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35 Cards in this Set

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What is Pulsed Sound?
A pulse of ultrasound is a collection of cycles that travel together. A pulse must have a beginning and an end. Although a pulse is made up of individual cycles, the entire pulse moves as a single unit.
Pulsed Ultrasound has 2 components.
1. tranmit or on time
2. receive or off time
A pulse is similiar to a train. A train consists of individual cars, but travels as a single entity. Similarly, a pulse consists of individual cycles, but propagates as a single unit.
What is pulse duration?
Pulse duration is the actual time from the start of a pulse to the end of that pulse. Pulse duration is a single transmit, talking or on time.
What units are pulse duration reported?
Pulse duration is reported in unites of time, such as us, ms, or seconds.
What is the typical value of pulse duration in diagnostic ultrasound?
Typical values of pulsewave duration in diagnostic ultrasound is 0.3 to 2.0 us(microseconds or millionths of a second)
Pulse duration is determined by?
Pulse duration is determined by the sound source only, not by the medium through which the sound travels.
Is pulse duration adjustable by the sonographer?
No. The sonographer cannot alter pulse duration while using a particular ultrasound system and transducer.
Pulse duration is equal to the number of cycles in each pulse, multiplied by the period of each cycle.
pulse duration (us)= # cycles x period )us)

Pulse duration (us) = # of cycles / frequency (MHz)
Pulse duration is :
Directly proportional to the number of cycles in the pulse
Directly proportional to period
inversely proportional to the frequency
What characteristics distinguish pulses with long duration from those with short duration?
Long Duration: many cycles in the pulse or individual cycles with long periods.

Short duration: Few cycles in the pulse or individual cycles with short periods.
Typically in clinical imaging a pulse contains 2 to 4 cycles
Which type of pulse is more desirable in diagnostic imaging and why?
Shorter duration pulses ane desirable for imaging because they create images of greater accuracy.
What is Spatial Pulse Length?
Spatial Pulse Length is the distance that a pulse occupies in space from the start of the end of a pulse expressed in units of distance such as mm. In clinical imaging spatial pulse length in soft tissue ranges from .01 to 1.0 mm.
Spaitial Pulse Length is determined by?
Pulse length is determined by both the source and the medium. It equals the number of cycles in each pulse times the wavelength of each cycle. Wavelength is determined by both the source and medium, and so is the spatial pulse length.
Spatial Pulse length is not adjustable by sonographer. In a particular medium, a transducer's pulse has a fixed length that cannot change.
Spatial pulse length is directly proportional to and inversely proportional to ?
Spacial Pulse Length is directly proportional to the number of cycles in the pulse and directly proportional to wavelength
Inversely proportional to frequency.
What is the difference between pulse duration and spatial pulse length?
Pulse duration is the time that a pulse is on and measured in us or microseconds
Pulse length is measured in distance in milimeters mm.
Which characteristics distinguish pulses with long pulse length from those with short length?
Long pulse lengths= many cycles in the pulse and cycles with longer wavelengths

