Male rats classified as copulators and noncopulators respond differentially on the hot plate test.

Sexually naive male rats that fail to copulate with a sexually receptive female (noncopulators) have been shown to be less responsive to a variety of environmental stimuli in comparison to rats that do engage in copulation (copulators). In this experiment, it was found that noncopulators were less responsive than copulators to noxious thermal stimulation as determined by their latency to paw lick on a 50 degrees C hot plate. Pain sensitivity was not influenced in either noncopulators or copulators by exposure to a sexually receptive female. These results add to the list of differences between copulators and noncopulators.

Inclusion characterization in a scattering slab with time-resolved transmittance measurements: perturbation analysis.

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.

Dual-spatial integration for longitudinal localization of inclusions in turbid media.

We introduce a technique called dual-spatial integration (DSI) that is used to isolate and enhance inclusions that differ only by their longitudinal placement within a scattering medium. DSI uses three different source-detector configurations to section a scattering medium into three longitudinal zones. This sectioning permits the extraction of structures close to surfaces and the enhancement of those structures located in the central part of the medium. Both the simulation and the experimental results indicate that DSI has potential interest for applications in biomedical imaging such as optical mammography.

Hybrid Monte Carlo for photon transport through optically thick scattering media.

A Monte Carlo simulation code developed to model time-domain transillumination measurements with small-area detectors through an optically thick scattering slab is presented. A hybrid approach has been implemented to reduce calculation times. Most of the scattering slab is treated stochastically, albeit with variance reduction techniques and the isotropic diffusion similarity rule. The contribution to the output signal per unit area and time of photon packets propagating in a thin slice near the output face of the slab is calculated analytically after each propagation step. This approach drastically reduces the calculation time but produces spikes in the temporal signals.