Ch. 4 Pulsed Waves Flashcards
What are the 5 parameters to describe pulsed sound?
- pulse duration
- pulse repetition period
- pulse repetition frequency
- duty factor
- spatial pulse length
_____________ _____________________ is the actual time from the start of a pulse to the end of that pulse, it is a single transmit, talking or “on” time
pulse duration is the actual time from the start of a pulse to the end of that pulse, it is a single transmit, talking or “on” time
What are the units for pulse duration?
Units of time (us, ms, or sec)
- microseconds
- milliseconds
or just seconds
The pulse duration is determined by the:
Sound source only
Is pulse duration adjustable by the sonographer?
no, the sonographer cannot alter pulse duration while using a particular ultrasound system and transducer
Pulse Duration Formula:
= # cycles times period (ms)
or
= # cycles divided by frequency (MHz)
Pulse duration is _____________________________ to the number of cycles in the pulse and period
Pulse duration is directly proportional to the number of cycles in the pulse and period
Pulse duration is ____________________________ to frequency
Pulse duration is inversely proportional to frequency
_______________ duration pulses are desirable in diagnostic imaging because they create images of greater accuracy.
shorter duration pulses are desirable in diagnostic imaging because they create images of greater accuracy
_________ _____________ __________ is the distance that a pulse occupies in space from the start to the end of a pulse.
spatial pulse length is the distance that a pulse occupies in space from the start to the end of a pulse
What are the units for Spatial Pulse Length?
SPL has units of distance, such as mm
Spatial Pulse length is determined by:
Both the source and the medium
Is spatial pulse length adjustable by the sonographer?
No. The sonographer cannot alter pulse length. In a particular medium, a transducer’s pulse has a fixed length that cannot change
Spatial Pulse Length formula:
SPL (mm) = # of cycles in a pulse times wavelength (mm)
Spatial pulse length is _____________________ proportional to the number of cycles in the pulse and wavelength
Spatial pulse length is directly proportional to the numbers of cycles in the pulse and wavelength
Spatial pulse length is ____________________ proportional to frequency
Spatial Pulse Length is inversely proportional to frequency
Pulse Duration is the __________ that a pulse is “on” and is typically measured in microseconds (us)
And Spatial Pulse Length is the ___________________ of the pulse end to end, typically measured in millimeters (mm)
Pulse Duration is the time that a pulse is “on” and typically measured in microseconds (us)
And Spatial Pulse Length is the distance of the pulse end to end, typically measured in millimeters (mm)
__________________ ___________________ _______________ is the time from the start of one pulse to the start of the next pulse. It included one pulse duration plus one listening time.
Pulse Repetition Period (PRP) is the time from the start of one pulse to the start of the next pulse. It included one pulse duration plus one listening time.
Pulse Repetition Period is determined by the:
Sound source and imaging depth
Is PRP pulse repetition period adjustable by the sonographer?
yes. the sonographer can change the PRP. when the sonographer adjusts the scan’s depth of view, the pulse repetition period is also altered.
When the system is imaging at shallow depth, the time from one pulse to the next is __________________
When the system is imaging at shallow depth, the time from one pulse to the next is short
When the system is imaging more deeply, the time from one pulse to the next is ______.
When the system is imaging more deeply, the time from one pulse to the next is longer
As depth of view increases, PRP ____________________
As depth of view decreases, PRP _____________________
As depth of view increases, PRP increases
As depth of view decreases, PRP decreases
What are the two components of PRP?
transmit time or on time
and receive time or off time
The transmit time is also called:
pulse duration
_______________ _______________ ______________________ is the number of pulses that an ultrasound system transmits into the body each second
pulse repetition frequency is the number of pulses that an ultrasound system transmits into the body each second
With regard to PRF, the number of ______________ in each pulse is meaningless, However we are interested only in the number of _____________ created each second
With regard to PRF, the number of cycles in each pulse is meaningless, However we are interested only in the number of pulses created each second
The PRF is determined by the:
sound source & the maximum imaging depth
PRF and depth of view are _______ related
inversely
As depth of view increases, pulse repetition frequency ______.
decreases
As depth of view decreases, pulse repetition frequency _______.
increases
PRP and PRF are ______ related.
inversely
PRF=
1/PRP
PRP=
1/PRF
Which of these four values for pulse repetition frequency would have the longest pulse repetition period?
A. 2 kHz
B. 4,000 Hz
C. 6 Hz
D. 1 kHz
C. 6 Hz. pulse repetition period is the reciprocal of pulse repetition frequency. This choice has the lowest pulse repetition frequency, and thus, the longest pulse repetition period
Four pulses have pulse repetition periods as listed below. Which of the following four waves has the highest pulse repetition frequency?
A. 8 s
B. 80 ms
C. 5 ms
D. 400 ks
C. 5 ms. The pulse with the shortest pulse duration will have the highest pulse repetition frequency.
which of these four pulses with PRFs listed below has the shortest PRP?
