X-ray imaging uses ionising electromagnetic radiation to produce images of structures inside the body. X-rays pass through tissue and are absorbed to different degrees depending on density and atomic number, so bone appears white, soft tissue grey and air black on the resulting image. It remains the most widely performed form of medical imaging.
Plain radiography is the familiar single projection image, used for suspected fractures, chest pathology, bowel obstruction and dental assessment. Related modalities extend the same physics: computed tomography (CT) rotates the source and detectors to reconstruct cross-sectional images, fluoroscopy provides a live moving image for guided procedures, and mammography uses low energy X-rays optimised for breast tissue.
Plain radiography is fast, inexpensive, widely available and excellent for bone and for gross chest pathology. Its limitations are that it compresses three dimensions into two, giving limited soft tissue contrast, and that some significant injuries and early disease are simply not visible. Where soft tissue detail matters, ultrasound and MRI are usually preferred, neither of which uses ionising radiation.
Because ionising radiation carries a small stochastic risk of inducing cancer, every examination must be justified and optimised. In the UK this is governed by the Ionising Radiation (Medical Exposure) Regulations, which place duties on referrers, practitioners and operators. Justification means the examination must offer sufficient net benefit for that individual, and optimisation means the dose should be as low as reasonably practicable while still answering the clinical question. Pregnancy status is checked, and paediatric protocols use substantially reduced doses.
Modern departments are entirely digital, with images acquired on flat panel detectors, stored in a picture archiving and communication system (PACS), exchanged using the DICOM standard and reported on calibrated diagnostic displays. Artificial intelligence tools are increasingly used for triage, for flagging suspected findings and for reporting support. Any such tool intended to inform a diagnosis is regulated as a medical device and requires evidence of performance in the population where it will actually be deployed.
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