Name the two main beam-limiting devices used in diagnostic radiography.

• A. Collimators and Positive Beam Limitation (PBL) devices
• B. Collimators and Grids
• C. PBL devices and Lead shielding
• D. AEC and Backup timer

Answer: (A)

Limiting the size and shape of the primary X-ray beam is essential to protect the patient and improve image quality. The two main devices that do this in diagnostic radiography are collimators and Positive Beam Limitation (PBL) devices. Collimators are adjustable shutters built into the X-ray tube housing that physically restrict the beam to a chosen field size and shape. PBL devices automatically adjust the field to match the size of the image receptor so the beam does not extend beyond the area being imaged, reducing unnecessary exposure and ensuring consistency with the image receptor dimensions.

Grids are used to reduce scatter within the image but do not limit the beam size. Lead shielding te­chniques protect portions of the patient but do not control the primary beam’s dimensions. AEC and the backup timer control exposure duration or termination but are not beam-limiting devices.