Panoramic Radiography Flashcards
What is the definition of “panorama”?
Complete survey of a subject.
What is the definition of radiography?
To obtain a picture by use of x-rays.
What is the definition of tomography?
A method of radiography displaying details of a selected plane (layer/slice) within the body.
What is an image layer/focal trough?
A layer in the patient that contains different structures of interest that are demonstrated with sufficient resolution to make them recognisable (both superficial and deeper) are not clearly seen.
How many rotation centres do we have in an image layer?
2.
How does the layer formation happen?
Movement of the xray source (and therefore xray beam, through the desired objects the teeth) and movement of of the xray image receptor through the xray beam at the correct speed so that desirable object will be recorded as clear images.
REMEMBER: the further from the rotation centre the faster the beam passage round the circumference.
.
What is the speed of the beam passage through anterior and posterior teeth?
- Faster beam through posterior teeth as they are further from their rotation centre. Image receptor also fast.
- Anterior teeth are closer to their rotation centre so there is a slower beam through the teeth and the image receptor becomes slower to match the distortion.
What does the focal trough depend on?
- width of xray beam
- distance to rotation centre
- closer to rotation centre (anterior)- narrower layer. Vice versa for posterior.
What is the bit on the xray machine that goes around the patients head?
Gantry.
Give a summary of panoramic image formation.
- Patient positioned with gantry containing xray source and image receptor, standing or seated. Remove all metal objects.
- Frankfort plane horizontal (lower border of orbit to upper border of external auditory meatus).
- Patient remians stationary.
- Vertical beam of xrays passes through patient from lingual to buccal.
- Xray beam angled up at 8 degrees (due to curve of monson).
- Image receptor rotates around front of patient and passes through xray beam.
- Speed of beam through teeth and image receptor through the beam must be synchronised to produce an accurate image (dependent on correct patient positioning and machine adjustments).
What is the curve of monson?
When the buccal cusps of molar teeth are slightly higher than the palatal cusps.
What are the limitations of a panoramic radiograph?
- Patients occlusion
- Long exposure time
- Big shoulders
- Horizontal distortion
- If you cant see it it does not mean its not there- width of later in focus
- Positioning difficulties (class 2 d1, class 3, children, obese etc).
- Movement (if patient stops biting on bite peg there may be a wavy lower border of mandible).
What happens if the patients canine behind canine guideline is closer to the xray source than the machine expects?
The speed of beam is slower through teeth as closer to the rotation centre. If not compensated- image receptor is too fast and image is magnified horizontally.
What happens if the patients canine infront of canine guideline is further from the xray source than the machine expects?
Speed of beam is faster through the teeth as furthur from rotation centre. If compromised, the image receptor is too slow and image of tooth reduced in width horizontally.
