vett 116 coursework - wk 5 exposure variables

How does the kilovoltage affect the quality of a radiograph?

- Higher kVp = greater scale of contrast (more visible grays - defines structures better.) -Higher kVp penetrates through dense tissues (soft tissue = higher kVp in combo with lower mAs to produce different shading) - limits, ranges, appropriate settings. - increased amount of scatter radiation with higher kVp (artifacts - pen. too strongly)

How would you increase radiographic density?

1. to double the radiographic density => increase the kVp by 20% 2. to halve (or reduce) the radiographic density => decrease the kVp by 16%

Calculate mAs for the following: a.20 mA x ½ sec = __________ mAs b.100 mA x 1/10 sec = _______ mAs c.1000 mA x 1/10 sec = ______ mAs d.300 mA x 1/160 sec = ______ mAs

20 x 1 divided by 2 = 10 100 x 1 divided by 10 = 10 1000 x1 divided by 10 = 100 300 x 1 divided by 160 = 1.875 = 2

What is the standard focal-film distance?

36-40

What type of mAs and kVp setting is used for soft tissue radiographic examinations? What types of settings would you use for bone structures?

Higher kVp - lower mAs

Why should you always use the highest mA setting and the lowest time setting available when calculating mAs?

Higher mA and shorter time will decrease motion blur on radiographs.

What happens if you increase the FFD? What happens if you decrease the FFD?

Low - Image overexposed High - Image underexposed

What are the 3 variables to be set to create/provide a diagnostic radiograph?

Time of exposure Milliamperage Kilovoltage = kVp

Please define the following: a.Radiographic detail b.Radiographic contrast c.Radiographic density

contrast - levels, differences, and shades between structures. density - degree of blackness on the film

How is the technique of magnificationused to produce a diagnostic radiograph?

distance from the object being imaged to the recording surface (film) - distance should be as short as possible to minimize the penumbra effect and the magnification that occurs with a large OFD. where this can become a factor are in some patients that have a larger body or muscle mass,

The milliamperage setting will control the number of x-rays produced. What would the result be if you increase the mA? What about if you decrease the mA?

increased mA = increases amount of radiographic density as an increased number of xrays are generated. - decrease in density (gray/lighter color)

Which exposure factor has the greatest influence on radiographic contrast?

kvp

How does the exposure time effect the amount of electrons produced?

longer exposure time - allows electrons a longer period to cross from the cathode from anode, generating more xrays

Which exposure factor has the greatest impact on radiographic density?

ma