Cone Beam CT Flashcards
What is CBCT (cone beam computed tomography)?
A form of cross-sectional imaging suitable for assessing radiodense structures
Cross-sectional means you can look at anatomy in slices and look at them separately and at different angles
What are the basic principles of CBCT?
Ionising radiation
–conical/pyramidal x-ray beam & square digital detector rotate around the head (no more than 1 full rotation)
Captures many 2-D images (e.g. 200) which are reconstructed into a cylindrical 3D image
What are the benefits of CBCT over plain radiography?
No superimposition as it is cross-sectional
Ability to view subject from any angle
No magnification/distortion
Allows for volumetric (3D) reconstruction
What are the disadvantages of CBCT over plain radiography?
Increased radiation dose to patient
Lower spatial resolution (i.e. not as sharp, more course + blurry)
Susceptible to artefacts
Equipment more expensive
Images more complicated to manipulate & interpret
Requires additional training (to justify, operate & interpret)
What are the main benefits of CBCT compared to conventional CT?
Lower radiation dose
Potential for ‘sharper’ images (higher resolution)
Cheaper (initial, running & maintenance)
Smaller footprints
What are the main benefits of Conventional CT over CBCT?
Able to differentiate soft tissues better (CBCT shows bone and hard structures but is unable to differentiate between soft and hard tissues)
‘Cleaner’ images (better signal to noise ratio)
Larger field of view possible
What are some CBCT common uses in Dentistry?
Clarifying relationship between impacted mandibular third molar & inferior alveolar canal
Measuring alveolar bone dimensions to help plan implant placement
Visualising complex root canal morphology to aid endodontic treatment
Investigating external root resorption next to impacted teeth
Assessing large cystic jaw lesions & their involvement of important anatomical structures
What are the 3 common orthogonal planes used in CBCT?
Axial
–looking at patient from above or below
Sagittal
–looking at patient from the side
Coronal
–from the front or back
What are the drawbacks of 3D volume reconstruction?
It is a modified reconstruction of the data & so can create misleading images - particularly poor at showing thin bone
What is the field of view?
What does increasing the size lead to?
Size of the captured volume of data
Increased size = increased radiation dose + increased number of tissues + increased scatter
What is an increased scatter in x-rays?
X-ray photons pass through the object rather than reaching the receptor or being absorbed, they deflect off in different directions and that can irradiate things around the patient and also result in a worse contrast on image and more to report
What is the voxel size in CBCT?
The image resolution (3D pixels)
Never as small as intraoral radiograph pixels (why intraorals have better resolution)
What does decreased voxel size lead to?
Increased radiation dose
Increased scan time
What is the approximate effective dose of radiation for CBCT?
How much more than OPT?
13-82 uSv
Dento-alveolar CBCT is roughly 2-3x dose of OPT
What are artefacts?
What are the 2 main types?
Visualised structures on the scan that were not present in the object investigated
2 main types
–movement artefact
–streak artefact
