Extra-Oral Views Flashcards
What do maxillofacial views show?
-facial bones/skull from either a lateral or an AP or basal perspective (basal rarely indicated nowadays)
What is collimation?
-control of the size and shape of the X-ray beam
How is the correct collimation determined for extra-oral views?
Light beam shows area on pt which will be exposed to the primary beam and X shows where central beam will be
What is an x-ray cassette?
A light-proof rigid holder that supports intensifying screen and film.
What are the sections/structure of an x-ray cassette (with everything in it)?
-front
-intensifying screen (phosphor)
-radiographic film
-intensifying screen (phosphor)
-lead foil
-cassette back
How does an intensifying screen work/what is its benefit?
-intensifying screen close to the film
-made of phosphor which turns the x-rays into photons
-this light will activate the film
The benefit is that you need a lower dose of radiation to activate the film (it basically reinforces the action of the x-rays by subjecting the emulsion on the film to the effect of light as well as ionising radiation)
What is a grid in radiology?
-a grid that is compromised of thin lead strips which is placed adjacent to the cassette
What is the purpose of a grid in radiology/how does it work?
The purpose is to improve the image quality (get images as clear as possible)
The lead strips attenuate obliquely travelling photons before they reach the film (it cuts out any x-rays that have scattered/aren’t approaching straight-on)
What is the disadvantage of using a grid in radiology?
-they are vgood at absorbing x-rays/photons so for enough photons to reach the film, the radiation dose must be increased
Otherwise, you get insufficient blackening of the film
What are commonly used anatomical planes/lines for extra-oral radiology?
-frankford plane
-orbitomeatal line (OM line)
-interpupillary line
-mid-sagittal plane
What are the radiographic/bone landmarks for the frankford plane?
-orbitale (most inferior infraorbital rim) to porion (superior externa auditory meatus)
How is the Frankford plane positioned for panoramic and cephalometric radiographs?
horizontally
What is the orbitomeatal line?
-soft tissue feature line
-central part of external auditory meatus with outer canthus of eye (where upper and lower eyelids meet)
Note: black line in pic
The OM line differs from the Frankfort plane by about what?
10 degrees
The OM line is used as a what?
Radiographic baseline
(there are radiographic baselines all over the body - just features which help us get the pt into the right position)
What does a lateral skull view show?
-similar to a lat ceph
-shows lateral view of whole skull as well as facial bones and upper cervical spine (doesn’t include all the facial bones)
What does an occipitomental view show?
-orbit
-frontal sinus
-maxillary sinus
-zygoma, zygomatic arch
-nasal septum
-coronoid process
-odontoid pegs/dens of C2
How is occipitomental view taken?
-OM line at 45 degrees to IR (nose-chin position)
-mid sagittal plane perpendicular to IR, interpupillary line parallel to floor
-X-ray beam perpendicular to IR centered in midline, level with region of interest
-beam goes thru occipital region of head and comes out at mental region
Why might you alter the standard positioning for an occipitomental radiographic view?
-it alters the projection of bones onto radiograph
-gives better view of some areas e.g. zygomatic arch
-gives diff view of displacement e.g. displacement at infraorbital rim in zygomatic complex fractures
How is a PA of the mandible take?
How is SMV view taken?
How do you adapt AMV view to show the zygomatic arch?
-need to change exposure factors but lose the pic of everything else as the skull is then underexposed (and is white)
