What is the role of the photomultiplier tube in a CR system?

• A. Collect light photons and convert them to a digital image
• B. Collect and multiply the light photons and convert them to electrons
• C. Release the latent image from the imaging plate
• D. Convert the analog data to a digital signal

Answer: (B)

In the readout of a computed radiography system, the photomultiplier tube is the light detector that turns the light emitted by the phosphor screen into an electrical signal. When the laser scans the plate, the stored energy is released as light photons. The PMT’s photocathode captures those photons and emits electrons. Those electrons are then multiplied through a series of dynodes, producing a much larger current that accurately reflects the light intensity. This amplified electrical signal is what the rest of the system digitizes to form the image. The PMT isn’t the device that directly erases the latent image or converts the signal to digital by itself, and it doesn’t by itself create a digital image; it provides the amplified analog signal that downstream electronics convert to digital.