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23 Radiology > 9 - CBCT > Flashcards

9 - CBCT Flashcards

1
Q

what acquires data volumetrically providing 3D radiographic imaging for the assessment of the dental and maxillofacial complex.

A

principles of CBCT

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2
Q

does CBCT require SINGLE or MULTIPLE rotational scan to acquire full volume of images (data for imaging reconstruction)

A

single

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3
Q

scan time of CBCT

A

<30 seconds

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4
Q

steps of CBCT

A
  1. image acquisition
  2. raw data (2D projections)
  3. image reconstruction (3D dataset)
  4. visualization (2D slices, etc.)
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5
Q

main difference between CBCT and MCDT (cat scan?)

A

CBCT = whole volume with single rotation
MDCT = one slide every rotation

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6
Q

components of CBCT

A
  • xray generation
  • xray detection
  • image reconstruction
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7
Q

CBCT: continous or pulsed

A

pulsed preferred since it reduces patient radiation dose

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8
Q

what is selected accoring to patient size in CBCT

A

mA and kVp

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9
Q

what happens with faster CBCT scans

A

fewer basis images (lower frame rate) - less radiation exopsure, less motion artifact but more noise

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10
Q

what happens with slower CBCT scans

A

more basis images (higher frame rate), more radiation exposure, better images, less metal artifacts

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11
Q

why do you limit field size to region of interest (ROI) in CBCT

A

less radiation exposure, less scatter, improved imaged quality

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12
Q

rotation angle of CBCT

A

180-360 degree
less rotation angle, less radiation exposure, but greater noise

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13
Q

what is used for xray detection in older machiens

A

image intensifier tube/charge coupled device combination

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14
Q

what are flat panel detectors

A
  • Cesium iodide scintillator applied to a thin film transistor made of amorphous silicon
  • Most common
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15
Q

what is the most commonly used for xray detection

A

flat panel detectors

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16
Q

the smallest elements of digital picture is what

A

pixel

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17
Q

what is a pixel called in a detector

A

dixel

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18
Q

how are pixels arranged

A

in rows and columns to form the matrix

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19
Q

what is a 3D representation of pixel and is isometric (cube) in CBCT

A

voxel

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20
Q

what is the ability of an image to reveal fine detail

A

spatial resoltuon

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21
Q

the prinsipal determinant of voxel size in CBCT image is what

A

pixel size of the detector

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22
Q

what has a better resolution: smaller or larger pixel/voxel

A

smaller

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23
Q

distadvantages of voxel

A

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

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24
Q

what is number of gray shades that can be displayed (related to contrast resolution)

A

bit depth

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25
what is bit depth of current CBCT units
12 bit depth
26
what happens at a higher bit depth
increased computational time and substantially larger file sizes
27
what is the bit depth form lowest to highest
28
how to calculate bit depth and grey shade
if 1 BIT: 2^1=2 grey shades 4 BIT: 2^4 = 16 grey shades etc.
29
It is desirable to limit the field size to the ___ that provide sufficient images to the ROI.
smallest volume
30
procedure for taking CBCT
1. Calibrate machine daily or before each exposure 2. Seat patient 3. Set field of view and voxel size 4. Head position with lights & use a restraint 5. Scout image 6. Reposition head if needed and repeat scout 7. 360° exposure for approximately 10 30 seconds 8. Primary reformat of data 30 seconds 9. Secondary reformat
31
where is primary reconstruction completed
acquisition computerd
32
describe acquitision stage
1. acquiring basis projections 2. image correction for inconsistencies 3. sinogram formation
33
describe reconstruction stage
1. sinogram 2. applying feldkamp reconstruction with filtered back projection 3. 3D volumetric data
34
where is secondary reconstruction completed
workstation computer
35
what is a full-thickness image that can be used to generate stimulated projections, such as lateral ceph images or pano images)
ray sum
36
what allows visualization of volumetric data by selective display of voxels within a data set
volume rendering
37
what is a distortion or error in the quality of the image
image articants
38
types of image articants
1. inherent artifacts 2. procedure-related artifacts 3. introduced artifacts
39
what artifact is the limitation in the physical process of CBCT acquisition? exmaples
inherent artifacts - scatter - partial volume averaging - cone beam effects
40
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
41
what artifact is produced by high energy photons? examples
Introduce artifacts - beam hardening: cupping articact - beam heardening: extraction of missing artifact - patient motion
42
what artifact
scatter
43
is partial volume averaging representative of either bone or soft tissue?
NO! it is an average of the tissues included
44
what artifact
partial volume averaging (shows loss of cortical border when actually a thin border is present)
45
what artifact is present due to undersampling of cone beam angle
cone-beam effect
46
what artifact from alternating light and dark lines due to undersampling
aliasing artifact
47
what artifact results due to imperfect scanner detection or poor calibration
scanner related artifact
48
what artifact results due to misalignment of xray source to the detector
double contour artifact
49
what artifact when xray beam passes thru an object, lower energy photons are absorbed in preference to higher energy photons
beam hardening artifacts
50
2 types of beam hardening artifacts
1. cupping artifact 2. extinction of missing value artifacts
51
what artifact is distortion of metallic structures as a result of differential aborption
cupping artifact
52
what artifact has dark bands present between two dense onjects
extinction or missing value artifacts
53
54
what artficat
patient motion
55
when to use CBCT
1. diagnosis and preoperative assessments 2. tx planning and virtual simulations 3. image guided surgery and additive manufacturing
56
pano on left and CBCT on right
57
strenghts of CBCT
1. Reduced size compared with conventional CT equipment. 2. Fast acquisition 3. Submillimeter resolution 4. Relatively low patient radiation dose
58
limitations of CBCT
Image noise Poor soft tissue contrast
59
A
axial
60
B
coronal
61
C
sagittal
62
A
ethmoid air cells
63
B
superior concha
64
C
maxillary sinus
65
D
hard palate
66
E
middle concha
67
F
zygomatic arch
68
G
inferior concha
69
A
lateral wall of orbit
70
B
infraorbital fissure
71
C
mandibular ramus
72
D
mandibular body
73
E
ethmoid air cells
74
F
superior concha
75
G
nasal septum
76
H
alveolar process
77
A
roof of sphenoid sinus
78
B
infraorbital fissure
79
C
mandibular ramus
80
D
mandibular body
81
E
sphenoid sinus
82
F
pterygopalatine fossa
83
G
lateral pterygoid plate
84
H
medial pterygoid plate
85
A
sphenoid sinus roof
86
B
sphenoid bone
87
C
vidian pretygoid canal
88
D
choana
89
E
mandibular canal
90
F
optic canal
91
G
sphenoid sinus
92
H
foramen rotundum
93
I
lateral pterygoid plate
94
A
anterior clenoid process
95
B
zygomatic process of temporal bone
96
C
sphenosquamosal suture
97
D
sphenoid sinus roof
98
E
foramen ovale
99
F
palatine tonsiles
100
G
hyoid bone
101
what is this xray of
mandible
102
what is this xray of
TMJ
103
what is this xray of
base of skull
104
what is this xray of
airway

23 Radiology (15 decks)

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