Panoramic Imaging: Focal Trough, Positioning & Artifacts

How it works

The tube and receptor rotate around the patient's head in opposite directions, keeping one curved zone sharp: the focal trough (image layer). Objects outside it blur and change size.
Anterior focal trough is narrow, so incisors are most sensitive to positioning errors.
Horizontal magnification depends on the object's distance from the trough; vertical magnification is fairly constant, so horizontal measurements are unreliable.
Indications: third molars, developing dentition, trauma, large lesions, overall survey. Poor for small caries and fine periodontal detail.

Error	Image appearance
Head too far forward (anterior to trough)	Anterior teeth narrow and blurred; spine may overlap the ramus
Head too far back	Anterior teeth wide (magnified) and blurred
Chin tipped down	Exaggerated 'smile' curve of the occlusal plane; anterior roots blurred; condyles may be cut off the top
Chin tipped up	Flat or 'frowning' occlusal plane; hard palate superimposed over maxillary roots
Head rotated or tilted	One side's teeth wider than the other; unequal ramus widths
Tongue not against the palate	Dark (radiolucent) band over the maxillary root apices (palatoglossal air space)
Patient slumped	Pyramid-shaped radiopacity (cervical spine) over the anterior teeth
Lips open	Dark shadow over the incisor crowns

Image type	Object position	Appearance
Real image	In or near the focal trough	Sharp, one image on its own side
Double image	Behind the rotation center in the midline (hyoid, epiglottis, posterior hard palate)	Two images, one on each side
Ghost image	Between the x-ray source and the rotation center (earrings, opposite ramus, metal)	Opposite side, higher, larger and blurrier than the real object

Remove earrings, necklaces, glasses, hairpins, tongue piercings and removable appliances before exposure.

Measuring horizontal distances on a panoramic image.
Placing a ghost image on the same side and lower than the real object.
Mixing up forward (narrow anteriors) and backward (wide anteriors) positioning errors.
Using a panoramic image to diagnose early interproximal caries.

Pick an answer to see right away whether it is correct and why.

On a panoramic image, the incisors look narrow and blurred. The patient was positioned:
A dark band crosses the maxillary root apices. What went wrong?
A patient wearing a left earring has a panoramic image taken. The ghost appears:
Which structure normally produces a double image on a panoramic radiograph?
The occlusal plane looks like an exaggerated smile. The chin was:

0 of 5 answered

Answer key: 1 D · 2 D · 3 B · 4 A · 5 B