The X-ray beam is directed towards the patient and the image intensifier. The beam strikes the input screen which first contains a phosphor screen. This turns the X-rays into light. This light then strikes the photocathode which generates electrons. These electrons are accelerated and focused onto the output screen, which converts electrons back into a light image. This process intensifies the image brightness by 5000–10,000 times. Digital processing then produces a final image
2.2 Image intensifier overview
An overview of a body part can be gained without magnification
2.3 Image intensifier magnification
Image intensifiers have a built-in magnification mode that allows ‘expansion’ of the central portion of the input screen, which fills the output screen to provide magnification of a body part. This means exposing a smaller area of the body to radiation. However, the dose to the body part of interest increases because the X-ray beam intensity is increased in order to maintain the brightness of the image
Fluoroscopy allows dynamic real-time imaging of the patient, which can provide information regarding the movement of anatomical structures or devices within the patient. Fluoroscopy is based on X-ray imaging and the physical principles are similar to the plain X-ray imaging chain from X-ray beam generation to image display (see Chapter 1). However, the procedure is performed using a specifically designed X-ray machine and uses real-time acquisition techniques and hardware.
Pulsed X-ray production systems – these are used more commonly in practice due to the lower radiation dose given to the patient (and to radiological staff).
Fluoroscopy machines are designed to specifically manage the heat generated from the repeated exposure in fluoroscopic imaging. They also use lower beam energies and exposures compared with plain X-ray imaging techniques and thus image intensifiers
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