Pulsed Sound Flashcards
What is a collection of cycles that travel together?
Pulse
What type of pulses are used to create anatomic images in diagnostic imaging?
Short pulses of acoustic energy
What are the two components of pulsed ultrasound?
“On” or “transmit” time, and the “dead”, “off”, or “receive” time
What are the parameters of pulsed sound?
Pulse duration, pulse repetition period, PRF, Duty Factor, spatial pulse length
The time from the start of a pulse to the end of that pulse
Pulse duration
In what units is pulse duration measured?
Microseconds, or any unit of time
What is the equation for pulse duration?
Pulse duration = # of cycles in pulse x period
In clinical imaging, how many cycles is a pulse comprised of?
2–4 cycles
Can the pulse duration be changed by the sonographer?
No, pulse duration is a characteristic of each transducer. It does not change when sonographer alters imaging depth. Remember, a pulse is a pulse is a pulse. A transducer’s talking time does not change.
The length or distance that an entire pulse occupies in space
Spatial pulse length
In what units is spatial pulse length measured?
Millimeters, or any unit of distance
Can spatial pulse length be changed by the sonographer?
No
What is the equation for spatial pulse length?
Spatial pulse length (mm) = # of cycles x wavelength (mm)
Which creates higher-quality images, short pulses or long pulses?
Shorter pulses create higher-quality images because spatial pulse length determines axial resolution, which affects image quality.
What is the time from the start of one pulse to the start of the next pulse? It includes one pulse duration and one listening time.
Pulse repetition period
Can the pulse repetition period be changed by the sonographer?
Yes, the operator changes the listening time when adjusting the depth of you, but never the pulse duration.
As imaging depth increases what happens to pulse repetition period?
As imaging depth increases, pulse repetition period increases.
As imaging depth decreases, what happens to pulse repetition period?
As imaging depth decreases, pulse repetition period decreases.
What is PRF?
The number of pulses that occur in one second
What is the units of measure for PRF?
Hertz
What happens to PRF as imaging depth increases?
PRF decreases, they have an inverse relationship.
What is the relationship between PRF and pulse repetition period?
They have an inverse relationship, they are reciprocals.
What is duty factor?
The percentage or fraction of time that the system transmits sound.
What are the units for duty factor?
It is unitless.
What is the duty factor of a continuous wave sound beam?
100%
Can duty factor be changed by the sonographer?
Yes, by changing imaging depth the duty factor is changed.
What happens to duty factor with deeper imaging?
The duty factor decreases as imaging depth increases.
Which of the following parameters of pulsed waves are changed when imaging depth is adjusted?
Pulse repetition period, PRF, duty factor, pulse duration, or spatial pulse length?
Pulse repetition period, PRF, duty factor
Of the parameters of pulsed waves, which are determined by the sound source and which is determined by both the source and the medium?Pulse duration, pulse repetition period, PRF, duty factor, spatial pulse length
Pulse duration, pulse repetition period, PRF, and duty factor are determined by the sound source while spatial pulse length is determined by both the source and the medium.
The speed of a 5 MHz continuous wave is 1.8 km/s. The wave is then pulsed with a duty factor of 0.5. What is the new propagation speed?
Speed depends only upon the medium through which the sound travels, so the new propagation speed is exactly the same as the old propagation speed.
What is the duty factor of a 7 MHz continuous wave sound beam at a depth of 10 cm?
100%
