CT Image Quality Flashcards Preview

CT Physics and Instrumentation (ARRT) > CT Image Quality > Flashcards

Flashcards in CT Image Quality Deck (20)
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1
Q

Define spatial resolution.

A

the ability of a CT system to display fine details separately; the degree to which a CT system can distinguish very small parts

2
Q

Define MTF. What is its range?

A

modular transfer function. used to show accurately a CT system can display an object. an MTF of 1.0 is 100% to scale, while an MTF of 0.0 does not show the object

3
Q

A small focal spot ________ spacial resolution.

A

increases/improves

4
Q

How can detector size and geometry affect spacial resolution?

A

smaller, closely spaced detectors IMPROVE spacial resolution

5
Q

High frequency reconstruction algorithms (kernels) are used for what type of anatomy? How would this kernel affect spacial resolution?

A
  1. bones, or edges (of anatomy)

2. improve spacial resolution

6
Q

What combination of large/small matrix size and large/small pixels/DFOV gives the best spacial resolution?

A

large matrix size and small pixels (small DFOV)

7
Q

What element affects longitudinal spacial resolution? How is LS resolution measured?

A

how quickly the patient moves through the gantry (pitch). it is measured by the slice sensitivity profile

8
Q

By increasing pitch, you ______ longitudinal spacial resolution.

A

decrease

9
Q

Define contrast resolution.

A

the ability of a CT system to differentiate two objects with very similar densities, or linear attenuation coefficients

10
Q

What is the smallest difference, in HU, a modern CT system can differentiate?

A

3 HU

11
Q

A decrease in noise results in a(n) _______ of contrast resolution.

A

increase

12
Q

What algorithm results in increased contrast resolution?

A

low frequency

13
Q

Increasing detector collimation _______ contrast resolution.

A

decreases: this will increase noise which reduces contrast

14
Q

Define temporal resolution.

A

the ability of a CT system to “freeze” motion

15
Q

What is the main factor controlling temporal resolution?

A

the speed of the gantry rotation

16
Q

What type of artifact is common in CT systems with low temporal resolution?

A

misregistration.

17
Q

An increase in x-ray photon flux causes a(n) ______ in image noise.

A

decrease

18
Q

How does voxel dimension affect image noise?

A

by increasing voxel dimension, there is more space for radiation to interact therefore reducing noise.

19
Q

What does a CT system’s Uniformity measure?

A

uniformity measures the system’s ability to maintain relatively consistent CT numbers of an entire object of equal density

20
Q

What does a CT system’s Linearity measure?

A

how well the system displays CT numbers based on known and accepted HU for certain objects, i.e. -1000 for air and 0 for water. when scanning water, the HU should be as close to 0 as possible