Chapters 15-16 Flashcards Preview

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Flashcards in Chapters 15-16 Deck (77):
1

bistable image are composed of how many shades?

2- black and white

2

Define contrast

the range of brilliancies within the displayed image.

3

What does low contrast mean?

many grey shades

4

what does high contrast mean?

bistable- white and black

5

What does brightness determine?

the brilliance of the displayed image

6

What does the scan converter do?

translates the info from the spoke format into video format

7

What are analog numbers?

"real world numbers"
unlimited number of choices and continuous range of values

8

What are digital numbers?

associated with computer numbers
they only have discrete values
limited choices

9

How does the analog scan converter work?

funnel shaped vacuum tube with a stream of charged particles called electrons, contain the image info, and are shot out of the electron gun. the larger end of the tube contains a dielectric matrix or silicon wafer.

10

What are limitations of analog scan converters?

image fade-silicon wafer dissipate over time
image flicker-caused by switching between read and write modes
instability- image quality depends on many factors like length of use, room temp, and humidity
deterioration- image degrades as device ages

11

What is superb with analog scan converter?

spatial resolution or image detail

12

Digital scan converters use computer technology to convert images into numbers, a process called what?

digitizing

13

What are the advantages for digital scan converter?

uniformity- consistent gray scale quality throughout the image
stability- does not fade or drift
durability- no affected by age or heavy use
speed- nearly instant processing
accuracy- error free

14

What are the two important elements of digital scan converters?

pixel and bit

15

What is a pixel?

smallest building block of a digital picture
(checkerboard)

16

What is the number of picture elements per inch?

pixel density

17

How is pixel density and spatial resolution related?

directly

18

How is higher pixel density achieved with?

smaller pixels =many pixels per in

19

What is a bit?

smallest amount of computer memory

20

What makes up a byte?

8 bits

21

What does a word of computer memory consists of?

two bytes, or 16 bits

22

Images with many gray shades have better what resolution?

contrast resolution

23

how is contrast resolution and bits per pixel related?

directly
more bits per pixel improved contrast resolution

24

How many gray shades in a 5 bits?

32
2x2x2x2x2=32

25

What is the difference between a pixel and a bit?

pixels:
image element
image detail
spatial resolution

Bits:
computer memory
gray shades
contrast resolution

26

What is the five step process of translating image info?

1. A-to-D converter
2. digital info is stored in the scan converter. any processing of the reflected signals before storage is preprocessing.
3.post processing
4. D-to-A converter
5. video display

27

What is an example of an A-to-D converter?

a computer mouse

28

What is an example of an D-to-A converter?

iPod

29

What is preprocessing?

the manipulation of image data before storage in the scan converter.
cant be undone or reversed

30

What is postprocessing?

manipulation of image data after storage in the scan converter
can be reversed

31

When does postprocessing occur?

occurs after A-to-D conversion (digitization) and storage

32

What are examples of preprocessing?

TGC
log compression
write
persistence
spatial compounding
edge enhancement
fill-in interpolation

33

What are examples of post processing?

any change after freeze frame
black/white inversion
read
contrast variation
3D rendering

34

What is it called when you enlarge a portion of an image to fill the entire screen?

magnification

35

What are the two types of magnification?

write
read

36

When does the read magnification occur?

after the image is stored in the scan converter
post processing

37

When does write magnification occur?

before the storage in the scan converter
preprocessing

38

What are some characteristics of read magnification?

uses old data
larger pixel size
same # of pixels as the original ROI
unchanged spatial resolution
unchanged temporal resolution

39

What are some characteristics of write magnification?

acquires new data
identical pixel size
more pixels than the original ROI
improved spatial resolution
may improve temporal resolution

40

When does temporal resolution improve with write magnification?

if the bottom of the region of interest is shallower than the original images depth of view.

41

What is a sophisticated method of improving image quality?

coded excitation

42

Where does coded excitation occur?

in the pulser

43

What does coded excitation provide?

higher signal to noise ration
improved axial resolution
improved spatial resolution
improved contrast resolution
deeper penetration

44

What does compound imaging do?

reduces speckle and minimizes shadowing artifacts

45

What are limitations of spatial compounding?

reduced frame rates and reduced temporal resolution

46

What type of steering is used in spatial compounding?

electronic steering
only available with phased array transducers

47

What is an advanced technique that reduces speckle artifact and noise in ultrasound images?

frequency compounding

48

What imaging process make pictures looks sharper?

edge enhancement
create subtle bright and dark highlights on either side of these boundaries to make them appear more defined.

49

What is it called when reflected sound wave is divided into parts with different freq ranges with frequency compounding?

sub bands

50

What are other names for temporal compounding?

persistence or temporal averaging

51

What is the process technique that continues to display info from older imaging?

temporal compounding

52

What is a limitation of persistence?

reduction in displayed frame rate, which reduces temporal resolution.

53

What is persistence more effective with?

slow moving structures.
cannot display rapid moving structures accurately

54

What is the purpose of fill in interpolation?

to fill in the gaps of missing data in a way that cannot be detected by the observer

55

What does fill in interpolation increase?

line density, which improves spatial resolution

56

What does PACS stand for?

picture archiving and communications system

57

What are three advantages for PACS?

virtually instant access to archived studies
no degradation of data-which happens with analog archiving
store and forward telemedicine

58

What are the primary digital storage devices used in PACS?

computer hard drives

59

What does DICOM stand for?

digital imaging and computers in medicine
is the set of rule that allows the components of network to communicate

60

Define dynamic range

a method of describing the extent to which a signal can vary and still maintain accuracy
"number of available choices"

61

Weak signals are below the systems ____

threshold

62

What are the units for dynamic range?

decibels

63

What is dynamic range?

a comparison, a relative measurement, or a ratio between the largest and smallest signals that are measured accurately.

64

The strong signals ____the system

saturate

65

The dynamic range of info ___(increases or decreases) the more it is processed?

decreases

66

What eliminates inaccuracies in the dynamic range?

the process of compression

67

What is the technique that reduces the dynamic range of a signal without introducing errors?

compression

68

What are the requirements of compression?

the largest signal remains the largest
the smallest signal remains the smallest
the range of signals is reduced

69

What is an alternative description of dynamic range?

number of choices

70

What does a narrow dynamic range?

fewer gray shades. bistable image, only contains black and white, has the narrowest dynamic range.

71

Images that display few shades of gray are also called what?

high contrast

72

What does wide dynamic range?

many shades of gray, a gray scale image- contains many shades of gray has the widest dynamic range

73

Images that display many shades of gray are also called what?

low contrast

74

Few choices have a ____ dynamic range

narrow

75

many choices have a ____ dynamic range

wide

76

What do fewer shades have?

few choices
black and white (bistable)
narrow dynamic range
high contrast

77

What do more shades have?

many choices
gray scale
wide dynamic range
low contrast