Chapter 4 Instruments -notes

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1

must not exeed

Pen(cm)*PRF(kHz)=<77(cm/ms)

2

voltage ratio formula

output/input

3

power ratio formula

(voltage ratio) 2

4

Name the components of the system

transducer
beam former
signal processor
image processor
Display

5

Name the componenents of the Beam former.

pulser
pulse delays
transmit / receiver

summer
echo delays
ADCs
amplifier

6

What is the function of the Master Synchronizer?

conductor of all parts Pulser

7

What is the function of the Pulser?

Receives a signal from the master synchronizer then sends a voltage to the element.

Pulser varies signal

8

Relationship between volts from pulser and pulse intensity

direct

The higher the volts the higher the pulse intensity

9

Explain the relationship between voltage from the pulser and an ultrasound pulse.

voltage pulse frequency = U/S frequency

voltage duration = pulse duration

voltage PRF = U/S PRF

voltage PRP = U/S PRP

10

The receiver and memory must also know when a pulse has been sent.

Where is this taken care of?

Master synchronizer

11

What is the range of PRF?

4 - 15 kHz

12

What happens if the PRF is too high?

amgiuity occurs

13

What happens to frame rate with deeper penetration?

frame rate decreases with deeper echoes

Frame rate as an indirect relationship with depth.

14

What happens to frame rate with longer listening time?

longer listening time = lower frame rate

Frame rate has an indirect relationship with listening time (PRP).

15

Before an echo may go out what must happen?

all echoes at at any given depth must be received prior to sending of another pulse.

16

What happens to frame rate when you decrease PRF?

Direct relationship

framerate decreases.

17

Why is input lower when output is reduced?

The input echoes are generaly lower than the out put signals due to loss of intensity as they travel out an back. If a signal is lowered to as it is formed the beam traveling back to the transducer will be even lower.

18

What are the other names for Output?

output gain
acoustic power
pulser power
energy output
transmitter output

19

Increasing the power used to be an option on old systems. This adjustment has been removed but you can still change the output power.

Explain

Change output by changing package (presets)

ex. echo to DMS

20

Why was output power adjustment removed from old machines?

higher power COULD cause bioeffects

21

What is the purpose of coded excitation?

to make the system more sensitive

22

Define coded excitation.

coded excitation is using multiple pulses to make one scan lines.

pulse wait pulse wait pulse wait
decoder collects all data and uses it to make one scan line

23

What is the purpose of pulse delays?

(sequencing and phasing) to control the shape and direction of the beam.

-steering
-focusing
-aperture
-apodization

24

How many inputs come from the pulser to pulse delay?

How many outputs from pulse delay to transducer element?

one input is received into the pulse delay but many are transmited to the element

25

Where are the pulser and transformer located?

in the beam former

26

What are the two types of channels?

Transmission - pulse delay and element

Reception - element, amplifier, ADC, echo delay

27

There must be _______ set of wires for each _________ ______.

one, delay path

28

What is the function of the beam former during reception?

*Receive

*sequence
-dynamic focus
-steering
-apodization
-aperture sequencing
-creation of single line

*summation

29

What is the function of summer

puts it all together

30

Voltage ratio formula

output/input

31

power ratio formula

(voltage ratio) 2

32

What is the power ratio for an input of 4 and an output of 400?

40 dB

400/4 = 100

1002 = 10,000

10,000 = 10 * 10 * 10 * 10 = 40 dB

33

If you have a system that is running at 18 dB and decibels are halved what is left?

15 dB

34

Define amplification

conversion of small voltages into larger voltages

aka gain

35

Why is amplification nessecesary?

echoes returning to system are weak.

36

What makes system gain adjustment acceptable when output power adjustment was unacceptable?

gain controls pulses already in the system whereas output power was being transmitted

37

What does gain do?

more gain allows weaker echos to be imaged
less gain, weaker echoes are ignored

38

What is the quality of thick wires and why?

higher quality with thick wires

there is high resistance in small wires

39

TGC

time gain compensation

selected amplification by depth

(brightness by depth)

* compensation will make bone look identical reguardless of depth.

