Pulsed Waves and Intensity

These flashcards encompass key concepts and definitions related to pulsed waves and intensity measurements in sound systems, aiding in exam preparation.

What is a pulsed wave in sound systems?

A collection of cycles traveling together to create images.

What parameters describe pulsed sound?

Pulse duration, pulse repetition period, pulse repetition frequency, duty factor, and spatial pulse length.

What is pulse duration (PD)?

The time it takes from the start of a pulse to the end of that pulse.

What is the typical value range for pulse duration?

0.3 to 2.0 microseconds (\mu s).

What is the formula for pulse duration?

PD (\mu s) = # \text{ cycles} \times \text{period } (\mu s)

What controls pulse duration and is it adjustable?

It is controlled only by the sound source (transducer) and cannot be adjusted by the sonographer.

What characteristics create a long pulse duration?

Many cycles in the pulse or cycles with long periods.

What is the impact of pulse duration on imaging?

Shorter pulse durations translate to better image accuracy, while long durations lead to lower accuracy.

What is spatial pulse length (SPL)?

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

What is the value range for spatial pulse length in soft tissue?

0.1 to 1.0 mm.

What is the equation for spatial pulse length?

SPL (mm) = # \text{ cycles} \times \text{wavelength } (mm)

Which factors determine spatial pulse length?

Both the sound source and the medium (since wavelength depends on both).

How does spatial pulse length relate to image quality?

Shorter spatial pulse lengths lead to greater image accuracy (better axial resolution).

What is pulse repetition period (PRP)?

The time from the start of one pulse to the start of the next pulse, including both 'on' (transmit) and 'off' (receive) time.

What is the value range for pulse repetition period?

100 microseconds to 1 millisecond.

How is PRP related to imaging depth?

They are directly related; as imaging depth increases, PRP increases. It is adjustable by the sonographer.

What components make up the PRP?

The transmit time (pulse duration) and the receive time (listening time).

What is pulse repetition frequency (PRF)?

The number of pulses that an ultrasound system transmits into the body each second, typically ranging from 1,000 to 10,000 Hz.

What is the relationship between PRF and depth?

They are inversely related; as imaging depth increases, PRF decreases.

What is the mathematical relationship between PRP and PRF?

They are reciprocals: PRF \times PRP = 1. An increase in PRP results in a decreased PRF.

What is duty factor?

The percentage or fraction of time that the system is transmitting a pulse.

What is the formula for duty factor?

\text{Duty Factor (\%)} = \frac{\text{Pulse Duration}}{\text{Pulse Repetition Period}} \times 100

What are the typical values for duty factor in clinical imaging?

0.2\% to 0.5\%, meaning the machine spends most of its time listening.

How does depth affect duty factor?

Inversely; as depth increases, duty factor decreases because listening time (part of PRP) increases.

What is the duty factor for continuous wave sound?

1.0 or 100\%, as the system is always transmitting.

How is intensity defined in sound systems?

Sound beam power divided by its area: \text{Intensity } (W/cm^2) = \frac{\text{Power}}{\text{Area}}

What is spatial peak intensity (I_{sp})?

The beam's intensity at the location where it is at its maximum.

What is spatial average intensity (I_{sa})?

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

What is temporal peak intensity (I_{tp})?

The intensity of the beam at the instant in time of its maximal value.

What is I{max} or I{m}?

The average intensity during the most intense half-cycle of a pulse.

What is pulse average intensity (I_{pa})?

The average intensity during the pulse duration (transmit time).

What is temporal average intensity (I_{ta})?

The average intensity during the entire pulse repetition period (both transmit and receive time).

Why is it important to measure intensity variations?

To study sound beam bioeffects on tissue, as intensity varies over distance and time.

What is I_{sptp}?

Spatial peak, temporal peak: measured at the location where intensity is maximum at the instant in time when the pulse is most powerful.

What does I_{sppa} represent?

Spatial peak, pulse average: average intensity at the maximum location over the pulse duration (transmit time).

What is I_{sata}?

Spatial average, temporal average: measured over the entire cross-sectional area of the beam over all time (PRP).

Rank the temporal intensities from largest to smallest.

I{tp} > I{max} > I{pa} > I{ta}

Which intensity measurement is most closely linked to tissue heating (bioeffects)?

I_{spta} (Spatial Peak Temporal Average).

What are the units for all intensity measurements?

Watts per square centimeter (W/cm^2).

What is the Beam Uniformity Coefficient (SP/SA factor)?

A unitless number describing the spread of a beam in space; a value of 1 means the beam is perfectly uniform.

What happens to the listening time when the sonographer decreases depth?

The listening time decreases, which shortens the PRP and increases the PRF.

Why does a higher frequency result in a shorter pulse duration?

Higher frequency sounds have shorter periods; since PD = # \text{ cycles} \times \text{period}, a shorter period reduces the pulse duration.

Rank intensity values from highest to lowest overall.

I{sptp} is the highest; I{sata} is the lowest.