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Position-sensitive scintillation-detector arrays (PSSDA) are used in nuclear imaging such as PET. The PSSDA-production method determines the imaging resolution, sensitivity, labor/part cost, and reliability of the system. It is especially challenging and costly for ultra high-resolution systems that have large numbers of very small crystal-needles. A new slab-sandwich-slice (SSS) production method was developed. Instead of using individual crystal needles, the construction started with crystal slabs that are 15-crystal-needles wide and 1-needle thick. White-paint was deposited onto slab surfaces to form shaped optical windows. The painted slabs were grouped into two crystal-sandwich types. Each sandwich-type was a stack of 7 slabs painted with a distinctive set of optical windows, held together with optical glue. For a 40,000-crystal system, only 192 type-A and 144 type-B sandwiches are needed. Sandwiches were crosscut into another slab formation ("slices"). Each slice was again 1-needle thick; each slice is basically a stack of needles glued together, optically coupled by the glue and the painted windows. After a second set of white-paint optical-windows was applied on the slices' surface, 3 slices of type-B are grouped between 4 slices of type-A forming a 7×7 PSSDA. The SSS production method was applied in the construction of high-resolution 12-module prototype PET camera (HOTPET). The method reduces the more than 400,000 precision painting and gluing steps into 55,000 steps for a 40,000-BGO-crystal system, leading to lower labor cost. Detectors were fabricated with the method with good results. 2.66×2.66 mm2 crystals are separated only by a 0.06-mm gap; this is a 98% linear detector packing fraction or 96% area packing fraction. Compared to 90% linear-packing (81% area) from conventional methods, the 20% higher crystal-packing density would translate into a 1.2-1.44 times higher coincidence-detection sensitivity in PET. The SSS method cut the crystal cost by half, and improved production yield by 94%. Crystal-positioning error was σ=0.09mm.