Which of the following is TRUE about film focal distance? Mark ALL correct answersGroup of answer choicesIncreasing FFD increases magnificationIncreasing FFD requires less mAs to keep the same density.Increasing FFD increases penumbraIncreasing FFD decreases magnificationIncreasing FFD decreases penumbraIncreasing FFD requires more mAs to keep the same density
Question
Which of the following is TRUE about film focal distance? Mark ALL correct answersGroup of answer choicesIncreasing FFD increases magnificationIncreasing FFD requires less mAs to keep the same density.Increasing FFD increases penumbraIncreasing FFD decreases magnificationIncreasing FFD decreases penumbraIncreasing FFD requires more mAs to keep the same density
Solution
The correct answers are:
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Increasing FFD decreases magnification: This is true because as the distance between the film and the focal spot increases, the size of the projected image decreases, thus reducing magnification.
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Increasing FFD decreases penumbra: This is also true. Penumbra refers to the blurring at the edges of an image. As the FFD increases, the penumbra decreases, resulting in a sharper image.
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Increasing FFD requires more mAs to keep the same density: This is true because as the distance increases, the intensity of the x-ray beam decreases (due to the inverse square law). Therefore, to maintain the same image density, more mAs (milliampere-seconds, a measure of total x-ray exposure) is required.
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