CT Image Appearance Flashcards

1
Q

The resolution of a CT scanner is often expressed in terms of…

A

“Line pairs”

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2
Q

How can you determine spatial resolution?

A

Centimeter divided by lines (in a line pair)

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3
Q

What can we adjust to affect resolution?

A

Pixel size
Slice thickness
Reconstruction filter

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4
Q

What factor would make an image appear more noisy?

A

Insufficient number of photons contributing to the pixels

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5
Q

What are some factors that influence parameter selection?

A

Contrast
Resolution
Noise
Dose

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6
Q

Why would applying a noise-reducing algorithm during image reconstruction be a preferred method?

A

Can minimize the dose without compromising the image quality

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7
Q

What determines the number of x-ray photons produced by the CT x-ray tube?

A

mA

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8
Q

What happens when you increase the mAs / kVp?

A

Dose increases while noise decreases

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9
Q

What determines the maximum energy of the x-ray photons produced by the CT x-ray tube?

A

kVp

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10
Q

What does it mean when you increase the kVp?

A

Increases the photon’s ability to penetrate the tissues of the patient’s body

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11
Q

Which parameter controls the contrast in a CT image?

A

kVp

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12
Q

On single-row detector scanners, slice thickness is partially defined by:

A

The size of the focal spot in the CT x-ray tube

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13
Q

On single-row detectors, the acquired slice thickness is equal to:

A

The collimated x-ray beam thickness (as well as the final image thickness)

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14
Q

What does the acquired slice thickness indicate?

A

Which rows of detectors are being used to measure the photons

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15
Q

What are the two slice thickness parameters?

A

Acquired slice thickness

Reconstructive (“effective”) slick thickness

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16
Q

What does the reconstructive (“effective”) slice thickness indicate?

A

The thickness of the final image

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17
Q

On multi-row detector scanners, the final slice thickness must be equal to or greater than:

A

The acquired slice thickness

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18
Q

What happens when you increase the slice thickness?

A

Decreases noise

Increases amount of anatomy being covered

19
Q

The result of a decrease in resolution due to slices that are too thick:

A

Partial voluming

20
Q

If you increase the slice thickness while covering the same anatomical region, what happens to the radiation dose to the patient?

A

May decrease

21
Q

How can you achieve contiguous slices?

A

The table increment must be equal to the slice volume

22
Q

What does selecting a value for the pitch specify?

A

How compressed or stretched the path of the x-ray beam takes on a helical scan

23
Q

On a single-row detector, what is the pitch equal to?

A

Movement of the patient table in one gantry rotation divided by the slick thickness

24
Q

On a multi-row detector, what is the pitch equal to?

A

Movement of the patient table in one gantry divided by total slice volume or thickness of a single slice

25
A pitch that is increased / decreased results in a _____ / _____ helix
Stretched / Compressed
26
What are some reasons to increasing the pitch?
Greater anatomical coverage in less time Faster scan for trauma patients Appropriate contrast timing during a CTA study Decrease dose to the patient
27
How is the radiation dose to the patient related to the pitch?
Reducing the pitch increases dose to the patient
28
Reconstruction interval may be modified and the new value may be applied through:
Retrospective reconstruction
29
If the reconstruction interval is equal to the reconstructed slice thickness, the reconstructed slice thickness will be:
Contiguous
30
If the reconstruction interval is less than the reconstructed slice thickness, the reconstructed slice thickness will be:
Overlapped
31
Increasing the reconstruction FOV will make the anatomy appear:
Smaller
32
Increasing the reconstruction FOV will make the image appear:
Less noisy
33
The size of a single pixel is equal to:
The reconstruction FOV divided by the number of pixels in the image matrix
34
What happens when the image matrix increases?
Yield smaller pixels (better resolution) | Increases noise
35
How is the degree of beam hardening determined?
By dense structures and travelling further through the tissues of the body
36
Where may you might see beam hardening manifesting itself as a cupping artifact?
In the supratentorium of the brain
37
What are ways in which you can minimize beam hardening artifacts?
Use correction algorithms Using thin slices Don't scan through very dense contrast media
38
What can be the result of a partial volume artifact?
Blurriness Incorrect CT numbers Missed pathology / false positives
39
How can you minimize partial volume artifacts?
Using thinner slices
40
A high window level will make the image appear:
Darker allowing more dense structures to be evaluated
41
A low window level will make the image appear:
Brighter allowing less dense structures to be evaluated
42
A display filter is applied directly to the _____ data.
Digital image
43
Why would you not want to apply a display filter when taking ROI measurements?
Can vary the pixel values | False ROI readings
44
Magnification is a post-processing technique applied to the ____ data.
Image