b. Setting the Technique Factors. Radiographic technique affects the quality
of the X-ray and the film density; it also influences patient dose. The control panel, the
heart of the X-ray system, controls the X-ray tube output through the technique factors.
Based on measurement of the part, you can set the technique factors for milliampere
seconds (mAs) and kilovoltage peak (kVp). Required film density and contrast can be
obtained by adjusting either the mAs up to 1000 or applying an extended kilovoltage
range up 150 kVp, where applicable. By balancing these factors (mAs and kVp)
correctly to make the necessary adjustments, you can then regularly produce
radiographs of high technical quality and diagnostic value. With experience, you will
learn to make quick factor exchange calculations between mAs and kVp.
film (radiographic) density: quantify of blackness (exposure) appearing on
radiograph; photo-radiographic property that affects image visibility; without density,
contrast couldn't be achieved film would be clear.
contrast (scale): a noticeable difference between adjacent radiographic densities seen
as varying shades of gray on the radiograph.
(1) Milliampere-seconds (mAs). The milliampere-seconds (mAs)
determines the length of time the patient is exposed to radiation. Milliamperage (mA) is
measured in thousandths of an ampere. Selecting a given mA station (setting) controls
the amount of current (electrons) flowing from the negative cathode filament wire of the
X-ray tube. One of the cardinal rules of radiation protection is to keep the time of
exposure to the minimum necessary to obtain the desired view. The milliampere-
seconds (mAs) setting controls the time of exposure and provides the required film
density (blackness or exposure). Correct exposure in combination with optimum
kilovoltage peak (kVp) produce the most suitable density and contrast that can be
obtained. Over-exposure results in excessive density and low contrast. Underexposure
leads to a lack of density and contrast.
milliamperage: the number of electrons flowing from the cathode to the anode end of
the X-ray tube, measured in thousandths or an ampere.
milliampere seconds (mAs): the milliamperage multiplied by the duration of exposure
cathode: negative end of X-ray tube, source tram which electrons flow.