Intensity of Pulsed Waves chapter 5

These flashcards cover key concepts related to the intensity of pulsed ultrasound waves, including definitions and relationships between different types of intensities.

What is intensity in terms of ultrasound beams?

Intensity is a beam's power divided by its area.

What are the 5 key relations to intensity in pulsed waves?

Spatial distance, peak, average, temporal, and pulsed duration.

What does peak intensity refer to?

Peak intensity refers to the maximum value of the ultrasound beam.

What is average intensity?

Average intensity is the mathematical middle value across the beam's area.

How does ultrasound beam intensity vary spatially?

The intensity is not uniform and varies at different locations in space.

What is spatial peak intensity (Isp)?

Spatial peak intensity is the maximum intensity at a specific location.

What is spatial average intensity (Isa)?

Spatial average intensity is the average intensity across the entire cross-sectional area of the beam.

In pulsed ultrasound, how is the temporal aspect described?

The temporal aspect considers that the transducer is primarily receiving but occasionally transmitting.

What is temporal peak intensity (Ilp)?

Temporal peak intensity is the maximum intensity of the beam at any instant in time.

What is average intensity during the most intense half-cycle (Imax)?

It is the average intensity during the most intense half-cycle of the pulse.

What is pulse average intensity (Ipa)?

Pulse average intensity is the average intensity during the pulse duration of the transmit time.

What does temporal average intensity (Ita) refer to?

Temporal average intensity is the average intensity during the entire pulse repetition period.

The energy in a sound beam is strongest at the most intense at its ______

Center

The beam’s spatial peak intensity is at the ____ of the beam

Center

The beam’s spatial peak average is the mathematical _____ of the intensities of the beam.

Center

The spatial peak intensity is _____ than the spatial average intensity.

Stronger.

What is temporal peak?

The strongest intensity in a pulse.

What is pulse average?

Pulse average is the mathematical center of the intensities found in a pulse. Weaker than TP, but stronger than TA.

What is temporal average?

The mathematical center of the intensities found in the pulse and listening time. It is typically VERY low due to the off- time intensity being 0. The weakest intensity.

What is the formula for temporal average?

TA= PA X DF

What is the difference between pulsed average and temporal average?

Pulse average intensity is measured during the transmit time only. Temporal average is measured during both the transmit and receive times.

Continuous wave u/s PA is _____ to TA because there is no listening time

Equal ( duty factor is 1 or 100%)

temporal intensities from largest to smallest

Itp, Imax, Ipa, and Ita

Bioeffects mechanical vs thermal.

Mechanical, causes cavitation, SPPA.

Thermal, causes heating, SPTA

_______ may be reported in various ways with respect to time and space.

Intensities

The different measurements of intensities are important in the study of _____

Bioeffect

_____ is the most relevant intensity with respect to tissue heating.

SPTA

What are the units for all intensities?

Watts/cm²

Because peak measurements are larger than average measurements, ____ intensity has the highest value, and _____ has the lowest value.

SPTP intensity has the highest value, and SATA has the lowest value.

A number called the ___ ___ ___ or SP/SA factor describes the spread of a beam in space. The SP/SA factor is unit less, with a value of 1 or greater.

A number called the beam uniformity coefficient.

What describes the relationships of beam intensities with time?

The duty factor is a unit less number with a value between 0 and 1.

For continuous wave ultrasound, the beam is always “on” and the pulse average and temporal average intensities are the same.

SPTA= SPPA and SATA=SAPA

T/F When pulsed and continuous wave sound beams have the same SPTP intensities, the continuous wave beam has the higher SPTA intensity.

True

T/F When pulsed and continuous wave sound beams have the same SATP intensities, the continuous wave beam has the higher SATA intensity.

True

What is maximum intensity in time?

Temporal peak intensity (Itp).

What is the average over the most intense half- cycle?

Im intensity

What is averaged only during the pulse duration (“on” time only)?

Pulse average intensity

What is averaged during the PRP (both “on” and “off” times).

Temporal average intensity (Ita)

T/F spatial peak intensity is the maximum in space.

True

T/F spatial average intensity is averaged over the cross- sectional area of the beam.

True

T/f spatial average intensity (Isa) is averaged over the cross- sectional area of the beam.

True

What is the intensities from largest to smallest:

SPTP, Im, SPPA, SPTA, and SATA

What is the formula for beam uniformity ratio?

BUR= SP/SA

BUR is also known as

SP/SA Factor, BUC, or BUF. Value is usually over 1 (SP is stronger than SA)

When the machine is off, the Duty Factor is ?

0%

When the machine is imaging in grayscale, the DF is usually ?

< 1%

When the machine is using Doppler the DF is usually?

1-10%

When the machine is using continuous wave, the DF is ?

100%