RADIATION HAZARDS AND PROTECTION

X-RAY BEAM QUANTITY AND QUALITY

The quality of the x-ray beam is controlled by the voltage, while the milliamperes control the quantity. An increase in the voltage and milliamperes reduces exposure time for the patient.

a. X-ray Beam Quality. The quality of the x-ray beam is controlled by the amount of voltage. Voltage provides contrast to the film. T he desired contrast appears as various shades of gray, black and white in the x-ray negative (radiograph). Increased voltage provides less contrast (or more shades of gray). However, the beam has more penetrating power. Decreased voltage, on the other hand, provides more contrast (fewer shades of gray and more black and white shades). However, there is less penetrating power in the low voltage exposure. The technique most commonly used to expose periapical and bite-wing X-rays is a 90 kilovolt peak and 15 milliamperes.

 

b. X-ray Beam Quantity. The x-ray beam quantity is controlled by the milliamperes. The more x-rays (photons) in the x-ray beam, the more dense (dark) the x-ray negative (radiograph) becomes. By increasing the milliamperes, we increase the number of available electrons at the cathode filament. When electrical current (voltage) is applied to the x-ray tube, the electrons cross the gap. When they impact on the anode (tungsten target), a greater number of x-rays (photons) are also produced. The more x-rays that are available to penetrate an object, the more dense (dark) is the x-ray negative (radiograph).