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An illustration of a module of the TOS-phantom image that consists of five circle objects. In each object, a circle ROI of 4.32 was drawn. The ROI is labeled with some numbers, as follows: 1 for the air object, 2 for the polypropylene object, 3 for the nylon object, 4 for the acrylic object, and 5 for the Delrin object.
