Radiology - Extra-oral & Plain views

Question 1

What is collimation?

Answer 1

Collimation is the control of the size and shape of the X-Ray beam (Occurs at tube head)

Question 2

How does the x-ray machine ensure the correct collimation?

Answer 2

the machine produces a light beam to show what area of the patient will be exposed to the primary beam

Question 3

Where should the edge of the x-ray beam be in relation to the image receptor and why?

Answer 3

should be within the edge of the IR

= no x-rays going beyond the IR and irradiating the patient without contributing to the diagnostic image.

Question 4

What film do we use for maxillofacial views?

Answer 4

Film 18x24 cm or 24x30 cm

Question 5

What is the function of a grid?

Answer 5

Lies between x-ray source and IR
– used to cut out x-rays that aren’t approaching the IR straight on - attenuate obliquely travelling photons before they reach the film

Question 6

What is the minimum film speed used in maxillofacial views???? **

Answer 6

400

Question 7

What planes do we use to position the patient for maxillofacial views? (4)

Answer 7

• Frankfort plane
• Orbitomeatal line (OM line)
• Interpupillary line
• Mid-sagittal plane

Question 8

Describe the landmarks for the Frankfort plane.

Answer 8

From the orbitale (most inferior infraorbital rim) to the porion (superior external auditory meatus)

Question 9

Describe the landmarks for the orbitomeatal plane.

Answer 9

from the central part of external auditory meatus to the outer canthus of eye

Question 10

What is the difference in the angles from the Frankfort plane tp the orbitomeatal plane (in degrees)?

Answer 10

about 10 degrees

Question 11

What plane is used as the radiographic baseline?

Answer 11

orbitomeatal

Question 12

What patient positioning do we use to take a lateral skull radiograph?

Answer 12

free positioning - no standardised position

Question 13

When would we use lateral skull radiographs? (CT used instead of these now) (4)

Answer 13

• Fractures of skull/skull base when CT not available
• Facial fractures: to show vertical and anteroposterior displacement
• Skull pathology (e.g. Pagets, myeloma)
• Pituitary fossa enlargement, sphenoid sinus pathology

Question 14

What is the most commonly used direction of the beam in maxillofacial views?

Answer 14

posteroanterior
- tube head behind patient and IR infront of patient

Question 15

Why do we commonly use posteroanterior maxillofacial views? (2)

Answer 15

• Reduced magnification = Objects closer to film are magnified less than objects that are further away
• Dose Reduction = Low energy photons entering back of head are attenuated before they reach radiosensitive tissues (e.g. lens of eye or salivary glands)

Question 16

What anatomical features does the occipitomental view show? (7)

Answer 16

(middle 1/3rd of face)
- Orbit
- Frontal sinus
- Maxillary sinus
- Zygoma, zygomatic arch
- Nasal septum
- Coronoid process
- Odontoid peg/dens of C2

Question 17

Describe the patient positioning for the occipitomental view. (4)

Answer 17

(nose-chin position)
- Orbitomeatal line at 45o 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 18

When are occipitomental views used? (2)

Answer 18

• Middle 1/3 facial fractures: zygomatic complex, Le Fort (fractures going across from LHS to RHS)
• Coronoid process fracture

Question 19

What are posteroanterior views of the mandible used to visualise?

Answer 19

view of posterior body, angle and ramus of mandible

Question 20

When are posteroanterior views not used? (2)

Answer 20

Not used for anterior mandible as Superimposition of cervical spine obscures

Not used for the condyle as Superimposition of mastoid process and zygomatic arch obscure

Question 21

Describe patient positioning for a PA view of the mandible. (4)

Answer 21

(forehead-nose position)
- Orbitomeatal line perpendicular to image receptor
- 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 22

When are PA mandible views used? (3) and what other view do they have to be used alongside? (1)

Answer 22

Used alongside OPT;

• 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 (often then taken in a cephalostat)

Question 23

When is the submentovertex view used?

Answer 23

• Fracture of zygomatic arch
• Expansion of more posterior mandible

Question 24

What must we do if we want to take a submentovertex view of the zygomatic arch and why?

Answer 24

Since the zygomatic arch is very thin, the normal beam is too penetrating - we must reduce the energy and quantity (reduce exposure factors - kV and time)

Question 25

In what radiographic techniques can the floor of the maxillary sinus be seen? (5)

Answer 25

• Panoramic
• Occipitomental
• Lateral
• Coronal CT/MRI
• CBCT

Question 26

In what radiographic techniques can the roof of the maxillary sinus be seen? (5)

Answer 26

• Panoramic
• Occipitomental
• Lateral
• Coronal CT/MRI
• CBCT

Question 27

In what radiographic techniques can the anterior wall of the maxillary sinus be seen? (3)

Answer 27

• Lateral
• Axial CT/MRI
• CBCT

Question 28

In what radiographic techniques can the posterior wall of the maxillary sinus be seen? (4)

Answer 28

• Panoramic
• Lateral
• Axial CT/MRI
• CBCT

Question 29

In what radiographic techniques can medial walls of the maxillary sinus be seen? (4)

Answer 29

• Panoramic
• Occipitomental
• Axial + coronal CT/MRI*
• CBCT

Question 30

In what radiographic techniques can the lateral walls of the maxillary sinus be seen? (3)

Answer 30

• Occipitomental
• Axial + coronal CT/MRI*
• CBCT