Extra-Oral and Other Plain Views Flashcards
What equipment is required to take an EO radiograph?
X-ray tubehead
Cassette - film or digital
What is collimation?
Collimation is the control of the size and shape of the X-Ray beam
-> should be as small as possible in line with diagnostic requirement
How is collimation checked?
Light beam shows area on patient which will be exposed to primary beam
-> middle of cross is central beam
What are the cassette sizes?
18 x 24
24 x 30
What is the minimum speed of the intensifying screen in EO radiography?
400
What is the function of the grid?
Thin lead strips adjacent to cassette prevent oblique rays disrupting the image
Attenuates a lot of photons- film dose is increased to allow enough blackening
Which lines are commonly used in EO radiography?
Frankfort plane- OPTs/cephs
Orbitomeatal line (OM line)
Interpupillary line
Mid-sagittal plane- down middle of head
Where is the OM line located?
centre of EAM to outer canthus of the eye (where upper and lower eyelids come together)
Known as radiographic baseline
-> 10 degrees difference from FP
Where is the Frankfort plane located?
Connects orbitale (most inferior infraorbital rim) with porion (superior external auditory meatus)
What are the features of a lateral skull radiograph?
Does not include all of the facial bones
Different from lateral ceph as there is no cephalostat (free positioning)
Doesn’t include soft tissues
What are the uses of a Lateral Skull radiograph?
Fractures of skull/skull base
Facial fractures to show vertical and anteroposterior displacement (although both sides are superimposed on each other – not widely used)
Skull pathology (e.g. Pagets, myeloma)
Pituitary fossa enlargement
Sphenoid sinus pathology
If CT not available or managable
What is the difference between AP/PA?
PA- tube posterior to head and image receptor anterior (AP is opposite)
-> most commonly used for maxillofacial views
Why is PA preferred?
Reduced magnification
Dose Reduction- low energy photons entering back of head are attenuated before they reach radiosensitive tissues (e.g. lens, salivary glands)
Where does the beam pass through in the occiptomental view?
Beam goes in through occipital region of head then mental region (point of the chin)
What is shown in the occiptomental view?
Orbit
Frontal sinus
Maxillary sinus
Zygoma, zygomatic arch
Nasal septum
Coronoid process
Odontoid peg/dens of C2
How is an occiptomental radiograph taken?
OM line at 45 degrees to image receptor
Mid-sagittal plane perpendicular to IR
Interpupillary line parallel to floor
X-Ray beam perpendicular to IR centred in midline, level with region of interest
What does varying the beam angulation (vertical angle) in occiptomental radiographs achieve?
Changes way facial skeleton looks in middle third (can make fractures more obvious)- multiple views are required for diagnosis
How do steeper OMV views make the mandible look?
Mandible becomes more curved
What are the indications for Occipitomental radiographs?
Sinus disease - no longer indicated (CT/CBCT)
Maxillary, frontal and ethmoid sinuses
Middle 1/3 facial fractures- zygoma/Le Fort
Coronoid process fracture
In what instance would CT be better option for middle face fractures?
If there is a suspected brain injury
What are le fort fractures?
Go across right to left (3 levels- separation of midface from the skull base)
What does a posterior mandible radiograph show?
Good view- 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 a posterior mandible radiograph taken?
Forehead and nose touch image receptor (OM line is parallel)
Mid-sagittal plane perpendicular to floor and IR, interpupillary line parallel to floor
X-Ray beam perpendicular to IR centred between angles of mandible
What are the indications for taking a posterior 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
Facial deformity- if surgery a ceph is preferred
*CBCT preferred
What can weaken the mandible and make it more prone to fracture?
Unerupted 8s at angle of the mandible
What does a Submentovertex view show?
Base of skull (including foramina)
Sphenoid sinus
Maxillary sinus
Plan view of mandible, including condyle
Zygomatic arches*
Where does the beam pass through in the SMV view?
Through chin and out through top of the head
What must be checked when taking an SMV radiograph?
Patient has no head or neck disease that would prohibit them from tilting head all the way back
-> this has to be done as chest would obscure view otherwise
How is an SMV radiograph taken?
Extend head and neck as far as possible
Orbitomeatal line parallel to image receptor
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 radiographs?
Fracture of zygomatic arch
Expansion of more posterior mandible- buccal and lingual cortical plates
Cranial base pathology (now replaced by CT)
Why does reducing the exposure factor in SMV radiographs help surgeons with zygomatic arch fractures?
Makes everything else become white but allows you to see zygomatic arch (allows surgeon to understand what part exactly needs to be replaced)
Which wall of the maxillary sinus in not seen on an OPT
Lateral wall (medial wall and posterior are seen)
What radiographs are best for looking at anterior wall of maxillary sinus?
Lateral
Axial CT/MRI
CBCT
What radiographs are best for looking at posterior wall of maxillary sinus?
OPT
Lateral
Axial CT/MRI
CBCT
What radiographs are best for looking at the medial wall of maxillary sinus?
OPT
Occipitomental
Axial + coronal CT/MRI*
CBCT
What radiographs are best for looking at the lateral wall of maxillary sinus?
Occipitomental
Axial + coronal CT/MRI*
CBCT
