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The mosaic solution isn't perfect, of course. The format specification was never accepted by other manufacturers, so Siemens was alone in providing this format to its users, which led to more division amongst researchers eager to share data and processing tools & techniques. It also suffered from its own inefficiencies. The format specification required that the number of tiled slices be square (1, 4, 16, 32, 64, ...). If the acquisition dindidn't use a square number of slices, the tiled array would be up-sized to the next larger square number, and the space was padded with zeros, or, pure black images. For instance, in the figure above, the run had only 60 slices, so the mosaic included 4 blank slices to create a square tiled grid. Those blank images use the same amount of space as actual images, so some of the space savings might be given back if the number of slices was, say, 36. That would mean that the mosaic DICOM would still need to have 64 images, but 28 of them would be nothing but zeros. Almost half the hard drive space dedicated to image storage was wasted. Additionally, the format specification does not permit slice-by-slice parameters. Although almost unheard of, images of this type need not be acquired with the same orientation. Nor does each slice need to be acquired with the same flip angle. In cases like those, the mosaic format could not be used at all because it could not save the individual slice parameters.
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