As small animal optical imaging and tomography are gaining popularity for interrogating functional and molecular events in vivo, it becomes increasingly necessary to gain knowledge of the optical properties of the species investigated to better understand and describe photon propagation through their tissues. To achieve characterization of the spatial variation of average optical properties through murine chest cavities, time- and spatially resolved measurements of femto-second laser pulse transmission are performed through mice using a high-speed gated image intensifier. Application of time-resolved diffusion theory for finite slab geometry is first confirmed on phantoms and then applied to in vivo measurements for spatially resolving and quantifying mouse optical properties. Photon transmission images through mouse chest cavities are further obtained at different time gates to visualize the spatial variation observed and confirm the optical coefficient patterns calculated.