Extra-Oral Views; Other Plain Views Flashcards
what 3 maxillofacial views show the facial bones / skull
lateral
anterior / posterior
basal perspective
in terms of the equipment needed; when setting up the patient are they closer to the image receptor or closer to the tube head
closer to the image receptor
what is collimation
Collimation is the control of the size and shape of the x-ray beam
Smallest field of view consistent with the diagnostic requirements
Ie for periapicals we use rectangular collimation
where on the equipment does collimation occur
at the tube head
what ensures correct collimation
To ensure correct collimation, light beam shows area on patient which will be exposed to the primary beam
what dimensions is the cassette
○ Film:
§ 18 x 24 cm
§ Or 24 x 30 cm
○ Intensifying screen:
Minimum speed 400
what is the grid
○ Comprising thin lead strips adjacent to cassette which attenuate obliquely travelling photons before they reach the film
○ But for same number of photons to reach film the dose must be increased otherwise insufficient blackening
○ A grid is put in between the x-ray source and the IR to try and cut out x-rays which are not approaching the IR pretty much straight on
§ Photons which are not approaching it straight on will be going through obliquely and will be picking up information about structures but not superimposing them in the anatomically most correct place
do you always need to use a grid
○ Don’t always need to use a grid
Eg where you don’t need great details like in large things like pathological lesions where there could be a little overlay of other structures it wouldn’t stop us using / diagnosing from the image
what are commonly used planes / lines for extra-oral views
○ Frankfort plane
○ Orbitomeatal line (OM line)
§ Probably the most important one
○ Interpupillary line
Mid-sagittal plane
remember to use visible anatomical landmarks
what is the frankfort plane
- Connect orbitale (most inferior infraorbital rim) with porion (superior external auditory meatus)
- Skeletal - select overlying soft tissues
○ Must have hair behind ears to actually be able to see the ears
If you cannot see where the features are then you need to feel for the features on the patient eg if patient has fleshy cheeks
- Skeletal - select overlying soft tissues
how should the frankfort plane be positioned for panoramic and cephalometric radiographs
Position horizontally for panoramic and cephalometric radiographs
what is the orbitomeatal line
- Links central part of external auditory meatus with outer canthus of eye
○ Soft tissue feature line
Outer canthus = where upper and lower eyelids come together
how does the ortbitomeatal line differ from the frankfort plane
- Differs from frankfort plane by about 10˚
○ Lines are closer together posteriorly, but further apart anteriorly
Doesn’t sound like a big difference but it does make a difference to the positioning of the paitent
which line is more easier visualised; frankfort plane or orbitomeatal line
Orbitomeatal Line
what does the lateral skull extra-oral view show
- Similar to lateral ceph.
○ When lateral ceph is taken it is taken with the head in a standardised position to best produce an image which is reproducible within one patient but also comparable between different patients
○ This radiograph is more free positioning
§ Eg it is the radiographer positioning the patient using planes and lines and doesn’t include images of soft tissues - Shows lateral view of whole skull and facial bones & upper cervical spine
○ Does not show all of the facial bone
No cephalostat or wedge for soft tissue profile
what are the indications for lateral skull radiographs
- Fractures of skull / skull base
○ Historically - But might still be a first line investigation in a situation where a CT is not available or whether this radiograph would be manageable and a CT would not be manageable
§ Can help move forward along the diagnostic pathway - Facial fractures to show vertical and anteroposterior displacement
○ Although both sides are superimposed on each other - not widely used
○ Can be used when there are severe middle third fractures where the facial bones are being fractured off from the cranium but patients with this level of trauma are likely to have cranial / head trauma as well so they are probably more likely to have CT - Skull pathology
○ Eg Pagets, myeloma - Pituitary fossa enlargement
○ Similar to situations above - CT probably used instead - Sphenoid sinus pathology
what is Pagets
Bone turnover disorder (opaque patches on the above rdaiograph are probably due to pagets)
what are lateral skull radiographs being replaced by
Increasingly replaced by CT
As it also detects intra-cranial abnormalities
what is the difference between anterior-posterior or posterior-anterior
- Refers to direction of beam and therefore position of tube and image receptor (IR) relative to patient
- PA:
○ Posteroanterior
○ Tube posterior and IR anterior - AP:
○ Anteroposterior
○ Tube anterior and IR posterior
Maxillofacial views are usually PA
why are maxillofacial views usually PA
- Reduced magnification
○ Objects closer to film are magnified less than more distant objects
○ As a general rule the objects we want to see we want as close as possible to the IR for all radiography so they are magnified less than more distanced objects - Dose reduction
○ Low energy photos entering back of head are attenuated before they reach radiosensitive tissues eg lens
○ Some of the low energy photons are going to be absorbed by the posterior portions of the head because it is quite dense bone to get through so inevitably some of the photons that are going to be absorbed but not contribute to the useful image will be absorbed before they reach the lens of eye which is probably the most radio sensitive tissue we have to think about in this situation
are salivary glands radiosensitive? how do they affect maxillofacial views
