2 - Cone beam CT Flashcards
(27 cards)
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)
