Panoramic radiography Flashcards
What are the principles of panoramic radiography?
Uses tomography to display a cross section of the human body with x-rays
tube and image receptor both move to generate an in-focus slice of anatomy
Any structures outside of this slice are blurred
What is the focal trough?
curved in-focus slice
in the dynamic movement of the machine
anatomy of interest should coincide with the focal trough
What happens if patient is not positioned in the focal trough?
structures outside of the focal trough are blurred and not seen clearly
– they are still present in
the image and potentially visible as a ghost image
At what degree and incline is the image generated?
8 degree upward incline
What are ghost images generated by?
anything between the centre of rotation and the x-ray source during the rotation of the x-ray source and image receptor during image generation.
How do ghost images appear compared to the object that generated them?
- Larger (due to beam divergence)
- Higher (due to the upward angle of the beam)
- On the opposite side of the image
- Blurred (more vertically than horizontally)
How can we compare the ghost image and real image?
ghost
- out of focus
- higher
- bigger
- produced when the object to image receptor distance is long
real
- in focus
- produced when the object to image receptor distance is short
What objects can produce ghost images?
- Earrings
- Tongue studs
- Anything else which is situated between the x-ray source and centre of rotation
How can the normal anatomy be a ghost image?
imaged twice
- on the second image when receptor is on opposite side of the patient
eg opposite angle of mandible
What are some common positioning errors?
Chin down
Chin up
Too far forward
Too far back
Off-centre (rotational)
What happens when the patient’s chin is down?
The lower incisors are out of focus
There is a distorted occlusal plane (looks like a smiley face)
What happens when the patient’s chin is up?
The upper incisors are out of focus
There is a distorted occlusal plane (looks like a grumpy face)
What happens when the patient is too far forward?
The subject is too close to the image receptor
Appears narrow, out of focus anterior teeth
Shows excessive cervical spine
What happens when the patient is too far back?
The subject is too far away from the image receptor
They are magnified, the anterior teeth are out of focus
What happens when the patient is off-centre (rotational)?
when one side is too far back, and the other is too far forward
image is rotated to one side
molars on that side are closer to image receptor and smaller
molars on other side are further from image receptor and magnified
What are the advantages of panoramic radiography?
Shows the entire dentition in one image
Time efficient
Radiation dose may be lower than full mouth series of periapical
Well-tolerated by patients
Can be used even when the patient can’t fully open mouth or has pronounced gag reflex
What are the disadvantages of panoramic radiography?
Only structures in the focal trough are in focus
Overlapping teeth in some areas (reduced sensitivity to detect caries)
Technique sensitive (careful positioning required)
Superimposition of soft tissue and air shadows can cause misinterpretation
Image is a distorted and magnified version of an object
The resolution of detail is not as good as intraoral techniques (eg caries detection and imaging of fine periodontal tissues)
There is long exposure so patient may be susceptible to movement
What are the indications of panoramic radiographs?
bony lesions
grossly neglected dentition prior
assessment of wisdom teeth to planned surgical intervention
orthodontic assessment
In hospital for assessment of mandibular fractures
Assessment of periodontal support
