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Radiology > S2 - CBCT > Flashcards

S2 - CBCT Flashcards

1
Q

What is CBCT

A

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

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2
Q

Disadvantages of sitting position CBCT systems vs moving

A
  • high radiation
  • larger space
  • sitting position (accessibility)
  • more expensive
  • lower dose
  • occupies less space
  • cheaper
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3
Q

Requirements for ideal CBCT image for diagnosis (5)

A
  • good density and contrast
  • sharpness
  • good resolution
  • accuracy in measurements (1:1 ratio)
  • free of artefacts (but some may have)
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4
Q

Advantages of CBCT

A
  • 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
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5
Q

Disadvantages of CBCT

A
  • artifacts - motion artifacts due to increased scan time compared to medical CT
  • poor contrast resolution, thus soft tissue cannot be a viewed
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6
Q

Effective radiation doses of dental radiation (average in adult, microsieverts µSv)

A

digital OPG - 10

intraoral x-ray - 5

CBCT - 80

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7
Q

Limitations of panoramic imaging (5)

A
  • 2D image of 3D structure
  • horizontal and vertical magnification
  • distortion
  • superimposition
  • positioning errors
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8
Q

Why is there vertical magnification in OPGs?

A

all panoramic beam angles are approximately at 8 degrees which gives the image inherent vertical magnification (approx 10%)

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9
Q

What is the degree of rotation of a CBCT and what does it result in?

A

180-360 deg

scanned volume

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10
Q

4 components of CBCT image acquisition (stupid ass useless question, L if he asks)

A
  • xray generation
  • image formation/detection
  • image reconstruction
  • image display
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11
Q

What is the x-ray generator?

What does it consist of? (4,1)

A

high voltage generator that modifies incoming voltage and current into an x-ray bea, of desired peak kilo-voltage (kVp) and current (mA)

  1. x-ray tube - anode, cathode, tube envelop, tube housing
  2. collimator
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12
Q

How is a CBCT taken? (Briefly)

A
  1. generator produces xray beam of desired voltage
  2. 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
  3. images are then reconstructed in 3 planes (axial, sagittal, coronal) aka ‘secondary reconstructions’ via software
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13
Q

Label

A
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14
Q

What is field of view?

What is meant by full FOV?

What is the standard/medium FOV vs smaller

A

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

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15
Q

How big should FOV - scan volume be?

A

limit to smallest volume that can accomodate region of interest

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16
Q

dunno if need to know

A
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17
Q

What is frame rate?

What is measured as?

How does it affect imaging?

A

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

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18
Q

2 types of image detectors

A

image intensifier tube/CCD/CMOS combination (IIT/CCD)

flat panel detector - most common (smaller, used at JCUD)

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19
Q

What is a digital image

A

series of pixels organised in matrix of rows and columns

pixel size varies from 10-70 microns

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20
Q

What is a pixel vs voxel

A

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

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21
Q

What is an isotropic voxel and how does it defer from anisotropic voxel, when is it used?

A

CBCT is always an isotropic voxel aka perfect cube, measurements are exact

conventional CT is anisotropic voxel, always a brick

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22
Q

How does image reconstruction differ between CBCT and CT?

A

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

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23
Q

3 tomographic planes/CBCT reference planes

A

axial - slices superior to inferior

coronal - front to back

sagittal - side to side

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23
Q

3 tomographic planes/CBCT reference planes

A

axial - slices superior to inferior

coronal - front to back

sagittal - side to side

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24
Q

What is Multiplanar Refomatting (MPR)

A

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
25
Q

Space between 2 cross sectional images of an area

A

0.5-5mm

26
Q

Minimum distance the base implant should be from a vital structure

A

2mm

27
Q

What is the structure shown

A

lingual foramen

28
Q

Data volume vs single image storage size

A
29
Q

Types of resolution (ability to differentiate between 2 closely placed objects)

A

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)

30
Q

What is shown

A

FS - frontal sinus

SS- sphenoid air sinus

S - sella turcica

NPC - nasopalatine canal

NP - nasopharynx

OC - oral cavity

31
Q

What is shown

A

MS - mx sinus

INC - inf nasal concha

ZP - zygomatic process

NF - nasopharynx

MR - ramus

PP - pterygoid plates

32
Q

What is shown

A
33
Q

What is high definition mode (HD)

A

certain indications i.e. visualisation of fine root canals, high radiation

34
Q

When is CBCT indicated vs not indicated for endo tx complications

A
  • 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
35
Q

Why was this PA RL not seen from IOPA but can be from CBCT?

A

overlap from thick buccal cortical plane

36
Q

Indications of CBCT in OMFS (6)

A
  1. investigate exact location of jaw pathologies
  2. assess impacted and supernumerary teeth and their relationship to vital structures
  3. consideration of resorption of an adjacent tooth
  4. pre and post-surgical assessment of bone graft recipient sites
  5. some paranasal sinus pathology (NOT ALL)
  6. planning orthognathic surgeries
37
Q

Which diseases of the mx sinus is/isnt CBCT advised for?

A

polyp - no

retention pseudocyst (no)

mucocele (yes)

38
Q

What is this structure and would CBCT be advised for it? Give description of structure

A

nasopalatine cyst

axial section - large nasopalatine cyst, thinning and discontinuation of B and P cortical plate

39
Q

For which tumours of the mandible is CBCT advised?

A

you MUST advise CBCT for any tumours in the mandible

40
Q

Uses of CBCT in Implantology (6)

A
  • 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

41
Q

VItal structures in upper anterior region

A

nasopalatine canal

incisive foramen

42
Q

Vital structure in posterior mx region

A

mx sinus

43
Q

What happened in the images?

A

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

44
Q

Vital structures in mandible

A

mental foramen

accessory mental foramens (0.1-0.2% ppl)

lingual foramen

IAN nerve

45
Q

What may detecting accessory mental foramens decrease risk of?

A

risk of hemorrhage, post-op pain and paralysis in implant surgeries

46
Q

What is nerve mapping?

A

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)

47
Q

What is shown

A

bifid md canals

48
Q

What is shown

A

lingual cortical bone perforation by implant

49
Q

What is shown?

A

implants displaced into mx sinus, associated with mucositis

50
Q

3 types of md ridge morphology

A

line A represents line of reference - 2mm coronal to IAN

51
Q

Orthodontic applications of CBCT in DIAGNOSIS (6)

A
  • 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
52
Q

Orthodontic applications of CBCT - TX PLANNING & RISK ASSESSMENT

A
  • 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
53
Q

Indication of CBCTs to assess TMJ

A

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

54
Q

What is characteristic of degenerative joint disease?

A

bird beak shaped condyle

55
Q

Use of CBCT in dentoalveolar trauma

A
  • 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
56
Q

Use of CBCT for IRR and ERR

A

shows true size/position of all resorptive defects

57
Q

Use of CBCT for caries and periodontal tissue assessment

A

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

58
Q

When is CBCT indicated in oral cancer?

A
  • 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
59
Q

Pros of CBCT vs medical CT (6)

A
  • faster
  • smaller
  • safer (lower dose)
  • cheaper
  • more convenient
  • specific to dentistry
60
Q

What must you do when referring pt for CBCT

A

give sufficient clinical info including patient history and results of examination to allow CBCT practitioner to perform justification process

e.g. vitality of tooth

61
Q

T or F - routine or screening CBCT is encouraged

A

F - unacceptable practice!

Radiology (2 decks)

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