Extra-Oral Views Flashcards by Fiona Rankin

What do maxillofacial views show?

-facial bones/skull from either a lateral or an AP or basal perspective (basal rarely indicated nowadays)

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What is collimation?

-control of the size and shape of the X-ray beam

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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

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What is an x-ray cassette?

A light-proof rigid holder that supports intensifying screen and film.

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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

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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)

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What is a grid in radiology?

-a grid that is compromised of thin lead strips which is placed adjacent to the cassette

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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)

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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

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What are commonly used anatomical planes/lines for extra-oral radiology?

-frankford plane
-orbitomeatal line (OM line)
-interpupillary line
-mid-sagittal plane

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What are the radiographic/bone landmarks for the frankford plane?

-orbitale (most inferior infraorbital rim) to porion (superior externa auditory meatus)

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How is the Frankford plane positioned for panoramic and cephalometric radiographs?

horizontally

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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

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The OM line differs from the Frankfort plane by about what?

10 degrees

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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)

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What guidelines are there to select the right investigation?

Royal Collage of Radiologists guidelines - Making the best use of clinical radiology - referral guidelines

Can access on NHS computers (iRefer)

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 are the indications for taking a lateral skull view?

-fractures of skull/skull base
-facial fractures to show vertical and AP displacement
-skull pathology (Pagets, myeloma)
-pituitary fossa enlargement, sphenoid sinus pathology

Lateral skull views are being increasingly replaced by what? Why?

By CT - these also detect intra-cranial abnormalities

What is the difference between an AP or PA view?

Refers to direction of beam and therefore position of tube and image receptor relative to the pt

PA (posteroanterior) - back to front so tube posterior and IR anterior

AP (anteroposterior) - front to back so tube anterior and IR posterior

Maxillofacial views are usually PA or AP?

Why are maxillofacial views normally PA?

-reduced magnification (get less magnification if object is closer to the film - so want tissues as close to the image receptor as possible)
-dose reduction

How is there dose reduction in maxillofacial PA radiographs vs AP?

In PA low energy photons entering the back of the head are attenuated before they reach radiosensitive tissues (e.g. lens)

-they are absorbed by back of head as its thick
Note: salivary glands are radiosensitive but not much we can do about this

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

What are the indications for occipitomental views?

-sinus disease (no longer) -middle 1/3rd facial fractures (zygoma, le fort) - can just use CT if already need CT tho -coronoid process fracture (now would use CT)

Why is occipitomental view no longer indicated for sinus disease?

-you can see sinuses very clearly but sinusitis can be diagnosed and treated clinically so no need for radiograph

What does a PA view of the mandible show?

-good view of posterior body, angle and ramus of mandible -superimposition of cervical spine obscures anterior mandible -superimposition of mastoid process and zygomatic arch obscure condyle Basically not good for anterior mandible or condyle

How is a PA of the mandible take?

What are the indications for PA mandible?

-fractures of angle, posterior body and ramus of mandible - medial and lateral displacement -cysts/tumours (same areas of mandible) - medial and lateral expansion/destruction (CBCT better) -Facial deformity (often take cephalostat

What does a submentovertex (SMV) view show?

-base of skull (including foramina) -sphenoid sinus -maxillary sinus -plane view of mandible including condyle -zygomatic arches

How is SMV view taken?

What are the indications for a submentovertex view?

-fracture of zygomatic arch (not anymore) -expansion of more posterior mandible -cranial base pathology (now replaced by CT)

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)

In what radiographic views can you see the floor and the roof of the maxillary sinus?

-panoramic -occipitomental -lateral -coronal CT/MRI -CBCT

In what radiographic views can you see the anterior wall of the max. sinus?

-lateral -axial CT/MRI -CBCT

In what radiographic views can you see the posterior wall of the maxillary sinus?

-panoramic -lateral -axial CT/MRI -CBCT

In what radiographic views can you see the medial and lateral walls of the maxillary sinus?

-occipitolmental -axial and coronal CT/MRI -CBT medial wall in panoramic you NEVER see the lateral wall in a panoramic radiograph