Radiation NoiseRadiation noise is information present in a radiation beam that does not contributeto the usefulness of the image. For example, many x-ray beams exhibit a nonuniformintensity from one side to the other. This nonuniformity, termed the heel effect, is aresult of the production and filtration of the beam in the anode of the x-ray tube.Although the nonuniformity provides information about these mechanisms, that information is irrelevant to diagnosis of the patient’s condition. Similarly, the radiationbeam exiting from the patient contains considerable scattered radiation. This radiation contains information about the patient, although in such a complicated formthat it cannot be easily decoded. As it impinges on the image receptor, scattered radiation interferes with the visualization of patient anatomy. Hence, scattered radiationis radiation noise. In projection radiography, the contribution of scattered radiationto image noise is so severe that it must be removed by a grid to permit the structuresof interest to be seen clearly.
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