Panoramic Radiography Flashcards
Greater absorption =
No absorption eg air =
Greater absorption = radio plaque
No absorption eg air = radiolucent
How is an X-ray generated
X ray beam passes through the patient
Then hits the image receptor
Image is generated based on how much of the X-ray beam has passed through the patient and hit the image receptor
What is this radiograph and what is the difference between it and an intra oral
Panoramic radiograph
Sectional panoramic
Same situation as intra oral
Difference is covering wider area of anatomy
What is the difference between how much X-ray air and bone transmits?
Air transmits lots of X-rays bone transmits very little
Principle of panoramic radiography
Generation of panoramic relies on tomography
Image large area of pt but move image receptor and X-ray source relative to each other… therefore
Relative movement = in focus slice
Everything else that is still imaged is blurred out
Importance of this technique - area within gantry that is pre determined and will determine which parts of anatomy you will demonstrate on the radiographic image
Incorrectly positioned pt = in focus image of wrong area
So patient positioning is very important
Panoramic technique
The dynamic movement of the panoramic machine creates a curved in focus slice called the
Focal trough
How is the patient positioned in panoramic radiography?
The patient is positioned so that the anatomy of interest (their dentition) coincides with the focal trough
How is the image generate din panoramic radiography?
The image is generated as the tube head and image receptor moves around the patient
Difference between x ray beams in intra oral and panoramic radiography?
Intra oral - press button once and it sends a single beam of x rays through the patient and then you expose the image receptor
Panoramic - multiple exposures through the patient whilst the gantry (arm that holds the X-ray source and image receptor) is rotating 360 degree
This means x ray beams passes through cervical spine, cheeks etc - exposure varies (more through cheeks and less through spine)
When the image receptor is on the pt right you are taking an image of?
The RHS of the pt
You are still generating an image of the LHS of the jaw because the X-ray beam is still passing through that area but bc of tomography this is blurred out
What are ghost images?
Structures which are outside the focal trough are blurred and not seen clearly
However, they are still present in the image, and potentially visible as a ghost image
What is the discrepancy between level of X-ray source and image receptor
Discrepancy between level of X-ray source and image receptor - 8 degree upward inclination
(Imaging pt from slightly lower down than where youre generating the image)
What view do you have anteriorly?
Anterior posterior view
What view do you have posteriorly?
Lateral view
Is there a single point of rotation
No it moves during the exposure
How should the occlusal plane look in a radiograph
Gentle curvature of the occlusal plane in an upwards direction
What happens if the pt is too far back
What happens in off centre rotational error
One side in focus (less magnified) and one side out of focus and (more magnified)
In this image, the LHS is in the focal trough and the RHS is out of the focal trough
What happens if the pt has their chin down
- occlusal plane more accentuated (U shape curve)
- more chin shown
- out of focus lower incisors (they fall back and out of focal trough)
What happens if the pt has their chin up?
- inverted occlusal plane (n shape)
- out of focus incisors (they fall out of focal trough)
- mandibular anteriors (they fall further back so there’s a greater degree of magnification so they’re blurred and magnified)
The distance between the x ray beam and the image receptor is fixed
Where should you position the anatomy of the pt that you would like a radiograph of?
In the focal trough
If the patient is positioned too far away from the image receptor…
There is more magnification
If the patient is positioned too close to the image receptor…
There is less magnification
If the patient is positioned too far away from the image receptor, what does the radiograph look like?
Out of focus, magnified, blurred teeth and you don’t see the cervical spine at the periphery of the image
If the patient is positioned too close to the image receptor, what does the radiograph look like?
Teeth look small and out of focus + more cervical spine
Disadvantages of panoramic radiography
Only structures in the focal trough are in focus
Overlapping teeth in some areas - especially premolars (reduced sensitivity for inter-proximal bone loss / caries in those areas)
Technique sensitive - careful patient positioning required
Superimposition of soft tissue and air shadows can cause misinterpretation (pt needs to put tongue to roof of mouth) - air gap results in radiolucent line that crosses the ramus of the mandible - this can be hard to differentiate from a fracture in the context of trauma (shown in image)
Image is a distorted and magnified version of the object
Resolution of detail (eg. caries detection and imaging of fine periodontal tissues) not as good as intra-oral techniques
Long exposure - susceptible to movement
