Anatomy - Skull, Mandible & Facial Bones

Question 1

Describe the steps in preparing the room for Skull-related radiography.

Answer 1

Get IR ready and place it in portrait/longitudinal orientation in the errect bucky

Prepare the correct anatomical markers

Place chair facing errect bucky/ IR

Ensure that the X-Ray tube is moved to a safe position

Clean surface of errect body with disinfectant wipes

Pre-set Exposure Factors

Question 2

Patient Positioning for PA Skull/Mandible

Answer 2

Patient is asked to sit facing the erect bucky

The palm of each hand can be placed on the bucky surface, out of the primary beam or on his/her lap.

Question 3

Head Positioning for PA Skull/Mandible

Answer 3

Ensure MSP is aligned to midline of bucky

Ensure that the head is not rotated.
EAM is equidistant to erect bucky, MSP perpendicular to IR.

Question 4

Head Positioning for PA Mandibular Rami

Answer 4

Patient is asked to flex his/her neck so that OML is perpendicular to IR (Similar to OF 0)

Tip - nose & forehead in contact with bucky

Question 5

Position of Central Ray for PA Mandibular Rami

Answer 5

Direct CR perpendicularly to IR along the MSP and exit the acanthion

Question 6

Head Positioning for PA Mandibular Body

Answer 6

Patient raise the head so that the acanthiomeatal line (AML) is perpendicular to IR.

Tip - nose & chin in contact with the bucky.

Question 7

Position of Central Ray for PA Mandibular Body

Answer 7

Direct CR perpendicular to IR along the MSP and centred to level of the lips

Question 8

Patient Positioning of Mandible - Axiolateral/Axiolateral Oblique

Answer 8

From the PA position, the patient is turned and shoulders rotated slightly

Head is then rotated to the left and right side in turn

Ensure that head is in true lateral position

Midsagittal plane (MSP) should be parallel to IR.

Interpupillary line perpendicular to IR
Mouth should be closed with the teeth together

Extend patient’s neck until long axis of the mandibular body is parallel with transverse axis of the image receptor to prevent superimposition of the cervical spine

Centre x-ray tube to erect bucky & direct Central Ray 25 degrees cephalad to pass through the mandibular region of interest.

Both sides should be examined to demonstrate a possible contrecoup fracture.

Question 9

Where is the region of interest for Mandible - Axiolateral?

Answer 9

Mandibular ramus.

Question 10

Where is the region of interest for Mandible - Axiolateral Oblique

Answer 10

Mandibular body and symphysis

Question 11

What is the direction of turning and degree of angulation for Mandibular Body?

Answer 11

Turn patient’s head 30 degrees towards IR

Question 12

What is the direction of turning and degree of angulation for Mandibular Symphysis?

Answer 12

Turn patient’s head 45 degrees towards IR

Question 13

Collimation area for PA Mandibular Rami/Body

Answer 13

Superiorly: 2.5cm above EAM

Inferiorly: Symphysis Menti

Laterally: Lateral skin margins

Question 14

Collimation area for Mandible - Axiolateral Oblique

Answer 14

Superiorly: EAM of side remote from IR

Inferiorly: Prominence of thyroid cartilage

Anteriorly: Lips/symphysis menti

Posteriorly: 2 cm posterior to EAM of the side remote to IR (away from IR)

Question 15

Head Position for TMJ - Modified Townes - Fronto-occipital 35 degrees projection

Answer 15

Facing the x-ray tube, patient is asked to flex the neck to bring the OML perpendicular to the bucky

Closed-mouth position:
Posterior teeth, not incisors, must be in contact

Open-mouth position:
If not contra-indicated, the patient opens his/her mouth wide just before exposure

Question 16

Central Ray position for TMJ - Modified Townes - Fronto-occipital 35 degrees projection

Answer 16

CR is directed 35 degrees caudad and centred along the MSP 7.6cm above the nasion or 2 cm superior to glabella exiting at the base of skull.

42 degrees caudal if IOML is perpendicular to bucky. IOML = Infraorbital meatal line

Question 17

Head Position for Temporo-mandibular Joints - Axiolateral 30 degrees, open & closed mouth

Answer 17

True lateral position:
MSP parallel to IR
Interpupillary line perpendicular to IR

Question 18

Central Ray position for Temporo-mandibular Joints - Axiolateral 30 degrees, open & closed mouth

Answer 18

Directed 30 degrees caudad and centred to a point 1.3cm anterior and 5 cm superior to upside EAM

Closed-mouth/open mouth position:
TMJ localized to a point 1.3cm anterior and 2.5cm inferior to the EAM
To perform both projections for comparison

Question 19

Head Position for TMJ - Axiolateral Oblique 15 degrees projection - Modified Law

Answer 19

After ensuring that head is in the true lateral position, rotate head 15 degrees towards the bucky

Question 20

Central Ray Position for TMJ - Axiolateral Oblique 15 degrees projection - Modified Law

Answer 20

Directed 15 degrees caudad, centred 4cm superior to upside EAM

Question 21

Collimation Area for TMJ - Modified Townes

Answer 21

Superiorly: 5 cm above the glabella

Inferiorly: Level of mandibular angles

Laterally: Lateral skin margins

Question 22

Collimation Area for Temporo-mandibular Joints - Axiolateral 30 degrees

Answer 22

Superiorly: 5cm above centring point

Inferiorly: 5cm below centring point

Anteriorly: 5cm anterior to centring point

Posteriorly: 5cm posterior to centring point