Which exposure factor regulates the quantity of the x-ray beam?

• A. Exposure time
• B. mA
• C. kV
• D. Distance

Answer: (B)

The correct answer is mA (milliamperes) because it directly controls the quantity of x-ray photons generated during an exposure. When the mA setting is increased, more electrons are available to be accelerated across the x-ray tube, resulting in a higher number of x-ray photons being produced. This directly correlates to the overall intensity or quantity of the x-ray beam that reaches the patient and the image receptor.

Exposure time also influences the amount of radiation the patient receives, but it does so in conjunction with mA, representing a time factor rather than a direct control over the quantity of radiation produced at any moment. The kV (kilovoltage) setting primarily affects the energy (quality) of the x-ray beam, dictating its penetration power rather than the number of x-rays generated. Distance is an important factor in determining exposure, as the intensity of the x-ray beam diminishes with increased distance (following the inverse square law), but it does not directly regulate the production of x-rays. Thus, mA is the primary factor for regulating the quantity of the x-ray beam itself.