CBCT - Amar Flashcards
Can CBCT see soft tissues?
Nein
Estimated scanning time of CBCT
1-10
Compare the radiation dose of OPG vs CBCT
1 small CBCT = 1 pan
1 large CBCT (ortho) = around 10 OPG
What is the issue with these cbct machines
Takes up a lot of space
$$$
High radiation dose
pros of this machine (3)
Cheaper Occupies
less space
Lower dose
Required characteristics for ideal diagnostic cbct (5)
Good density and contrast
Sharpness
Good resolution
Accuracy in measurements
Free of artifacts
What are some advantages of CBCT (5)
- 3D
- Good image accuracy and resolution
- Rapid scan time
- Allows for selective FoV
- No magnification
- Low radiation dose compared to Med CT
*
How does CBCT radiation differ from med CT
CBCT - 0.052 – 1.025 mSv
Med CT - 1.4 - 2.1 mSv
Disadvantages of CBCT
- Artifacts
- Motion artifacts due to increased scan time compared to med ct
- Poor contrast resolution (no soft tissue observation)
Limitations of Panoramic imaging (5)
- 2D
- Horizontal and vertical magnification
- Distortion
- Superimposition
- Positioning errors
What are the 4 components of CBCT image acquisition
- XRay generation
- Image formation / detection
- Image reconstruction
- Image display
Describe how the xray generator works in CBCT (4)
During rotation, many exposures are made at fixed intervals, each offset from one another - called basis images
150-600 basis images produced
Complete series of basis images called projection data // (step called image acquisition)
Projection data then reconstructed in 3 planes (axial, sagittal and coronal) using complicated algorithm
Sagittal, axial, coronal
What is CBCT FoV and how can it change?
Visible Field of View
- Can be adjustable
- Full FoV = nearly full skull (used for ortho)
- Medium / standard = both arches and TMJ
- Small FoV = one arch or quadrant
Want to limit the field size to the smallest volume that can accomodate the region of interest
What is CBCT frame rate? Pros (1) and cons (2) of high frame rate?
Speed at which images are acquired
Higher frame rates = more pics = increased primary reconstruction time
Higher frame rate = higher radiation dose
Higher frame rate reduces metallic artifacts
2 types of image detectors for CBCT
Image intensifier tube / CCD / CMOS
Flat panel detector
What are these two cbct image detectors
- CCD / CMOS
- Flat panel detector
Pixel vs Voxel
Pixel = digital equivalent of silver halide crystal in conventional. Smallest controllable element of a picture on screen
Voxel = volumetric pixels, cubic in nature (CBCT is 3D
CBCT vs CT voxels
CBCT = isotropic voxel
- Perfect cube 0.1 - 0.7 mm
CT = anisotropic voxel
- Brick shaped
What is a “tomographic plane”
Single slice of the area interest in a CBCT shown by a line
What are the 3 image types that can be produced by Multiplanar Reformatting (MPR)
Axial images with computer generated superimposed curve of alveolar process
Cross sectional Images
Panoramic like images
What are the two types of radiograph resolution?
Spatial resolution - differentiate btw two objects of different radio density
Contrast resolution - differentiate two objects of the same color type
Lingual foramen
- careful when placing implant
What should you do medico-legally when you take a full-volume / full size CBCT
Refer to dento-maxillofacial radiologist for proper reporting of radiograph
- May not need to refer for small section CBCT
Arrows - eustachian tube
mental foramen
What is the dotted line and what happens if it gets blocked
Sinus ostium
If blocked - Mucocele
AES - anterior ethmoidal sinus
MNC - middle nasal concha
INC - inferior nasal concha
Purposes of CBCT in endodontics (3)
Diagnosis of treatment failure (missed canals)
Identifying root fractures
Assessment of endo tx complications (ex. broken file, extrusion of material into IAC)
Evaluation of anatomy / complex morphology (dens invaginatus)
Root canal morphology
When should CBCT NOT be used for Endo
- Assessing outcome when there were no difficulties
- To determine working length
What type of CBCT should be taken for endo purposes
Small volume CBCT
indications for CBCT in OMFS
- Investigate exact location of jaw pathologies
- Assess impacted and supernumary teeth and proximity to vital structures
- Consideration of resorption of adjacent tooth
- pre-post surgical assessment of bone graft sites
- paranasal sinus pathology
- planning orthognathic surgery
nasopalatine cyst
retention pseudocyst of maxillary sinus
Should NOT have taken CBCT - unnecessary
What diseases of the maxillary sinus warrant a CBCT?
Mucocele - painful expanding lesion
A. Polyp
B. Retention pseudocyst
C. Mucocele
What should be advised
CBCT to see effect on IAC
“Breach in continuity of lingual cortical plate”
Uses of CBCT in implantology (6)
Determine presence of disease at site
Measure available jaw bone to see if its feasible
Determine quality and quantity of bone
Nerve mapping / determine proximity to critical structures
Determine implant orientation
Select the right size of implant for optimal stability
What is the required distance between implant and any vital structure
at least 2mm
What 2 important structures must you be aware of when placing an implant in the mx anterior region
Incisal foramen
Nasopalatine canal
Accessory mental foramen
Very rare
What must you do before placing mandibular posterior implant
CBCT nerve mapping - manually, not automatic
- Choose best panoramic-like slice that shows good nerve anatomy
- Start at mental foramen
- Trace it all the way back
Bifid mandibular canal
Bifid mandibular canal
Orthodontic applications of CBCT
Plus:
orthognathic surgery tx planning
Accurate estimation for space requirement for unerupted/impacted teeth
Assessment of ortho induced RR
Post treatment TMD
Transposition of 12/13
Why is CBCT effective for TMJ assessment
Ability to accurately define the true position of condyle in the fossa
Degenerative joint disease
“birds beak condyle”
What is the ALARA principle
As Low As Reasonable Achievable
- take conserative xrays/CBCT, based on diagnostic yield expected
Dentoalveolar trauma
Is CBCT suitable for internal/external root resorption?
Yes - could potentially be hiding palatally/lingually
- Use small volume CBCT
External/internal RR
- Couldnt see clinically bc subgingival
Is CBCT indicated for caries?
No
Is cbct indicated for perio?
Not for determining perio bone levels
However
can be used for infra-bony defects and furcations
Perio furcation involvement
Is cbct indicated for soft tissue assessment / oral malignancy?
No - should do medical CT or MRI instead
HOWEVER, if cancer involves bone - CBCT indicated
Benefits of CBCT over med CT
Faster
Smaller
Safer (lower dose)
Less expensive
More convenient
Specific to dentistry
Compare CT with CBCT
Update scan time: CBCT 5-10s
Med CT - <10s