Short pulse
fewer cycles in the pulse and cycles with shorter wavelengths.
Which type of pulse is more desirable in diagnostic imaging and why?
Shorter pulses are desirable because they create more accurate images.
What is Pulse Repetition Period?
Pulse repetition period is the time from the start of one pulse to the start of the next pulse. It includes one pulse duration plus one listening time. Pulse repetition period is reposted in units of time, such as ms. The typical value of pulse duration in diagnostic ultrasound is 100 microseconds (us) to 1 milisecond(ms). Pulse repetition period is generally about 100 to 1,000 times longer than pulse duration.
Pulse Repetition Period is determined by?
Pulse repetition period is determined by the sound source only, not by the medium through which the sound travels. Pulse repetition period is determined by the imaging depth that the sonographer selects.
Is the Pulse Repetition Period adjustable?
Yes, The sonographer can change the pulse repetition period by adjusting the scan depth of view, the pulse repetition period is also altered.
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.
Hint: PRP is unrelated to period. It is related to depth of view
PRP What is depth of view?
Depth of view describes the maximum distance into the body that an ultrasound system is imaging. The sonographer controls the depth of view. The markers along the edge of an image indicate depth
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 period increases
As depth of view decreases, pulse repetition period decreases.
What are the two components of pulse repetition period? Which one can the sonographer change?
The two comoponents of the pulse repetition period are:
The transmit time
and the receive time
The transmit time is called the pulse duration. The sonographer cannot change the pulse duration because it is a characteristic of the transducer and has a fixed value.
Sonographer changes the listening time by altering the depth of the image.
With deeper imaging the listening time and the pulse repetition period lengthen.
With shallow imaging, the listening time and the pulse repetion period shorten.
Only listening time portion of the pulse repetition period is changed when the sonographer alters imaging depth.
PRF - Pulse Repetition Frequency
PRF is the number of pulses that an ultrasound system transmits into the body each second. With regard to PRF the number of cycles in each pulse is meaningless.
Pulse repetition frequency is reported in untis of hertz or per second. Typical values are 1,000 to 10,000 herts or one to ten thousand pulses per second and is determined by the sound source only, not by medium.
Pulse repetition frequency is determined by the maximum imaging depth of the system.
The sonographer can change the pulse repetition frequency by adjusting the depth of view of a scan.
When the system is imaging shallow, the pulse repetition frequency is higher
When the system is imaging deeper, the pulse repetition frequency is lower.
Hint: PRF is unrelated to frequency. It is related only to the depth of view.
How are pulse repetition freqyency and depth of view related?
Pulse repetition frequency and depth of view are inversely related.
As depth of view increases, pulse repetition frequency decreases.
As depth of view decreases, pulse repetition frequency increases.
An ultrasound machine is imaging to a depth of 2 cm. 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 anfter pulse; therefore, the PRF frequency is high
When a sonographer adjusts the depth of view to 20 cm, 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 is the relationship between Pulse repetition period and pulse repetition frequency?
Pulse Repetition Period (PRP) and Pulse repetition frequency (PRF) are inversely related to each other.
When PRF increases, the PRP decreases
When PRF decreases, the PRP increases.
Called a reciprocal relationship in which when two parameters are multiplied together the result is 1.
Use complimentary metric units
seconds (PRP) and hertz (PRF)
millisecs (PRP) and Kilohertz (PRF)
What is Duty Factor?
Duty factor is the percentage or fraction of time that the system is transmitting a pulse.
What are typical values of Duty Factor in clinical imaging?
In clinical Imaging, duty factor ranges from 0.002 to 0.005 or .2% to .5% When creating anatomic imcages, duty factors are in the range of .2% indicating that ultrasound systems spend a very small percentage of time transmitting and a very large percentage of time (99.8%) receiving. The duty factor is 1.0 (100%) for continuous wave sound, because the system is always transmitting.
Duty factor is determined by the sound source only.
Is Duty Factor Adjustable?
Yes. Changing the depth of view of a scan also changes the duty factor. Duty factor is inversely related to imaging depth. Duty factor is higher when the system is imaging at shallow depths. and lower when imaging to greater depths.
How is duty factor calculated?
Duty Factor is the fraction of time during which an ultrasound system transmits a wave. The time required to create a pulse is the pulse duration. The pulse repetition period includes both one transmit time and one receive time. Duty factor can be represented mathematically as:
duty factor%=pulse duration/pulse rep. period X 100
What are the maximum and minimum values for duty Factor?
The mas value for duty factor is 1 or 100% this value is only achieved with continuous wave sound. continous wave sound cannot create anatomiv images; therefore, duty factors for imaging systems must always be less that 100%.
The minimum value of duty factor is 0% which exists only when the transducer is silent. While creating anatomic images, a typical value for the duty factor is 0.2%, which means that the system is listening approx. 500 times longer than it is transmitting.
How does the sonographer change duty factor?
The sonographer changes duty factor when imaging depth is altered.
Depth increases, transmit time remains constant while listening time is prolonged. As a result, the duty factor decreases as a system images deeper. Duty factor increases when systems image superficially.