Image Quality (CTBC 8)

Question 1

Spatial Resolution

Answer 1

(Sharpness)
Clarity level of small parts, spaces b/w small parts, edges of parts

Question 2

Spatial Resolution & Pitch

Answer 2

Decreased pitch requires less interpolation and increases potential spatial resolution in z-axis (reformations)

Question 3

Spatial Resolution & Matrix Size

Answer 3

Larger matrix = more pixels
More pixels allow for greater detail

Question 4

Decreased acquisition slice thickness produces _______ spatial resolution in z-axis (reformations)

Answer 4

Higher

Question 5

Reconstructing with thin slices –> _______ spatial resolution in z-axis (reformations)

Answer 5

highest

Question 6

Edge-enhancing algorithms (bone/lung) _______ sharpness & spatial resolution

Answer 6

increase

Question 7

Spatial Resolution & DFOV

Answer 7

Smaller DFOV creates smaller pixel dimensions w/ability to resolve smaller parts

Question 8

Increasing spatial resolution can have the effect of increasing the appearance of _______ _______

Answer 8

Image Noise

Question 9

Eventually the appearance of image noise will disguise any increase in _______ ________

Answer 9

Spatial Resolution

Question 10

Smoothing algorithms are utilized instead of edge-enhancing algorithms when…

Answer 10

Decrease in apparent image noise is needed

Question 11

Unit for measuring spatial resolution: visualization of more line pairs indicates higher spatial resolution

Answer 11

Line-pairs per mm (lp/mm) [or line-pairs per cm (lp/cm)]

Question 12

Contrast Resolution (2)

Answer 12

Ability of CT machine to create visible difference in brightness levels (aka “contrast”)
Ability of the scanner to visually discriminate between objects with similar physical density

Question 13

Sensitivity of the System

Answer 13

Ability to create visible contrast b/w objects with very similar LAC

Question 14

Increasing kVp causes more uniform penetration of patient and _______ contrast

Answer 14

Decreases

Question 15

Measurable difference in photon intensity striking detector array

Answer 15

Differential Attenuation

Question 16

Factors influencing display contrast (3+)

Answer 16

kVp
Filtration (applied?)
Patient Morphology
Etc.

Question 17

Decreasing kVp results in (3) _______ Scatter, _______ Differential Attenuation, _______ Contrast Resolution

Answer 17

Less Scatter
More Differential Attenuation
Increased Contrast Resolution

Question 18

Smaller patients result in _______ Scatter, _______ Differential Attenuation, _______ Contrast Resolution

Answer 18

Less Scatter
More Differential Attenuation
Increased Contrast Resolution

Question 19

Window Width controls the range of displayed tissues thereby changing

Answer 19

Displayed Contrast

Question 20

Image Noise typically results from

Answer 20

Inadequate exposure to detectors

Question 21

Higher Standard Deviation (within ROI) indicates _______ variance and, therefore, _______ image noise

Answer 21

Higher Variance–> Higher Image Noise

Question 22

2 methods for quatifying noise

Answer 22

Contrast Resolution Test

Measure Standard Deviation using a Simple ROI

Question 23

Decreased Image Noise usually results in _______ patient dose, _______ spatial resolution

Answer 23

Increased Patient Dose
Decreased Spatial Resolution

Question 24

Increasing kVp increases detector exposure and _______ image noise

Answer 24

Reduces Image Noise

Question 25

Increasing mA increases detector exposure and _______ image noise

Answer 25

Reduces Image Noise

Question 26

Increasing Rotation Time _______ detector exposure and _______ image noise

Answer 26

Increases Detector Exposure Reduces Image Noise

Question 27

Increasing (acquisition or reconstruction) Slice Thickness _______ image noise

Answer 27

Reduces Image Noise

Question 28

Smoothing Algorithms (e.g., standard) _______ image noise

Answer 28

Reduce Image Noise

Question 29

Temporal Resolution

Answer 29

Ability to produce still images of moving parts (similar to shutter speed of film camera: faster avoids blurring)

Question 30

Decreasing Rotation Time _______ temporal resolution

Answer 30

Increases Temporal Resolution

Question 31

Increasing Acquisition Thickness _______ total scan time, thus _______ temporal resolution

Answer 31

Decreases total scan time, Increasing temporal resolution

Question 32

Increasing Pitch _______ total scan time, thus _______ temporal resolution

Answer 32

Decreases total scan time, Increasing temporal resolution

Question 33

Half-scan algorithms

Answer 33

Use only 180 deg of scan info to reconstruct complete data (thus doubling scan speed), enhancing temporal resolution

Question 34

Certain algorithms improve _______ _______ by reducing motion artifacts

Answer 34

Temporal Resolution

Question 35

Gating technology diminishes _______ _______, _______ temporal resolution

Answer 35

cardiac motion increasing temporal resolution

Question 36

CT number Accuracy

Answer 36

Assurance that specific materials (and, in turn, specific tissues) generate specific CT numbers

Question 37

HU Water

Answer 37

0

Question 38

HU Air

Answer 38

-1000

Question 39

Air Calibration typically corrects problems with:

Answer 39

HU accuracy

Question 40

Linearity

Answer 40

Relationship b/w attenuation properties of material and resulting CT number

Question 41

As attenuation (tissue density) increases, CT numbers increase at a _______ rate

Answer 41

Linear rate

Question 42

A linearity test phantom includes several cylinders with varying materials of differing _______

Answer 42

Density

Question 43

For a Linearity Test Phantom, the resulting graph (of LAC for the respective cylinders) should be _______.

Answer 43

Linear

Question 44

Uniformity

Answer 44

Ability of scanner to yield same CT number for same substance regardless of ROI-position

Question 45

Factors impacting Uniformity (3)

Answer 45

Beam Hardening Scatter Radiation Limited Stability of Scanner

Question 46

Capping Artifact

Answer 46

Higher CT numbers in center (of uniform phantom)

Question 47

Cupping Artifact

Answer 47

Lower CT numbers in center (of uniform phantom)