We have developed two prototype micro insert devices based on a novel virtual-pinhole PET geometry. These devices can be integrated into an animal PET scanner to significantly enhance its image resolution. The first system consists of a rotation stage that rotates a high-resolution detector module within the animal port. The second system consists of 18 detector modules arranged in a ring. While both systems are capable of higher resolution PET imaging, the second approach enables dynamic and gated imaging, as well as higher sensitivity. Image reconstruction algorithms that specifically model the virtual-pinhole PET geometry are developed for the PET insert systems. Preliminary imaging experiments show improvement in transverse image resolution. To achieve quantitative accuracy, refined correction techniques for attenuation and scatter, as well as system normalization and detector dead time, will need to be developed for PET insert devices.