Cone Beam Computerised Tomography - CBCT

Question 1

What is the Development of CBCT?

Answer 1

• A relatively new imaging modality in dentistry.
• Currently used in hospitals and private (not NHS) specialist practices
• Basic knowledge of medical grade CT scanning and its development is useful to know so that the place and indications for CBCT can be appreciated.
• Computerised tomography began its development in the years following the second world war & was often call CAT scanning – Computer Axial Tomography

Question 2

What are the Basics of a CT scanner?

Answer 2

Question 3

What are the Uses of CT in the head and neck?

Answer 3

• Intracranial
  
  • bleed, infarct, tumour
• Trauma
• Evaluation of osseous lesions
• Salivary glands
• Neoplasia (benign/malignant)
  
  • primary tumour
  • metastases
• Orthognathic assessment and treatment planning -
• Implant planning

Question 4

What are the Advantages of CT?

Answer 4

• Not subject to same magnification and distortion as plain radiographs
• Multi-planar (manipulate, reconstruct images)
  
  • avoids superimposition
• Images bone and soft tissue
  
  • Differentiate different tissues

(Head injury, see bone and brain)

• Speed (cf MRI)
• Both CT and MRI are still expensive pieces of equipment.

Question 5

What are the Disadvantages of CT?

Answer 5

• Patient Dose
• Artefacts (metallic objects, amalgam in head and neck)
• May require intravenous contrast to distinguish tissues (iodine based, risk of reaction)
• Expensive in comparison with plain radiography
• Interpretation more difficult

Question 6

Why use CBCT?

Answer 6

• Much lower radiation dose than medical grade CT
• Overcomes the issues of 2D imaging
• Conventional images may not give the whole information required for diagnosis & treatment planning
• Should only be used if the information gained has an impact on patient care
• Some machines have a large field of view (FOV) and are usually within hospital departments
• Dental practices are more likely to have small FOV machines

Question 7

How is a CBCT acquired?

Answer 7

• Patient positioned either seated or lying supine, depending on machine.
• The x-ray tube and the flat panel receptor are opposite each other and rotate around the patient in the same direction at the same time.
• The receptor send the information to the computer where an image will appear on the screen
• The x-ray beam is cone shaped and the area of the face and jaws to be scanned is in the path of the beam for the whole rotation, passing through structures in all of the 360 degree directions.

Question 8

Why would you take a CBCT?

Answer 8

• Localisation of unerupted tooth e.g. maxillary canine
• Assessment of any resorption from unerupted tooth
• Cleft palate patients
• Orthognathic surgery assessment

Few indications – only if conventional radiographs are unhelpful.

• Can be used to assess periapical lesions, root canal anatomy, perforations
• Dental trauma
• Dental anomalies

Question 9

Examples of effective dose in mSv (radiation dose)?

Answer 9

Bitewing or periapical 0.0003 – 0.022

DPT 0.0027 – 0.038

Lateral ceph. 0.0022 – 0.0056

Upper occlusal 0.008

CT head 1.4

CT mandible & maxilla 0.25 – 1.4

Dento-alveolar CBCT 0.01 – 0.67

Craniofacial CBCT 0.03 – 1.1

Question 10

What are the Advantages of CBCT?

Answer 10

• Multi-planar reformatting - MPR - allows image to be viewed from all directions
• Geometrically accurate images
• Fast scanning time
• Compatible with other software
• Good spatial resolution
• Lower radiation dose than medical CT

Question 11

What are the Disadvantages of CBCT?

Answer 11

• Patient must be still to avoid movement artefacts
• Soft tissues are not imaged well
• Radio-dense materials such as restorations and RF material produce beam hardening artefacts – streak artefacts
• Images can be difficult to interpret particularly if a large FOV is used