A prototype physiologically gated micro-computed tomography (micro-CT) system based on a field emission
micro-focus x-ray source has been developed for <i>in vivo</i> imaging of small animal models. The novel x-ray
source can generate radiation with a programmable waveform that can be readily synchronized and gated with
non-periodic physiological signals. The system performance is evaluated using phantoms and sacrificed and
anesthetized mouse models. Prospective respiratory-gated CT images of anesthetized free-breathing mice are
collected using this scanner at 100msec temporal resolution and 10 lp/mm of 10% system MTF.