Extra-oral views + other plain views Flashcards
What do maxillofacial views show
facial bones/skull from either a lateral or an anterior/posterior or a basal perspective (basal is rarely indicated nowadays)
What equipment is there
x-ray tubehead
casette with film or digital direct/indirect
grid
special collimator
What were cassettes and film previously used with
intensifying screens that have a phosphor layer in them that give out light when x-rays interact with them with a minimum speed of 400
What is the grid
The grid is put between the x-ray source and the image receptor to try and cut out x-rays that aren’t approaching the image receptor straight on and instead are approaching obliquely
What is the grid made of
thin lead straps adjacent to the cassette
What is the function of the grid
o Will reject scattered radiation and transmit a majority of primary radiation and therefore will enhance image quality
What does collimation do
control of the size and shape of the X-ray beam
Where does collimation occur
at the tubehead
What is the frankfurt plane
Connects orbitale (inferior infraorbital rim) with porion (superior border of the external auditory meatus)
Parallel to floor in OPT & cephalometric radiographs
What is alatragus line
Tragus of the ear to the alar of the nose
Used for upper oblique occlusal
What is the orbitomeatal line
Links central part of external auditory meatus with outer canthus of the eye (where the eyelids come together)
By how many degrees does the orbitomeatal line differ from the frankfurt
10 degrees
What are teh commonly used radiographic/anatomical planes
- frankfort plane
- alatragus line
- orbitomeatal line
- interpupillary
- midsaggital
What does PA or PA refer to
direction of the beam and therefore position of the tube and IR relative to the patient
What does PA mean
posteroanterior
tube is posterior and the image receptor is anterior
What does AP mean
tube is anterior and image receptor is posterior
Are maxillofacial views commonly PA or AP
PA
Why are views usually PA
Dose reduction
How does PA result in dose reduction
as lower energy photons entering the back of the head are attenuated by the dense bone before they reach radiosensitive tissues such as the lens (salivary glands are also radiosensitive but not much can be done due to their presence in the field of view)
How does PA result in reduced magnification
Reduced magnification as the objects closer to the film are magnified less than more distant objects
What is a lateral skull view similar to
lateral ceph
What makes a lateral ceph different from a lateral skull
lateral ceph has a head in a standard position to make it reproducible and comparable
What does a lateral view show
a lateral view of the whole skull as well as facial bones and upper cervical spine
How is the px positioned for lateral skull
No cephalostat or wedge for soft tissue profile so free positioning, looking at the planes and lines
No image of the soft tissues
What are the indications for lateral skull
o Fractures of skull/skull base
o Facial fractures to show vertical and antero-posterior displacement (although both sides are superimposed on each other)
o Skull pathology e.g pagets/myeloma
o Pituitary fossa enlargement
o Sphenoid sinus
What are the indications for lateral skull
o Fractures of skull/skull base
o Facial fractures to show vertical and antero-posterior displacement (although both sides are superimposed on each other)
o Skull pathology e.g pagets/myeloma
o Pituitary fossa enlargement
o Sphenoid sinus
Generally superceded by CBCT
What is a occipitomental view
- Beam goes in through occipital region of head and comes through the mental region of the chin
What does the occipitomental view show
o Orbit
o Frontal sinus
o Zygoma, zygomatic arch
o Nasal septum
o Coronoid process
o Odontoid peg/dens of C2
How is a occipitomental view taken
o Orbitomeatal line is at 45 degrees to the image receptor (nose chin position)
o Mid saggital plane perpendicular to the image receptor
o Interpupillary line parallel to the floor
o X-ray beam perpendicular to the image receptor centred in the midline, level with the region of interest
What does changing the angulation of the x-ray beam alter on occiptomental views
alters the projection of bones onto the radiograph and can give a better view of some areas as it changes the middle third of the facial skeleton on the x-ray e.g may be done to view the zygomatic arch & can also give a different view of displacement if required
What are the indications for an occiptomental view
o Sinus disease – however it is no longer indicated, CT or CBCT or MRI can be used instead
o Middle 1/3 fractures (zygoma or le fort (le fort go right to left) –> CT or CBCT more likely to be done over this
o Coronoid process fracture (very rare fracture)
What does a PA mandible show
o Good view of posterior body, angle and ramus of mandible
o Superimposition of cervical spine obscures anterior mandible
o Superimposition of mastoid process and zygomatic arch obscure condyle (CBCT better for condyle)
How is a PA mandible taken
o Orbitomeatal line perpendicular to image receptor (forehead-nose position)
o Mid-saggital plane perpendicular to floor and IR, interpupillary line parallel to floor
o X-ray beam perpendicular to IR centred between angles of mandible
What are the indications for a PA mandible
o Fracture of angle, posterior body and ramus of mandible and lateral displacement (still widely used), may be used with OPG to look for displacement of fracture line
o Cysts/tumours (same areas of mandible) – medial and lateral expansion/destruction
Superseded by CBCT
o Facial deformity (often then taken in a cephalostat when considering surgery)
What is a submentovortex view
- Enters from underneath the chin and comes out at the top of the head
What does a submentovortex view show
o Base of the skull (including foramina)
o Sphenoid sinus
o Maxillary sinus
o Plain view of mandible including condyle
o Zygomatic arches won’t always show as so thin and therefore normal beam is too penetrating so the energy and quantity need to be reduced. Skull is therefore underexposed and so shows up as white
What are the indications for a submentovertex view
o Fracture of zygomatic arch
o Expansion of more posterior mandible (if pathology is in the anterior jaw then better seen with a true occlusal)
o Cranial base pathology (now replaced by CT)
How is a submentovertex view taken
o Ensure no history of neck injury/disease
o Extend head and neck as far as possible
o Orbitomeatal line parallel to image receptor (IR)
o Mid-saggital plane perpendicular to IR and floor
o Vertex of head contacts IR
o Beam centred between angles of mandible
Which view shows the anterior wall of the maxillary sinus
o Lateral
o Axial CT/MRI
o CBCT
Which views show the posterior wall of the maxillary sinus
o Panoramic
o Lateral
o Axial CT/MRI
o CBCT
Which views show the medial wall of the maxillary sinus
o Panoramic
o Occipitomental
o Axial + coronal CT/MRI
o CBCT
Which views show the lateral wall of the maxillary sinus
o Occipitomental
o Axial + coronal CT/MRI
o CBCT
