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oral radiology > CBCT > Flashcards

CBCT Flashcards

1
Q

CBCT is what form of image processing?

A

image reconstruction

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2
Q

is CBCT a direct image capture

A

no, indirect
many images captured and used by software to create 3d

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3
Q

Computed Tomography (CT) defined

A

Use of computers to generate multiple images of an object from digitized density information obtained from various signals; x radiation (MDCT, CBCT), magnetic fields (MRI), sonar radiation (ultrasound), etc.

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4
Q

forms of xray CT

A
  • Two forms of x ray CT
    -CBCT (Cone Beam Computed Tomography)
    –MDCT (Multi Detector Computed Tomography)
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5
Q

when did CBCT development begin?

A

around 2000, EU and japan

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6
Q

pt position options of CBCT

A

standing or sitting

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7
Q

CBCT machine developed in US

A

i-CAT FLX
V8, V10, or V17 models (sit down system)

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8
Q

pros of a stand up machine

A

faster, less space taken up

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9
Q

cons of stand up machine

A

more likely pt will move

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10
Q

benefit of sit down machine

A

less pt movement

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11
Q

cons of sit down machine

A

more space/time

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12
Q

CBCT units quality

A
  • Nearly all CBCT units are good quality high-end
    imaging equipment made for a very competitive market
    place
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13
Q

why do CBCT unit become outdated

A
  • Become outdated due to competition from competitor brands technical innovations:
  • memory
  • bit depth
  • FOV options
  • operating systems
  • compatibility with software technologies, etc.
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14
Q

lifetime of typical CBCT unit

A

6-8 yrs

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15
Q

radiation of CBCT compared to other CT, why?

A

Less radiation than other forms of CT (i.e. MDCT) for hard tissue imaging because of:
less scanning of X-radiation
lower radiation

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16
Q

CBCT effective dose compared to PSPP,CMOS,CCD

A

usually more but wide range

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17
Q

why do CBCT dosimetry studies values vary

A

because Studies are not Directly Comparable!!!
* Variations in experimental methodologies
* Different devices and settings
* Different size FOVs including shapes of FOV
* Differences in high and low resolution scans
* Dosimetry phantoms
* ICRP E1990 vs E2007 (dif calculations)

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18
Q

facotrs affecting CBCT dose

A
  • FOV
  • Exposure
  • Voxel
  • Sensors
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19
Q

CBCT FOV
Flat Panel Detector shape

A

Cylindrical shape and measurement characteristics
Diameter (mm) x Height (mm)

20
Q

CBCT FOV
Image Intensifier Detector

A

Sphericalshape and measurement characteristics
Diameter (mm) only

21
Q

can FOV be selected? why?

A

yes, based on diagnostic task

22
Q

CBCT units and FOV options

A

CBCT units have capabilities for
scanning a range of FOV sizes

23
Q

exposure factors of CBCT

A
  • kV ranges between various units 75 kV – 120 kV
  • mA 7 mA – 20 mA
  • Time – affected by basis image data (# images)
24
Q

CBCT Image Production

A
25
Q

CBCT image capture

A

rotation of source and receptor around head with many scans occurring each capturing a basis image used for projection data to form volumetric data set

26
Q

how many basis images are captured

A

can be hundreds

27
Q

effect of # of basis images

A

number of basis images/projection angles increased will improve image reconstruction

28
Q

CBCT quick scans

A

can take decreasaed images with decreased image quality when not an issue, allows for decresed dose (ortho)

29
Q

ways # basis images affects the image

A
  1. Image Quality, more = increased detail/quality
  2. Dose, more = increased dose
30
Q

voxels

A

smallest imaging component
smallest area of info we can obtain
make up the FOV

31
Q

effect of voxel size on res/sharpness

A

smaller voxels yield greater resolution and sharpness

32
Q

issues with small voxels

A
  • small voxel yields LOWER signal to noise ratio, i.e., degraded image quality due to wider scatter effect
  • small voxel yields high radiation dose
33
Q

why do small voxels have a lower signal to noise ratio?

A

more scatter occurs resulting in scatter photons at receptor= blurred image

34
Q

why do small voxels increase exposure

A

small voxel yields high resolution but requires more
x-ray photons (higher exposure) to capture signal in
the greater number of the smaller voxels

35
Q

voxel size for larger FOVs (>5x5cm)

A
  • > 0.2mm = 200μm – for larger FOVs
36
Q

voxel size for smaller FOVs (less than or = to 5x5cm)

A
  • <0.200mm = 200 μm – for smaller FOVs
37
Q

current scanners and long scans/processing times for large FOV with small voxels?

A

Current scanners are not configured for the longer scan times and longer processing times for a large FOV with a small voxel size

38
Q

how do small voxels increase radiation dose

A

Smaller voxels need more photon signal which
yields a higher radiation dose

39
Q

CBCT image detector types

A

flat panel and image intensifier

40
Q

cons of the image intensifier

A

bulkier, heavier, more money to make

41
Q

pro of image intensifier

A

decreased dosage

42
Q

Image Detector Distortion Patterns

A

image intensfier will have peripheral distortion
not seen in flat panel

43
Q

peripheral distortion of image intensifier

A

Distortion of the image grid when moving away
from the center.

44
Q

Flat Panel Detector
Distortion Patterns

A

Image receptor area receiving the signal from the
flat-panel detector’s scintillator is flat. Even at more
distant areas from the center of the grid, there is
minimal to no distortion of the grid pattern.

45
Q

flat panel image vs image intensifier

A

flat panel with improved quality and higher signal to noise ratio (more sharp)

46
Q

other names used?

Cone Beam terminology

A
  • CBCT
    *CBVT (volume tomograhpy)
  • DCT (dental)
  • MCT (microCT)
  • 3DI (3D image)

oral radiology (22 decks)

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