Image detection and enhancement (A-level only) Flashcards – AQA A-level Physics (7408)

What is the role of the scintillator in a flat-panel X-ray detector?

It absorbs X-ray photons and emits visible light.

What do the photodiode pixels in a flat-panel X-ray detector produce, and what determines the amount at each pixel?

They convert light into electrical charge; the charge at each pixel depends on the received radiation intensity.

How are pixel signals turned into an image in a flat-panel X-ray detector?

Electronic scanning reads the pixel signals, which are then digitised to form an image.

What speed advantage does a flat-panel X-ray detector have over photographic detection?

It produces an image rapidly without film processing.

What three things can be done electronically with a digital image from a flat-panel X-ray detector?

It can be stored, transmitted and adjusted.

Why can flat-panel X-ray detectors reduce the need for repeat exposures?

They have a wide useful exposure range and detect radiation efficiently.

How is a visible image produced on photographic X-ray film?

X-rays create an exposure pattern on the film, which becomes visible after chemical processing.

How does an intensifying screen help expose X-ray film?

Its phosphor absorbs X-rays and emits visible light, which also exposes the film.

How does an intensifying screen affect the X-ray exposure needed for a suitable image and the patient’s dose?

It makes more effective use of incident X-rays, so less exposure is needed than with film alone, reducing patient dose.

What are the main stages of fluoroscopic image intensification?

1. The input phosphor converts X-rays transmitted through the patient into visible light.
2. The light releases electrons from a photocathode.
3. The electrons are accelerated and focused onto a smaller output phosphor.
4. The output phosphor produces a brighter visible image that can be displayed.

How does image intensification affect the X-ray exposure rate needed for useful fluoroscopic images?

It allows useful images at a lower exposure rate than would be needed for direct viewing.

What does real-time display of a sequence of fluoroscopic images allow clinicians to observe?

Internal movement.