Week 2 Amar- CBCT Flashcards
What direction do x-rays run in CBCT?
Divergent
What are CBCT’s good for?
Imaging hard tissues in maxillofacial region. (can’t differentiate between different soft tissues e.g. b/w parotid gland and masseter).
What imaging methods are best for visualising soft tissues?
CT or MRI
What is the scanning time and radiation dose of CBCT imaging?
Scanning time 1-10 secs
Radiation dose equivalent to 1-10 panoramic radiographs
What is the difference between sitting and standing Cone Beam Maxillofacial Imaging Systems?
Sitting: high radiation, larger space and more expensive
Standing: lower radiation, less space and cheaper
What are required characteristics for ideal CBCT?
- Good density and contrast
- Sharpness
- Good resolution
- Accuracy in measurements
- Free of artifacts
What are advantages of CBCT?
- Rapid scan time
- Image accuracy
- Multiplanar reformatting
- 3D volume rendering
- Optimum FOV can be selected
- Better images with good resolution
- No magnification
- Less $$ and lower radiation dose than CT
- Better suited for imaging osseous structures
- Comfortable & safe
What are disadvantages of CBCT?
- Artifacts
- Motion artifacts due to inc scan time compared to medical CT
- Poor contrast resolution (soft tissues can’t be viewed)
What is the μSv for OPG, intraoral x-ray and CBCT?
- OPG: 10
- Intraoral x-ray: 5
- CBCT: 80
What are limitations of panoramic imaging?
- 2D image of 3D structure
- Distortion
- Superimposition
- Positioning errors
- Horizontal & vertical magnification
What is the angulation of panoramic beam?
-7-8
What are the 4 components of CBCT image acquisition?
- X-ray generation
- Image formation/detection
- Image reconstruction
- Image display
How does x-ray generator work?
- During rotations, many exposures are made at fixed intervals (basis images)
- 150-600 images are produced
- Basis images → projection data → images reconstructed in 3 planes (axial sagittal and coronal)
Describe terminology of images for CBCT
Basis images (150-600) converted to secondary reconstructions (sagittal, axial and coronal images). Whole data set is known as projection.
What is field of view and the different types?
Area of anatomy captured by scan
- 5x5: single arch
- 8x8: mx, md but not TMJ
- 11x10: both jaws with TMJ
What is frame rate?
Speed that individual images are acquired (projected images/sec)
What does a higher frame rate mean?
- More info is available to reconstruct the image (therefore primary reconstruction time is increased)
- Reduces metallic artifacts
- Longer scan time, higher radiation dose
What is a digital image comprised of?
Series of pixels organised in matrix of rows and columns
What is a voxel?
Originates from word “pixel” with
- “vo” representing volume
- “el” representing element
They are cubic in nature (in CBCT)- equal in all dimensions
What type of voxel does CBCT vs CT have?
- CBCT: isotropic voxel (cube)
- CT: anisotropic voxel (brick)
What are the 3 different planes for CBCT? What is the blue line indicating?
- Axial (slices sup-inf)
- Coronal/cross-sectional image (front-back)
- Sagittal image (side to side)
(Blue line in image is tomographic plane)
What is multiplanar reformatting?
Reformatted images of CBCT data set result in 3 basic image types
- axial images with computer generated superimposed curve of alveolar process
- Cross sectional images
- Panoramic images
How close can cross sectional images be spaced?
0.5 to 5mm spacing between images
What is resolution?
Ability of image to differentiate between 2 closely placed objects
What are the 2 types of resolution?
Spatial: ability to visualise diff between 2 objects of diff radiodensity
Contrast: ability to differentiate 2 objects of same colour type
Label the following anatomic landmarks on CBCT
- FS – Frontal sinus
- S – Sella
- SS – Sphenoidal air sinus
- NPC – Nasopalatine canal
- NP – Nasopharynx
- OC – Oral cavity
- Black airspace in figure A starts as nasopharyngeal airspace and leads to oropharyngeal airspace
Label the following landmarks on CBCT
- MS – Max sinus
- INC – Inferior nasal concha
- ZP – Zygomatic process
- NF – Nasopharynx
- MR – Ramus
- PP – Pterygoid plates (medial and lateral)
- Red arrows: eustachian tube
Label the following landmarks on CBCT
- AES – Anterior Ethmoidal sinus
- MNC- Middle nasal conchae
- Green dotted line- Mx ostium
- OC- oral cavity
- FS- frontal sinus
What does this CBCT reveal?
Untreated 47DB canal
What has happened in this situation?
Obturation material has extruded out apex of 37 and a CBCT was taken to see if the material was in the IAC or lingual/buccal to it. Numbness was also associated.
What is the issue with this case?
Perforation was made and obturation material extruded buccally. Exo indicated.
What is the reason for ordering CBCT in this case?
Pt had crown and obturation done and presented with pain. Internal root resorption present in IOPA- dentist wanted to rule out external RR. CBCT found that were was external RR and tooth was indicated for exo.
Interpret this CBCT
- 4 roots of tooth 26 can be easily followed until the apices
- Dentist wanted to identify which root perforated mx antrum and was causing mx sinusitis
- P root was culprit as the floor of mx sinus has been lifted above this root
Interpret this IOPA and CBCT
Pt came in with pain. In IOPA, thick buccal cortical plate was superimposed over root apices so couldn’t see PA radiolucency in 2D imaging. Small volume CBCT was taken and radiolucency could be visualised at apex.
Interpret this CBCT of nasopalatine cyst
Discontinuation and B and P cortical plate
Would record size
Which of the following require CBCT?
- A: polyp (not required)
- B: retention pseudocyst (not required)
- C: mucocele (required)
Is CBCT required in this case?
Yes, always advise CBCT for these cases
Interpret CBCT in this case
Axial and coronal images show right mandibular abnormality
- Discontinuation of lingual cortical plate
- Expansion of B and L cortical plate
Why is this CBCT important for implant placement?
Arrows pointing to nasopalatine canal and incisive foramen. In figure B, bone is too thin and implant wouldn’t be able to be placed here
What is the benefit of identifying accessory mental foramens?
Detecting AMFs may decrease the risk of hemorrhage, postoperative pain and
paralysis in implant surgeries.
Very rare
What is the blue arrow pointing to?
Lingual foramen
What is being carried out in this CBCT?
Nerve mapping (place dots close together to draw nerve)
Why was a small volume CBCT taken for this case before implant placement?
Bifid mandibular canal
Why was an implant contraindicated in this case?
Bone too thin
What has happened in this case?
Lingual cortical perforation by implant (common when there is sublingual undercut and no CBCT was taken prior)
What has happened in this case?
Implants displaced into the maxillary sinus, associated with mucositis
What has happened in this case?
- Protrusion of pulpal contents B aspect of 11
- Internal RR in IOPA of 11.
- Small volume CBCT was done. CBCT displayed that internal RR had extended with buccal and palatal perforations. Poor prognosis and indicated for exo
Compare CBCT and CT
