* CT Image Quality Quiz *

Which of the following would be an example of an image rendering technique (uses only image data)?

Maximum intensity projection

The service engineer performed a slice thickness accuracy test. He measured a slice that was supposed to be 4mm thick. If his measurement was 5mm would this be within acceptable limits?

No

Given the scenario in question 25 and it is possible to change the DFOV from the original 12cm to 24 cm, which of the following best describes what this will do to the spatial resolution of the image?

decreases the spatial resolution

Given that all other parameters stay the same, which of the following occurs when slice thickness is reduced:

spatial resolution increases

Given a WW of 2000 and WL of 0, which of the following HU would appear white?

Any HU greater than +1000 will appear white

Given a WW of 400 and a WL of 50, which of the following HU would appear white?

Any HU greater than +250 will appear white

Which of the following would have the longest gray scale?

A wider WW = more shades of gray = longer gray scale.

Which description best defines noise?

a point to point fluctuation in the CT number within

a uniform material; speckled appearance of the CT image

caused by insufficient photons reaching the detectors;

grainy appearance

Which of the following best describes spatial resolution in CT?

ability to resolve small objects that are very close together

The value of a CT number is related principally to:

the tissue's linear attenuation coefficient

Which of the following best describes contrast resolution in CT?

the ability to distinguish between similar tissues; the ability to differentiate a structure that varies only slightly in density from its surroundings

Which of the following represents the Hounsfield's established unit for Bone?

+1000 HU

When viewing a CT image, the term window level refers to the:

the central value of the window width; "the center CT number"

Which of the following describes a process of producing a new set of images u

Retrospective reconstruction

Which of the following describes how fast a CT system can acquire its data?

Temporal resolution

The principal advantage of a larger matrix size in a reconstructed CT image is:

Better (higher) spatial resolution.

Which of the following display options is similar to a ruler in that it can m...

Distance Measurements

Which of the following display options would be useful in determining where a....

ROI

Which of the following describes the process of using raw data to create an i...

Image reconstruction

Which of the following is NOT affected by changing the slice thickness?

Matrix size

Which of the following image rendering processes produces a new set of images...

Multi-Planar Reformation (MPR)

Which type of data is needed to perform a retrospective reconstruction?

raw data

When CT numbers are expressed in HU, the value of air is represented

as:

-1000 HU

Which of the following represents the Hounsfield Unit for water?

0 HU

Which of the following matrix size would result in best spatial resolution?

largest matrix = best spatial resolution

Which of the following would be an example of an image rendering technique

Image reformation: uses image data to produce

images in different planes or to produce 3D images; uses only image data

Spatial resolution in CT refers to the:

The ability of the CT scanner to discriminate objects of varying density a small distance apart

Which of the following is NOT describing spatial resolution?

Low contrast resolution

A change in which of the following would affect spatial resolution in CT?

Reconstruction algorithm, focal spot size, and slice thickness (1, 2, 4)

Which of the following matrix sizes would result in the best spatial resolution?

512 x 512

Contrast resolution in CT refers to the:

The ability of the scanner to demonstrate small changes in tissue contrast

Which of the following improves contrast resolution?

Larger slice thickness, higher mAs, and smaller pixels (1, 3, 4)

The fluctuation of CT numbers from point to point in an image is called:

Noise

Which of the following decreases noise in CT?

Larger DFOV, increased slice thickness, and higher mAs/kVp (1, 2, 3)

An increase in slice thickness will do which of the following?

Decrease spatial resolution, increase contrast resolution, decrease noise, and decrease patient dose

An increase in pixel size will do which of the following?

Decrease spatial resolution, increase contrast resolution, and decrease noise

Going from a 1024 x 1024 image matrix to a 512 x 512 matrix will do which of the following?

Decrease spatial resolution, increase contrast resolution, and decrease noise

Which of the following is affected by a change in DFOV?

Contrast resolution, spatial resolution, and noise

Given a WW of 3000 and WL of 500, is this image going to have high or low scale contrast?

Low scale contrast, because a wide window width = low contrast and a long gray scale

For WW 3000 and WL 500, which CT number will appear white?

2500

For WW 3000 and WL 500, which CT number will appear gray?

200

For WW 3000 and WL 500, which CT number will appear black?

-2000

What tissue type is best imaged with WW 3000 and WL 500?

Bone tissue, because WL is in bone range on Hounsfield scale

Given a WW of 100 and WL of 40, is this image going to have high or low scale contrast?

High scale contrast, because short window width = high contrast, short gray scale

For WW 100 and WL 40, which CT number will appear gray?

10

For WW 100 and WL 40, which CT number will appear white?

100

For WW 100 and WL 40, which CT number will appear black?

-100

What tissue type is best imaged with WW 100 and WL 40?

Soft tissue, because WL falls in soft tissue HU range

Given a WW of 2000 and WL of 500, is this image going to have high or low scale contrast?

Low scale contrast, because wide window width = low contrast, long gray scale

For WW 2000 and WL 500, which CT number will appear white?

2000

For WW 2000 and WL 500, which CT number will appear gray?

0

For WW 2000 and WL 500, which CT number will appear black?

-1000

What tissue type is best imaged with WW 2000 and WL 500?

Bone, because the WL is in the bone HU range

Given a WW of 2000 and WL of -500, is this image going to have high or low scale contrast?

Low scale contrast, because wide window width = low contrast, long gray scale

For WW 2000 and WL -500, which CT number will appear white?

500

For WW 2000 and WL -500, which CT number will appear gray?

0

For WW 2000 and WL -500, which CT number will appear black?

-1500

What tissue type is best imaged with WW 2000 and WL -500?

Lung tissue, because WL is in lung HU range

What happens to tissues above the maximum window range?

They appear white

What happens to tissues below the minimum window range?

They appear black

What do tissues within the window width appear as?

Shades of gray