We report the progress in development of carbon nanotube (CNT) field emission micro-focus x-ray tubes for dynamic small animal imaging with high spatial and temporal resolution. Extensive electron optics simulations were performed to study the focusing structure and optimize the tube design. 3D finite element analysis was used for modeling and simulating electron beam optics. A simple and intuitive model is developed to model the field emission properties of CNT cathodes. The dependence of focus spot size and the anode current on the gate extracting voltage, the focusing voltages, the gate mesh geometry, and other geometric parameters were studied. Several tubes were built according to the optimal design. The experimentally measured focus spot size and its dependence on the focus voltages were found to be in quantitative agreement with simulations.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.