3.10.5.3
X-ray detection methods
Medical Physics | AQA A-Level Physics
- Flat-panel (FTP) detectors: a scintillator layer converts X-ray photons into visible light, which is then detected by an array of photodiodes. An electronic scanner reads the photodiode signals to produce a digital image. This is the modern standard.
- Photographic film: X-rays darken silver halide film. Intensifying screens (phosphor layers on either side of the film) convert X-rays to visible light, reducing the dose needed. Film is being replaced by digital detectors.
- Image intensifier: used for real-time fluoroscopy.
- X-rays hit a fluorescent screen, producing visible light.
- The light strikes a photocathode, releasing electrons by the photoelectric effect.
- Electrons are accelerated and focused by anodes onto a smaller viewing screen.
- The output image is about 5000 times brighter than the input, allowing real-time viewing with a much lower X-ray dose.