CBCT Flashcards

1
Q

Image reconstruction

A

Data is utilized by other software programs
and produces different image presentations

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1
Q

Image reconstruction

A

Data is utilized by other software programs
and produces different image presentations

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2
Q

Computed Tomography (CT)
* Use of computers to generate multiple
images of an object from digitized density
information obtained from various signals;
(3)

A

x radiation (MDCT, CBCT), magnetic fields
(MRI), sonar radiation (ultrasound), etc.

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3
Q

Two forms of x ray CT
(2)

A

-CBCT (Cone Beam Computed Tomography)
–MDCT (Multi Detector Computed Tomography)

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4
Q

Nearly all CBCT units are

A

good quality high-end
imaging equipment made for a very competitive market
place

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5
Q

Become outdated due to competition from
competitor brands
technical innovations:
(5)

A
  • memory
  • bit depth
  • FOV options
  • operating systems
  • compatibility with
    software technologies, etc.
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6
Q

The lifetime of a CBCT unit is

A

~6 - 8 years

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7
Q

Benefits of Cone Beam Imaging
Less radiation than other forms of CT (i.e. MDCT) for hard
tissue imaging because of:
(2)

A

less scanning of X-radiation
lower radiation

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8
Q

1 day of background radiation ~

A

8.5μSv

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9
Q

skipped
CBCT Dosimetry Study Values Vary
because
Studies are not Directly Comparable!!!
(6)

A
  • 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
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10
Q

Factors Affecting Dose
(4)

A
  • FOV
  • Exposure
  • Voxel
  • Sensors
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11
Q

CBCT FOV
Flat Panel Detector

A

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

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12
Q

CBCT FOV
Image Intensifier Detector

A

Cylindrical shape and measurement characteristics
Diameter (mm) only

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13
Q

Multiple FOV Options
CBCT units have capabilities for
scanning a range of

A

FOV sizes

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14
Q

Exposure Factors
* kV ranges between various units
kV
mA

A

75 kV – 120 kV
7 mA – 20 mA

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15
Q

• Time – affected by

A

basis image data

16
Q

Multiple basis image projections form the

A

projection data.

17
Q

A —- is then constructed by an imaging software program which then
displays various image reconstructions. The latter is dependent on the power of the
programs as specified by the

A

volumetric data set
software manufacturers.

18
Q

CBCT Basis-image Capture
Two basis-image capture sequences as the machine
rotates — from

A

counterclockwise
Position 1 to Position 2

19
Q

CBCT Image Production
Number of basis images affects image
(2)

A
  1. Image Quality
  2. Dose
20
Q

skipped
Resolution: Voxel size

A

0.4mm3 (400um)
0.30mm3 (300 um)
0.20mm3 (200 um)
0.08mm3 ( 80 um)
0.076mm3 ( 76 um)
0.075mm3 ( 75 um)
0.050mm3 ( 50 um)

21
Q

Voxel size
* 0.3mm = 300μm
* 0.075mm = 75 μm

  • small voxel yields —
    resolution
  • small voxel yields
    — signal to noise
    ratio, i.e.,
  • small voxel yields —
    radiation dose
A

high
LOWER, degraded
image quality
high

22
Q

Voxel size
* —- – for larger FOVs
* —- – for smaller FOVs
~ < 5cm x 5cm

A

> 0.200mm = 200μm
<0.200mm = 200 μm

  • small voxel yields high resolution but requires more
    x-ray photons (higher exposure) to capture signal in
    the greater number of the smaller voxels
  • Current scanners are not configured for the longer
    scan times and longer processing times for a large
    FOV with a small voxel size
  • Smaller voxels need more photon signal which
    yields a higher radiation dose
23
Q

CBCT Image Detectors
(2)

A

charge-coupled image
intensifier detector.
flat-panel detector

24
Q

Cone Beam terminology

A
  • CBCT
    *CBVT
  • DCT
  • MCT
  • 3DI