Ultrasound Physics Ch 4

pulse duration

actual time from the start of a pulse to the end of that pulse

Units: microseconds

pulse duration is determined by:

the sound source only

not adjustable by sonographer

pulse duration equation

pulse duration (microseconds) = #cycles/frequency (MHz)

two characteristics create pulses of long duration

many cycles in the pulse

OR

individual cycles with long periods

two characteristics create pulses of short duration

few cycles in the pulse

OR

individual cycles with short periods

spatial pulse length

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

Units: units of distance (i.e. mm)

spatial pulse length is determined by:

both the source and the medium

not adjustable by sonographer

two characteristics create long pulses

may cycles in the pulse

cycles with longer wavelengths

two characteristics create short pulse length

fewer cycles in the pulse

cycles with shorter wavelengths

pulse repetition period (PRP)

time from the start of one pulse to the start of the next pulse

Units: units of time

pulse repetition period is determined by:

sound source only

imaging depth

can be changed by sonographer

two components of pulse repetition period

transmit time/on time

receive time/off time

pulse repetition frequency (PRF)

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

Units: Hz

pulse repetition frequency is determined by:

sound source only

can be changed by the sonographer

relationship between PRP and PRF

inversely related

duty factor

percentage or fraction of time that the system transmits a pulse

duty factor is determined by:

sound source only

adjustable by sonographer

duty factor equation

duty factor (%) = (pulse duration/pulse repetition period)x100

duty factor for imaging systems must always be below

100%

shallow imaging

less listening

shorter PRP

higher PRF

higher duty factor

deep imaging

more listening

longer PRP

lower PRF

lower duty factor

determined by sound source

pulse duration

PRP

PRF

duty factor

determined by sound source and medium

spatial pulse length

change with imaging depth

PRP

PRF

duty factor

do not change with imaging depth

spatial pulse length

pulse duration