Ct Imaging

Question 1

are being used to create a gradient in the intensity of the X-ray beam

They are sometimes called “bow-tie” filters

They are mounted close to the X-ray tube.

The purpose of is to ⚫ reduce the dynamic range of the signal recorded by the CT

detector • Reduce the dose to the periphery of the patient

• Attempt to normalise the beam hardening of the beam - to aid with calibration

Answer 1

Beam shaping filters

Question 2

CT scanner detectors

⚫___-__ detector elements along the detector arc •

Answer 2

800-1000

Question 3

___-___detectors along z-axis

Answer 3

1-320

Question 4

CT detectors are ___ in the axial plane (x-y plane), and ____ along the longitudinal axis (z-axis)

Answer 4

curved
rectangular

Question 5

2 Detector type of CT & THEIR EFFICIENCY

Answer 5

Xenon gas filled-70%
Solid state- approaching 100%

Question 6

Better detection efficiency

Answer 6

Solid state detector

Question 7

Solid state detectors are generally
____

the photons interact with the detector and generate light.

Answer 7

scintillators

Question 8

The light is converted into an electrical signal by ____

Answer 8

photodiodes

Question 9

The septa and the strips of the anti scatter grid should be as __ as possible, since they reduce the effective area of the detector and thus reduce the detection of X-rays.

Answer 9

small

Question 10

Detector sizes are the effective size at the ____

Answer 10

iso-centre

Question 11

The minimum number of detector elements should be approximately ___to achieve a spatial resolution of d in the reconstructed image

Answer 11

2 FOV)/d

Question 12

→___- detector elements are required to achieve aspatial resolution of 1 mm within a reconstructed image at a field of view of 400 mm

Answer 12

800

Question 13

Spatial resolution can be improved by use of the ______ or_____

Answer 13

quarter detector shift
Dynamic focal spot

Question 14

By shifting the detector elements by a distance of a quarter of the size of the detector elements, the theoretical achievable spatial

resolution becomes twice as good. It is generally implemented in detectors of all CT scanners.

Answer 14

Quarter detector shift

Question 15

• Focal spot position on anode is rapidly oscillated during gantry rotation, doubling the number of projections

Answer 15

Dynamic or flying focal spot

Question 16

With the current detector rows and/or quarter detector shift and/or flying focal spot a spatial resolution of ~___-___mm in the axial plane can be achieved

Answer 16

0.6-0.9

Question 17

4 active detector rows -19__

16 active detector rows-20__

64 active detector rows in- 20__
320 active detector rows - 20__

Answer 17

98
01
04
07

Question 18

A typical acquisition with a single detector row scanner covered ___.

Answer 18

5 mm

Question 19

In clinical practice the CT scanners with __active detector rows were primarily used to enhance longitudinal
could also be used for enhanced longitudinal coverage, for example by selecting a 4 x 2 = 8 mm, or even a 4x4 = 16 mm coverage.

Enhanced longitudinal coverage would allow for shorter scan times but without the benefit of improved longitudinal resolution.

Answer 19

4

Question 20

• These scanners provided excellent longitudinal spatial resolution high quality 3D reconstructions, and at the same time reduced scan times.

Answer 20

16 or 64

Question 21

The CT scanners with up to __ active detector rows generally cover a scan volume with a helical acquisition with multiple rotations.

Answer 21

64

Question 22

The __ detector row CT scanner covers 160 mm on one

rotation, for organs such as the brain or the heart within one rotation.

Answer 22

320

Question 23

An x ray tube (with a rotating __ anode) and high voltage generator are used for generating the x ray beam.
The beam is collimated to create the ‘dose slice’ (or’__’)

Answer 23

tungsten
cone

Question 24

In fast CT scanners with rotation times in the order of magnitude of __ seconds, rotating parts are exposed to
several tenths of g forces

Answer 24

0.35

Question 25

For multi-slice scanners where the longitudinal beam width
is no longer small the X-ray beam is often referred to as __
‘

Answer 25

cone beam

Question 26

between detectors to
prevent photons crossing to
neighbouring detectors

Answer 26

septa

Question 27

Resolution in the reconstructed images depends on
• ___ - along the detector arc and the z-axis
• The ___

Answer 27

The size of detector elements
angular separation of the projection