= Radiology
\b[Radiology] is the medical specialty that uses imaging to investigate disease and guide treatment. It encompasses interpretation of acquired images and procedures in which imaging guides an intervention. Its tools include <radiography>, <computed tomography>, <magnetic resonance imaging> and <ultrasound>; the specialty is not limited to techniques using ionizing radiation.<What does a radiologist do? by RadiologyInfo.org>[Professional description of imaging methods and diagnostic/interventional roles.]{ref}
The physical motivation is illustrated by <Wilhelm Conrad Röntgen>'s experiments. An energized discharge tube enclosed in light-blocking paper caused a nearby fluorescent screen to glow. Materials between the tube and screen transmitted the new radiation differently; a hand showed darker bone shadows against fainter surrounding tissue. Photographic recording turned such transmission differences into persistent images.<On a New Kind of Rays by Wilhelm Conrad Röntgen>[1895 communication, English translation 1896; sections 1–2 and 14: screen, intervening objects and photographic shadow images.]{ref}
An invented measurement example makes the contrast explicit: if identical incident signals of 1,000 counts give 500 and 100 transmitted counts along two paths, their transmissions are 50% and 10%. The measurement distinguishes paths, but does not by itself name a disease. Anatomy, projection geometry, technique and other evidence are needed for interpretation.
A <radiologist> connects such physical measurements to clinical questions. <Interventional radiology> additionally uses images to guide instruments or treatment. Image acquisition, interpretation and intervention are related activities, but each requires its own evidence and expertise.<What does a radiologist do? by RadiologyInfo.org>[Physician interpretation and image-guided therapeutic procedures.]{ref}
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