2 - Cone beam CT Flashcards
What does CBCT stand for?
Cone beam computed tomography
What is CBCT?
Cross sectional imaging suitable for assessing radiodense structures
Describe the process of CBCT.
- conical or pyramidal x-ray beam exposes a square digital receptor
- rotates around head once
- captures many 2D images that can be reconstructed into 3D image
Describe the patient head positioning for a dental CBCT machine.
Frankfort plane horizontal to floor
What are the benefits of CBCT over plain radiography?
- no superimposition
- ability to view at multiple angles
- no magnification or distortion
- allows 3D volumetric reconstruction
What are the drawbacks of CBCT compared to plain radiography?
- increased radiation dose
- lower spatial resolution
- susceptible to artefact
- equipment is expensive
- images are complicated manipulate and interpret
- requires additional training
What are the benefits of CBCT over CT?
- lower radiation dose
- potential high resolution
- cheaper
- smaller machine
What are the benefits of CT over CBCT?
- differentiate soft tissues better
- better signal to noise ratio giving cleaner image
- larger field of view
What are the common uses of CBCT in dentistry?
- M3M relationship to ID canal
- alveolar bone measurements for implant placement
- root canal morphology
- ERR investigation
- assessment of large cystic jaw lesions
What are the different views of a CBCT scan?
- axial
- sagittal
- coronal
Define an axial view.
Looking down on head
Define a sagittal view.
Looking side on
Define a coronal view.
Looking at patient straight on
What are the benefits of 3D volumetric reconstruction?
- aid visualisation of extent or shape of lesion/disease
- teaching aid
What are the drawbacks of 3D volumetric reconstruction?
- modified reconstruction so can create misleading images
- poor at showing thin bone
What is the FOV?
- field of view
- size of captured volume of data
- based on clinical case
If you increase the FOV of a CBCT, what else increases?
- radiation dose
- number of tissues irradiated
- scatter
Define a voxel.
3D pixel
What gives a clearer image - larger or smaller voxels?
Smaller
What effect does decreasing the size of the voxel have?
- increased radiation dose
- increased scan time
What is an approximate value for the dose of a CBCT?
13-82 uSv
What are the two types of artefacts found in CBCT?
- movement
- streak
What is a movement artefact?
- when patient moves during scan
- leads to general blurriness or extra contours
How do you prevent movement artefacts?
Fixation aids (eg chin rest, head strap)
What are streak artefacts?
- caused by high-attenuation objects ie metal
- can prevent caries/canal assessment adjacent to restorations
What are contraindications for CBCT?
- plain radiography sufficient
- pathology requiring soft tissue visualisation
- patient factors (unable to stay still, unable to fit into machine)
What training is required for CBCT?
Postgraduate training level 1 and 2, requires refreshed every 5 years
