panoramic radiography Flashcards
what are the principels of panoramic radiography?
A combination of tomography and scanography
how does vertical and horizontal magnification change ?
In terms of vertical magnification/distortion, the image behaves as if the x ray source was located at the rotation centre. The vertical magnification of a panoramic image is constant throughout the image, but horizontal magnification is dependent on the position of a structure in the “focal trough”.
what is the focal trough (or “image layer”)
A three-dimensional curved zone where the structures lying within this layer are reasonably well defined on the final image.
Is created primarily by the manner in which the x ray source and receptor move relative to one another and the patient, and the speed of this movement at given points during the movement.
The closer a structure is to the centre of the focal trough, the sharper and more dimensionally accurate it will be.
Structures outside the focal trough will be blurred, magnified, or reduced in size, and may be so distorted that they are unrecognizable!!!
what happens if there is improper positioning?
Correct positioning. Dental arches in centre of focal through. Vertical and horizontal magnification match - undistorted image.
In outer part of focal trough. Image horizontally narrowed and out of focus.
In inner part of focal trough. Image horizontally magnified and out of focus.
when obtaining a panoramic image, the goal is to position…
When obtaining a panoramic image, the goal is to position the patient’s dental or alveolar ridges as close as possible to the centre of the focal trough!!
why is the patients dental or alveolar ridges not always as close as possible to the centre of the focal trough?
- Operator error
- Patient’s anatomy does not closely “match” the focal trough
- Patient cannot be correctly positioned (physical limitations, physically or mentally challenged)
- Patient unwilling to co-operate
what are ghost images like
“Ghost” images are projected slightly superiorly, are reversed, and are magnified and out of focus compared to the real images. They are most noticeable when created by relatively radiopaque objects or structures that are far from the centre of the focal trough.
what are the evaluation criteria of panoramic radiographs?
- Teeth and alveolar bone accurately shown.
- “Smile line”.
- Minimal “ghosts”.
- No processing or handling artifacts.
- Areas of interest and normal anatomy well demonstrated.
what are 9 indications for panoramic radiographs?
- Trauma.
- Assessment of third molars.
- Presence of pathological lesions.
- Evaluation of dental development.
- Evaluation of growth and developmental
anomalies. - Pre- and post-surgical evaluation.
- Orthodontic treatment.
- Orofacial pain.
- Initial survey / “screening”.
what are 7 advantages of panoramic radiography?
- Broad scope of examination.
- LOW DOSE.
- Convenient.
- Time-saving (compared to CMS).
- Good for patients who cannot tolerate
intraoral radiographs. - Patient education / case presentation.
- Better contrast than on intraoral radiographs.
what are 9 disadvantages to panoramic radiography?
- Detail and resolution not as good.
- Distortion and magnification (~20-30%).
- Some tooth images may be overlapped.
- COST – higher than intraoral dental x ray
machine. - Items of interest may be out of “focal
trough”. - “Ghost” images may obscure information.
- Cannot shield the thyroid gland.
- Poor registration of inclined anterior teeth, or other malposed teeth.
- OVERUSE - ABUSE?
