Which device may be used in place of the photomultiplier tube (PMT) within a CR image reader system?

• A. Thin-film transistor (TFT)
• B. Amorphous selenium (a-Se)
• C. Charge-coupled device (CCD)
• D. Analog-to-digital converter (ADC)

Answer: (C)

In CR image readers, the light emitted by the photostimulable phosphor after laser stimulation must be detected and converted into an electrical signal. A photomultiplier tube does this with very high sensitivity, but a solid-state detector like a charge-coupled device can perform the same role. A CCD is a light-sensitive device made of an array of pixels that converts incoming photons into charge in each pixel, which is then read out as an electrical signal. With appropriate optics and readout electronics, a CCD can capture the light from the PSP just as a PMT does, providing high spatial resolution and good signal-to-noise characteristics, making it a viable replacement in the readout path.

The other options don’t fit the same role in this context. A thin-film transistor array is typical for certain flat-panel detectors (DR) rather than CR readout from a photostimulable phosphor. Amorphous selenium serves as a photoconductor in DR systems, not as the light detector in CR readout. An analog-to-digital converter handles converting analog signals to digital, but it does not detect light itself.