DMS Physics Ch. 4 Pulsed Wave Parameters

SPL (spatial pulse length) definition

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

Typical SPL Values

It ranges from 0.1 - 1.0mm in soft tissues

How does high frequency affect SPL?

High frequency = shorter periods = shorter pulse duration = shorter wavelength = shorter SPL

How does low frequency affect SPL?

Low frequency = longer periods = longer pulse duration = longer wavelength = longer SPL

SPL formula

# of cycles x wavelength

What is SPL determined by?

sound source and medium

Is SPL adjustable?

Not operator controlled

PRF (pulse repetition frequency) definition

number of pulses transmitted each second

Typical PRF values

1,000-10,000 Hz or 1khz-10khz (one to ten thousand pulses per second)

Is PRF related to frequency?

It's not related to frequency, only to depth of view

How are depth and PRF related?

They are inversely related: more depth means lower PRF. (Consider the longer travel time of the transmission when the depth increases.)

How exactly does depth affect the PRF?

affects the "off" time of the transmission

PRF formula

1/PRP

What is PRF determined by?

sound source ONLY (not by the medium)

Is PRF adjustable by the sonographer?

Yes, by adjusting the depth of view (FOV)

DF (duty factor) definition

the percentage of time (basically percentage of PRP) the ultrasound unit transmits a pulse

Typical DF values

0.2%-0.5% indicates that ultrasound systems spend more time receiving than transmitting

How is DF related to depth?

inversely related, depth increases the "off time" of the PRP which in the makes the DF decrease

DF formula

PD/PRP

What is DF determined by?

sound source ONLY

Is the DF adjustable by the sonographer?

Yes, the sonographer can adjust it by changing the depth of view.

PRP (pulse repetition period) definition

-Time from the start of one pulse to the start of the second (imagine one round of "on" & "off" time)
-Time between repeating transmit pulses

Typical PRP values

100 microseconds to 1 millisecond (about 100 to 1000 times longer than PD)

How does depth affect PRP?

-They are directly related. When depth increases the receiving time increases which makes the PRP longer
-PRP has nothing to do to with period

PRP formula

1/PRF

What is PRP determined by?

sound source ONLY

Is the PRP adjustable?

Yes, by adjusting the depth of view

PD (pulse duration) definition

Time one pulse lasts, a single transmit

Typical PD values

0.3 - 2.0 microseconds in diagnostic ultrasound

How does high frequency affect PD?

High frequency lowers PD because it allows the pulse to complete quicker

How does low frequency affect PD?

Low frequency increases PD because the # of cycles will need more time to complete

If the period or wavelength is high, how will it reflect on the PD?

If they are high the PD will be high

if # of cycles increases, PD ____

increases because PD = # cycles x period

PD formula

# cycles x period

What is PD determined by?

sound source ONLY

Is the PD adjustable?

No, the sonographer cannot adjust the PD