An apparatus, system, and method involving one or more sparse detectors are provided. A sparse detector may include an array of scintillator crystals generating scintillation in response to radiation and an array of photodetectors generating an electrical signal in response to the scintillation. A portion of the scintillator crystals may be spaced apart by substituents or gaps. The distribution of the substitutes or gaps may be according to a sparsity rule. At least a portion of the array of photodetectors may be coupled to the array of scintillator crystals. An imaging system including an apparatus that may include one or more sparse detectors is provided. The imaging system may include a processor to process the imaging data acquired by the apparatus or system including the one or more sparse detectors. The method may include preprocess the acquired image data and produce images by image reconstruction.