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