We are designing a modular SPECT camera for specialized imaging applications. We proposed to use NaI(Tl) as our scintillation crystal whose shape is hexagonal with \sim 100 mm side lengths and > 5 mm thickness. Our target average spatial resolution is \sim 1.5 mm (FWHM) which corresponds to a\sigma (RMSE) of 0.45 mm. We propose putting SiPMs on the edges to help improve the spatial resolution. Our preliminary simulation result shows that with 8 mm crystal thickness, 6 mm light guide, and 37 close-packed photomultiplier tubes (1.0'' diameter), the root mean squared error (RMSE) across the detector plane is 2.84 mm, due to the very high bias and variance in regions close to the edges; By attaching 4 SiPMs on each edge, the RMSE is improved to 1.34 mm; If the SiPMs' window material and coupling medium's refractive index is increased to 1.82, the RMSE is improved to 1.00 mm. We are still optimizing the detector design by tuning the parameters such as thickness of crystal, thickness of light guide, positions of SiPMs on the edges and number of PMTs to achieve the target spatial resolution without a significant trade-off on the detection sensitivity.