Cone Beam Computed Tomography

Question 1

What are the basics of CT scanning?

Answer 1

• high kV tube - 120kV - much higher than dental machines
• tomographic image 0 looks at slices of tissue and these slices can be stacked together in order that 3D images can be produced
• x-rays panthrough body
• attenuation of beam measured by detectors
• computer assesses radio-opacity of each voxel
• different hounsfield number for every tissue

Question 2

What are some uses of CT in the head and neck?

Answer 2

• 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 3

What are some advantages of CT?

Answer 3

• not subject to same magnification and distortion as plain radiographs
• multi-planar (manipulate, reconstruct images)
• images bone and soft tissue
• speed
• both CT and MRI are still expensive pieces of equipment

Question 4

What are some disadvantages of CT?

Answer 4

• patient dose
• artefacts e.g. amalgam
• may require intravenous contrast to distinguish tissues –> risk of reaction
• expensive in comparison to plain radiography
• interpretation more difficult

Question 5

Why use CBCT?

Answer 5

• 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 and 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 6

What is the positioning or scout view?

How is a CBCT image acquired?

Answer 6

Positioning or scout view: an initial positioning view to ensure area of concern is in the FOV

How the image is acquired:

• x-ray tube and flat panel receptor are opposite each other and rotate around the patient in the same direction at the same time
• receptor sends information to the computer where an image will appear on the screen

Question 7

What are some indications for CBCT?

• developing dentition:
• localisation of UE teeth e.g. max canine
• assessment of any resorption from UE tooth
• cleft palate patients
• orthognathic surgery assessment
• can be used to assess periapical lesions, root canal anatomy, perforations, dental trauma, dental anomalies

Question 8

Indications of CBCT for surgery:

Answer 8

Surgery:

• assess lower 3rd molars to inferior dental canal
• assess morphology of all 3rd molars
• implant assessment
• assess pathology involving jaws
• assess TMJ bone surfaces
• facial fractures - especially if unclear on plain views

Question 9

What affects the dose?

Answer 9

• scan times can be varies
• volume size - FOV
• type of equipmentused
• part of maxillofacial region being imaged

Question 10

Advantages of CBCT?

Answer 10

• multiplanar reformatiing - 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

Disadvantages of CBCT?

Answer 11

• patient muse be still to avoid movement artefacts
• soft tissues 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