Which substance is a negative contrast medium?

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Multiple Choice

Which substance is a negative contrast medium?

Explanation:
Negative contrast media are radiolucent substances that appear darker on X-ray or CT because they have very low density compared with surrounding tissues. Air is the classic example: as a gas, it has extremely low attenuation, so it creates a dark background that helps outline hollow structures like the gastrointestinal tract or air-filled spaces. In contrast, substances such as barium, Omnipaque (iodinated contrast), and iodine-based agents increase attenuation and show up as bright areas on imaging, highlighting walls and luminal contours. Gas like CO2 or other air-based mixtures is also used as negative contrast in some studies, which is why air is the correct choice here.

Negative contrast media are radiolucent substances that appear darker on X-ray or CT because they have very low density compared with surrounding tissues. Air is the classic example: as a gas, it has extremely low attenuation, so it creates a dark background that helps outline hollow structures like the gastrointestinal tract or air-filled spaces. In contrast, substances such as barium, Omnipaque (iodinated contrast), and iodine-based agents increase attenuation and show up as bright areas on imaging, highlighting walls and luminal contours. Gas like CO2 or other air-based mixtures is also used as negative contrast in some studies, which is why air is the correct choice here.

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