Chapter 4: Describing Pulsed Waves
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49 Terms
5 parameters needed to describe pulsed sound
Pulsed duration
Spatialize pulse length
Pulse repetition period
Pulse repetition frequency
Duty factor
What is pulsed ultrasound and what does it contain/what does it need
A collection of cycles that travel together. Must have a beginning and end, and it contains multiple individual cycles but the entire pulse moves as a single unit.
What are the 2 components of pulsed ultrasound
transmit, talking, or “on” time
Receive, listening, or “off” time
What is pulse duration and it’s units
The actual time from the start of a pulse to the end of that pulse. It is reported in units of time (s,μs )
Typical clinical ultrasound pulse duration range
Ranges from 0.3-2.0μs (microseconds) or 0.5-3μs
What is pulse duration determined by and can sonographer adjust it
It is determined by the sound source only and sonographer cannot adjust it. Each transducer emits a pulse with a fixed duration and it cannot be changed for that transducer
Pulse duration equation/calculation
It is equal to the number of cycles in each pulse, multiplied by period of each cycle
Pulsed duration (μs) = # cycles x period (μs)
How is pulse duration and number of cycles in a pulse related
They are directly proportional
How is pulse duration and period related
They are directly proportional
How is pulse durations and frequency related
They are inversely proportional
Characteristics that create pulses with long durations
many cycles in a pulse
Individual cycles with long periods
Characteristics that create pulses with short durations
few cycles in the pulse
Individual cycles with short periods
How many cycles does a typical clinical imaging pulse have
2-4 cycles
Is short or long duration pulses more desirable for diagnostic imaging and why
Short duration pulses because they create images of greater accuracy
What is spatial pulse length (SPL) and its units
The distance that a pulse occupies in a space from start to end of the pulse. It is reported in units of distance/length (mm,cm)
Clinical imaging spatial pulse length range
Is ranges from 0.1-1.0mm
What is spatialize pulse length determined by and can it be adjusted by the sonographer
It is determined by there source and the medium (since wavelength is determined by both, so is SPL). It is not adjustable by sonographer bc in a particular medium, transducer pulse has a fixed length
Spatial Pulse length calculation/equation
It is equal to number of cycles in each pulse, times the wavelength of each cycle
Spatialize pulse length (mm) = # cycles x wave length (mm)
How is spatial pulse length and number of cycles in a pulse related
They are directly proportional
How is spatial pulse length and wavelength related
They are directly proportional
How is spatial pulse length and frequency related
They are inversely proportional
Difference in pulse duration and spatial pulse length
Pulse duration is the time that a pulse is “on” and typically measured in microseconds (μs), whiles
Atrial pulse length is the distance of the pulse end to end and typically measured in millimeters (mm)
Characteristics that create long spatial pulse lengths
many cycles in a pulse
Cycles with longer wavelengths
Characteristics that create short spatial pulse lengths
fewer cycles in a pulse
Cycles with shorter wavelengths
Is a shorter or longer spatial pulse length more desirable and why
Shorter length because they create more accurate images
What is pulse repetition period (PRP) and it’s units
The time from the start of one pulse to the start of the next pulse. It includes one pulse duration and one listening time. It is reported in units of time (ms)
Diagnostic ultrasound clinical imaging PRP
0.1-1.0ms (100-1000 times more than pulse duration, which is usually 100 microseconds - 1 milliseconds)
What is pulse repetition period determined by and can sonographer adjust it
It is determined by sound source only and is adjustable by sonographer. It is determined by the imaging depth. Shallow depth means that the time from one pulse to the next is short, and deep depth means the time from one pulse to the next is longer.
How is pulse repetition period and period related
They are unrelated. PRP is only related to depth of view
What does depth of view describe and can sonographer adjust it
The max distance into the body that an ultrasound system is imaging. Sonographer can control depth of view
How is pulse repetition period and depth of view related
They are directly related. As depth of view increases, PRP increases (and same for decreasing)
what are the 2 components of pulse repetition period
Transmit time or “on” time (pulse duration)
Receive time or “off” time
What happens during the receive time of PRP
The transducer receives reflections from anatomic reflectors in the body
How can sonographer alter listening time in PRP
By adjusting depth (the transmit time will remain unchanged). Deeper images result in longer listening time/PRP length, and shallow images have shorter listening time/PRP length
What is pulse repetition frequency (PRF) and it’s units
The number of pulses an ultrasound system transmits into the body each second. this is reported in units of Hz (hertz), or per second
What is meaningless in regards to PRF
number of cycles
Typical value of pulse repetition frequency
1,000-10,000 hertz (1-10kHz) or 1,000-10,000 pulses per second
What is pulse repetition frequency determined by and is it adjustable by sonographer
It is determined by sound source only, specifically the max imaging depth of the system. it is adjustable by sonographer by adjusting the depth of view of a scan
How do different depths of imaging effect PFR
shallow imaging = higher PFR
Deep imaging = lower PFR
How is pulse repetition frequency and frequency related
they are unrelated. PRF only relates to depth of view
How is pulse repetition frequency and depth of view related
they are inversely related. as depth of view increases, PFR decreases (and same for opposite)
How is pulse repetition frequency and pulse repetition period related
They are inversely related. a longer PRP results in lower PRF, and shorter PRP results in higher PRF.
They are also reciprocal (PFR x PRP = 1) (use complimentary metric units)
What is duty factor and its units
percentage or fraction of time that a system transmits a pulse. doesn’t have units, its a percentage and therefore dimensionless
Clinical imaging duty factor range
0.002-0.005 or 0.2-0.5%. meaning ultrasound machine spends small percent of time transmitting and a large percent receiving
When is duty factor 100% and 0%
100% for continuous wave sound because the system is always transmitting sound and 0% when the transducer is silent
What is duty factor determined by and is it adjustable by sonographer
it is determined by sound source only and it is adjustable by sonographer by adjusting depth of view
How is duty factor and imaging depth related
they are inversely related. duty factor is high with shallow depth and low with deeper depth. with increase in depth, transmit time (or pulse duration) remains constant while listening time is prolonged
Calculating duty factor
duty factor (%) = (pulse duration / pulse repetition speed) x 100
What parameters describe both pulsed and continuous waves
Period, frequency, wave length, and propagation speed