Pulsed Waves

Question 1

What is pulsed sound?

Answer 1

• systems create short pulses of sound waves to create images
• collections of cycles that travel together
• talking & listening (on & off time)

Question 2

What are pulsed wave parameters?

Answer 2

• pulse duration
• pulse repetition period
• pulse repetition frequency
• duty factor
• spatial pulse length

Question 3

What is pulse duration? Unit? Value range? Controlled by? Adjustable?

Answer 3

• time from start to end of pulse
• unit: time (microseconds)
• range: 0.3-2.0 microseconds (2-4 cycles per pulse)
• controlled by source (transducer)
• not adjustable

Question 4

Pulse duration is ______ to the number of cycles in a pulse.

Answer 4

directly proportional

Question 5

Pulse duration is ______ to period.

Answer 5

directly proportional

Question 6

Pulse duration is ______ to frequency.

Answer 6

inversely proportional

Question 7

How is pulse duration calculated?

Answer 7

number of cycles x period (microseconds) or
number of cycles / frequency (MHz)

Question 8

What results in long pulse duration?

Answer 8

many cycles or cycles with long periods

Question 9

What results in short pulse duration?

Answer 9

few cycles or cycles with short periods, greater image accuracy

Question 10

What is spatial pulse length? Unit? Value range? Controlled by? Adjustable?

Answer 10

• length/distance from start to end of pulse
• units: distance (mm)
• range: 0.1-1.0 mm
• controlled by source and medium
• not adjustable

Question 11

Spatial pulse length is _____ to the number of cycles in a pulse and wavelength.

Answer 11

directly proportional

Question 12

Spatial pulse length is _____ to frequency.

Answer 12

inversely proportional

Question 13

How do you calculate spatial pulse length?

Answer 13

number of cycles x wavelength (mm)

Question 14

What results in long spatial pulse length?

Answer 14

many cycles or cycles with long wavelength

Question 15

What results in short spatial pulse length?

Answer 15

few cycles or cycles with short wavelength, greater image accuracy

Question 16

What is pulse repetition period? Unit? Value range? Controlled by? Adjustable?

Answer 16

• time from the start of one pulse to start of the next including on/off time
• unit: time
• range: 100 microseconds to 1 millisecond
• controlled by source & imaging depth
• adjustable

Question 17

How much longer is PRP than pulse duration?

Answer 17

100 to 1000x longer

Question 18

How does imaging depth affect PRP?

Answer 18

shallow imaging = shorter PRP
deeper imaging = longer PRP

Question 19

PRP is _____ to period.

Answer 19

unrelated

Question 20

What is pulse repetition frequency? Unit? Range? Controlled by? Adjustable?

Answer 20

• number of pulses the system transmits into the body each second
• unit: frequency (Hz)
• range: 1000-10,000 Hz
• controlled by source & imaging depth
• adjustable

Question 21

PRF is _____ to frequency.

Answer 21

unrelated

Question 22

PRF is ______ to depth.

Answer 22

inversely related

Question 23

How does deep imaging affect PRF?

Answer 23

Lower PRF

Question 24

How are PRP and PRF related?

Answer 24

inversely related
- longer PRP = lower PRF, increased PRP = decreased PRF
- shorter PRP = higher PRF, decreased PRP = increased PRF

Question 25

PRP and PRF have a _____ relationship. What equations are used to calculate them?

Answer 25

reciprocal (PRF x PRP = 1) PRF = 1/PRP PRP = 1/PRF

Question 26

What is duty factor? Unit? Range? Controlled by? Adjustable?

Answer 26

- percentage of time the system transmits a pulse - unit: % - range: 0.2-0.5%, listening > talking - controlled by source & depth - adjustable

Question 27

Duty factor is ______ to depth.

Answer 27

inversely related

Question 28

When is duty factor at its maximum?

Answer 28

DF is at 100% with continuous wave

Question 29

When is duty factor at its minimum?

Answer 29

At 0% when transducer is not in use

Question 30

How is duty factor calculated?

Answer 30

pulse duration/PRP x 100

Question 31

What is the result of shallow imaging on PRP, PRF, and duty factor?

Answer 31

Shallow imaging = less listening, more talking - shorter PRP - higher PRF - higher duty factor

Question 32

What is the result of deeper imaging on PRP, PRF, and duty factor?

Answer 32

- more listening, less talking - longer PRP - lower PRF - lower duty factor

Question 33

What is intensity? How is it calculated?

Answer 33

- sound beam's power divided by area - watts/cm^2

Question 34

What is spatial intensity?

Answer 34

- distance/space - beam does not have same intensity at different locations

Question 35

What is peak intensity?

Answer 35

max intensity value

Question 36

What is average intensity?

Answer 36

middle intensity value

Question 37

What is temporal intensity?

Answer 37

- all time, pulse duration and receive - beam does not have same intensity at different times

Question 38

What is pulsed intensity?

Answer 38

- only transmit time - beam does not have same intensity at different times during pulse, average intensity for pulse duration only

Question 39

Intensity of the sound beam varies over ______ and ______.

Answer 39

distance and time, important when studying sound beam bioeffects

Question 40

How can spatial intensity be compared to a flashlight?

Answer 40

- beam is strongest centrally, highest intensity - dimmer around edges, lower intensity

Question 41

What is Spatial Peak Intensity?

Answer 41

- beam's intensity at location where it is highest - always higher than the average

Question 42

What is Spatial Average Intensity?

Answer 42

average intensity across entire cross-sectional area of beam

Question 43

What is Temporal Peak Intensity?

Answer 43

intensity of beam at time of max value

Question 44

What is Imax?

Answer 44

average intensity during most intense half cycle

Question 45

What is Pulse Average Intensity?

Answer 45

average intensity during pulse duration (transmit time)

Question 46

What is Temporal Average Intensity?

Answer 46

average intensity during PRP (transmit/receive time)

Question 47

What is I sptp?

Answer 47

measurement at location where intensity is at its max & at the instant in time when the most powerful part of the pulse passes

Question 48

What is I sppa?

Answer 48

measurement at location where intensity is at its max, averaged over pulse duration (transmit time)

Question 49

What is I spta?

Answer 49

measurement at location where intensity is at its max, averaged over all time (PRP)

Question 50

What is I sata?

Answer 50

measurement over the entire beam cross-sectional area over all time (PRP)

Question 51

What is the most important intensity in regard to bioeffects?

Answer 51

SPTA

Question 52

What is the unit for all intensities?

Answer 52

watts/cm^2

Question 53

Which intensity has the highest value? Which has the lowest?

Answer 53

Highest: SPTP Lowest: SATA

Question 54

What is the beam uniformity coefficient? What is it also called?

Answer 54

It describes the spread of a beam in space, AKA SP/SA factor, unitless, value of 1 or greater

Question 55

How is duty factor related to intensity?

Answer 55

Describes the relationship of beam intensities with time

Question 56

How does continuous wave ultrasound affect intensity?

Answer 56

Beam is always on, pulse average intensity = temporal avg intensity SPTA = SPPA, SATA=SAPA

Question 57

When pulsed and continuous wave sound beams have the same SPTP intensities, which beam has the higher SPTA intensity?

Answer 57

continuous wave

Question 58

When pulsed and continuous wave sound beams have the same SATP intensities, which beam has the higher SATA intensity?

Answer 58

continuous wave

Question 59

Rank the following from largest to smallest: SPTA, Im, SPPA, SATA, SPTP

Answer 59

SPTP, Im, SPPA, SPTA, SATA