CBCT - Cone beam computed tomography Flashcards
What is the uses of CT in the head and neck?
- Intracranial - bleed, infarct, tumour
- trauma
- evaluation of osseous lesions
- salivary glands
- neoplasia (benign/malignant) - primary tumour/metastases
- orthognathic assessment and treatment planning
- implant planning
What are the advantages of CT?
- 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)
Disadvantages of CT?
- 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
what is dentascan?
software that is available mainly for implant planning
Why use CBCT?
- 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
CBCT - how the image is acquired?
- 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
How is the image displayed?
- 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
Indications for CBCT - the developing dentition?
- Localization of unerupted tooth e.g. maxillary canine
- Assessment of any resorption from unerupted tooth
- cleft palate patients
- orthognathic surgery assessment
Restorative dentistry and CBCT
- Few indications - only if conventional radiographs are unhelpful
- can be used to assess periapical lesions, root canal anatomy, perforations
- dental trauma
- dental anomalies
CBCT and surgery
· 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.
Trauma and Pathology: - How CBCT helps with diagnosis and treatment planning.
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.
football injury
· 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.
What affects the dose?
· 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.
Advantages of CBCT
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
Disadvantages of CBCT
· 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.
