X-rays penetrating the lead housing are termed leakage radiation . X-rays passing through the port constitute the primary beam. A box-like device attached at the port contains an adjustable shutter or collimating mechanism that shapes and changes the size of the primary beam. This use of filters reduces skin dose, since the low energy X-rays are primarily absorbed by the skin. Low energy X-rays are not used for imaging since their energy is too low to penetrate the patient.
Fluoroscopy uses either continuous or pulsed X-ray beam.
Patient and staff exposures are reduced when pulsed progressive fluoroscopy is used in place of continuous fluoroscopy with interlaced TV cameras. In order to pulse the beam, some pulsed fluoroscopy systems use a grid in the X-ray tube to control the number of electron pulses traveling to the anode. Other systems pulse the generator. Rapidly pulsing the beam and maintaining image quality requires fast, accurate, and consistent X-ray output. Additional beam on time is frequently needed while the mechanical arm of the conventional autotransformer moves into the position required to produce the kilovoltage designated by the computer.