Which layer in a photostimulable phosphor (PSP) screen is placed last in order?

• A. Lead
• B. Reflective layer
• C. Protective coat
• D. Phosphor layer

Answer: (A)

In a photostimulable phosphor (PSP) screen, the last layer added is the lead layer. This lead layer serves an important function in the radiation detection process; it is designed to prevent any ambient light from reaching the sensitive phosphor layer. By being the last layer, the lead effectively acts as a barrier against stray light, ensuring that only the desired signal from the exposure contributes to the imaging process.

The order of layers in a PSP screen is significant for its operation and effectiveness in radiography. The reflective layer typically sits under the protective coat and serves to enhance the efficiency of light collection emitted by the phosphor when stimulated. The protective coat safeguards the phosphor layer from damage and contamination, while the phosphor layer, where the actual imaging occurs, is situated above the lead layer to interact directly with the incoming radiation. Each layer has a designated purpose that supports the overall function of the PSP system, and the lead being the last layer is crucial for ensuring the clarity and quality of the radiographic image.