Abstract : The pinhole camera is a well-established direct-imaging system that produce good quality images, in terms of spatial resolution, but has an associated limited field of view. When used in the context of nuclear medicine imaging, the limited angular acceptance and poor geometric efficiency means the imaging process suffers from lengthy acquisition times as it suffers from low efficiency due to its single small pinhole size. The collimator image formation such as the parallel-hole is limited by the design and also provides a low detection efficiency. The forthcoming review focuses on methods of removing these limitations by investigation using a Coded Aperture (CA) instead of a conventional collimator, coupled to a standard clinical gamma camera for breast tumour imaging applications. This paper introduces the concept of CA imaging and provides an historical background of the different types of CA, families with their mathematical imaging properties. Then, it describes their shape and correlation properties. These include Fresnel zone plate, random array, non-redundant arrays, L shape geometric array, X shape geometric, uniformly redundant, modified uniformly redundant, mosaic uniformly redundant and no-Two-Hole-Touching patterns. Finally, this paper illustrating the principle of pinhole camera to appreciate the theory and the formation of coded image. Then describe the potential of CA imaging in breast tumour imaging. It a general overview of the entire imaging problems associated with the collimator-based SM system closes the paper.