Describing Pulsed Waves Flashcards

A set of practice questions and answers about the five parameters describing pulsed ultrasound waves, their formulas, and their relationships to imaging depth.

What is the definition of pulse duration (PD)?

The actual time from the start of a pulse to the end of that pulse; a single transmit, talking, or "on" time.

What are the typical units used to report pulse duration in diagnostic ultrasound?

Microseconds ($\mu s$).

What is the typical range of pulse duration values in diagnostic ultrasound?

$0.3$ to $2.0 \, \mu s$ ($0.5$ to $3.0 \, \mu s$ according to summary table).

Which factor determines the pulse duration of an ultrasound transducer?

The sound source only.

Can the sonographer adjust the pulse duration while using a specific ultrasound system and transducer?

No.

What is the mathematical formula for pulse duration involving the number of cycles and the period?

$$\text{pulse duration} (\mu s) = \# \text{cycles} \times \text{period} (\mu s)$$

How is pulse duration related to frequency?

Pulse duration is inversely proportional to frequency ($PD = \frac{\# \text{cycles}}{\text{frequency (MHz)}}$).

How many cycles does a typical pulse in clinical imaging contain?

$2$ to $4$ cycles.

Why are shorter duration pulses desirable in diagnostic imaging?

They create images of greater accuracy.

What is the definition of spatial pulse length (SPL)?

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

In what units is spatial pulse length typically reported in clinical imaging?

Millimeters ($mm$).

What factors determine the spatial pulse length?

Both the sound source and the medium.

What is the formula for calculating spatial pulse length?

$$\text{spatial pulse length} (mm) = \# \text{cycles} \times \text{wavelength} (mm)$$

What is the primary difference between pulse duration and spatial pulse length?

Pulse duration is the time it takes for a pulse to occur ($\mu s$), while spatial pulse length is the distance the pulse occupies ($mm$).

Define pulse repetition period (PRP).

The time from the start of one pulse to the start of the next pulse, including one pulse duration and one listening time.

What factors determine the pulse repetition period?

The sound source and the imaging depth selected by the sonographer.

How is pulse repetition period related to imaging depth?

They are directly related; as depth of view increases, pulse repetition period increases.

Define pulse repetition frequency (PRF).

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

What is the unit of measurement for pulse repetition frequency?

Hertz ($Hz$) or per second.

How is pulse repetition frequency related to imaging depth?

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

What is the mathematical relationship between pulse repetition period (PRP) and pulse repetition frequency (PRF)?

They are reciprocals; $PRF \times PRP = 1$.

What is the definition of duty factor (DF)?

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

What is the typical range of duty factor values for clinical imaging?

$0.002$ to $0.005$ (or $0.2\%$ to $0.5\%$).

What is the duty factor for continuous wave sound?

$1.0$ (or $100\%$).

How does the sonographer change the duty factor?

By adjusting the imaging depth; duty factor is inversely related to imaging depth.

What is the formula for calculating duty factor as a percentage?

$$\text{duty factor} (\%) = \frac{\text{pulse duration}}{\text{pulse repetition period}} \times 100$$

Which parameters of pulsed sound change when the sonographer adjusts the imaging depth?

Pulse repetition period, pulse repetition frequency, and duty factor.

Which parameters of pulsed sound remain unchanged when the imaging depth is altered?

Pulse duration and spatial pulse length.