S2 - CBCT Flashcards
What is CBCT
form of x-ray computed tomography where x-rays are divergent, forming a cone
for imaging hard tissues of maxillofacial regions
provides clinicians with sub-milimeter spatial resolution images of high diagnostic quality with relatively short scanning time (1-10s) and reported radiation dose equivalent to that needed for 1-10 panoramic radiographs
Disadvantages of sitting position CBCT systems vs moving
- high radiation
- larger space
- sitting position (accessibility)
- more expensive
- lower dose
- occupies less space
- cheaper
Requirements for ideal CBCT image for diagnosis (5)
- good density and contrast
- sharpness
- good resolution
- accuracy in measurements (1:1 ratio)
- free of artefacts (but some may have)
Advantages of CBCT
- rapid scan time (similar to OPG, 1-10s)
- image accuracy
- multiplanar reformatting
- 3D volume rendering
- x-ray beam allows optimum Field of View (FOV) to be selected - only that area is irradiated
- better images with good resolution
- no magnification
- specific to dentistry
- less expensive compared to CT
- reduced radiation (0.052-1.025mSv) when compared to medical CT (1.4-2.1mSv)
- better suited for imaging osseous structures
- comfortable and safe
Disadvantages of CBCT
- artifacts - motion artifacts due to increased scan time compared to medical CT
- poor contrast resolution, thus soft tissue cannot be a viewed
Effective radiation doses of dental radiation (average in adult, microsieverts µSv)
digital OPG - 10
intraoral x-ray - 5
CBCT - 80
Limitations of panoramic imaging (5)
- 2D image of 3D structure
- horizontal and vertical magnification
- distortion
- superimposition
- positioning errors
Why is there vertical magnification in OPGs?
all panoramic beam angles are approximately at 8 degrees which gives the image inherent vertical magnification (approx 10%)
What is the degree of rotation of a CBCT and what does it result in?
180-360 deg
scanned volume
4 components of CBCT image acquisition (stupid ass useless question, L if he asks)
- xray generation
- image formation/detection
- image reconstruction
- image display
What is the x-ray generator?
What does it consist of? (4,1)
high voltage generator that modifies incoming voltage and current into an x-ray bea, of desired peak kilo-voltage (kVp) and current (mA)
- x-ray tube - anode, cathode, tube envelop, tube housing
- collimator
How is a CBCT taken? (Briefly)
- generator produces xray beam of desired voltage
- during rotation, many exposures are made at fixed intervals, making single projection images called ‘basis images’ (similar to lat cephs but each offset from one another) → about 150-600 base images produced → complete series is called projection data
- images are then reconstructed in 3 planes (axial, sagittal, coronal) aka ‘secondary reconstructions’ via software
Label
What is field of view?
What is meant by full FOV?
What is the standard/medium FOV vs smaller
area of anatomy captured by the scan (aka scan volume)
full FOV = nearly full skull
standard/medium FOV = both arches including TMJ area, smaller = arch or quadrant
How big should FOV - scan volume be?
limit to smallest volume that can accomodate region of interest
dunno if need to know
What is frame rate?
What is measured as?
How does it affect imaging?
speed at which individual images are acquired, measured as projected images per second
with higher frame rate, more info available to reconstruct image ∴ primary reconstruction time increased
higher frame rate reduces metallic artifacts BUT higher radiation dose
2 types of image detectors
image intensifier tube/CCD/CMOS combination (IIT/CCD)
flat panel detector - most common (smaller, used at JCUD)
What is a digital image
series of pixels organised in matrix of rows and columns
pixel size varies from 10-70 microns
What is a pixel vs voxel
pixel - smallest controllable element of a picture represented on screen, is digital equivalent of silver halide crystal used in conventional radiograph, unlike SH they have an ordered arrangement
voxel - pixel with volume (vo, el = element), CUBIC in nature (in CBCT), equal in all dimensions
size of voxel 0.1-0.7mm typically
What is an isotropic voxel and how does it defer from anisotropic voxel, when is it used?
CBCT is always an isotropic voxel aka perfect cube, measurements are exact
conventional CT is anisotropic voxel, always a brick
How does image reconstruction differ between CBCT and CT?
