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A radiologist is a physician specializing in diagnosis and treatment using medical imaging. The role includes choosing or advising on suitable imaging methods, interpreting measurements in anatomical and clinical context, and communicating their significance. Some radiologists also perform procedures under imaging guidance through interventional radiology.^[ref]

The distinction from image acquisition matters. A radiologic technologist often operates the acquisition equipment, while a radiologist interprets the resulting images and relates them to the question being investigated. The work is collaborative; neither the instrument's output nor a single visual feature automatically supplies a diagnosis.^[ref]

A scientific example is phase-encoded imaging of cerebrospinal fluid. D. R. Enzmann and collaborators used a sequence synchronized to the cardiac cycle to distinguish motion in different fluid spaces. Interpretation required more than recognizing their outlines: opposite flow directions and different timing provided information about fluid dynamics.^[ref]

This illustrates the role's technical content: understand which physical quantity an image encodes, separate acquisition artifacts from biological structure or motion, and state what the evidence supports. A bright pixel can have different meanings in different imaging sequences.

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.^[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.^[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.^[ref]

RadiologyInfo.org is an institutional author of patient-oriented explanations of medical imaging and the work of a radiologist. Its professional-role material distinguishes interpreting images, helping choose an appropriate imaging method and communicating the resulting findings.^[ref]

Its procedure pages give useful physical examples. The venous ultrasonography explanation connects sound-based imaging with examination of blood vessels and measurement of moving blood. The magnetic resonance cholangiopancreatography explanation describes a specialized magnetic resonance imaging method for the biliary and pancreatic systems.^[ref][ref]

These are educational explanations of what an examination measures and how it is performed. Such a procedure description supplies context for interpreting a technique; it is a different kind of evidence from a controlled experiment comparing diagnostic performance in a defined population.