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
Is there a greater degree of vertical or horizontal magnification?
Vertical slit is the only part of the x ray beam that passes through the patient that results in image formation
There is a greater degree of vertical magnification in the image than horizontal magnification
Difference between the real image and ghost image and how are they produced?
Real image is in focus and is produced when the object to image receptor distance is short, the ghost image is out of focus, higher, bigger and is produced when the image receptor distance is long
Long distance = ghost image
Short distance = real image
What else produces ghost images
Normal anatomy
How do positioning errors occur
Any time the pt position within the focal trough does not match with the pre determined position of the focal trough in the machine
This results in areas of anatomy that should be outside of the focal trough within the focal trough being imaged clearly and areas of anatomy that should be in the focal trough falling outside resulting in them being blurred
How should the occlusal plane look in a radiograph
Gentle curvature of the occlusal plane in an upwards direction
What are the different positioning errors
- pt too far forwards = too close to image receptor = narrow, out of focus anterior teeth, excessive cervical spine
- pt too far back = toot far away from image receptor, magnified, out of focus anterior teeth
- rotational = one side too back, one side too forward
- off centre (rotational) = if rotated to the left, left molars closer to image receptor and smaller, right molars further away from image receptor and magnified
- chin down
- chin up
What happens if the pt is too far back
How does rotational error occur
One side too far back
One side too far forward
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
Advantages of panoramic radiograph
Shows the entire dentition on one image
Therefore, Time efficient
Radiation dose may be lower than full mouth series of periapicals
Well tolerated by patients
Can be used even when pt cant fully open mouth or has pronounced gag reflex (no intra oral req)
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
Indications of a panoramic radiograph
Assessment of periodontal support - you need to see the entire dentition to quantify the type and extent of periodontal disease
Bony lesion not completely demonstrated on intra-orals
Grossly neglected dentition prior to GA
For the assessment of wisdom teeth prior to planned surgical intervention
As part of an orthodontic assessment
In hospital - for assessment of mandibular fractures
