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focal spot |
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focal spot, n See spot, focal. focal spot the area on the target of the x-ray tube which the electron stream strikes and from which x-rays are emitted. Called also focus. The larger the area of the focal spot, the poorer is the detail in the x-ray image. actual focal spot the actual area of the focal spot on the radiographic target as viewed at right angles to the plane of the target. broad focal spot a relative term which refers to the effective dimension of the x-ray focal spot usually greater than 1 mm2. See also fine focal spot (below). effective focal spot the face of the anode that carries the target in an x-ray tube is slanted from the vertical to increase the volume of the target but to reduce the size of the origin of the x-ray beam. focal spot-film distance see focal-film distance. fine focal spot a focal spot of less than 1 mm2 which is used in radiography studies where high detail is required. focal spot-skin distance distance from the film spot to the skin of a patient receiving radiation therapy. |
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High-Power transmission target has an interaction layer of tungsten and a special backing layer that provides improved heat transfer and lower focal spot temperature. Even at such high magnifications the latest 1000 x 1000 pixel detectors can easily resolve the resulting x-ray images, so image resolution depends almost entirely on focal spot size of the x-ray source. The lens system would be even more effective at longer wavelengths were it not for the spreading of the focal spot in the vertical direction due to gravity. |
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focal spot
