Image quality

Question 1

Several quality control (QC) tests were performed on four different scanners. Based on the results of these tests, Which scanner has the least amount of image noise?

Answer 1

Water phantom average = 1.0 HU
water phantom standard deviation = 0.2
Line pairs = 13 Ip/cm

Question 2

excessive noise in a CT image may result

Answer 2

1. Decreased spatial resolution

2. Decreased contrast resolution

Question 3

The motion artifact is a quality control issue related to:

Answer 3

Temporal resolution

Question 4

When scanning a water phantom for quality control, you notice that a region of interest (ROI) in the center of the phantom reads 0 HU but an ROI on the edge of the phantom read 4 HU. This is a problem with:

Answer 4

Uniformity

Question 5

What combination of variables will result in the least amount of image noise?

Answer 5

Pitch = 0.9, reconstruction thickness = 5.0, Tube voltage = 140, matrix = 512 x 512

The tube voltage (kVp) is the primary factor influencing the image noise. using a large voltage, such as 140 kvp, will increase the amount of photons getting to the receptors and therefore decrease the image noise

Question 6

After performing a CT of the chest, a region of ROI placed in the air outside of the patient yields an average CT number of -1,223. This error represents a problem with:

Answer 6

Accuracy

Question 7

A CT of the cranium calls for 2.0 mm slices in the posterior fossa and 5.0 mm slices through the vertex. What change in image quality will be observed in the 5.0 mm slices?

Answer 7

Decreased noise

Question 8

Which of these variable changes may decrease the spatial resolution of the resulting CT image?

Answer 8

Increased reconstruction thickness.

Sometimes an increase in size thickness is preferred to decrease the image noise, but this does result in a decrease in spatial resolution

Question 9

The ability of the scanner to visually discriminate between objects with similar physical density is called

Answer 9

contrast resolution

Question 10

While imaging an infant, the rotation time may be decreased to prevent motion artifacts. A decrease in rotation time represents a change in:

Answer 10

Temporal resolution

Question 11

What QC test evaluates the ability of the CT scanner to produce the same CT number for the same material regardless of where the region of the interest is placed

Answer 11

Uniformity

Question 12

Temporal resolution is defined as the ability to

Answer 12

produce still images of objects in motion

Question 13

Several QC tests were performed on four different scanners. Based in the results of the tests, which scanner has the best CT number accuracy?

Answer 13

Water phantom average = -0.5 HU
Water phantom standard deviation = 3.1
Line pairs = 12 Ip/cm

CT number accuracy refers to the ability of the scanner to produce a HU reading that is very similar the expected reading. A water phantom should produce an average HU very close to zero.

Question 14

Which of these variable changes is most likely to improve the contrast resolution of the resulting images?

Answer 14

Decrease patient size.

Question 15

of the following options, what reconstruction slice thickness will display images with the highest level of spatial resolution?

Answer 15

0.625

The major side effect of using thin reconstructed slices is an increase in image noise

Question 16

Which of these variable changes will increase temporal resolution?

Answer 16

Increase pitch

Question 17

Which of these reconstruction algorithms are likely to produce the best spatial resolution?

Answer 17

bone algorithms

Question 18

Consider a CT scan used to evaluate the brain for metastatic disease. If the average CT number of the tumors differs only slightly from the surrounding brain matter, What characteristic of the scanner might cause limited visibility of the tumors/

Answer 18

Contrast resolution

Question 19

Motion artifact in the heart can be minimized by using

Answer 19

EKG gating

Question 20

Which of the following describes the ability of CT scanners to produce detailed images of small parts?

Answer 20

Spatial resolution

Question 21

Scanning a large patient without changing the exposure factors could result in increased:

Answer 21

image noise

Question 22

spatial resolution is defined as the ability to

Answer 22

visualize small parts

Question 23

When a region of ROI is placed over a homogenous structure, which of these values represent the image noise?

Answer 23

HU standard deviation

Question 24

Which of the following us measured in line-pairs per centimeter?

Answer 24

spatial resolution