40

What is the standard attenuation of soft tissue?

.5 dB/cm

round trip 1 dB/cm

41

What are the sliders of TGC called?

potentiometers

42

When comparing a

...

43

What are other names for compensation

TGCs
time gain compensation
swept gain compensadtion

44

What is the ADC and where is if located?

ADC - Analog to Digital converter - converts varying voltage into discrete #'s

It is located in the Beamformer.

45

What is the summer responsible for?

Summer - responsible for a single line of information by receiving and sorting all channels of info.

sums up all information
Apodization
Aperture
creation of single line of information

46

Signal Processor Functions

Harmonics imaging
rejection
demodulation/detection
smoothing
rectification
compression

47

Where is the Band Pass Filter?

Image processor

48

What is the purpose of the Band Pass Filter?

Allows harmonics imaging

will accept all frequencies with in its bandwidth and will reject all frequencies outside its bandwidth.

49

Where is the Band Pass Filter located?

Tuned Amplifier

50

What does the Signal processor do with the signals as they arrive from the Beam former?

Filter/rejection
Demodulation
Compression

51

What does the Image processor do with the signals as they are arrive from the signal processor?

scan converter
pre-processing
image memory
post processing
DAC

52

What are the benefits of Harmonics?

Makes the primary Beam narrower which improves lateral resolution.

53

If the Beam fits between two structures they would be seen as _____ two structures

Two

Think of diagram

54

What is the fundemental frequency?

operating frequency of the transducer

55

What is the 2nd Harmonics?

is a higher frequency that is created at the same time as fundemental frequency

56

Explain Harmonics

Send at a low frequency which allows greater depth but receive at (higher) 2nd harmonic which allows better resolution

- Transducer with a bandwidth

- Set band pass filter to center frequency of 2dn harmonics

- Band pass filter will accept all frequencies within its bandwidth.

- Since band pass filter is set to 2nd harmonics returning signals from the fundemental frequency are rejected (they are out of the filters bandwidth)

57

Harmonics

Low Frequency =
High Frequency (2nd Harm) =

Low Frequency = deeper depth
High Frequency (2nd Harm) = Better resolution

58

Why are grating lobes not created with Harmonics imaging?

card image

Harmonic energy is concentrated in the center of the beam.

59

Reverberation

Sound waves hitting bone and bouncing

60

How does Harmonics reduce reverberation?

With harmonics sound waves are so thin

61

Why does harmonics effect axial resolution?

transducer frequency must accommodate 1st & 2nd harmonics - without overlap. Wide bandwidth

Harmonics will NOT work with overlap!

62

Disadvantage of Harmonics?

Decrease framerate

Decrease temporal resolution

Increase SPL
- decrease axial resolution

63

What compensates for the decrease in axial resolution with harmonics?

Pulse Inversion

64

Explain Pulse Inversion

- A second pulse opposite of 1st is fired at same time

- they come back at same time

- destructive interference - DISAPEAR

- Both pulses send out 2nd Harmonics which are not opposite and interfere constructively

65

What is the purpose of Rejection/Filtering?

Suppression, threshold affects weak echoes (weak echoes produce noise)

Get rid of

-Electric Noise
-Grating Lobes
-Side Lobes
-Scattering

66

What is Demodulation/Detection

conversion of the signal to a from that is more suitable for TV display

- from radio form to video form

- Can also do modulation?

67

What is Modulation?

method of keeping frequencies close to center frequencies

68

What is Rectification

turns all negative voltages into positive

69

What is smoothing

creates envelope around the voltages and take all spikes out which creates nicer image

70

How many shades of gray can the eye see?

100

71

How many decibels does the eye see with?

