Chapters 14 Flashcards Preview

SPI Edelman > Chapters 14 > Flashcards

Flashcards in Chapters 14 Deck (62):
1

What are the six major components of the ultrasound system?

transducer
pulser/beam former
receiver
display
storage
master synchronizer

2

What does the pulser of the US system do?

determines the amplitude, PRP. and PRF
creates electrical signals that excite the PZT crystals and create sound beams

3

What does the beam former of the US system do?

determines the firing delay patterns for phased array systems

4

What does the receiver do?

transforms the electrical signals from the transducer (produced by the reflected sound) into a form suitable for display

5

What does the display do?

presents processed data. the display may be a flat screen monitor, a transparency, a spectral plot. or a variety of other formats

6

What does the storage do?

archives the ultrasound studies. typical storage devices (or media) include computer hard drives, CD, DVD, videotape, magneto-optical discs, paper printouts, photographs, and USB drives

7

What does the master synchronizer do?

maintains and organizes the proper timing and interaction of the systems components

8

When does the pulser function?

during transmission

9

What happens when changes are made to the pulser voltage?

it modifies the brightness of the entire image displayed on the systems screen

10

What happens when the pulser voltage is set too low?

PZT vibrates gently, and a weak sound beam is transmitted into the body. The reflected echoes are weak, and the entire image tends to be dark

11

What happens when the pulser voltage is set too high?

PZT vibrates more forcefully, and transmits a stronger sound beam into the body. the reflected echoes are stronger, and the entire image is brighter

12

What happens to the entire image when the gain is increased?

brighter

13

What happens to the entire image when the gain is decreased?

darker

14

What are synonyms for pulser voltage?

output gain, acoustic power, pulser power, energy output, transmitter output , power, or gain

15

Is the pulser adjustable?

yes

16

Why are lower output power desirable?

decrease transmitted acoustic energy and minimize patient exposure to ultrasonic energy . lower pulser voltages minimize the likelihood of bioeffects

17

What is noise?

a random and persistent disturbance that obscures or reduces a signals clarity. Noise contaminates images with low level, undesirable info

18

What is siginal to noise ratio?

a comparison of the meaningful info (signal) in an image compared to the amount of contamination (noise)

19

What does high signal to noise ratio mean?

the signal is much stronger than the noise and the image is of high quality

20

What does low signal to noise ratio mean?

the strength of the signal is closer to the strength of the noise. the image contains a larger amount of visible contamination and has less diagnostic value

21

How is signal to noise ratio related to output power?

directly

22

What does the PRP determines?

the max imaging depth also called depth of view

23

What happens when the PRP is short?

higher PRF and the system spends less time listening. This results in superficial imaging

24

What happens when the PRP is long?

low PRF, more listening time. the imaging is deeper

25

When you change depth of view, what are you changing?.

PRP

26

What is it called when the beam former adjusts electrical spike voltages to reduce lobe artifacts?

apodization

27

What things does the beam former control?

dynamic receive focusing and dynamic aperture

28

What are advantages of digital beam formers?

software programming
more flexible
extremely stable
versatile

29

What part of the US systems contains the transmit receive switch?

beam former

30

What does the switch do?

protects the delicate receiver components from the powerful signal that are created for pulse transmission
Also directs the electrical signals from the transducer to the appropriate electronic and processing components within the US system

31

What is a channel?

is made up of a single PZT element, the electronics in the beam former/pulser, and the wire that connects them.

32

What are the receiver operations?

amplification
compensation
compression
demodulation
reject

33

What is other word for amplification?

receiver gain

34

How are all electrical signals in the receiver affected?

identically by amplification

35

When amplification is adjusted what is affected?

the entire image is made brighter or darker

36

is amplification adjustable?

yes- the gain control

37

What are the units for amplification?

dB

38

What are typical values for amplification?

60-100 dB

39

What is preamplification?

the process of improving the quality of a signal before it is amplified. are designed to prevent electronic noise.

40

What does preamplification occur?

as close to the active elements as is practical, often within the transducer itself

41

The receiver function that corrects for attenuation?

compensation or TGC

42

What does compensation do?

creates an image that is uniformly bright from top to bottom

43

is compensation adjustable?

yes

44

What are the units for compensation?

is a form of variable amplification so the units are the same dB

45

What are synonyms for compensation?

TGC, DGC or swept gain

46

Can compression be adjustable?

yes
alters the gray scale mapping

47

Define compression

rank of signals large to small or vice versa

48

What are synonyms for compression?

log compression, or dynamic range

49

Why is log compression important in clinical US?

b/c most meaningful backscattered signals form biologic tissues are very weak and the sonographer must be able to see differences in these weak reflections

50

What does demodulation do?

a two part process that changes the electrical signals within the receiver into a form more suitable for display on a monitor

51

Define rectification

coverts all negative voltages into positive voltages. Corrects negative voltages

52

is demodulation adjustable?

no

53

What is the purpose of demodulation?

change the form of the electrical signal

54

What are synonyms for reject?

threshold or suppression

55

What does reject do?

gets rid of low level signals and allows the sonographer to control whether low level gray scale info within the data will appear on the displayed image

56

Is reject adjustable?

yes

57

What kind of effect on the image does reject have?

affects all low level signals on the image, regardless of their location. rejection does not affect bright echoes.

58

Signals treated differently based on reflector depth is what receiver function?

compensation

59

Signals treated differently depending on strength is what receiver function?

compression

60

what receiver function prepares electrical signals to be suitable for display?

demodulation

61

what receiver function affects only weak signals and does not affect strong signals?

reject

62

increasing amplification, what happens to the signal to noise ratio

remains unchanged