CBCT

Question 1

Conventional CT

Answer 1

-Collimated into a narrow (fan) beam
– Image slice by slice
– 1d detector
– Patient is moved

Question 2

Cone Beam CT

Answer 2

– Wide (cone) beam
– Wider, flat detector (2d)
– Image whole volume at once

Question 3

MV

Answer 3

Poor contrast resolution because of the higher energy
» CE rather than PE
-No need to extrapolate LAC from kV to MV for dosimetry
‒ Less susceptibility to artefacts due to high metallic objects

Question 4

kV

Answer 4

-New equipment and software needed
‒ Better resolution
‒ Ideal for new systems

Question 5

CBCT is not

Answer 5

Not sliced based tf resolution is the same in all axes.

Question 6

Scan Parameters: kV

Answer 6

-determines max energy
-determinded by seperation
-60kV to 150kV = normal values

Question 7

Scan Parameters: mA

Answer 7

-number of photons used needs to be high
-to be considered per slice
-anything up to 500

Question 8

Bow tie filter: use

Answer 8

ensure homogeneity
harden beam

Question 9

Not using a bow tie filter gives

Answer 9

-⇣ HU accuracy
-loss of image uniformity

Question 10

There are 4 different ways of imaging when using kv CBCT equipment:

Answer 10

-plain film radiograph
-fluoroscopy
-volumetric CT imaging
-4DCT

Question 11

CBCT compares favourably with

Answer 11

helical CT with (comparably) large pitch

Question 12

CBCT will increase

Answer 12

soft tissue contrast and signal to noise ratio

Question 13

advantages of half scan

Answer 13

• Shorter scan time
• Higher exposure in each individual projection
  ‒ i.e. Higher signal to noise ratio.

Question 14

Disadvantage of half scan

Answer 14

• Fewer projections
• Therefore probably lower image quality