Ch.4 Describing Pulsed Waves

pulsed sound

collection of cycles that travel together

pulsed sound

3 pulses

how many pulses?

pulses

short bursts of acoustic energy to create every picture of anatomy

talking (on) time or listening (off) time

pulsed ultrasound has two components

transmit

another name for talking (on) time

transmit, talking, on time

receive, listening, off time

fixed duration

each particular ultrasound transducer emits a pulse with a ___

pulse duration

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

transmit, talking, on time

pulse duration is a single ___

time, microseconds

pulse duration is reported in units of

0.5 to 3.0 microseconds

the typical value of pulse duration is

sound source only

pulse duration is determined by the

pulse duration, spatial pulse length, pulse repetition period, pulse repetition frequency, duty factor

the 5 parameters that describe pulsed sound

5

how many parameters describe pulsed sound

no

yes/no: is pulse duration adjustable?

pulse duration

pulse duration

# cycles x period =

pulse duration

# cycles / frequency =

microseconds (pulse duration)

# cycles / MHz =

directly proportional

pulse duration is ____ to the number of cycles in the pulse

directly proportional

pulse duration is ____ to period

inversely proportional

pulse duration is ___ to frequency

many cycles in the pulse or individual cycles with long periods

2 characteristics create pulses of long duration:

few cycles in the pulse or individual cycles with short periods

two characteristics create pulses of short duration:

long duration

short or long duration?

short duration

short or long duration?

2 to 4 cycles

in clinical imaging, a pulse typically contains ___

shorter duration pulses

what type of pulse is more desirable for diagnostic imaging?

they create images of greater accuracy

why is the shorter duration pulse more desirable in diagnostic imaging?

spatial pulse length

the distance from the front of the pulse to the end of the pulse

spatial pulse length

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

spatial pulse length

distance, mm

spatial pulse length has units of

0.1 to 1.0 mm

in clinical imaging, spatial pulse length in soft tissue ranges from

both the source and the medium

pulse length is determined by

no

yes/no: is spatial pulse length can be adjusted?

spatial pulse length (mm)

# cycles x wavelength (mm) =

directly proportional

spatial pulse length is ___ to the number of cycles in the pulse.

directly proportional

spatial pulse length is ___ to wavelength

inversely proportional

spatial pulse length is ___ to frequency

many cycles in the pulse, cycles with longer wavelengths

two characteristics create long pulse lengths:

fewer cycles in the pulse, cycles with shorter wavelengths

two characteristics create short pulse lengths:

shorter length

what type of pulse length is more desirable in diagnostic imaging?

they create more accurate images

why is the shorter pulse length more desirable in diagnostic imaging?

pulse repetition period

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

pulse repetition period

includes one pulse duration plus one listening time

time, milliseconds

pulse repetition period is reported in units of

100 microseconds to 1 millisecond

the typical value of pulse duration in diagnostic ultrasound

100 to 1000 times

pulse repetition period is generally about ___ longer than pulse duration

sound source

pulse repetition period is determined by

yes

is pulse repetition period adjustable?

also altered

when sonographer adjusts the scan's depth of view, the pulse repetition period is ___

pulse repetition period

short

when the system is imaging at shallow depths, the time from one pulse to the next is ___

longer

when the system is imaging more deeply, the time from one pulse to the next is ___

unrelated

pulse repetition period is ___ to period

related

pulse repetition period is ___ only to depth of view

listens 1,000 times more

pulse repetition period ___ than it talks

depth of view

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

control

sonographers ____ the depth of view

directly related

pulse repetition period and imaging depth are ___

increases

as depth of view increase, pulse repetition period ___

decreases

as depth of view ___, pulse repetition period decreases

transmit time, receive time

two components of the pulse repetition period are:

pulse duration

the transmit time is called the ___

cannot

sonographer CAN/CANNOT change the pulse duration

reflections

the transducer receives ___ from anatomic reflectors in the body during receive time

listening time

sonographer can adjust the ____ when adjusting the imaging depth

increase, lengthen

with deeper imaging, the listening time and pulse repetition period ___

decrease, shorten

with shallower imaging, the listening time and the pulse repetition period ___

alters imaging depth

only the listening time portion of the pulse repetition period is changed when the sonographer ___

shallow imaging

deep or shallow imaging?

deep imaging

deep or shallow imaging?

pulse repetition frequency

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

pulses created each second

with pulse repetition frequency, we are interested only in the number of ___

Hz, per second

pulse repetition frequency is reported in units of

1,000-10,000 Hz (1-10 kHz)

typical value of pulse repetition frequency is

sound source

pulse repetition frequency is determined by the

imaging depth of the system

pulse repetition frequency is determined by the maximum

yes

is pulse repetition frequency adjustable?

adjusting depth of view of a scan

how can sonographer change pulse repetition frequency?

higher

when the system is imaging shallow, the pulse repetition frequency is __

lower

when the system is imaging deep, the pulse repetition frequency is __

unrelated

pulse repetition frequency is ___ to frequency.

related

pulse repetition frequency is only ___ to depth of view

inversely related

pulse repetition frequency and depth of view are

increases

as depth of view __, pulse repetition frequency decreases

increases

as depth of view decreases, pulse repetition frequency __

shallow depth

the pulse repetition frequency is high when systems image only to a

short

when the depth of view is shallow, the system waits a __ time and then creates a new pulse

the pulse repetition frequency is high

an ultrasound machine is imaging to a depth of 1.5cm. would a pulse repetition frequency be described as high or low?

pulse repetition frequency is reduced

when sonographer adjusts the depth of view to 18cm, what happens to the pulse repetition frequency?

reduced

the pulse repetition frequency is ___ when systems image to a greater depth

inversely related

pulse repetition frequency and pulse repetition period are __

lower

a longer pulse repetition period results in a __ pulse repetition frequency

shorter

a __ pulse repetition period results in a higher pulse repetition frequency

reciprocal relationship

pulse repetition period and pulse repetition frequency have a special relationship called __

1

in a reciprocal relationship, when the 2 parameters are multiplied together, the result is __