The phosphor layer of the computed radiography (CR) imaging plate is composed of:

• A. Barium Fluorohalides and Europium Activators
• B. Amorphous Silicon and Europium Activators
• C. Barium Fluorohalides and Amorphous Selenium
• D. Amorphous Silicon and Cesium Iodide

Answer: (A)

The main idea is that the storage phosphor layer in a computed radiography plate is made of europium-activated barium fluorohalides. These materials (such as BaFBr:Eu2+ and BaFI:Eu2+) trap electrons when the plate is exposed to x-rays, creating a latent image stored in metastable states. The europium activator provides the traps and luminescent centers needed to hold that information. When the plate is later read with a laser, the trapped electrons are released as light, and the emitted photons are collected to form the digital image.

Other materials listed aren’t used as the storage phosphor in CR plates. Amorphous silicon and amorphous selenium are more typical for other digital detector technologies, and cesium iodide is a scintillator used in indirect detectors rather than the CR storage phosphor layer.