Ultrasound Physics Chapter 4: Understanding Pulsed Waves and Duty Factor

What is pulsed sound?

. a collection of cycles that travel together,

.a pulse must have a beginning and an end.

what are the 2 components of pulsed ultrasound?

.Transmit, talking, or on time

.Receive, listening, or off time

What is Pulse Duration (PD)?

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

. a single transmit, talking, "on" time

Pulse Duration (PD) is reported in units of

time

ex. microseconds (us)

The typical value of pulse duration in diagnostic ultrasound is...

0.3 to 2.0 us (microseconds, or millionths of a second)

What is pulse duration determined by?

Sound source only

Can a sonographer alter pulse duration?

No, it is not adjustable

What is pulse duration (us) equal to?

the number of cycles in each pulse, multiplied by the period (us) of each cycle

How is pulse duration related to the number of cycles in each period?

its directly proportional

How is pulse duration related to period?

directly proportional

How is pulse duration related to frequency?

inversely proportional

What equation is used for pulse duration, frequency and # of cycles?

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

The following 2 characteristics describes:

. many cycles in the pulse, or

. individual cycles with long periods

pulses of long duration

The following 2 characteristics describes:

. few cycles in the pulse, or

. individual cycles with short periods

pulses of short duration

What types of pulses are more desirable in diagnostic imaging?

short duration pulses, they create images of greater accuracy

What is Spatial Pulse Length (SPL)?

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

What units does Spatial Pulse Length (SPL) have?

Units of distance

ex. mm

Spatial pulse length in soft to ranges from...

0.1 to 1.0 mm

Just like wavelength, pulse length is determined by....

both the source and the medium

Can a sonographer alter pulse length?

No

What equation is used for spl, cycles and wavelength?

Spatial pulse length (mm) = # cycles x wavelength

SPL is ___________ the number of cycles in the pulse

directly proportional to

What is the relationship between SPL and wavelength?

they are directly propotional

SPL is ____________ proportional to frequency

inversely

The following describes:

. many cycles in the pulse

. cycles with longer wavelengths

Pulses with long pulse length

The following describes:

. fewer cycles in the pulse

. cycles with shorter wavelengths

Pulses with short pulse length

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

Pulses of short pulse length, more accurate images

The following describes:

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

. includes one pulse duration("on" time) plus one listening time?

Pulse Repetition Period (PRP)

Pulse repetition is reported in units of....

time

ex. ms

The typical value of pulse repetition period is

100 microseconds (us) to 1 millisecond (ms)

PRP is generally about how many times longer than pulse duration?

100 to 1,000 times

Pulse repetition period is determined by....

. the sound source only, not the medium

. the imaging depth the sonographer selects

Can the sonographer change the PRP?

yes, by changing depth

When imaging is at shallow depth the time from one pulse to the next is _________.

short

When the system is imaging more deeply, the time from one pulse to the next is _________.

longer

what is depth of view?

maximum distance into the body that an ultrasound system is imaging

How are PRP and depth of view related?

Directly - as depth of view increases pulse repetition period increases.

. Dov decreases = prp decreases

What are the 2 components of pulse repetition period?

. the transmit time or on time

. the receive time or off time

Which of the 2 components of PRP can the sonographer change?

The receive/listening time of the pulse

. deeper imaging = longer prp and listening time

. shallower imaging = shorter listening time and prp

The following describes:

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

. the # of cycles in each pulse is meaningless, only interested in pulses each second

Pulse Repetition Frequency (PRF)

Pulse repetition frequency is reported in units of.....

Hz (hertz), or per second

What are the typical values of PRF

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

. or 1 to 10 thousand pulses per second

Pulse repetition frequency is determined by.....

. the sound source only

. the max imaging depth of the system

Can PRF be changed by the sonographer?

yes, with depth of view

When the system is imaging shallow, the pulse repetition frequency is_______.

higher

When the system is imaging deep, the pulse repetition frequency is _______.

lower

How are PRF and depth of view related?

Inversely related (as depth of view increases, PRF decreases)

How are PRP and PRF related?

inversely related

. A longer PRP results in a lower PRF

. A shorter PRP results in a higher PRF

What type of relationship do PRP and PRF have?

.reciprocal relationship (when multiplied they = 1)

complementary units

> seconds (PRP) and hertz (PRF)

> milliseconds (PRP) and kilohertz (PRF)

What is Duty Factor (DF)?

the percent of time the machine is doing work, PD/PRP

What are the units duty factor is reported in?

None

.DF is a percentage, therefore dimensionless

duty factor ranges from

. 0.2% to 0.5% or 0.002 - 0.005

When creating anatomic images duty factors are in the range of _____ indicating that ultrasound systems spend a very small percentage of time _____ and a very large percentage of time (98.8%) ______.

0.2%, transmitting, receiving

What is the duty factor for a continuous wave?

. 1.0 or 100%

. because the system is always transmitting; always on

What is duty factor determined by?

Sound source only

is duty factor adjustable by sonographer?

yes, by changing the depth of view

Duty factor is _____ related to imaging depth.

inversely.

>High duty factor at shallow depths, low duty factor with deeper depths

How can DF be represented mathematically?

DF (%) = pulse duration divided by PRP > x 100

The following describes:

. 1 or 100%

. this value is only achieved w/ continuous wave

. continuous wave can't create anatomic images; therefore DF for imaging systems must always be less than 100%

The maximum value for duty factor

The following describes:

. 0%, which only exist when the transducer is silent

. with anatomic imaging a typical value for DF is 0.2%, which means the system is listening approximately 500 times longer than it is transmitting

Minimum value of DF

The following are characteristics of:

. Less listening

. Shorter PRP

. Higher PRF

. Higher DF

Shallow Imaging

The following are characteristics of:

. More listening

. Longer PRP

. Lower PRF

. lower DF

Deep Imaging