Cone Beam CT Flashcards
What is cone beam computed tomography?
Form of cross-sectional imaging suitable for assessing radio dense structures.
Describe the basic principles of CBCT.
Conical/pyramidal x-ray beam on one side of the patient.
Square receptor on the other side.
They both rotate around the patient/area of interest, always staying opposite each other.
Captures many 2D images and computer then recreates a 3D image.
What is the patient positioning for CBCT?
Same as for OPT.
Frankfurt plane perpendicular to the floor.
Mid-sagittal plane as the vertical reference point.
What are the benefits of CBCT compared to plain film?
No superimposition
No magnification/distortion
Ability to view subject from any angle
Allows for 3D reconstruction.
What are the disadvantages of CBCT compared to plan film?
Increased radiation dosage to the patient.
Lower spatial resolution
Equipment is more expensive
Images more complicated to manipulate and require specialist training to manipulate.
Not available in primary care settings under the NHS.
What are the advantages and disadvantages of CBCT compared to conventional CT?
CBCT
- reduce ionising radiation dose compared to CT
- Higher resolution
- Cheaper
CT
- Able to differentiate soft tissues better
- Cleaner images
Larger field of view possible
What are the common uses for CBCT in dentistry?
Determine proximity of IAC to third molar
Location of supernumerary teeth
Assessing large cystic jaw lesions and their involvement with anatomical structure.
Measure alveolar bone dimensions to help plan implant placement
Visualising complex root morphology prior to endo treatment
What skull views are commonly used in CBCT?
Axial
Sagittal
Coronal
What imaging factors/variables are set prior to the scan being taken?
Field of view
Voxel size
Acquisition time
What is the field of view?
Size of the captured volume of data
- You want to reduce this as much as possible to reduce the radiation dose and number to tissues irradiated while also getting the information you require.
What is Voxel size?
voxels are 3D pixels- they determine the image resolution.
Smaller the voxel size- increase resolution but increased dosage and scan time.
What factors would influence voxel size?
Endodontic cases- FOV as small as possible, smaller voxel size.
Implant planning cases- FOV depends on number.pisition of implants, larger voxel size.
What is the approximate effective dose of CBCT compared to plain film?
CBCT- 13-82 microsieverts
- roughly 2-3 times more than panoramic radiographs.
OPT- 3-24 microsiverts
Intraoral- 4 microsievert.
What are artefacts?
Visualised structures on the scan that were not present in the object investigated.
What kind of artefacts might be present on a CBCT?
Movement artefact- typically reduced using fixation devices.
Streak artefacts- seen when high-attenuation objects look brighter than others.
- Can prevent caries assessment.
