Chapter 4
PRP/PRF equation
PRF= 1/PRP or PRP = 1/PRF PRP x PRF = 1
Relationship between pulse repetition period(PRP) and Pulse repetition frequency(PRF).
PRP and PRF are inversely related. * A longer prp relsults in a lower PRF * A shorter PRP results in a higher PRF
PRP/PRF units
PRP= seconds/PRF = hertz PRP= miliseconds/PRF = kilohertz
A sonographer is using a 3 MHz transducer & increases the output power in order to visualize structures that are positioned deeper in the patient. No other controls are adjusted. What will happen to each of the following parameters? (Increase, decrease, unchanged)
Period - Remains the same Frequency - Remains the same Wavelength- Remains the same Speed- Remains the same Power- increases Intensity- increases Pulse duration- Remains the same PRF- Remains the same duty factor- Remains the same spatial pulse length- Remains the same pulse repetition period- Remains the same
A Sonographer is using a 3 MHz transducer and changes to a 6 MHz transducer. The imaging depth remains unchanged. Would each of the following parameters increase, decrease, or remain the same ?
Period - decreases Frequency - Increases wavelength - decreases speed - remains the same intensity - remains the same PRF - remains the same pulse repetition speed - remains the same
Pulse duration equation
Pulse Duration (us) = # cycles X period (us) Pulse Duration (us) = # cycles / Frequency (MHz)
______ is the time from the start of a pulse to the end of that pulse
Pulse duration
What is the difference between pulse duration and spatial pulse length?
Pulse duration is the TIME that a pulse is "on" and is typically measured in mircroseconds. While spatial pulse length is the DISTANCE of the pulse end to end, typically measured in millimeters(mm).
What are the five parameters that describe pulsed sound waves ?
Pulse duration, pulse repetition period, pulse repetition frequency, spatial pulse length, duty factor.
How are pulse repetition frequency and depth of view related?
Pulse repetition frequency and depth views are inversely related. * As depth of view increases, pulse repetition frequency decreases. * As depth of view decreases, pulse repetition frequency increases.
Pulse repetition frequency is the reciprocal of _______.
Pulse repetition period
____________ is the time from the start of a pulse to the start of the next pulse
Pulse repetition period
How are pulse repetition period and depth of view related?
Pulse repetition period and imaging depth are directly related. * As depth of view increases, pulse repetition increases. * As depth of view decreases, pulse repetition period decreases.
Spatial pulse length equation
SPL (mm) = # cycles x wavelength (mm)
With shallower imaging, the listening time and the pulse repetition period ...
Shorten
What type of pulse is more desirable in diagnostic imaging?
Shorter duration pulses are desirable for imaging because they create images of greater accuracy.
Pulse repetition period is determined by ?
Sound source only, not by the medium through which th sound travels. It is determined by the imaging depth that the sonographer selects.
the length of the train, from beginning of the locomotive to the end of the caboose, is the _____________.
Spatial pulse length.
What is the typical value for the duty factor ?
0.2 % This means the system is listening approx 500 times longer than it is transmitting.
In clinical imaging, a pulse typically contains _____ cycles
2 to 4 cycles
What is the duty factor if the pulse duration is 1 milisecond, 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 is the duty factor if the pulse duration is 1 microsecond, and the pulse repetition period is 1 ms ?
The duty factor is 0.001 or 10^-3. 10^-6 divided by 10^-3 = 10^-3, or 0.001
The speed of a 5MHz continous wave is 1.8km/sec. The wave is then pulsed with a duty factor of 0.5. Calculate the new propogation speed
The propogation speed for pulsed and continous wave sound is the same; in this case, 1.8km/s. It depends only upon the medium through which the sound travels.
As ultrasound machine is imaging to a depth of 2cm. Would the pulse repetition frequency be described as high or low ?
The pulse repetition frequency is high when systems image only to a shallow depth. When the depth of view is shallow, the system waits only a short time and then creates a new pulse. This procedure is repeated rapidly, over and over. The system continues to produce pulse after pulse; therefore the PRF frequency is high.
When the sonographer adjusts the depth of view to 20cm, what happens to the pulse repetition frequency ?
The pulse repetition frequency is reduced when systems image to a greater depth. A pulse is directed into the body. However, the system waits longer before creating a new pulse. This procedure is repeated, but fewer times per second than when imaging to shallow depths.
What are the two components of pulse repetition period. ? Which one can the sonographer change ?
The two components of the pulse repetition period are: * The transmit time or on time * The receive time or off time
Pulse duration typical values
The typical value of pulse duration in diagnostic ultrasound is 0.3 to 2.0 microseconds or millionths of a second.
Pulse ultrasound components
Transmit, talking or "on" time. Receive, listening, or "off" time.
True or false. PRF and PRP are determined only by the imaging depth.
True.
True or false? Pulse repetition period is unrelated to period. It is related only to depth of view.
True.
True or false. Two waves can have identical PRFs, even if their frequencies are different?
True. Frequency and PRF are unrelated.
What characteristics distinguish pulses with long duration from those with short duration ?
Two characteristics create pulses of long duration: * Many cycles in the pulse * individual cycles with long periods Two charachteristics create pulses of short duration: * few cycles in the pulse, or * individual cycles with short periods
pulse repetition frequency typical values
Typical values of pulse repetition frequency is 1,000 to 10,000 hertz, or one to ten thousand pulses per second.
Is the duty factor adjustable?
