Pulsed Waves Flashcards
What is pulsed sound?
- systems create short pulses of sound waves to create images
- collections of cycles that travel together
- talking & listening (on & off time)
What are pulsed wave parameters?
- pulse duration
- pulse repetition period
- pulse repetition frequency
- duty factor
- spatial pulse length
What is pulse duration? Unit? Value range? Controlled by? Adjustable?
- 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
Pulse duration is ______ to the number of cycles in a pulse.
directly proportional
Pulse duration is ______ to period.
directly proportional
Pulse duration is ______ to frequency.
inversely proportional
How is pulse duration calculated?
number of cycles x period (microseconds) or
number of cycles / frequency (MHz)
What results in long pulse duration?
many cycles or cycles with long periods
What results in short pulse duration?
few cycles or cycles with short periods, greater image accuracy
What is spatial pulse length? Unit? Value range? Controlled by? Adjustable?
- length/distance from start to end of pulse
- units: distance (mm)
- range: 0.1-1.0 mm
- controlled by source and medium
- not adjustable
Spatial pulse length is _____ to the number of cycles in a pulse and wavelength.
directly proportional
Spatial pulse length is _____ to frequency.
inversely proportional
How do you calculate spatial pulse length?
number of cycles x wavelength (mm)
What results in long spatial pulse length?
many cycles or cycles with long wavelength
What results in short spatial pulse length?
few cycles or cycles with short wavelength, greater image accuracy
What is pulse repetition period? Unit? Value range? Controlled by? Adjustable?
- 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
How much longer is PRP than pulse duration?
100 to 1000x longer
How does imaging depth affect PRP?
shallow imaging = shorter PRP
deeper imaging = longer PRP
PRP is _____ to period.
unrelated
What is pulse repetition frequency? Unit? Range? Controlled by? Adjustable?
- 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
PRF is _____ to frequency.
unrelated
PRF is ______ to depth.
inversely related
How does deep imaging affect PRF?
Lower PRF
How are PRP and PRF related?
inversely related
- longer PRP = lower PRF, increased PRP = decreased PRF
- shorter PRP = higher PRF, decreased PRP = increased PRF
PRP and PRF have a _____ relationship. What equations are used to calculate them?
reciprocal (PRF x PRP = 1)
PRF = 1/PRP
PRP = 1/PRF
What is duty factor? Unit? Range? Controlled by? Adjustable?
- percentage of time the system transmits a pulse
- unit: %
- range: 0.2-0.5%, listening > talking
- controlled by source & depth
- adjustable
Duty factor is ______ to depth.
inversely related
When is duty factor at its maximum?
DF is at 100% with continuous wave
When is duty factor at its minimum?
At 0% when transducer is not in use
How is duty factor calculated?
pulse duration/PRP x 100
What is the result of shallow imaging on PRP, PRF, and duty factor?
Shallow imaging = less listening, more talking
- shorter PRP
- higher PRF
- higher duty factor
What is the result of deeper imaging on PRP, PRF, and duty factor?
- more listening, less talking
- longer PRP
- lower PRF
- lower duty factor
What is intensity? How is it calculated?
- sound beam’s power divided by area
- watts/cm^2
What is spatial intensity?
- distance/space
- beam does not have same intensity at different locations
What is peak intensity?
max intensity value
What is average intensity?
middle intensity value
What is temporal intensity?
- all time, pulse duration and receive
- beam does not have same intensity at different times
What is pulsed intensity?
- only transmit time
- beam does not have same intensity at different times during pulse, average intensity for pulse duration only
Intensity of the sound beam varies over ______ and ______.
distance and time, important when studying sound beam bioeffects
How can spatial intensity be compared to a flashlight?
- beam is strongest centrally, highest intensity
- dimmer around edges, lower intensity
What is Spatial Peak Intensity?
- beam’s intensity at location where it is highest
- always higher than the average
What is Spatial Average Intensity?
average intensity across entire cross-sectional area of beam
What is Temporal Peak Intensity?
intensity of beam at time of max value
What is Imax?
average intensity during most intense half cycle
What is Pulse Average Intensity?
average intensity during pulse duration (transmit time)
What is Temporal Average Intensity?
average intensity during PRP (transmit/receive time)
What is I sptp?
measurement at location where intensity is at its max & at the instant in time when the most powerful part of the pulse passes
What is I sppa?
measurement at location where intensity is at its max, averaged over pulse duration (transmit time)
What is I spta?
measurement at location where intensity is at its max, averaged over all time (PRP)
What is I sata?
measurement over the entire beam cross-sectional area over all time (PRP)
What is the most important intensity in regard to bioeffects?
SPTA
What is the unit for all intensities?
watts/cm^2
Which intensity has the highest value? Which has the lowest?
Highest: SPTP
Lowest: SATA
What is the beam uniformity coefficient? What is it also called?
It describes the spread of a beam in space, AKA SP/SA factor, unitless, value of 1 or greater
How is duty factor related to intensity?
Describes the relationship of beam intensities with time
How does continuous wave ultrasound affect intensity?
Beam is always on, pulse average intensity = temporal avg intensity
SPTA = SPPA, SATA=SAPA
When pulsed and continuous wave sound beams have the same SPTP intensities, which beam has the higher
SPTA intensity?
continuous wave
When pulsed and continuous wave sound beams have the same SATP intensities, which beam has the higher SATA intensity?
continuous wave
Rank the following from largest to smallest:
SPTA, Im, SPPA, SATA, SPTP
SPTP, Im, SPPA, SPTA, SATA
