Acoustic Parameters in Sonography

Flashcards covering the seven acoustic parameters (period, frequency, amplitude, power, intensity, wavelength, propagation speed) and their definitions, relationships, units, and typical values.

What are the seven acoustic parameters used to describe sound waves in ultrasound?

Period, frequency, amplitude, power, intensity, wavelength, and propagation speed.

What does the period of a sound wave represent?

The time for one complete cycle, from the start of one cycle to the start of the next (or from one compression to the next).

In ultrasound, what unit is the period typically measured in?

Microseconds (µs); typical values range from about 0.06 to 0.5 ms.

Who determines the period in ultrasound equipment?

The sound source (ultrasound machine); it is not adjustable by the sonographer.

What is frequency in ultrasound?

The number of vibrational cycles that occur in one second; units are Hz (or MHz); typically 2–15 MHz for diagnostic ultrasound and set by the source.

What is the relationship between period and frequency?

They are inversely related; Period × Frequency = 1.

What is wavelength in ultrasound?

The distance of one complete vibrational cycle; units are millimeters; λ = c / f.

What is the typical speed of sound in soft tissue?

About 1,540 m/s (1.54 mm/µs).

What determines wavelength and is it adjustable?

Wavelength is determined by both the sound source (frequency) and the medium (propagation speed); with a basic transducer it cannot be adjusted.

What is propagation speed?

The speed at which a sound wave travels through a medium; determined by the medium’s stiffness (bulk modulus) and density.

How does stiffness affect propagation speed?

Increased stiffness leads to faster propagation speed.

How does density affect propagation speed?

Increased density leads to slower propagation speed.

Are propagation speed values affected by frequency or amplitude?

No—the speed of sound in a given medium is independent of frequency and amplitude.

What is the 'big three' size descriptors of a sound wave?

Amplitude, power, and intensity.

What is amplitude?

The size of the wave; measured from baseline to crest or baseline to trough; units depend on the variable; if undefined, amplitude can be in decibels (dB). Typical values for pressure: ~1 MPa to 3 MPa.

What is peak-to-peak amplitude?

The difference between the maximum and minimum values; equal to 2 × amplitude.

What is power in ultrasound?

The rate of energy transfer; energy per unit time; units watts (J/s); determined by the source; adjustable; typical values 4–90 mW.

How is power related to amplitude?

Power ∝ amplitude^2; increasing amplitude by a factor increases power by the square of that factor.

How can you increase amplitude on an ultrasound machine?

By increasing the output power; amplitude tends to decrease with propagation due to attenuation.

What is intensity?

Concentration of energy in the beam; power per unit area; units W/cm^2; determined by the source; adjustable; typical range 0.01 to 300 W/cm^2.

What is the formula for intensity?

Intensity = Power / Area.

How are intensity and power related?

They are directly related; increasing power increases intensity, and decreasing power decreases intensity (assuming beam area constant).

How are intensity and amplitude related?

Intensity ∝ amplitude^2 (for a given beam area).

What is the relationship among intensity, power, and amplitude?

Power ∝ amplitude^2 and Intensity ∝ Power; therefore Intensity ∝ amplitude^2 (assuming constant area).

What is wavelength?

Distance of one complete cycle; units mm; typical soft-tissue range 0.1–0.8 mm; λ = c / f.

What is the wavelength formula in ultrasound units?

λ (mm) = 1.54 mm/µs ÷ f (MHz).

What determines wavelength?

Both the sound source (frequency) and the medium (propagation speed).

Can a basic transducer change wavelength?

No—wavelength is not adjustable with a basic transducer; it is determined by frequency and medium.

What are the frequency classifications by hearing?

Infrasonic < 20 Hz; Audible 20 Hz to 20 kHz; Ultrasound > 20 kHz.

What are typical speeds of sound in various tissues?

Lung ~500 m/s; Fat ~1450 m/s; Soft tissue ~1540 m/s; Liver ~1560 m/s; Blood ~1560 m/s; Muscle ~1600 m/s; Tendon ~1700 m/s; Bone ~3500 m/s.

Is the speed of sound affected by the medium’s tissue type?

Yes—the propagation speed varies with tissue stiffness and density.

What is the relationship between wavelength and frequency?

Wavelength and frequency are inversely related: higher frequency yields shorter wavelength; lower frequency yields longer wavelength.

What is the relationship between wavelength and propagation speed?

Wavelength is proportional to propagation speed for a given frequency: λ ∝ c.

What is the relationship between period and frequency in terms of units?

Period and frequency are reciprocal quantities; as period increases, frequency decreases (and vice versa); their product equals 1.