M1U2: Basic Principles of Sound Waves - Foundations and Wave Parameters

What is a wave?

Cyclical variation of some quantity of energy that is transmitted from one location to another

What is a sound wave?

A mechanical wave w/ cyclical changes leading to increases and decreases in PRESSURE and DENSITY in a material medium

What are compressions?

- An area of the wave that has a high pressure and density

- Region of high/max acoustic pressure

What are rarefractions?

- An area of the wave that has a low pressure and density

- - Region of low/mininum acoustic pressure

TRUE OR FALSE: Sound is an electromagnetic wave.

FALSE: Sound is a MECHANICAL wave because it MUST have a MEDIUM to travel through. EM waves can travel through mediums or vacuums

TRUE or FALSE: Sound is non-ionizing.

TRUE: Making it beneficial for imaging fetuses/newborns

What are the classifications of mechanical waves? Which one does sound fall under?

- Classifications: transverse or longitudinal

- Sound is a LONGITUDINAL mechanical wave

What is a transverse mechanical wave?

Particle movement is PERPENDICULAR to wave direction

What is a longitudinal mechanical wave?

Particle movement is PARALLEL to wave direction (ex. sound)

What are acoustic variables? What are the 4 variables?

Changes that occur in the medium as sound is propagated through it

- pressure

- density

- particle motion (distance in nanometers w/ no net movement)

- temperature

What is infrasound?

Sound waves with a frequency below human audible (0Hz-20Hz)

What is audible sound?

A sound wave that can be heard by humans

(20Hz - 20 kHz)

What is ultrasound?

Sound waves beyond the range of human hearing (over 20kHz)

What frequencies are used in diagnostic U/S?

2MHz - 20 MHz

TRUE or FALSE: Lower frequencies allow imaging deeper into the body but give low resolution.

TRUE: Therefore, high frequencies give better resolution but fail to penetrate far into the body

What are sound wave parameters? List the 4 parameters

Used to quantify/measure sound

- frequency

- period

- wavelength

- propogation speed

What is frequency? What are its units?

-The number of cycles per second

- Hertz (Hz)

TRUE or FALSE: Frequency and period have a proportional relationship.

FALSE: Frequency and time are INVERSELY proportional (ex. increasing frequency decreases the period, and vice versa)

What is the period? What is its formula?

- the time it takes for one cycle to occur

- for wave to go from compression --> rarefraction --> compression)

- P = 1/f

What is wavelength? What are its units?

- Distance (length) of one cycle (from one complete compression/rarefraction cycle)

- Millimeters (mm)

TRUE or FALSE: Increasing the frequency results in a longer wavelength.

FALSE: Wavelength and frequency have an INVERSE relationship. By increasing the frequencies, more cycles are occurring per second, resulting in less distance b/w peaks/cycles.

What is the wavelength formula?

Wavelength (λ) = propagation speed (c) /frequency (f)

What is propagation speed/velocity? What does it depend on?

- Distance sound can travel per unit time (ex. m/sec)

- Speed depends on physical properties of medium sound is travelling through

What is the averaged assumed speed in human tissue?

1540m/s

TRUE or FALSE: Wavelength and propagation speed have a proportional relationship.

TRUE: As wavelength increases, so does propagation speed

TRUE or FALSE: High frequencies = larger wavelengths = better resolution

FALSE: High frequencies = SMALLER wavelengths = better resolution

TRUE or FALSE: Period and wavelength are directly proportional.

TRUE: If the time it takes to complete one cycle increases (period), this results in increased distance b/w successive peaks of sound (increases wavelength).

Why are 2MHz - 20MHz used in diagnostic U/S?

They allow for adequate resolution for diagnoses. Anything below has too poor resolution to be used for diagnostic imaging

Which medium would stretch out the wave most (increase wavelength)?

a) soft tissue

b) bone

c) air

d) water

b) bone

- Wavelength equation: λ = c / f

- Therefore, since wavelength and propagation speed are proportional, the medium with the highest propagation speed would yield the largest wavelength.