(From Fauber TL: Radiographic imaging and exposure, ed 3, St Louis, 2009, Mosby.)īecause kVp affects the amount of radiation reaching the IR, its effect on the digital image is similar to the effect of mAs. A 10-kVp increase at 50 kVp (B) produces a greater change in density than a 10-kVp increase at 90 kVp (D). Produced at 50 kVp (A) and produced at 90 kVp with the mAs adjusted to maintain radiographic density (C). If the mAs selected is too high (high exposure to the digital IR), the brightness can also be adjusted, but the patient has received more radiation than necessary.įIGURE 10-5 kVp Range and Radiographic Density. Although the level of brightness has been adjusted, there may be increased quantum noise visible within the image. If the mAs is too low (low exposure to the digital IR), image brightness is adjusted during computer processing to achieve the desired level. However, exposure errors can adversely affect the quality of the digital image. When a greater change in mAs is needed, the radiographer should multiply or divide by 4, 8, and so on.ĭigital IRs can detect a wider range of radiation intensities (wider dynamic range) exiting the patient and therefore are not as dependent on the mAs as film-screen IRs. The minimum change needed to correct for a density error is determined by multiplying or dividing the mAs by 2. The mAs has a direct effect on the amount of radiographic density produced when using a film-screen IR. If the radiograph necessitates an adjustment greater than a factor of 2, the radiographer should multiply or divide the mAs by 4 (Figure 10-3). As mentioned previously, it may take more than doubling the mAs to correct for a density error. This typically brings the optical densities back within the straight-line portion of the film’s sensitometric curve to best visualize the anatomic area of interest. In general, for repeat radiographs necessitated by density errors, the mAs is adjusted by a factor of 2 therefore a minimum change involves doubling or halving the mAs. The radiographer must decide how much of a change in mAs is needed to correct for the density error. When the radiograph is deemed unacceptable, this means the optical densities lie outside the film’s sensitometric curve’s straight-line portion, and may need to be repeated. When using a film-screen IR, radiographers need to assess the level of density produced on the processed image and determine whether the density is sufficient to visualize the anatomic area of interest. The film characteristic, speed, and chemical processing determine the amount of optical density produced on the image for a given mAs. This relationship between radiation exposure intensity and density is discussed in more detail in Chapter 9. When a film image is too light (insufficient density), a greater increase in mAs may be needed to correct the density, or the mAs may need to be decreased to correct a film image that has excessive density. (From Fauber TL: Radiographic imaging and exposure, ed 3, St Louis, 2009, Mosby.) C, Increase in density when the mAs is doubled.
B, Decreased in density when the mAs is decreased by half. FIGURE 10-2 mAs and Radiographic Density.Ĭhanges in mAs have a direct effect on density.
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