With Single Photon Emission Computed Tomography (SPECT), images of minute concentrations of tracer molecules can be acquired, allowing in vivo molecular imaging. For human imaging, the SPECT system has a modest spatial resolution of 5-15 mm, a large field of view and a high sensitivity. Using multi-pinhole SPECT, one can trade in field of view for resolution with preserved sensitivity, which enables the implementation of a small animal SPECT system with an improved resolution, currently ranging from 0.3 to 2 mm, in a much smaller field of view. The unconventional collimation and the more stringent resolution requirements pose problems that are not present in clinical SPECT imaging. This paper discusses how these problems can be solved to implement micro-SPECT imaging on a rotating gamma camera. (C) 2009 Elsevier Inc. All rights reserved.