Yes. Changing the depth of view of a scan also changes the duty factor.
Is the pulse repetition period adjustable?
Yes. The sonographer can change the pulse repetition period. When the sonographer adjusts the scan's depth of view, the pulse repetition period is also altered.
Pulsed sound
a collection of cycles that travel together
Pulse ultrasound
a collection of cycles that travel together. A pulse must have a beginning and an end.
Pulsed duration
actual time from the start of a pulse to the end of that pulse.
Which of these four pulses with PRF's listed below has the shortest pulse repetition period ? A) 12 kHz B) 6,000 Hz C) 20 kHz D) 1 kHz
c. 20 kHz. PRP is the reciprocal of PRF. This has the hightest PRF therefore the shortest PRP.
Four waves have PRP as listed below. Which of the following four waves has the lowest PRF ? A) 8 S B) 80 microseconds C) 8000 mircroseconds D) 800 ms
A) 8 s. Pulse with longest pulse duration will have the lowest PRF
By changing the imaging depth, which of the following does the operator also change ? A) Pulse repetition frequency B) duty factor C) Pulse repetition period. D) pulse repetition period E) amplitude F) spatial pulse length
A) Pulse repetition frequency B) duty factor C) Pulse repetition period.
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 then PRP increases?
decreases
PRP is unrelated to period, it is related only to
depth of view
How is duty factor calculated?
duty factor(%) = pulse duration/pulse rep.period x 100
Pulse duration is inversely proportional to
frequency
spatial pulse length is inversely proportional to
frequency
duty factor typical values
from 0.1% to 1% or 0.001 to 0.01 little talking, lots of listening
When the system is imaging shallow, the pulse repetition frequency is ________.
higher
Spatial pulse typical values
in clinical imaging, spatial pulse length in soft tissue ranges from 0.1 to 1.0mm
With deeper imaging, the listening time and the pulse repetition period _______.
lengthen
When the system is imaging more deeply, the time from one pulse to the next is ______.
longer
When the system is imaging deep, the pulse repetition frequency is ________.
lower
Pulse Duration units
microseconds
Duty factor units
none, it's a percentage
Pulse duration is directly proportional to
period
The time that it takes the train to roll past us at a railroad crossing would be considered the ______.
pulse duration
The transmit time is called the _______.
pulse duration
To determine a duty factor, use a single pair of complete _______ and _______ times.
pulse duration and PRP times
Which of the following terms does not belong with the others?
B. Shallow imaging does not belong. The other three choices are all associated with deep imaging.
Pulse repetition frequency units
reported in units of Hz(hertz), or per second
Pulse Repetition Period units
reported in units of time, such as ms
PRP is short when imaging at ___ depths
shallow
When the system is imaging at a shallow depths, the time from one pulse to the next is _________.
short
Pulse
short bursts of acoustic energy that are produced by imaging systems and are used to create every picture of anatomy.
Duty factor is determined by?
sound source
Spatial pulse length
the distance that a pulse occupies in space from the start to the end of a pulse. ( from tip of imaginary "train" to end of the "caboose"
Pulse duration is direction proportional to
the number of cycles in the pulse
Spatial pulse length is directly proportional to
the number of cycles in the pulse
pulse repetition frequency
the number of pulses that an ultrasound system transmits into the body each second
Spatial pulse is determined by
Both the source and the medium. It equals the number of cycles in each pulse times the wavelength of each cycle.
Duty Factor
the percentage or fraction of time that the system transmits a pulse
pulse repetition frequency determined by _______
the sound source
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 values of pulse repetition frequency would have the longest pulse repetition period ? 1) 2 kHz 2) 4,000 Hz 3) 6 Hz 4) 1 kHz
C. 6 Hz. Pulse repetition period is the reciprocal of PRF. This choice has the lowest pulse repetition frequency, and thus the longest PRP.
pulse repetition period
the time from the start of one pulse to the start of the next pulse. It includes one pulse duration plus one listening time.
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.
Pulse repetition period typical values
the typical value of pulse repetition duration in diagnostic ultrasound is 100 microseconds to 1 milisecond. Pulse repetition period is generally about 100 to 1,000 times longer than pulse duration.
PRP is longer when imaging deep
true
True or false? Only the listening time portion of the pulse repetition period is changed when the sonographer alters imaging depth
true
spatial pulse length is directly proportional to
wavelength
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
What is depth of view ?
Depth of view describes the maximum distance into the body that an ultrasound system is imaging.
Pulse duration
Determined by: SOUND SOURCE
Spatial pulse units
Distance, such as mm
Duty factor equation
Duty factor = pulse duration/pulse repetition period
How does the sonographer change duty factor ?
Duty factor changes when the sonographer alters imaging depth. As imaging depth increases, transmit time, or pulse duration, remains constant while listening time is prolonged.
True or false. Two waves can have identical PRF, even if their PRP's are different ?
False. Two waves cannot have identical PRF if their PRPs are different.
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
Duty factor is _____ related to imaging depth.
Inversely *When depth increases, DF decreases When depth decreases, DF increases
What are the maximum and minimum values for duty factor ?
Maximum value is 1 or 100 %. This is only achieved with continuous wave sound minimum value is 0 %. This only exists when the transducer is silent.
Is pulse duration adjustable by the sonographer?
No, the sonographer cannot alter pulse duration while using a particular ultrasound system and transducer.
Is pulse duration adjustable?
No. The sonographer cannot alter pulse duration while using a particular ultrasound system and transducer.
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.
