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Depiction of phantoms used for measuring the effect of shift-varying system response models. (a) The sphere phantom consists of four sphere patterns, placed in the central plane of the CZT system. (b) The contrast phantom consists of a 2.5 cm-radius, 6 cm-long cylinder filled with a warm solution of activity, in which are placed five hot spheres, the activity in which is ten times more concentrated than the background.
