American Society of Radiologic Technologist (ASRT) Practice Exam

Until a photostimulable phosphor plate (PSP) is processed, where are the freed electrons stored?

1. Valence band

2. Photodetector

3. Conduction band

4. Conductive layer

The correct answer is: Conduction band

The correct answer is based on the principles of how photostimulable phosphor plates function in the context of digital radiography. When X-rays interact with the phosphor material in the plate, energy from the X-rays excites electrons, which leave their position in the valence band and become "trapped" in the conduction band. This trapping of electrons occurs until the plate is processed, at which point these trapped electrons are released, allowing the imaging data to be retrieved. The conduction band is essential in this process because it holds these freed electrons in a state that allows for eventual readout and image formation. When the plate is stimulated by a laser or other light source during the processing phase, the electrons in the conduction band revert to their lower energy state, releasing energy in the form of light. That emitted light is then detected and converted into an image. Understanding the role of the conduction band is crucial for radiologic technologists as it helps explain the image acquisition process in digital radiography, specifically in systems utilizing PSP technology.