Pulse Wave Operations

UT 200 (chapter 4 and 7)

it takes ___ microseconds to travel 1 cm deep

6.5

it takes ___ microseconds to travel 1 cm round trip

13

pulsed wave ultrasound

creation of images using sound by sending sound waves into the body, timing its return to determine the depth of the reflector

terms to describe pulsed waves

pulse repetition frequency (PRF)

pulse repetition period (PRP)

pulse duration (PD)

duty factor (DF)

spatial pulse length (SPL)

bandwidth

pulse

collection of cycles that travel together

must have a beginning and an end

an entire pulse moves as a single unit

two components of a pulse

transmit or “on” time

receive/listening or “off” time

pulse duration (PD)

group of periods/number of periods in a pulse

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

considered the “on” time or ringing time

ranges from 0.3 to 2.0 microseconds

PD is determined by the …

sound source (TDR frequency)

PD formula

PD = n x P

PD = number of cycles in a pulse x period

period and frequency are inversely related (P = 1/f), so if the frequency increases then …

period and PD decrease

pulse repetition period (PRP)

start of one pulse to the start of the next pulse

includes the on (transmit) and off (listening) time

PRP is determined by the …

sonographer (by adjusting depth) and sound source

PRP and PRF are ___ related

inversely

PRP is ___ related to depth

directly

as depth increases, PRP …

increases

as PRP increases, PRF …

decreases

as depth increases, PRF …

decreases

PRF is ___ related to depth

inversely

PRF is not the same as …

TDR frequency

as TDR frequency increases …

depth decreases

difference between PRP and PD

PD is only the on time

PRP is both the on and off time

how the source affects PD

PD is determined by the period

period is determined by the frequency

frequency is determined by the sound source

pulse repetition frequency (PRF)

number of pulses transmitted into the body by the US system each second

units for PRF

Herz (Hz) or per sec

units for PD

microseconds

units for PRP

milliseconds or microseconds

PRF is determined by the ___ ___ and is inversely related to depth

sound source

as depth increases, PRF …

decreases

PRF is ___ related to depth

only

PRF is ___ related to TDR frequency

not

if the transducer is excited 500 times, then the PRF is …

500 Hz

spatial pulse wavelength (SPL)

distance (length) a pulse occupies in space from start to end

formula for SPL

SPL = number of cycles in a pulse x wavelength

units for SPL

mm

SPL is determined by …

the source and the medium (because wavelength is determined by the source and the medium)

SPL is visually the same as the …

PD

SPL ___ be altered by the sonographer

cannot

US likes ___ pulses

shorter

high frequency = shorter period = shorter PD = shorter wavelength = shorter SPL =

better image quality

low frequency = longer period = longer pulse duration = longer wavelength = longer SPL =

worse image quality

duty factor (DF)

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

ranges between 0 to 1.0 or 0% to 100%

the DF of continuous wave (CW) ultrasound system is ___ because it is always transmitting

1.0 (100%)

DF formula

DF (fraction) = PD (sec) / PRP (sec)

DF (%) = PD (sec) / PRP (sec) x 100

the DF of pulse wave (PW) ultrasound system is …

less than 1% (ranges from 0.001 and 0.01)

the DF of clinical US imaging is very low because …

there is more receiving time (>99%) than transmitting time (<1%)

DF is determined by the …

source and depth

how PD is affected by the sound source

PD is affected by the period = period is affected by the frequency = frequency is determined by the sound source

as PD increases, DF …

increases

if the PD is 10 sec and the PRP is 100 sec, what is the DF?

10/100 × 100 = 10%

10/100 = 0.10

as PRP increases, DF …

decreases

as PRF increases, DF …

increases

as depth increases, DF …

decreases

as period increases, DF …

increases

DF is directly related to …

PD, PRF, and period

DF is inversely related to …

PRP and depth

factors determined by the sound source

PD, DF, PRP, and PRF

factors affected by depth

DF, PRF, and PRP

factors determined by the source and medium

SPL

bandwidth

the difference between the highest and lowest frequencies emitted by the TDR

TDRs emit frequencies ___ and ___ the operating frequency

above; below

a TDR with a ___ bandwidth emits few frequencies

narrow

examples of TDRs with narrow bandwidth

CW TDRs (cardiac and vascular)

examples of TDRs with wide bandwidth

PW TDRs (abdominal)

a TDR with a ___ bandwidth has short pulses (emits more frequencies)

wide

damping ___ the ring time

shortens

shorter ring time =

better image

narrow bandwidth

A

medium bandwidth

B

wide bandwidth

C

___ TDRs have damping

imaging (PW)

range equation

AKA time of flight or round-trip time

used to determine how far away a reflector is located to be displayed on the screen

ultrasound assumes that the beam is traveling through soft tissue at a speed of …

1.54 mm/microsecond

1540 m/s

13 microsecond rule

it takes 13 microseconds to travel to a depth of 1 cm and return

only applies in soft tissue (thus reflectors traveling faster or slower than soft tissue will be displayed inaccurately)