cone beam geometry vs fan beam geometry (for single slice)
in CBCT, basis projections form secondary reconstructions whereas in CT primary reconstructions form secondary reconstructions
3 tomographic planes/CBCT reference planes
axial - slices superior to inferior
coronal - front to back
sagittal - side to side
3 tomographic planes/CBCT reference planes
axial - slices superior to inferior
coronal - front to back
sagittal - side to side
What is Multiplanar Refomatting (MPR)
reformatting of images of CBCT data set resulting in 3 basic image types
- axial images with computer generated superimposed curve of alveolar process
- cross sectional images
- panoramic like images
Space between 2 cross sectional images of an area
0.5-5mm
Minimum distance the base implant should be from a vital structure
2mm
What is the structure shown
lingual foramen
Data volume vs single image storage size
Types of resolution (ability to differentiate between 2 closely placed objects)
spatial resolution: ability to visualise difference between 2 objects of different radio density (e.g. enamel and dentine)
contrast resolution: ability to differentiate 2 objects of same colour type (e.g. parotid and masseter)
What is shown
FS - frontal sinus
SS- sphenoid air sinus
S - sella turcica
NPC - nasopalatine canal
NP - nasopharynx
OC - oral cavity
What is shown
MS - mx sinus
INC - inf nasal concha
ZP - zygomatic process
NF - nasopharynx
MR - ramus
PP - pterygoid plates
What is shown
What is high definition mode (HD)
certain indications i.e. visualisation of fine root canals, high radiation
When is CBCT indicated vs not indicated for endo tx complications
- assessing accidental introduction of RC instruments or obturation material into vital structure
- evaluation of complex anatomy/morphology - anomalies e.g. dens invaginatus, root morphology, canal anatomy, root curvatures, additional roots, anomalies within canal (obstruction, narrowing, bifurcation)
- NOT for assessment of endodontic outcomes
- NOT for determining true WL compared to EAL
Why was this PA RL not seen from IOPA but can be from CBCT?
overlap from thick buccal cortical plane
Indications of CBCT in OMFS (6)
- investigate exact location of jaw pathologies
- assess impacted and supernumerary teeth and their relationship to vital structures
- consideration of resorption of an adjacent tooth
- pre and post-surgical assessment of bone graft recipient sites
- some paranasal sinus pathology (NOT ALL)
- planning orthognathic surgeries
Which diseases of the mx sinus is/isnt CBCT advised for?
polyp - no
retention pseudocyst (no)
mucocele (yes)
What is this structure and would CBCT be advised for it? Give description of structure
nasopalatine cyst
axial section - large nasopalatine cyst, thinning and discontinuation of B and P cortical plate
For which tumours of the mandible is CBCT advised?
you MUST advise CBCT for any tumours in the mandible
Uses of CBCT in Implantology (6)
- determine presence of absence of disease at implant site
- measure and localise the available jaw bone for virtual implant placement w accuracy and precision
- determine relationship of critical structures to implant site + nerve mapping
- determine quality* and quantity of bone
- determine implant orientation
- select right size of implant for optimal stability and integration
*not as reliable as medical CT
VItal structures in upper anterior region
nasopalatine canal
incisive foramen
Vital structure in posterior mx region
mx sinus
What happened in the images?
perforated lingual cortical plate
severe haematoma on the anterior floor of the mouth after implant placement
echymosis on the chin after implant placement in the anterior mandible
Vital structures in mandible
mental foramen
accessory mental foramens (0.1-0.2% ppl)
lingual foramen
IAN nerve
What may detecting accessory mental foramens decrease risk of?
risk of hemorrhage, post-op pain and paralysis in implant surgeries
What is nerve mapping?
2 methods - auto or manual (more accuracteO
take the best panoramic-like image, click from mental foramen all the way (red dots placed close tgt)
What is shown
bifid md canals
What is shown
lingual cortical bone perforation by implant
What is shown?
implants displaced into mx sinus, associated with mucositis
3 types of md ridge morphology
line A represents line of reference - 2mm coronal to IAN
Orthodontic applications of CBCT in DIAGNOSIS (6)
- assessment of skeletal and dental structures: skeletal jaw relation, symmetry/asymmetry
- 3D evaluation of impacted tooth position
- growth assessment
- pharyngeal airway analysis
- assessment of the TMJ complex in 3 dimensions
- cleft palate assessment
Orthodontic applications of CBCT - TX PLANNING & RISK ASSESSMENT
- orthognathic surgery planning
- planning for placement of temporary anchorage devices
- accurate estimation for space requirement for unerupted & impacted teeth
- assessment of orthodontics induced root resorption
- post treatment TMD
Indication of CBCTs to assess TMJ
effective to assess TMJs structures, thereby guaranteeing correct diagnosis and treatment - cant see articular disc (soft tissue)
one major advantage is ability to define true position of condyle in fossa
What is characteristic of degenerative joint disease?
bird beak shaped condyle
Use of CBCT in dentoalveolar trauma
- better to visualise location and angulation of root fractures compared to PA and occlusographs
- decision to use it should be based on expected diagnostic yield and ALARA principle
Use of CBCT for IRR and ERR
shows true size/position of all resorptive defects
Use of CBCT for caries and periodontal tissue assessment
not indicated for caries detection or determining perio bone levels
HOWEVER, high res CBCT may be indicated in selected cases of infra-bony defects and furcation lesions where other methods are not enough
When is CBCT indicated in oral cancer?
- NOT indicated for soft tissue/malignancy evaluation - would need MSCT (medical CT) or MRI
- Limited volume, high res CBCT may be indicated for evaluation of bony invasion of jaws
Pros of CBCT vs medical CT (6)
- faster
- smaller
- safer (lower dose)
- cheaper
- more convenient
- specific to dentistry
What must you do when referring pt for CBCT
give sufficient clinical info including patient history and results of examination to allow CBCT practitioner to perform justification process
e.g. vitality of tooth
T or F - routine or screening CBCT is encouraged
F - unacceptable practice!
