CBCT

Question 1

Image reconstruction

Answer 1

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

Question 1

Image reconstruction

Answer 1

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

Question 2

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

Answer 2

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

Question 3

Two forms of x ray CT
(2)

Answer 3

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

Question 4

Nearly all CBCT units are

Answer 4

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

Question 5

Become outdated due to competition from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

Answer 5

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

Question 6

The lifetime of a CBCT unit is

Answer 6

~6 - 8 years

Question 7

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

Answer 7

less scanning of X-radiation
lower radiation

Question 8

1 day of background radiation ~

Answer 8

8.5μSv

Question 9

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

Answer 9

• 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

Question 10

Factors Affecting Dose
(4)

Answer 10

• FOV
• Exposure
• Voxel
• Sensors

Question 11

CBCT FOV
Flat Panel Detector

Answer 11

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

Question 12

CBCT FOV
Image Intensifier Detector

Answer 12

Cylindrical shape and measurement characteristics
Diameter (mm) only

Question 13

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

Answer 13

FOV sizes

Question 14

Exposure Factors
* kV ranges between various units
kV
mA

Answer 14

75 kV – 120 kV
7 mA – 20 mA

Question 15

• Time – affected by

Answer 15

basis image data

Question 16

Multiple basis image projections form the

Answer 16

projection data.

Question 17

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

Answer 17

volumetric data set
software manufacturers.

Question 18

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

Answer 18

counterclockwise
Position 1 to Position 2

Question 19

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

Answer 19

1. Image Quality
2. Dose

Question 20

skipped
Resolution: Voxel size

Answer 20

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)

Question 21

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

Answer 21

high
LOWER, degraded
image quality
high

Question 22

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

Answer 22

> 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

Question 23

CBCT Image Detectors
(2)

Answer 23

charge-coupled image
intensifier detector.
flat-panel detector

Question 24

Cone Beam terminology

Answer 24

* CBCT *CBVT * DCT * MCT * 3DI