Radiographic exposure settings hints and tips

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Radiographic exposure settings hints and tips
29 March 2013

It is essential that radiographs taken in practice should be of diagnostic quality to enable accurate evaluation for the presence of disease/pathology.

Patient positioning
Whether you are working with companion animals, horses, farm or exotic species, it is important to properly restrain the patient and position them for optimal exposure of the region of interest and radiographic projection (view).

Centring and collimation
The beam should be centred over the primary region of interest and the collimation should always be adjusted to the region of interest.

Exposure factors
Radiographic Exposure Settings (1)

Milliamperage (mA)

Amount of electrical current applied to cathode
Affects number of X-rays produced
Usually combined with time (s) to enable mAs to be altered as a single setting
Alters the overall brightness of the image (overall more ‘light’ or ‘dark’)
Higher mAs = a greater number of X-rays will be produced and pass through the patient to reach the cassette (and vice versa)
Time in seconds (s)

Length of time current applied to cathode
Affects number of X-rays produced
Usually combined with milliamperage (mA) to enable mAs to be altered as a single setting
Kilovoltage (kV)

Voltage applied across the generator
Affects energy of X-rays produced
Alters the visible contrast between tissues (image more black and white or uniformly grey)
Higher kV = the X-rays leaving the generator will have greater energy and so will be able to pass through the patient more easily to reach the cassette (and vice versa)
Focal spot/film distance (FFD)

Distance between the source of X-rays (focal spot in the generator) and the cassette/plate
Increase/decrease in FFD requires alteration in other exposure factors (increase in FFD requires increase in mAs +/- kV and vice versa)
Object-film distance (OFD)

Distance between the patient and the cassette/plate
Increase in OFD results in image blurring and magnification
Radiographic Exposure Settings (1)
Object/area of interest (hand) farther away from ‘film/cassette’ (wall) – shadow cast is magnified with blurred edges.

Radiographic Exposure Settings (1)
Object/area of interest (hand) near to the ‘film/casette’ (wall) – shadow cast is of nearly equal size with sharp edges.

Remember that increasing either mAs or kV will cause the film to be darker, therefore a correctly exposed radiograph relies on both an appropriate mAs and kV setting to be used.

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