Molecular imaging studies using small animals such as mice require the development of high-sensitivity, high-resolution pinhole SPECT imaging systems. It is well known that the photon detection efficiency drops remarkably as the pinhole angle increases, and spatial resolution decreases as the magnification factor decreases. To obtain high efficiency and high resolution, the pinhole should be put as close as possible to the object while the pinhole angle remains as small as possible. To address these conflicting requirements, we proposed a half-cone imaging geometry in which the detector looks at only half of the FOV in each view, while the FOV being reconstructed remain the same. Our preliminary results demonstrated that SPECT system using this geometry could achieve higher sensitivity and better spatial resolution.