A. 12 kHz
B. 6,000 Hz
C. 20 kHz
D. 1 kHz
C. 20 kHz. PRP is the reciprocal os PRF. this answer has the highest pulse repetition frequency, and thus the shortest pulse repetition period
Four waves have pulse repetition periods as listed below. Which of the following four waves has the lowest PRF?
a) 8 s
b) 80 us
c) 8000 ns
d) 800 ms
A. 8 seconds. The pulse with the longest pulse duration with have the lowest pulse repetition frequency
True or False. Two waves can have identical pulse repetition frequencies, even if their pulse repetition periods are different
False. Two wave can never have identical PRF’s if their pulse repetition periods are different
True of False. Two waves can have identical pulse repetition frequencies even if their frequencies are different.
True. Frequency and pulse repetition frequency are unrelated
True or False. Two waves can have identical Pulse Repetition Frequencies, even if their frequencies are different
True. Frequency and pulse repetition frequency are unrelated
True or False. Pulse repetition frequency and pulse repetition period are determined only by imaging depth
True. This is a very important concept
_____________ _________________ is the percentage or fraction of time that the system transmits a pulse
Duty Factor is the percentage or fraction of time that the system transmits a pulse.
What are the typical values for Duty Factor?
0.2% to 0.5%
The duty factor is determined by the:
Sound source only
What is the formula for duty factor?
Duty Factor (%) = Pulse Duration/PRP x 100
What is the maximum value for duty factor?
1 or 100%
this is only achieved with only continuous wave sound
What is the minimum value for duty factor?
0 or 0%
typically is 0.2% which means the system is listening approximately 500 times longer than it is transmitting
If all other factors remain unchanged, what happens to the duty factor (increases, decreases, remains the same) when imaging depth increases?
decreases
If all other factors remain unchanged, what happens to the duty factor (increases, decreases, remains the same) when the pulse repetition frequency increases?
increases
If all other factors remain unchanged, what happens to the duty factor (increases, decreases, remains the same) when the sonographer uses a new transducer with a longer pulse duration?
increases
What is the duty factor if the pulse duration is 1 microsecond, and the pulse repetition period is 1 ms?
A. 100%
B. 0.1
C. 0.01
D. 0.001
D. 0.001
Which of the following terms does not belong with the others?
A. high duty factor
B. shallow imaging
C. low PRF
D. short pulse repetition period
C. low PRF is associated with deep imaging. The other three choices are all associated with shallow imaging.
Which of the following terms does not belong with the others?
A. low duty factor
B. shallow imaging
C. low PRF
D. long pulse repetition period
B. shallow imaging does not belong. The other three choices are all associated with deep imaging.
__________________ is the time from the start of a pulse to the end of that pulse.
pulse duration is the time from the start of a pulse to the end of that pulse
____________________ is the time from the start of a pulse to the start of the next pulse.
pulse repetition period is the time from the start of a pulse to the start of the next pulse
Pulse repetition frequency is the reciprocal of __________________________
pulse repetition period
By changing the imaging depth, which of the following does the operator also change? (more than 1 may be correct)
A. pulse repetition frequency
B. duty factor
C. propagation speed
D. pulse repetition period
E. amplitude
F. spatial pulse length
A. pulse repetition frequency
B. duty factor
D. pulse repetition period
The speed of a 5 MHz continuous wave is 1.8 km/sec. The wave is then pulsed with a duty factor of 0.5. Calculate the new propagation speed.
The propagation speed for pulsed and continuous wave sound is the same; in this case, 1.8 km/sec. It depends only upon the medium through which the sound travels.
What is the duty factor if the pulse duration is 1 microsecond, and the pulse repetition period is 1 millisecond?
The duty factor is 0.001 or 10^-3
10 to the negative sixth divided by 10 to the negative third or 0.001
What is the duty factor if the pulse duration is 1 millisecond, and the pulse repetition period is 1 second?
The duty factor is 0.001 or 0.1%
0.001 divided by 1.0 = 0.001
What determines the pulse duration?
A. the source of the wave
B. the medium in which the pulse travels
C. both A and B
D. neither A nor B
A. The pulse duration is the actual time that a transducer is creating one sound pulse and is determined by the ultrasound system. Pulse duration does not include the listening time.
What are the units of pulse duration?
A. units of frequency (Hz, etc.)
B. milliseconds only
C. units of time (sec, years, etc.)
D. units of distance (feet, etc)
C. The pulse duration is the actual time that a transducer is creating one pulse. Hence, it has units of time. The typical range of pulse durations found in diagnostic imaging equipment is 0.3 to 2 nanoseconds, but it is valid to report pulse duration in any unit of time.
True or False? The pulse duration of an ultrasound and transducer system does not change significantly as long as the system components remain unchanged.
True. The pulse duration is the timespan that a pulse exhists. It is determined by the ultrasound system and the transducer. Generally, it remains constant for a particular transducer.
The pulse duration is expressed in the same units as the _______________
A. period
B. PRF
C. wavelength
D. density
A. The pulse duration and the period are measured in units of time, such as seconds, minutes, or hours.
PRF has units of hertz. Wavelength has units of distance. Density has units of mass per volume.
True or False? A sonographer can adjust the duration of an acoustic pulse since it depends upon the pulses propagation speed.
False. A sonographer cannot change the pulse duration. It is a fixed feature of the transducer and ultrasound system. It does not depend upon propagation speed.
True or False? A sonographer can adjust the duration of an acoustic pulse since it depends upon the maximum imaging depth.
False. a sonographer cannot change the pulse duration. It has a constant value, and is not dependent on imaging depth.
