diffusing photons can provide information about the spatially dependent optical properties of turbid media. In biological tissues these optical properties may be correlated to physiological parameters, enabling one to effectively probe the physiological states of tissue for abnormalities such as tumors and hemorrhages. In this paper, we show that positional uncertainty in the source and detector lead to significant random errors which degrade the optical information available from diffusing photons. We investigate the limits for the detection, localization, and characterization of optical inhomogeneities using diffusing photons as a probe. While detection is sufficient for tumor screening, full characterization of the optical properties is desirable for specification of the tumor. Our findings in model breast systems with realistic signal-to-noise indicate tumors as small as 0.3 cm in diameter can be unambiguously detected and located; however the size and optical properties of the tumor can only be simultaneously determined if the diameter is of the order of 1.0 cm. On the other hand if a priori information is available then the optical properties (size) of tumors as small as 0.3 cm in diameter can be determined.