Plain X-ray (XR) imaging


A stream of high energy electrons produced by an electron gun accelerate from a cathode filament and strike a rotating tungsten anode. X-ray photons are generated within the anode which rotates to dissipate heat. The beam of X-ray photons is shielded and coned to reduce the scatter of X-rays produced

1.2 Characteristic radiation generation

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High energy electrons collide with and eject an inner shell tungsten electron (green) with subsequent promotion of an outer shell electron (red) to take its place. X-ray photons of a uniform ‘characteristic’ energy are generated

1.3 Bremsstrahlung radiation

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A high energy electron that passes near a tungsten nucleus is deflected and decelerated with generation of an X-ray photon. X-ray photons of variable energy are generated in this way and therefore a non-uniform energy spectrum is produced. This is known as Bremsstrahlung ‘Braking’ radiation

1.4 The X-ray spectrum

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Bremsstrahlung radiation produces a wide spectrum of X-ray energies within the X-ray beam. Characteristic radiation generation however produces a relatively narrow band of X-ray energy. Imaging techniques optimise this characteristic band of X-rays in producing a radiograph

1.5 Image generation

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A chest X-ray (CXR) is usually taken with the beam passing from posterior to anterior (PA). The X-ray beam is divergent and so the resultant image is magnified. The closer the patient is to the detector the less magnification is produced. X-rays which hit the detector uninterrupted appear black on the image. Those X-rays that pass into thick structures (e.g. heart) or dense structures (e.g. bones) are attenuated and appear white. Other structures such as the lungs and soft tissues appear as a range of grey, according to their density


Plain XR physics


On 8 November 1895, the German physicist Wilhelm Conrad Röentgen discovered the X-ray, a form of electromagnetic radiation which travels in straight lines at approximately the speed of light. X-rays therefore share the same properties as other forms of electromagnetic radiation and demonstrate characteristics of both waves and particles. X-rays are produced by interactions between accelerated electrons and atoms. When an accelerated electron collides with an atom two outcomes are possible:


Mar 7, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Plain X-ray (XR) imaging

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