Salivary glands are also radiosensitive but there isn’t a lot we can do about them as they are inevitably going to be in the field of view if we are looking at the maxillo-facial structures
where does the x-ray beam go in an occipitomental radiograph
X-ray beam goes in through the occipital region of the head and it comes out through the mental region of the chin
The name gives us the direction and the entry and exit points
Probably most complicated ones because it has variations
what does the occipitomental radiograph show
- Orbit
- Frontal sinus
○ Almost always asymmetrical
○ Unique to each person - Maxillary sinus
- Zygoma, zygomatic arch
- Nasal septum
- Coronoid process
- Odontoid peg / dens of C2
Useful for middle third of the facial skeleton but not the mandible except for the coronoid process
- Frontal sinus
how is the occipitomental radiograph taken
- Orbitomeatal line at 45˚ to image receptor (IR)
○ nose-chin position = good starting point to get the patient to put themselves into
○ Patient facing the IR - Mid-sagittal plane perpendicular to IR
- Interpupillary line parallel to the floor
- X-ray beam perpendicular to IR centred in midline
○ check there is no rotation - level with region of interest
Depends exactly on what you want to look at
what alterations can be made to standard 0˚ occipitomental projections
- Changing angulation of x-ray beam alters projection of bones onto radiograph
○ Ie changes the angulation of the beam to the IR
○ Reason for doing this because it changes the way the facial skeleton in the middle third appears - Gives better views of some areas
○ Eg zygomatic arch - Gives different views of displacement
○ Eg displacement at infraorbital rim in zygomatic complex fractures
what are the indicaitons for occipitomental radiographs
- Sinus disease - No longer indicated
○ Maxillary, Frontal And ethmoid sinuses
○ Used to be a very common view to take of a patient who presented with symptoms of sinusitis and you would see changes but often you could also see these changes in patients who do not have symptoms
○ CBCT in maxilla picks up changes in the sinus lining frequently - Middle 1/3 facial fractures*
○ Zygoma
○ Le fort
§ Fractures going across from right to left which happen at 3 levels
§ 3 different levels where part of the facial skeleton is fracturing off from the remainder of the skeletal structure - Coronoid process fracture*
Very rare fracture
what does a PA 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
how is PA mandible taken
- Orbitomeatal line perpendicular to image receptor (IR)
○ Forehead-nose position
§ Patient tucks their chin in a bit and places forehead against IR- Mid-sagittal plane perpendicular to floor
- IR and inter-pupillary line parallel to floor
X-ray beam perpendicular to IR centred between angles of mandible
what are the indications for a PA mandible
- Fractures of angle, posterior body and ramus of mandible
○ Medial and lateral displacement
○ Still widely used for fractures at the angle of the mandible - Cysts / tumours in the same areas of the mandible
○ Medial and lateral expansion / destruction
○ Now a days would use CBCT - gives more detailed information - Facial deformity
○ Often then taken in a cephalostat instead especially if you were planning on doing surgery for the deformity
what radiographic view is a PA mandible often used alongside
Often used alongside the OPT to give a second view because together you can work out the displacement of the fracture line
what makes the angle of the mandible more prone to fracture
an unerupted 3rd molar which makes that a weaker position ie a direct blow to this area and it is more likely to fracture than in other patients
what way does the x-ray beam travel in Submentovertex (SMV) radiograph
- Submento = under the chin
- Vertex = top of the head
- X-ray beam goes through the patient from under the chin to top of the head
Can be tricky with the chest underneath the head because this is where you want the tube head to be
what does the submentovertex radiograph show
- Base of skull
○ Including foramina - Sphenoid sinus
- Maxillary sinus
- Plan view of mandible including condyles
- Zygomatic arches*
○ Arches are so thin that when there is sufficient radiation to show the other bony features they don’t show up However it is possible to make them show
how is the SMV taken
- Ensure no history of neck injury / disease
*
Extend head and neck as far as possible - Rest crown of head on IR - Orbitomeatal line parallel to image receptor (IR)
- Mid-sagittal plane perpendicular to IR and floor
- Vertex of head contacts IR
Beam centred between angles of mandible
what are the indications for SMV
- Fracture of zygomatic arch
- Expansion of more posterior mandible
○ Anteriorly, true occlusal - Cranial base pathology
Now replaced by CT
how do you get the zygomatic arch to show on the SMV
- Arch very thin therefore normal beam too penetrating
○ Energy and quantity need to be reduced - Exposure factures (kV and time) reduced c.f. those to show skull
- Skull therefore underexposed appearing white
○ Cannot get the 2 things together, would need a separate exposure
What radiographic views are used to see the floor of the maxillary sinus
Panoramic
Occipitomental
Lateral
Coronal CT / MRI
CBCT
What radiographic views are used to see the roof of the maxillary sinus
Panoramic
Occipitomental
Coronal CT / MRI
CBCT
What radiographic views are used to see the anterior wall of the maxillary sinus
Lateral
Axial CT / MRI
CBCT
What radiographic views are used to see the posterior wall of the maxillary sinus
Panoramic
Lateral
Axial CT / MRI
CBCT
What radiographic views are used to see the medial wall of the maxillary sinus
Panoramic
Occipitomental
Axial + coronal CT / MRI*
CBCT
What radiographic views are used to see the lateral wall of the maxillary sinus
Occipitomental
Axial + coronal CT / MRI*
CBCT
