Cone Beam CT Flashcards
what is a cone-beam CT?
a form of cross-sectioning imagine suitable for assessing radiodense structures
Other than dental related imaging, why else might a cone-beam CT be used?
- temporal bone imaging
- paranasal sinus imaging
- orthopaedic imaging
What type of radiation is involved in CBCTs?
Ionising radiation
How is a CBCT taken?
- conical/pyramidal X-ray beam & square digital detector rotate around head
- captures many 2D images which are reconstructed into a cylindrical 3D image
How is the patients head usually positioned for a CBCT?
Horizontal = frankfort plane (level with floor)
Vertical = midsagittal plane
[same as OPT]
What are the benefits of a CBCT compared to plain radiography?
- no superimposition
- ability to view subject from any angle
- no magnification/distortion
- allows for volumetric (3D) reconstruction
What are the downsides of a CBCT compared to plain radiography?
- increased radiation dose to patient
- lower spatial resolution [not as sharp]
- susceptible to artefacts
- equipment more expensive
- images more complicated to manipulate & interpret
- required additional training
In what ways are CBCTs better than CTs?
- lower radiation dose
- potential for sharper images
- cheaper
- smaller footprint
In what ways are CTs better than CBCTs?
- able to differentiate soft tissues better
- cleaner images
- larger field of view possible
Give some indications for CBCTs in dentistry?
- clarify relationship between impacted mandibular 3rd molar & IANC
- measuring alveolar bone dimensions to help plan implant placement
- visualising complex root canal morphology to aid endo
- investigate external root resorption next to impacted teeth
- assess large cystic jaw lesions
What imaging factors/variables are set before the scan starts & why?
Will alter the information obtained & the patient dose (should be considered using ALARP principle)
- field of view
- voxel size
- acquisition time
What is the ‘field of view’ of a CBCT? what does this alter?
the size of the captured volume of data
increased FOV size –> increased pt dose –> increased number of tissues irradiated –> increased scatter
What is ‘voxel size’ in relation to CBCT?
The image resolution
- the 3D pixels of a CBCT are never as small as intraoral radiograph pixels
What does decreased voxel CBCT size do?
- increased radiation dose
- increased scan time
what range of ‘voxel size’ options are available for a CBCT?
0.4mm^3 - 0.085mm^3
