Introduction to imaging: Non-ionising radiation
In the second part of our series about imaging, John Frank takes you through the basics of non-ionising techniques
Whereas imaging with ionising radiation uses x rays or gamma rays, non-ionising radiation uses either sound waves, in the case of ultrasound, or magnetisation of protons in magnetic resonance imaging (MRI).
Ultrasound is high frequency sound waves in the megahertz range. These are produced by a special transducer, and pass into the body through what is called an acoustic coupler--a special jelly for abdominal and peripheral work, or a water bath when a structure such as the eye is being examined. The sound waves are reflected back in varying amounts from every anatomical interface and these reflected waves are detected to produce an image. Modern ultrasound machines contain a computer that generates the images and can send them either to film or a picture archiving communication system (fig 1).