Lecture 14: X-ray CT Image Quality Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What is the main source of noise in x-ray CT images?

A

The fluctuation in the number of photons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the standard deviation for the number of photons detected in x-ray CT?

A

Sqrt(N) for N photons detected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the signal to noise ratio for x-ray CT?

A

N = number of photons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

A high photon count gives a ____ signal to noise ratio.

A

High

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the risk of having a high number of photons in x-ray CT?

A

It increases the risk to the health of patients as the dose of ionising radiation is higher.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the width of each voxel recorded for an x-ray CT image depend on?

A

Collimation/the ability to collimate: poor collimation causes the beam to diverge with distance so there is a change in voxel size.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Define partial voluming

A

The effect when tissue only fills part of a voxel.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the two main forms of partial voluming, and what is the effect of each?

A

Multiple tissue types in one voxel/tissue only fills part of the voxel: blurred image

Effect of interest is small relative to the voxel size: it gets averaged out so missed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the result of diverging beams for x-ray CT? How can this be mitigated?

A

It results in a slice sensitivity profile that is not ‘rectangular’ but one that diverges. Projections can be taken from both sides of the body to mitigate this.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Define beam hardening

A

An x-ray beam that is poly-energetic. As it passes through tissue the low energy photons are easily absorbed, hence, the average energy of the beam increases with distance through the patient and the beam ‘hardens’. This means that µ appears to decrease with depth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly