Extra-Oral and Other Plain Views

Question 1

What equipment is required to take an EO radiograph?

Answer 1

X-ray tubehead

Cassette - film or digital

Question 2

What is collimation?

Answer 2

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

Question 3

How is collimation checked?

Answer 3

Light beam shows area on patient which will be exposed to primary beam

-> middle of cross is central beam

Question 4

What are the cassette sizes?

Answer 4

18 x 24

24 x 30

Question 5

What is the minimum speed of the intensifying screen in EO radiography?

Answer 5

400

Question 6

What is the function of the grid?

Answer 6

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

Question 7

Which lines are commonly used in EO radiography?

Answer 7

Frankfort plane- OPTs/cephs

Orbitomeatal line (OM line)

Interpupillary line

Mid-sagittal plane- down middle of head

Question 8

Where is the OM line located?

Answer 8

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

Question 9

Where is the Frankfort plane located?

Answer 9

Connects orbitale (most inferior infraorbital rim) with porion (superior external auditory meatus)

Question 10

What are the features of a lateral skull radiograph?

Answer 10

Does not include all of the facial bones

Different from lateral ceph as there is no cephalostat (free positioning)

Doesn’t include soft tissues

Question 11

What are the uses of a Lateral Skull radiograph?

Answer 11

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

Question 12

What is the difference between AP/PA?

Answer 12

PA- tube posterior to head and image receptor anterior (AP is opposite)

-> most commonly used for maxillofacial views

Question 13

Why is PA preferred?

Answer 13

Reduced magnification

Dose Reduction- low energy photons entering back of head are attenuated before they reach radiosensitive tissues (e.g. lens, salivary glands)

Question 14

Where does the beam pass through in the occiptomental view?

Answer 14

Beam goes in through occipital region of head then mental region (point of the chin)

Question 15

What is shown in the occiptomental view?

Answer 15

Orbit
Frontal sinus
Maxillary sinus
Zygoma, zygomatic arch
Nasal septum
Coronoid process
Odontoid peg/dens of C2

Question 16

How is an occiptomental radiograph taken?

Answer 16

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

Question 17

What does varying the beam angulation (vertical angle) in occiptomental radiographs achieve?

Answer 17

Changes way facial skeleton looks in middle third (can make fractures more obvious)- multiple views are required for diagnosis

Question 18

How do steeper OMV views make the mandible look?

Answer 18

Mandible becomes more curved

Question 19

What are the indications for Occipitomental radiographs?

Answer 19

Sinus disease - no longer indicated (CT/CBCT)

Maxillary, frontal and ethmoid sinuses

Middle 1/3 facial fractures- zygoma/Le Fort

Coronoid process fracture

Question 20

In what instance would CT be better option for middle face fractures?

Answer 20

If there is a suspected brain injury

Question 21

What are le fort fractures?

Answer 21

Go across right to left (3 levels- separation of midface from the skull base)

Question 22

What does a posterior mandible radiograph show?

Answer 22

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

Question 23

How is a posterior mandible radiograph taken?

Answer 23

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

Question 24

What are the indications for taking a posterior mandible?

Answer 24

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

Question 25

What can weaken the mandible and make it more prone to fracture?

Answer 25

Unerupted 8s at angle of the mandible

Question 26

What does a Submentovertex view show?

Answer 26

Base of skull (including foramina) Sphenoid sinus Maxillary sinus Plan view of mandible, including condyle Zygomatic arches*

Question 27

Where does the beam pass through in the SMV view?

Answer 27

Through chin and out through top of the head

Question 28

What must be checked when taking an SMV radiograph?

Answer 28

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

Question 29

How is an SMV radiograph taken?

Answer 29

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

Question 30

What are the indications for SMV radiographs?

Answer 30

Fracture of zygomatic arch Expansion of more posterior mandible- buccal and lingual cortical plates Cranial base pathology (now replaced by CT)

Question 31

Why does reducing the exposure factor in SMV radiographs help surgeons with zygomatic arch fractures?

Answer 31

Makes everything else become white but allows you to see zygomatic arch (allows surgeon to understand what part exactly needs to be replaced)

Question 32

Which wall of the maxillary sinus in not seen on an OPT

Answer 32

Lateral wall (medial wall and posterior are seen)

Question 33

What radiographs are best for looking at anterior wall of maxillary sinus?

Answer 33

Lateral Axial CT/MRI CBCT

Question 34

What radiographs are best for looking at posterior wall of maxillary sinus?

Answer 34

OPT Lateral Axial CT/MRI CBCT

Question 35

What radiographs are best for looking at the medial wall of maxillary sinus?

Answer 35

OPT Occipitomental Axial + coronal CT/MRI* CBCT

Question 36

What radiographs are best for looking at the lateral wall of maxillary sinus?

Answer 36

Occipitomental Axial + coronal CT/MRI* CBCT