What is a pulsed wave?

In diagnostic imaging, short pulses of acoustic energy are used to create anatomic images. It is also known as "pulse-echo technique." A pulse is a collection of cycles that travel together. A pulse must have a beginning and an end., otherwise the sound is continuous wave. Two components of pulsed ultrasound are the cycles of pulsed sound called the "transmit" time or "on" time, and the dead time or "received" time or "listening" time or "off" time.

Define:

Pulse Duration (PD)

Units?

Determined by?

Changed by sonographer?

Typical values?

Equation?

The time from the start of a pulse to the end of that pulse, the actual time that the pulse is on.

μsec or any unit of time

Determined by the sound source

The sonographer cannot change

(A pulse is a pulse is a pulse)

0.3 μs - 3 μs

PD = # cycles in pulse x period

Define:

Spatial Pulse Length

Units?

Determined by?

Changed by sonographer?

Typical values?

Equation?

The length or distance that an entire pulse occupies in space. The distance from the start to the end of one pulse.

mm or any unit of distance

Determined by BOTH the sound source & the medium. Since λ is determined by source & medium, so too is the SPL

No, cannot be changed by the sonographer

0.1 mm to 1 mm

SPL (mm) = # of cycles x wavelength (mm)

Define:

Pulse Repetition Period (PRP)

Units?

Determined by?

Changed by sonographer?

Typical values?

Equation?

Pulse repetition period is the time from the start of one pulse to the start of the next pulse. It includes one PD and one "listening" time.

ms or any unit of time

Determined by sound source

Yes, by changing the depth of view, the sonographer can change PRP. Only the "listening" time is changed.

100 μs to 1 ms

PRP (μs) = imaging depth (cm) x 13 μs/cm

What happens to PRP with a shallow image?

The PRP is short

What happens to PRP when an image is deep?

PRP is long

Define:

Pulse Repetition Frequency (PRF)

Units?

Determined by?

Changed by sonographer?

Typical values?

Equation?

PRF is the number of pulses that occur in one second.

Hertz, Hz, per second

Determined by the sound source

Yes, by changing the depth of view, the sonographer can change the PRF

1 - 10 kHz

PRF in soft tissue (Hz) = 77,000 cm/s ÷ imaging depth

What is the relationship between imaging depth and PRP?

Directly related

What is the relationship between PRF and imaging depth?

Inversely related

What is the relationship between PRP and PRF?

Reciprocal relationship

PRP x PRF = 1

PRP = 1/PRF

PRF = 1/PRP

Define:

Duty Factor (DF)

Units?

Determined by?

Changed by the sonographer?

Typical values?

Equation?

The percentage or fraction of time that the system transmits sound.

No units! %

Determined by the sound source

Yes, by changing the depth of view, the sonographer can change DF

PW: 0.1% - 1%

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

What happens to DF with a shallow image?

Higher DF

What happens to DF with deeper image?

lower DF

What is the relationship between DF and PRP?

Directly proportional

Define:

Intensity

What is equation

What are the units?

Intensity is the concentration of the power in a beam.

Intensity (w/cm²) = power/beam area

W/cm²

*

True or False?

Intensity is not uniform across a sound beam?

True

True or False?

With pulsed ultrasound, intensity is not uniform throughout time.

True

Name 2 Intensity key words that has to do with

LEVEL

Peak and Average

Name 3 Intensity key words that has to do with

LOCATION

Spacial, Temporal, Pulsed

True or False

Intensity is described with space and time

True

How is Spatial Intensity described?

Peak and Average

How is Temporal Intensity described?

Peak, Most intense half-cycle, Pulse Avg, and Temporal Avg

Name the six resulting intensity descriptions from highest to lowest

SPTP

SATP

SPTA

SATA

SPPA

SAPA

Which intensity description is most important in regards to bioeffects?

SPTA

Define:

Beam Uniformity Coefficient (BUC)

Units?

Typical value?

Equation?

a value which represents how equal the INTENSITY distribution is across a sound beam.

Unitless! %

Value is always greater than 1 if pulsed wave. 1 if CW.

SP/SA

Define:

Decibels

Units?

A logarithmic scale. A relative scale--ratio of the final to the initial strengths. A comparison, therefor, two intensities are need to calculate decibels.

dB

What does positive decibels signify?

Intensity is increasing

What does negative decibels signify?

Intensity is decreasing

The final intensity is 2 times bigger than the original intensity, how many decibels?

3dB

The final intensity is 4 times bigger than the original intensity, how many decibels?

6dB

The final intensity is 8 times bigger than the original intensity, how many decibels?

9db

The final intensity is 10 times bigger than the original intensity, how many decibels?

10db

The final intensity is 100 times bigger than the original intensity, how many decibels?

20db

What are the decibels if the final intensity is 10,000 times greater than the original intensity?

40dB

What are the decibels if the final intensity is 1/8 the original intensity?

-9dB