2 - Cone beam CT

Question 1

What does CBCT stand for?

Answer 1

Cone beam computed tomography

Question 2

What is CBCT?

Answer 2

Cross sectional imaging suitable for assessing radiodense structures

Question 3

Describe the process of CBCT.

Answer 3

• conical or pyramidal x-ray beam exposes a square digital receptor
• rotates around head once
• captures many 2D images that can be reconstructed into 3D image

Question 4

Describe the patient head positioning for a dental CBCT machine.

Answer 4

Frankfort plane horizontal to floor

Question 5

What are the benefits of CBCT over plain radiography?

Answer 5

• no superimposition
• ability to view at multiple angles
• no magnification or distortion
• allows 3D volumetric reconstruction

Question 6

What are the drawbacks of CBCT compared to plain radiography?

Answer 6

• increased radiation dose
• lower spatial resolution
• susceptible to artefact
• equipment is expensive
• images are complicated manipulate and interpret
• requires additional training

Question 7

What are the benefits of CBCT over CT?

Answer 7

• lower radiation dose
• potential high resolution
• cheaper
• smaller machine

Question 8

What are the benefits of CT over CBCT?

Answer 8

• differentiate soft tissues better
• better signal to noise ratio giving cleaner image
• larger field of view

Question 9

What are the common uses of CBCT in dentistry?

Answer 9

• M3M relationship to ID canal
• alveolar bone measurements for implant placement
• root canal morphology
• ERR investigation
• assessment of large cystic jaw lesions

Question 10

What are the different views of a CBCT scan?

Answer 10

• axial
• sagittal
• coronal

Question 11

Define an axial view.

Answer 11

Looking down on head

Question 12

Define a sagittal view.

Answer 12

Looking side on

Question 13

Define a coronal view.

Answer 13

Looking at patient straight on

Question 14

What are the benefits of 3D volumetric reconstruction?

Answer 14

• aid visualisation of extent or shape of lesion/disease
• teaching aid

Question 15

What are the drawbacks of 3D volumetric reconstruction?

Answer 15

• modified reconstruction so can create misleading images
• poor at showing thin bone

Question 16

What is the FOV?

Answer 16

• field of view
• size of captured volume of data
• based on clinical case

Question 17

If you increase the FOV of a CBCT, what else increases?

Answer 17

• radiation dose
• number of tissues irradiated
• scatter

Question 18

Define a voxel.

Answer 18

3D pixel

Question 19

What gives a clearer image - larger or smaller voxels?

Answer 19

Smaller

Question 20

What effect does decreasing the size of the voxel have?

Answer 20

• increased radiation dose
• increased scan time

Question 21

What is an approximate value for the dose of a CBCT?

Answer 21

13-82 uSv

Question 22

What are the two types of artefacts found in CBCT?

Answer 22

• movement
• streak

Question 23

What is a movement artefact?

Answer 23

• when patient moves during scan
• leads to general blurriness or extra contours

Question 24

How do you prevent movement artefacts?

Answer 24

Fixation aids (eg chin rest, head strap)

Question 25

What are streak artefacts?

Answer 25

• caused by high-attenuation objects ie metal
• can prevent caries/canal assessment adjacent to restorations

Question 26

What are contraindications for CBCT?

Answer 26

• plain radiography sufficient
• pathology requiring soft tissue visualisation
• patient factors (unable to stay still, unable to fit into machine)

Question 27

What training is required for CBCT?

Answer 27

Postgraduate training level 1 and 2, requires refreshed every 5 years