Test 2- Pulsed And Intensity Flashcards
Cycle is on….
Transmit
What is pulsed Ultrasound?
Collection of cycles that travel together.
Must have a beginning and an end.
Cycle is off…
Receive
What are Pulsed Wave Parameters?
- pulse duration
- spatial pulse length
- pulse repetition period
- pulse repetition frequency
- duty factor
What is Pulse Duration?
- on time - talking time - transmit time
- actual time from the start to the end of a pulse
- amount of time the pulse lasts
What are the units of pulse duration?
seconds, microseconds
Pulse Duration is the what?
Time it takes for one pulse to occur.
-determined by the number of cycles in each pulse and the period of the cycle
Can pulse duration be changed by the sonographer?
No.
Pulse duration is a characteristic of what?
the transducer/sound source
What is the pulse duration for clinical imaging?
0.5-2 microseconds
In clinical imaging, a pulse is comprised of _____ cycles.
2-4
What is the formula for pulse duration?
PD = # of cycles in pulse x period PD = # of cycles in pulse / frequency
Pulsed Duration - the transducer is made of _________ or _________ that stop the ringing and shorten the pulse for improved axial resolution.
backing layers, damping layers
short pulse = what?
better axial resolution
PD is directly related to ________ and number of _______ in the pulse.
Duty Factor, cycles
PD is inversely related to _______.
PRF
What is Spatial Pulse Length?
length or distance that a pulse occupies in space.
distance from the start of a pulse to the end of that pulse.
What are the units for Spatial Pulse Length?
mm
What is the spatial pulse length for clinical imaging?
0.1 to 1 mm
Spatial pulse length is determined by what?
the sound source and the medium
Can the Spatial Pulse Length be changed by the sonographer?
No.
What is the formula for Spatial Pulse Length?
SPL = # of cycles x wavelength
Why are shorter pulses desirable?
Better AXIAL RESOLUTION
SPL is directly related to _______ and ________.
wavelength, number of cycles
SPL is inversely related to ________.
frequency
What is Pulse Repetition Period?
Time from the start of one pulse to the start of the next pulse.
Includes talking and listening times.
Time when system has a pulse and when it has no pulse.
What are the units for PRP?
time
What is the PRP for clinical imaging?
100 microseconds to 1 msec
PRP is determined by what?
sound source
Can the PRP be changed by the sonographer?
Yes. PRP changes by the sonographer when depth of view is changed and then listening time increases.
PRP is directly related to what?
imaging depth
PRP is inversely related to what?
PRF
As imaging depth increases _________ increases.
PRP
As imaging depth decreases ________ decreases.
PRP
What is Pulse Repetition Frequency?
Number of pulses in one second.
Not related to the “frequency”
What is pulse repetition frequency determined by?
depth of view
What is the formula for PRF max?
PRF max = speed of sound in the medium / 2 x (max depth)
What are the units for PRF?
Hertz
What is the PRF in clinical imaging?
1,000-10,000 Hz (pulses per second)
What is PRF determined by?
sound source
PRF depends on what?
imaging depth
Can PRF be changed by the sonographer?
Yes. It changes by the sonographer when depth of view is changed
Shallow image = ______ PRF.
higher
Deeper image = ______ PRF.
lower
PRF is directly related to __________.
duty factor
PRF is inversely related to ________ and ________.
imaging depth and PRP
PRF determines what?
how fast images are generated
PRF of 5kHz means ________.
5000 pulses per second
What is Duty Factor?
Percentage of time that the system is “talking.”
Percentage of time that the system is ON
Duty factor of 100% = ?
continuous wave
DF of 1% or less = ?
pulsed wave
DF of 0% = ?
equipment is OFF
What is duty factor determined by?
sound source
Can duty factor be changed by the sonographer?
Yes. It is changed by the sonographer when the depth of view is changed.
The duty factor of clinical imaging is what?
0.1% to 1.0%
Duty factor for Doppler is what?
0.5% to 5.0%
What is the formula for duty factor?
