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in magnetic resonance imaging, a region emitting no radiofrequency signal, because there are no activated protons in the region (such as flowing blood), because a different element predominates, particularly calcium, or because of uncompensated dephasing, such as occurs at air-tissue interfaces in the lung.
Farlex Partner Medical Dictionary © Farlex 2012
A dark or blank space in a radiographic image of a fluid-filled structure. See: filling defect
See also: signal
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