Ch.4 Describing Pulsed Waves Flashcards
what are the five parameters that describe pulsed sound?
Pulse duration
Pulse Repetition Period
Pulse Repetition Frequency
Duty Factor
Spatial Pulse Length
what is a pulse?
is a collection of cycles that travel together as a unit
Pulsed Ultrasound has two components
transmit, talking, on time
receive, listenting, off time
Each particular ultrasound transducer emits a pulse with a fixed _____
duration that can not be changed for that transducer
Pulse duration
is the actual time from the start to the end of a pulse
-is a single transmit, talking, or on time
Pulse duration:
Units
Determined by
Typical Values
Adjustable
microseconds (us)
sound source ONLY
0.5 to 3.0 us
NOT
Pulse duration formula
(us) = # cycles x period (us)
Pulse Duration is:
directly proportional to the ____ of ____
directly proportional to _____
inversely proportional to ______
the number of cycles
period
frequency
Describe two characteristics of pulses with a long duration
many cycles in the pulse
or individual cycles with long periods
Describe the two characteristics of pulses with a short duration
few cycles in the pulse
or individual cycles with short periods
what type of pulse is more desirable in diagnostic imaging, and why?
Shorter duration pulses are better for imaging bc they create images of greater accuracy
Spatial Pulse Length
is the distance that a pulse occupies from the start to the end of a pulse
Spatial Pulse Length:
Units
Determined by
Adjustable
Typical Values
mm
Both Sound/Medium
No
in soft tissue 0.1 to 1.0 mm
Spatial Pulse Length:
directly proportional to the __ of ____
directly proportional to _____
inversely proportional to _____
of cycles
wavelength
frequency
Spatial Pulse Length formula
(mm) = # cycles x wavelength (mm)
What are the two characteristics that distinguish long pulse length pulses from short pulse length pulses?
Long pulses have
many cycles
longer wavelengths
vs
Short pulses have
fewer cycles
shorter wavelengths
Which type of pulse is more desirable in diagnostic imaging and why?
Pulses of shorter length are desirable bc they create more accurate images
Pulse Repetition Period (PRP)
is the time from the start of one pulse to the start of the next pulse (transmit and receive)
PRP:
Units
Determined by
Adjustable
Typical values
ms, us
Sound source ONLY
(imaging depth)
YES (Adjust Depth of View)
0.1 to 1.0 ms
(100 to 1000 times longer than pulse duration)
When the system is imaging at shallow depths, 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 ______
Longer
What is depth of view?
describes the maximum distance into the body that an ultrasound system is imaging. Sonographer controls this. The white dots along the edge of the screen indicate depth
How are pulse repetition period and depth of view related?
directly related
What are the two components of pulse repetition period? Which one can the sonographer change?
the transmit time (on)
the receive time (off)
Transmit time is called pulse duration which can NOT be changed since its a fixed value of the transducer
With deeper imaging, the listening time and the pulse repetition period _____
lengthen
With shallower imaging, the listening time and the pulse repetition period _______
shorten
Pulse Repetition Frequency (PRF)
is the number of pulses that an ultrasound system transmits into the body each second
(# of cycles are meaningless)
PRF:
Units
Determined by
Adjustable
Typical Values
Hertz (per second)
Sound Source ONLY
(MAX imaging depth)
YES (adjust depth of view)
1,000 to 10,000 Hertz
When the system is imaging shallow, the pulse repetition frequency is ______
higher
When the system is imaging deep, the pulse repetition frequency is _____
lower
PRP & PRF are ONLY related to?
Depth of view
How are PRF and depth of view related?
Inversely related
How are PRP and PRF related?
inversely related and reciprocal (1/PRP)
A longer PRP results in a _______ PRF
lower
A shorter PRP results in ______ PRF
higher
Duty Factor
is the percentage of fraction of time that the system transmits a pulse
Duty Factor:
Units
Determined by
Adjustable
Typical Values
None
Sound Source ONLY
YES (adjust depth of view)
0.2% to 0.5%
Duty Factor is inversely related to _______ _______
imaging depth
Duty Factor is _____ when the system is imaging at shallow depths, and ______ when imaging at greater depths.
higher
lower
How is Duty Factor calculated?
(%) = (pulse duration / pulse rep. period) x 100
What are the maximum values for duty factor?
maximum value is 1 or 100%; this value is only achieved with continuous wave sound (must always be less than 100%)
What are the minimum values for duty factor?
minimum value is 0% which exits only when the transducer is silent
typical: 0.2%
this means the system is listening approx 500 times longer than it is transmitting
How does the sonographer change duty factor?
changes when the sonographer alters imaging depth
As imaging depth increases, transmit time, or pulse duration, _____ _____ while listening time is ___________
remains constant
prolonged
Duty factor increases with ______ imaging.
Duty factor ______ with deeper imaging.
shallower
decreases
Duty Factor:
Shallow Imaging
4 Characteristics
Less listening
Shorter PRP
Higher PRF
Higher duty factor
Duty Factor:
Deep Imaging
4 Characteristics
More listening
Longer PRP
Lower PRF
Lower Duty Factor
Which of the 5 parameters that describe pulsed sound are determined by the sound source?
Pulse Duration
Pulse Repetition Period
Pulse Repetition Frequency
Duty Factor
Which of the 5 parameters that describe pulsed sound are determined by BOTH sound and medium?
Spatial Pulse Length
Which of the 5 parameters that describe pulsed sound can be changed with imaging depth?
Pulse Repetition Period
Pulse Repetition Frequency
Duty Factor
Which of the 5 parameters that describe pulsed sound can NOT be changed with imaging depth?
Pulse duration
Spatial Pulse length
What are the 4 parameters that describe a single cycle can describe both pulsed and continuous wave sound?
Period
Frequency
Wavelength
Propagation Speed
