Fiduciary marker

A fiduciary marker or fiducial is an object used in the field of view of an imaging system which appears in the image produced.

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Markers may be used to make otherwise invisible or difficult to distinguish features of an image more visible. Markers can simplify computerized image processing applications such as motion capture, by providing an easy-to-track feature in images which follows the movements of the marked subject.

The appearance of markers in images may act as a reference for image scaling, or may allow the image and physical object, or multiple independent images, to be correlated. By placing fiduciary markers at known locations in a subject, the relative scale in the produced image may be determined by comparison of the locations of the markers in the image and subject.

Images of the same subject produced with two different imaging systems might be correlated by placing a fiduciary marker in the area imaged by both systems. In this case, a marker which is visible in the images produced by both imaging modalities must be used. By this method, functional information from SPECT or positron emission tomography might be related to anatomical information provided by magnetic resonance imaging.