Key learning objectives

Describe basic principles of plain X-ray, fluoroscopy, computed tomography (CT), magnetic resonance imaging (MRI), nuclear medicine including PET and ultrasound (USS) as used in diagnostic imaging.

Describe the basic principles of image guided biopsy and interventional radiology techniques.

Highlight the potential risks and hazards related to diagnostic imaging techniques.

Plain film radiography

Wilhelm Conrad Röntgen first discovered X-rays in November 1895, with his work earning the 1901 Nobel Prize in Physics. Initial photographic images, using the newly discovered rays, quickly demonstrated potential for medical application, especially in the localization of foreign bodies and diagnosis of fractures. Plain radiographs are still regularly used in initial assessment of patients, especially after trauma and for the acute abdomen.

In order to obtain a plain radiograph, the area of interest is positioned between a beam of electromagnetic radiation and a radiosensitive detector. The radiation is produced by the interaction between high-energy electrons produced by a heated tungsten cathode with a tungsten anode. The energy of the photons in this radiation beam lies within the X-ray spectrum of energy. The patient's tissue interacts with the photons, either absorbing or scattering (deflecting) them. The degree and type of interaction depends on the thickness, density and atomic density of the matter as well as the energy of photons in the beam with the net effect of attenuating the beam, i.e. reducing beam intensity.