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X-Rays
An X-ray (radiograph) is a painless medical test that helps physicians diagnose and treat medical conditions. Radiography involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of medical imaging.
X-rays are a form of electromagnetic radiation, just like visible light. In a health care setting, x-rays are emitted by a machine as individual "particles" (photons) that pass through the body and then get detected by a sensitive film.
Structures that are dense (such as bone) will block most of the photons, and will appear white on developed film. Structures containing air will be black on film, and muscle, fat, and fluid will appear as shades of gray. Metal and contrast media (intravenous or oral contrast) blocks almost all the photons and will appear bright white.
The basic science of x-ray generation and detection is the key behind general radiographs of the body, mammography, fluoroscopy (real-time imaging on video screens), and computed tomography (CT).
During a single radiograph, a small fraction of the x-rays pass right through the body. The remaining photons are absorbed by tissues in the body. The energy of the absorbed photons can break apart (ionize) compounds, and this may cause cell damage. Most cell damage is soon repaired. However, some is permanent.
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Related topics - MRI or Magnetic Resonance Imaging, CT, Nuclear Medicine
