9 - CBCT Flashcards
what acquires data volumetrically providing 3D radiographic imaging for the assessment of the dental and maxillofacial complex.
principles of CBCT
does CBCT require SINGLE or MULTIPLE rotational scan to acquire full volume of images (data for imaging reconstruction)
single
scan time of CBCT
<30 seconds
steps of CBCT
- image acquisition
- raw data (2D projections)
- image reconstruction (3D dataset)
- visualization (2D slices, etc.)
main difference between CBCT and MCDT (cat scan?)
CBCT = whole volume with single rotation
MDCT = one slide every rotation
components of CBCT
- xray generation
- xray detection
- image reconstruction
CBCT: continous or pulsed
pulsed preferred since it reduces patient radiation dose
what is selected accoring to patient size in CBCT
mA and kVp
what happens with faster CBCT scans
fewer basis images (lower frame rate) - less radiation exopsure, less motion artifact but more noise
what happens with slower CBCT scans
more basis images (higher frame rate), more radiation exposure, better images, less metal artifacts
why do you limit field size to region of interest (ROI) in CBCT
less radiation exposure, less scatter, improved imaged quality
rotation angle of CBCT
180-360 degree
less rotation angle, less radiation exposure, but greater noise
what is used for xray detection in older machiens
image intensifier tube/charge coupled device combination
what are flat panel detectors
- Cesium iodide scintillator applied to a thin film transistor made of amorphous silicon
- Most common
what is the most commonly used for xray detection
flat panel detectors
the smallest elements of digital picture is what
pixel
what is a pixel called in a detector
dixel
how are pixels arranged
in rows and columns to form the matrix
what is a 3D representation of pixel and is isometric (cube) in CBCT
voxel
what is the ability of an image to reveal fine detail
spatial resoltuon
the prinsipal determinant of voxel size in CBCT image is what
pixel size of the detector
what has a better resolution: smaller or larger pixel/voxel
smaller
distadvantages of voxel
Disadv: Detectors with smaller pixels capture fewer x-
ray photons per voxel and result in more image noise.
Require higher dosages to achieve a reasonable signal-
to-noise ratio for improved diagnostic image quality.
E.g. Small FoV scan for endo purpose
what is number of gray shades that can be displayed (related to contrast resolution)
bit depth
what is bit depth of current CBCT units
12 bit depth
what happens at a higher bit depth
increased computational time and substantially larger file sizes
what is the bit depth form lowest to highest
how to calculate bit depth and grey shade
if 1 BIT: 2^1=2 grey shades
4 BIT: 2^4 = 16 grey shades
etc.
It is desirable to limit the field size to the ___ that provide sufficient images to the ROI.
smallest volume
procedure for taking CBCT
- Calibrate machine daily or before each exposure
- Seat patient
- Set field of view and voxel size
- Head position with lights & use a restraint
- Scout image
- Reposition head if needed and repeat scout
- 360° exposure for approximately 10 30 seconds
- Primary reformat of data 30 seconds
- Secondary reformat
where is primary reconstruction completed
acquisition computerd
describe acquitision stage
- acquiring basis projections
- image correction for inconsistencies
- sinogram formation
describe reconstruction stage
- sinogram
- applying feldkamp reconstruction with filtered back projection
- 3D volumetric data
where is secondary reconstruction completed
workstation computer
what is a full-thickness image that can be used to generate stimulated projections, such as lateral ceph images or pano images)
ray sum
what allows visualization of volumetric data by selective display of voxels within a data set
volume rendering
what is a distortion or error in the quality of the image
image articants
types of image articants
- inherent artifacts
- procedure-related artifacts
- introduced artifacts
what artifact is the limitation in the physical process of CBCT acquisition? exmaples
inherent artifacts
- scatter
- partial volume averaging
- cone beam effects
what artifact is under-sampling data that leads to miss-registration, noisier images? examples
procedure-related artifacts
- aliasing artifact
- scanner related artifact
- double contour artifact
what artifact is produced by high energy photons? examples
Introduce artifacts
- beam hardening: cupping articact
- beam heardening: extraction of missing artifact
- patient motion
what artifact
scatter
what artifact
partial volume averaging (shows loss of cortical border when actually a thin border is present)
what artficat
patient motion
pano on left and CBCT on right
A
axial
B
coronal
C
sagittal
A
ethmoid air cells
B
superior concha
C
maxillary sinus
D
hard palate
E
middle concha
F
zygomatic arch
G
inferior concha
A
lateral wall of orbit
B
infraorbital fissure
C
mandibular ramus
D
mandibular body
E
ethmoid air cells
F
superior concha
G
nasal septum
H
alveolar process
A
roof of sphenoid sinus
B
infraorbital fissure
C
mandibular ramus
D
mandibular body
E
sphenoid sinus
F
pterygopalatine fossa
G
lateral pterygoid plate
H
medial pterygoid plate
A
sphenoid sinus roof
B
sphenoid bone
C
vidian pretygoid canal
D
choana
E
mandibular canal
F
optic canal
G
sphenoid sinus
H
foramen rotundum
I
lateral pterygoid plate
A
anterior clenoid process
B
zygomatic process of temporal bone
C
sphenosquamosal suture
D
sphenoid sinus roof
E
foramen ovale
F
palatine tonsiles
G
hyoid bone
what is this xray of
mandible
what is this xray of
TMJ
what is this xray of
base of skull
what is this xray of
airway
