Ch 3 Ct Image Quality Flashcards Preview

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Flashcards in Ch 3 Ct Image Quality Deck (125)
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1

Influences on user parameter selection p 4

Contrast resolution
Spatial resolution
Temporal imaging
Image noise
Patient dose

2

Tissues with difference of _____% in density can be differentiated in ct

O.5%

3

Contrast resolution p 4

ability to,differentiate small differences in density on the image

4

Spatial resolution p 4

Measure of size of the smallest on object that can be visualized in an image

In line pairs

5

Spatial resolution affected by geometric factors of the scanner p 4

Focal spot size
Detector Aperture size
Focal spot to patient distance
Patient to detector difference

6

Spatial resolution factors that control it p 4

Slice thickness
Display for
Image matrix
Reconstruction filters

7

Temporal resolution p 5

Precision of measurement with respect to time

8

2 effects Increases temporal resolution p 5

Quicker scans
Increase rows of detectors

9

Noise p 6

Grainy image that makes it difficult to see subtle contrast differences or fine details

10

Dose p 7

Amount of ionizing radiation absorbed by patient per unit of mass

11

To maximize image quality sometimes there is increase in______ p 8

Patient dose

12

Attenuation p 9

Progressive reduction of intensity of the X-ray beam as it passes through patient tissue

13

Amount attenuation is dependent on p 9

Anatomic number
Density of electrons
Thickness
Photon energy

14

Number photons measure by detectors is reduced as thickness tissue ______ p 9

Increases

15

When X-ray beam passes through patient , number of photons in beam is reduced while mean energy of photons _____ p 10

Increase

16

Ct number p 11

Gray scale number assigned to each pixel in Ct image

17

Hounsfield number p 11

Aka Ct number named after inventor of Ct in 1967 aka HU

18

Water Ct number

0

19

Air Ct number

-1000

20

Fat Ct number

-80

21

Soft tissue Ct number range

30-80

22

Ct number shows calcification

Above 100

23

What calculates ct number p11

Filtered back projection

24

Higher ct numbers assigned to shades of grey?

Lighter shades of grey for dense structures

25

Lower ct numbers assigned to shades of grey? P 11

Darker shades for non dense structures

26

Ma p 13

Tube current

27

Mas p 13

Ma x time

28

Increasing the mas _____ image noise but _____ patient dose

Decrease
Increase

29

What doesn't affect image contrast or spatial resolution ?

Mas

30

Scan times should be short to minimize _____ and maximize _____

Motion
Patient throughput