Ghost image (orthopantomogram)
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A ghost image is a commonly observed artifact in an orthopantomogram whereby a dense, often metallic object is located between the source of x-ray and the focal center, resulting in a duplicate 'ghost' image at the contralateral aspect of the image.
Real image vs ghost image
In panoramic image such as the orthopantomogram, structures within the focal trough (a panoramic arch similar to that of the teeth) will be sharp, well defined and overall lacking in distortion. Objects outside of this focal trough that are dense enough to attenuate x-rays will occasionally present twice as the x-ray tube rotates around the patient, this is known as a ghost image. The density will appear at the true location and secondly on the contralateral aspect of the image as a distorted 'ghost' image. The ghost image is distorted and larger than the actual object projected and often not at the same height 1.
When positioning for an orthopantomogram take into account any metallic objects on the patient's face and head can impact the image. This includes earrings, cheek piercings and hair clips.