# US Physics Unit 3

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a pulse

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1

a pulse

short emission of sound (a few cycles)

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2

pulses are separated in time with ____ of no emission (gaps/listening time)

periods

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3

What is pulsed ultrasound based on

principle of echolocation

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4

echolocation

this distance between structures and the ultrasound probe can be calculated by using this formula

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5

2 way we look for

echo, round trip, time to reflector and back

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6

1 way we look for

time for reflector

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7

equation for 2 way

d=c(t/2)

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8

equation for 1 way

d=ct

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9

for imaging each pulse is ______ long for imaging

2-3 cycles

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10

for doppler each pulse is ____ long

5-30

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11

Determined by source of sound in PW

PRF, PRP, DF, PD, BW, QF

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12

Determined by the source and the medium in PW

SPL

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13

Pulse Repetition Frequency (PRF)

is the number of pulses per seconds (kHz)

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14

The PRF for imaging

4-15 kHz

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15

the PRF for Doppler

5-30 kHz

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16

equation for PRF in kHz

# of pulses/s

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17

Pulse Repetition Period (PRP)

is the time from the beginning of one pulse to the beginning of the next pulse (ms)

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18

PRF is _____ related to PRP, just like frequency and period

inversely

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19

A _____ PRF is desirable for image quality and Doppler sampling

high

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20

PRF is ______ by the speed of sound in soft tissues

speed

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21

Range ambiguity

when a pulse is sent out before all the echoes from the previous pulse have been received.

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22

If PRF is increased, penetration or depth must

decrease

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23

Pulse Duration (PD)

the time it takes for a single pulse to occur

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24

equation for PD

T (# of cycles/pulse)

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25

if frequency is increased, pulse duration is ______

decreased

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26

for most diagnostic medical ultrasound, there are short periods when the machine is sending pulses into the body and _____ times when the machine is waiting for echoes

longer

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27

Duty Factor (DF)

the percent of time that the sound is on (unitless)

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28

For imaging the DF ranges from

0.1-0.1%

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29

DF ranges from _____ in doppler

0.5-5%

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30

DF equation

PD/PRP

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31

Spatial Pulse Length (SPL)

the distance covered by a single pulse

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32

SPL equation

wavelength (# of cycles/pulse)

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33

Bandwidth (BW)

the range of frequencies contained in a pulse

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34

Equation for BW

highest f- lowest f

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35

CW Bandwidth

1

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36

fractional bandwidth

is equal to the bandwidth divided by the operating frequency

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37

equation for fractional bandwidth

BW/f0

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38

Shorter pulses have ________ bandwidths

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39

the _____ the pulse, the fewer number of cycles

shorter

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40

having a broader bandwidth will result in ______ frequencies present

more

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41

Quality Factor (QF)

refers to the purity of the beam or how close it is to the operating frequency

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42

Equation for QF

f0/BW

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43

we want _____ pulses so we can have a broad BW-improved resolution

short

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44

PRF is the number of ____ occurring in 1 s

pulses

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45

pulse-repetition ______ is the time from the beginning of one pulse to the beginning of the next

period

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46

the PRP ______ while PRF increases

decreases

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47

PD is the _____ it takes for a pulse to occur

time

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48

SPL is the _____ of _____ that a pulse occupies while it travels

length, space

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49

______ is the fraction of time that pulsed ultrasound is actually on

duty factor

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50

PD equals the number of cycles in the pulse multiplied by

period

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51

SPL equals the number of cycles in the pulse multiplied by _____

wavelength

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52

the DF of continuous wave sound is

1

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53

if the wavelength is 2 mm, the SPL for a 3 cycles pulse is _____mm

6

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54

How many cycles are there in 1s of continuous wave 5MHZ ultrasound

5,000,000

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55

Amplitude

difference between max value and equilibrium value of an acoustic variable

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56

Power equation

P= Energy/ Time

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57

Intensity equation

I=P/Area

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58

The Intensity of a sound beam is _____ at its center than on the periphery

higher

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59

the intensity of pulsed ultrasound also decreased toward the ____ of the pulse

end

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60

Spatial Peak (SP)

is the greatest intensity in a pulse in reference to space

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61

Spatial Average (SA)

is the average intensity across the pulse

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62

PW is ____ uniform in space or time in terms of Intensity

not

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The Beam Uniformity Ratio (BUR)

shows how uniform the intensity is in space

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64

BUR equation

BUR= SP/SA

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65

BUR will always be >1 because the peak will always be higher than the ____

average

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66

Temporal Peak (TP)

is the greatest intensity measured as the pulse passes by

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67

Pulse Average (PA)

is the average of all intensities measured as the pulse passes by

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Temporal Average (TA)

includes all the time between the pulse being measured and the next pulse

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69

SPTA

Spatial Peak/Temporal Average

Thermal interactions within tissue

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70

FDA Limit on SPTA

<720 mW/cm2

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Attenuation

the weakening of sound as it propagates

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gain

an increase in strength of the sound wave

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dynamic range

the ration of largest to smallest power in dB

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74

Intensity Ratio

I/Io

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75

I/I0 < 1

I<Io

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I/Io>1

I>Io

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I/Io=1

I=Io

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78

Equation for dB

10 log (I/Io)

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79

If I/Io <

=-dBi

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80

If I/Io>1

+dB

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81

If I/Io=1

=0 dB

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82

How do we get gain?

Constructive interference, and amplifiers

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83

Time Gain Compensation (TGC)

How to change this to make the picture stronger

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84

-3dB represents a reduction in intensity or power by a factor of

2

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85

-10dB represents a reduction in intensity or power by

10

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86

-6dB represents a reduction in amplitude by a factor of

2

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87

Amplitude is the maximum _____ that occurs in an acoustic variable

variation

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88

Intensity is the ___ in a wave divided by _____

power, area

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89

A unit for intensity is ______

mW/cm2

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90

Intensity is proportional to ______ squared

amplitude

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91

if power is doubled and area remains unchanged, intensity is ________

doubled

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92

if area is doubled and power remains unchanged, intensity is ______

halved

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93

if both power and area are doubled, intensity is ______

unchanged

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94

if amplitude is doubled, intensity is _______

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95

Attenuation is the reduction in ___ and ___ as a wave travels through a medium

amplitude, intensity

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