chapter 4: describing pulsed waves

what are the 5 parameters that describe pulsed sound?

• pulse duration

• PRP

• PRF

• duty factor

• spatial pulse length

pulse duration

the actual time from the start of a pulse to the end of that pulse and is a single transmit, talking or “on” time

units for pulse duration:

reported in units of time such as microseconds

what is pulse duration determined by?

the sound source only

can the pulse duration be adjusted by the sonographer?

no

how are pulse duration and the number of cycles related?

directly

how are pulse duration and period related?

directly

how are pulse duration and frequency related?

inversely

what 2 characteristics created pulses of long duration?

• many cycles in the pulse, OR

• individual cycles with long periods

what 2 characteristics created pulses of short duration?

• few cycles in the pulse, OR

• individual cycles with short periods

which type of pulse is more desirable in diagnostic imaging?

short duration pulses because they create images of greater accuracy

spatial pulse length

the distance that a pulse occupies in space from the start to the end of a pulse

units for spatial pulse length:

units of distance such as mm

what is spatial pulse length determined by?

both the source and the medium

can the spatial pulse length be adjusted by the sonographer?

no

how are spatial pulse length and the number of cycles related?

directly

how are spatial pulse length and wavelength related?

directly

how are patial pulse length and frequency related?

inversely

what 2 characteristics create long pulse lengths?

• many cycles in the pulse

• cycles with longer wavelengths

what 2 characteristics create short pulse lengths?

• fewer cycles in the pulse

• cycles with shorter wavelengths

which type of pulse is more desirable in diagnostic imaging?

pulses of shorter length because they create more accurate images

pulse repetition period (PRP)

the time from the start of one pulse to the start of the next pulse and it includes one pulse duration plus one listening time

units for PRP:

reported in units of time such as ms

what is PRP determined by?

by the sound source only

can PRP be adjusted by the sonographer?

yes, when the sonographer adjusts the depth of view, the PRP is also altered

how are PRP and period related?

unrelated

how are PRP and depth related?

directly

depth of view

describes the maximum distance into the body that an ultrasound system is imaging

what are the 2 components of PRP?

• the transmit time or on time

• the receive time or off time

which component of PRP can the sonographer change?

only the listening time portion is changed when the sonographer alters the depth

pulse repetition frequency (PRF)

the number of pulses that an ultrasound system transmits into the body each second

units for PRF:

hertz (Hz)

what is PRF determined by?

only by the sound source

can PRF be adjusted by the sonographer?

yes, by adjusting the depth of view

how are PRF and frequency related?

unrelated

how are PRF and depth related?

inversely

how are PRP and PRF related?

inversely, reciprocal

duty factor

the percentage or fraction of time that the system transmits a pulse

units for duty factor?

none

what is duty factor determined by?

the sound source only

can duty factor be adjusted by the sonographer?

yes, by changing the depth of view

how are duty factor and depth related?

inversely

what is the maximum value for duty factor?

1 or 100%

when is the maximum value of duty factor achieved?

only with continuous wave sound

what is the minimum value of duty factor?

0%

when is the minimum value of duty factor achieved?

when the transducer is silent

which parameters describe pulsed and continuous waves?

• period

• frequency

• wavelength

• propagation speed