cbct Flashcards
How does CBCT work?
A conical/pyramidal X-ray beam and square digital detector rotate around the head opposite each other
Uses ionising radiation to capture many 2D images which are reconstructed into a 3D image
When may CBCT be used outside of dentistry?
Temporal bone imaging
Paranasal sinus imaging
Orthopaedic imaging
Radiotherapy planning
What is the head positioning for CBCT?
Frankfort plane parallel to ground unless patient is lying down
Give 4 advantages of CBCT over plain radiography?
No superimposition
Ability to view subject from any angle
No magnification or distortion
Allows for volumetric (3D) reconstruction
Give 4 disadvantages of CBCT over plain radiography
Any from:
- increased radiation dose to patient
- lower spatial resolution (not as sharp)
- susceptible to artefacts
- equipment more expensive
- images more complicated to manipulate and interpret
- required additional training to justify, operate and interpret
Compare the radiation dose, image quality, price, soft tissue imaging and field of view of CBCT over CT
CBCT:
- lower radiation dose
- potentially sharper image quality
- cheaper
- worse differentiation of soft tissues
- smaller field of view
Name 4 common uses of CBCT in dentistry
Any from:
- clarifying relationship between impacted M3M and ID canal
- measuring alveolar bone dimensions to help plan implant placement
- visualising complex root canal morphology to aid endo tx
- investigating ERR next to impacted teeth
- assessing large cystic jaw lesions and their involvement of important anatomical structures
Name 3 common orthagonal planes
Axial - from above/below
Sagittal - from side
Coronal - from front/back
What are the benefits of 3D volume reconstruction?
May help clinician picture the extent/shape of disease
Can be informative teaching aid for the patient
What are the drawbacks of 3D volume reconstruction?
Is a modified reconstruction of the data so can create misleading image
Poor at showing thin bone
Name 3 imaging factors/variables that are set before the scan starts
Field of view
Voxel size
Acquisition time eg - 10 seconds
What is field of view (FOV) and what happens if it is increased?
The size of the captured volume of data
Increasing this increases radiation dose, the number of tissues radiated, the scatter and means there’s more to report
What is voxel size and what happens if this is decreased?
The image resolution - 3D pixels
Decreasing leads to increased radiation dose and increased scan time
What is the typical voxel size range for CBCT?
Between 0.4mm ³ and 0.085mm ³
What is the ideal FOV and voxel size for an endo case in CBCT?
FOV as small as possible unless large apical pathology
Smaller voxel size
What is the ideal FOV and voxel size for an implant planning case in CBCT?
FOV depends on number and position of implants
Larger voxel size
What are artefacts?
Visualised structures on the scan that were not present in the object investigated
2 main types:
- movement artefacts
- streak artefacts
What are movement artefacts and how can they be reduced?
Occurs if pt not completely still during the full exposure
Affects the full scan
Can lead to blurriness or extra contours
Reduced using fixation aids - chin rest, head strap
What are streak artefacts caused by and what do they prevent?
Caused by high-attenuated objects eg - amalgam
Can prevent caries assessment adjacent to restorations
Can prevent assessment of perforations/missed canals in root treated teeth
Give 4 contraindications for CBCT
If plain radiographs are sufficient
Pathology requiring soft tissue visualisation - malignancy or infection spreading in soft tissue
If high risk of debilitating artefacts
Patient factors - unable to stay still (Parkinson’s), unable to fit in machine
