Image Production
This domain tests how exposure data become a diagnostic image in computed radiography and direct radiography, and how processing choices affect contrast, noise, resolution and display.
Core rules
- The receptor converts X-ray energy into an electronic signal. CR uses a photostimulable plate; DR uses flat-panel detectors.
- The histogram and exposure index indicate receptor signal, not patient dose. Exposure index varies by vendor and must be interpreted with the receptor's calibration.
- Matrix and pixel size affect spatial resolution; bit depth affects gray-level display, not acquired resolution.
- Windowing and lookup tables change display contrast and brightness, not the raw acquisition data.
- Noise rises when too few photons reach the receptor. Overexposure can reduce noise but raises dose and may clip data.
Worked example
A DR chest image has an exposure index well above the department's target but looks acceptable on the monitor. The reasoning is that windowing can hide overexposure. The technologist should check the EI, receptor calibration, collimation and patient thickness, then correct technique rather than simply adjusting the display. Repeating with lower exposure may be appropriate only if the image is noisy or clinically inadequate.
Traps
Do not treat exposure index as a dose meter. Do not assume windowing improves a noisy raw image. Do not confuse matrix size with detector size. Do not accept overexposure simply because the image looks dark or light on the display.