Which type of AEC uses a photomultiplier tube?

• A. Ionization chamber
• B. Photo timer
• C. Solid-state detector
• D. Digital sensor

Answer: (B)

The type of AEC (Automatic Exposure Control) that utilizes a photomultiplier tube is the photo timer. This device is designed to measure the intensity of radiation using light. When x-rays pass through the patient and strike a fluorescent material inside the photomultiplier, it generates light photons. These photons are then converted to an electrical signal by the photomultiplier tube, allowing for precise measurement of the radiation exposure reaching the film or digital receptor.

Photo timers are typically used in radiographic applications that require close attention to detail and accuracy, such as in certain fluoroscopic procedures or when using film-screens. This capability stands in contrast to ionization chambers, which use gas ionization to detect radiation and are generally seen in solid-state AEC systems. Other technologies mentioned, like solid-state detectors and digital sensors, serve different functions and do not rely on the photomultiplier tube mechanism.