Production and use of X-rays — common mistakes

Remember that a higher accelerating voltage gives harder (more penetrating) X-rays and also increases intensity. A higher filament current only increases intensity (more photons), not the maximum energy of individual photons.

X-rays are absorbed differently by various tissues, a property called differential attenuation. Denser materials with higher atomic numbers, like bone, have a high linear attenuation coefficient (μ) and absorb many X-rays, appearing white on an image. Less dense tissues like muscle or fat have a lower μ and absorb fewer X-rays, appearing in shades of grey. This contrast allows for the visualisation of internal structures.

Key safety considerations involve minimising patient dose according to the ALARA (As Low As Reasonably Achievable) principle. This is done by using an aluminium filter to remove low-energy X-rays, using the shortest possible exposure time, and collimating the beam to the area of interest. Healthcare professionals use lead shielding (aprons, screens) and maintain distance from the source to protect themselves from ionising radiation.

'Hard' X-rays have high photon energies, short wavelengths, and high penetrating power. They are produced using a high accelerating voltage. 'Soft' X-rays have low photon energies, longer wavelengths, and are less penetrating. While useful for imaging thin or low-density materials, in medical imaging they are often filtered out as they contribute to patient skin dose without reaching the detector.

A conventional X-ray is a single 2D projection, like a shadow, where all structures are superimposed. A CT scan uses a rotating X-ray source and detector array to take hundreds of 'slice' images from different angles. A computer then reconstructs these slices into a detailed 3D image, eliminating overlap and providing far superior contrast and detail for both soft tissues and bone.