CBCT - Cone beam computed tomography

Question 1

What is the uses of CT in the head and neck?

Answer 1

• 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 2

What are the advantages of CT?

Answer 2

• Not subject to the same magnification and distortion as plain radiographs
• multi-planar (manipulate, reconstruct images)
• avoids superimposition
• images bone and soft tissue
• differentiate different tissues
• you can see the bone and brain for head injuries
• speed (very quick like an MRI)

Question 3

Disadvantages of CT?

Answer 3

• Patients 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 - both CT and MRI are still expensive
• interpretation more difficult

Question 4

what is dentascan?

Answer 4

software that is available mainly for implant planning

Question 5

Why use CBCT?

Answer 5

• CBCR is a variation on traditional computed tomography (CT)
• In CBCT an X-ray tube and detector panel rotate around the patient capturing data with a cone-shaped X-ray instead of slices
• it has a much lower radiation dose than medical grade CT
• overcomes the issues of 2d imaging - CBCT can give you 3d images
• conventional CT 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

Question 6

CBCT - how the image is acquired?

Answer 6

• patient positioned either seated or lying supine, depending on the 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 sends the information to the computer where an image will appear on the screen

Question 7

How is the image displayed?

Answer 7

• A DPT type image is usually the first image displayed on the PC screen
• the imaging software used will determine how the view can be modified
• if multi-planar imaging is available then three slices will be displayed - axial, coronal and sagittal
• some software will allow these planes to viewed obliquely - which is very useful if you want to slice through the dental arch
• 3D reconstruction can also available

Question 8

Indications for CBCT - the developing dentition?

Answer 8

• Localization of unerupted tooth e.g. maxillary canine
• Assessment of any resorption from unerupted tooth
• cleft palate patients
• orthognathic surgery assessment

Question 9

Restorative dentistry and CBCT

Answer 9

• Few indications - only if conventional radiographs are unhelpful
• can be used to assess periapical lesions, root canal anatomy, perforations
• dental trauma
• dental anomalies

Question 10

CBCT and surgery

Answer 10

· Assessment of the lower third molars to the inferior dental canal

· Assessment of the morphology of all third molars

· Implant assessment.

· Assessment of pathology involving the jaws

· Assessment of the TMJ bone surfaces

· Facial fractures – especially if unclear on plain.

Question 11

Trauma and Pathology: - How CBCT helps with diagnosis and treatment planning.

Answer 11

Patient with Facial Trauma

· Clinically thought to have a fractured condyle.

· Not seen clearly on plain radiographs – DPT and PA mandible

· Referred for a CBCT.

· Next slide show the 3D reconstruction with some anatomy removed.

· Fractured condylar head is seen to be displaced medially.

Question 12

football injury

Answer 12

· Patient a black eye left side

· Complaining of some double vision

· Plain radiographs Occipito Mental 10- & 30-degree films

· Left maxillary sinus is opaque (cloudy)

· Left infra-orbital margin uneven.

· CBCT requested for further information.

Question 13

What affects the dose?

Answer 13

· Some exposure factures are set by the manufacturer – kV, time & mA.

· Scan times can be varied.

· Volume size – FOV

· Type of equipment used.

· Part of maxillofacial region being imaged.

Question 14

Advantages of CBCT

Answer 14

— 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 15

Disadvantages of CBCT

Answer 15

· 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.