DF = Pulse Duration / Pulse repetition period x 100 DF = talking time / talking and listening time
Duty factor increases when….
- imaging depth decreases
- shallower imaging
- PRP decreases
- PRF increases
Duty factor is directly related to ______ and ______.
PRF and PD
Duty factor is inversely related to ______.
PRP
For shallow imaging in pulsed ultrasound there is……
- less listening
- shorter PRP
- higher PRF
- higher duty factor
For deeper imaging in pulsed ultrasound there is…..
- more listening
- longer PRP
- lower PRF
- lower duty factor
Duty Factor is important for determining _______. Why?
intensity, it relates to bioeffects
What is bandwidth?
range of frequencies
Shorter pulse has ________ bandwidth.
broad
Longer pulse has _______ bandwidth.
narrow
What parameters are changed by imaging depth?
PRP, PRF, Duty Factor
What is intensity?
the amount or degree of strength of sound per unit area
What is the unit of intensity?
W / cm^2
Intensity relates to what?
the strength of the sound beam
Intensity ~ ?
Intensity ~ ?
intensity ~ power
intensity ~ amplitude ^2
What is intensity determined by?
determined by the system
Why is intensity important?
related to bioeffects
Can intensity be changed by the sonographer?
Yes.
Intensity is the concentration of what?
the power in a beam
What is the formula for intensity?
power (watts) / beam area (cm^2)
Increasing _______, increasing intensity
power
increasing _______, decreases intensity.
area
decreasing _______, increases intensity.
area
What is energy?
the ability to do work
______ is energy transferred divided by time.
Power
Intensity varies across what?
the sound beam
Intensity is highest in the _______ and falls off at the ________.
center, periphery
intensity is not uniform across the ______ and with ______ ______ not uniform in time.
beam, pulsed wave
With pulsed wave, the intensity varies in _____.
time
With pulsed wave, the intensity varies in _______…..
space
Intensity
Peak-
Average-
Peak- the maximum value
Average - the middle value
Intensity
Spatial (where) Peak -
maximum intensity along the beam
determined by focusing
Intensity
Spatial (where) average-
Spatial (where) average- average over the beam
Spatial (where) -
referring to space
Which is higher SP or SA?
SP is always higher
For ultrasound the ________ ________ is at the center of the beam and it _______ as the beam spreads…..
strongest intensity, reduces
Temporal (when) -
referring to all time (transmit and receive)
temporal (when) peak-
maximum intensity in the pulse
temporal (when) average -
intensity over the time of the PRP
Pulse average -
the intensity averaged over the time of the pulse
For a given pulse, highest to lowest would be…..
TP, PA, TA
Why are the TA and PA equal for continuous wave?
because there is no pulse
Spatial peak, temporal peak SPTP
maximum value in space and time
SATP
Spatial average, temporal peak
SPPA
Spatial peak, pulse average
SAPA
Spatial average, pulse average
SPTA
Spatial peak, temporal average
What is the most relevant intensity with respect to tissue heating?
SPTA
SATA
Spatial average, temporal average
the beam is only transmitting _______% in PW.
less than 1%
99% of the time the intensity is _____.
0
Spatial intensity -
ultrasound beam does not have the same intensity at different locations
temporal intensity -
ultrasound beam does not have the same intensity at different times
List the intensities from high to low.
SPTP > SATP > SPPA > SAPA > SPTA > SATA
Beam uniformity factor or coefficient or ratio (BUR) SP/SA -
describes sound beam in space
BUR
ratio of center intensity to average
unitless
always greater than 1
For continuous wave - SPTA and SPPA and SPTP are _____.
the same
For continuous wave SATA and SAPA and SATP are ______.
the same
What is intensity determined by?
sound source
Can intensity be changed by the sonographer?
Yes. Sonographer changes when changing power
hydrophone or microprobe
device used to measure output intensity of the transducer
below 100 mW/cm^2 -
unfocused sound
below 1000 mW/cm^2 -
focused sound
higher intensities are needed to produce bioeffects with a ________ transducer.
focused