Dynamic Range - 20 dB

72

How many shades of gray can the eye see in the dark?

60

73

How many decibels does the eye see with in the dark?

Dynamic Range - 18 dB

74

How many shades of gray can the system handle?

Dynamic Range - 160 dB

75

How many shades of gray can Monitor show?

Dynamic Range - 30 dB

76

What happens to contrast during compression?

more contrasty - less shades of gray

77

Decibel review

10 dB = 10
20 dB = 100
30 dB = 1000

78

What is Dynamic Range?

is the ratio of the largest to the smallest amplitude that a system can detect

# of shades of gray a system can handle

79

compression AKA

Dynamic Range
Contrast

80

Higher Dynamic Range

more shades of gray

The higher the sensitivity of the system

81

What is the unit for Dynamic Range?

dB

82

_____ keeps the greyscale within the range the human eye can see.

Compression keeps the greyscale within the range the human eye can see.

83

Compression is done without altering the relative relationships between the voltages.

What does this mean?

Everything is smaller (compressed)
the smallest is still smallest
the largest is still the largest

84

Here Image Processor!

...

85

What is the scan converter

The scan converter translates the information from the spoke format into the video format

86

What happens during writing of memory?

-Scan line info placed in rows and columns
-process is rapid sequency of frames
-real time display

87

What is bistable memory?

-checkerboard of information (bits)
-2 states only On or Off

88

What is a bit?

Binary Digit

89

Explain Bistable images

Narrow dynamic range - low shades of grey
poor contrast resolution
High contrast images

90

What are the shades of gray dependent on?

The number of matrix available fro each pixel

91

How many bits in a byte?

8

0000 000

92

How does binary work?

card image

Powers of 2

93

What number does 10110001 represent?

card image

177

128 + 32 + 16 + 1 = 177

94

How many shades of gray can a byte display?

256

95

How many shades of gray can 9 bits display?

512

96

How many shades of gray can 10 bits display?

1024

97

Size of pixel formula

image size/matrix

98

If you have 20 cm image with a 512 matrix, How big is the pixel?

.4 mm

20 cm/512 = .04 cm
= .4 mm

99

If you have 10 cm image with a 512 matrix, How big is the pixel?

.2 mm

10 cm/512 =
= .2 mm

100

If you have 10 cm image with a 1024 matrix, How big is the pixel?

.09 mm

10 cm/512 = .009 cm
= .09 mm

101

What does pixel size have to do with memory?

pixel size = memory spatial resolution

102

What is done with echoes prior to storage into memory?

PreProcessing

103

What is done with echoes prior to storage into memory?

PostProcessing

104

Preprocessing vs. Postprocessing

preprocessing can NOT be changes on a frozen image

postprocessing CAN be changes on a frozen image

105

Brightness Modes

...

106

What is a cone?

cells in the eye that process color vision

107

What is a rod?

cells in the eye that process B/W vision

108

Spatial Compounding

...

109

Elastography

...

110

Volume Image

...

111

Matrix Transducer

...

112

Matrix Display

...

113

Surface rendering

...

114

reconstruction

...

115

4D

...

116

Here Display!

...

117

What are the different methods of Display?

M-mode
A-mode
B-mode

118

What is M-mode?
What is its common application?

motion mode

cardiac

119

What is A-mode?
What is its common application?

amplitude mode

opthamology

120

What is B-mode?
What is its common application?

brightness mode

general imaging

121

DAC

...

122

What is a frame?

each frame is made up of a set of scan lines

123

How many pulses are needed for one scan line with one focus?

two foci?

1 focus = 1 scan line
2 focus = 2 scan line

124

Short Depth = less listening time

...

125

More scan lines = wider depth

...

126

What is the formula for time per line?

# of foci * PRP

127

What is the formula for frame time?

time per line * line per frame

128

What is the formula for frame rate?

1/frame time

129

CRT frame rate

...

130

Digital Display

...