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A procedure for the time-domain optical characterization of an inclusion in a scattering slab is investigated theoretically and experimentally. The method relies on the measurement of a contrast function, which is defined as the time-dependent relative change in the transmitted signal resulting from the presence of the inclusion. Analytical expressions for the contrast functions of absorptive and diffusive inclusions are obtained through a perturbation solution of the diffusion equation. This procedure is used successfully to determine the optical properties of absorptive, diffusive, and mixed inclusions located at midplane in a scattering slab by use of time-resolved transmittance measurements.

An endoscope capable of Coherent Anti-Stokes Raman scattering (CARS) imaging would be of significant clinical value for improving early detection of endoluminal cancers. However, developing this technology is challenging for many reasons. First, nonlinear imaging techniques such as CARS are single point measurements thus requiring fast scanning in a small footprint if video rate is to be achieved. Moreover, the intrinsic nonlinearity of this modality imposes several technical constraints and limitations, mainly related to pulse and beam distortions that occur within the optical fiber and the focusing objective.Here, we describe the design and report modeling results of a new CARS endoscope. The miniature microscope objective design and its anticipated performance are presented, along with its compatibility with a new spiral scanningfiber imaging technology developed at the University of Washington. This technology has ideal attributes for clinical use, with its small footprint, adjustable field-of-view and high spatial-resolution. This compact hybrid fiber-based endoscopic CARS imaging design is anticipated to have a wide clinical applicability.

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A technique for discriminating between scattering and absorbing inclusions located in the center of a scattering slab is presented. The technique is based on an empirical model that provides a simple mathematical expression to describe the change in the time-resolved transmission resulting from the presence of an inclusion. Experimental results from various configurations show that the technique allows for proper recognition of the type of an inclusion whether it is scattering or absorbing. This technique is a significant step toward tissue differentiation.