Ultrasound Physics Chapter 3: Describing Sound Waves

What is a Parameter?

describes a feature of a soundwave

What are the 7 Acoustic Parameters?

period, frequency, amplitude, power, intensity, wavelength, speed

What are the 3 "determine by" Possibilities

Sound source (the transducer) Medium ( the tissue) and Both the sound source and the medium

Which parameters are determined by the sound source?

Period, frequency, amplitude, power, and intensity

Which parameter is determined by both sound source and the medium?

Wavelength

Which parameter is determined by the medium?

Propagation speed

Which parameters are not adjustable?

period, frequency, wavelength, and propagation speed

Which parameters are adjustable?

amplitude, power, intensity

Cycle

1 wave (1 compression & 1 rarefaction)

Period

the time it takes a wave to vibrate a single cycle (the time it takes from the start of one cycle to the next

Unit for Period

Units of time

Typical Value for Period

.06-.5 microseconds

What is the frequency of Infrasound?

Below 20 Hz

What is the frequency of Ultrasound?

over 20,000 Hz

How are period and frequency related?

They are inversely related (when frequency increases, period decreases, etc)

What other special relationship do period and frequency have?

They are reciprocals (Period X Frequency = 1)

What is The "Bigness" Parameters?

describe size, magnitude, strength, the "bigness" of the soundwave

What are The 3 "Bigness" Parameters?

Amplitude, power, and intensity

Amplitude

the "bigness" of a soundwave.

Unit for Amplitude?

It can have the units of any of the acoustic variables. Amplitude can also be expressed in decibels(dB)

Typical value of amplitude?

1 million pascals to 3 million pascals (1MPa - 3MPa)

What is Peak-to-Peak Amplitude?

the difference between the maximum and minimum value

Power

the rate of energy transfer/the rate at which work is performed

What us the unit for power?

Watts

What is the typical value for power?

4 - 90 milliwatts

What relationship do amplitude and power have?

they have a proportional relationship (When amplitude increases, power increases) Power= proportional to Amplitude^2

Intensity

the concentration of energy in a sound beam

What is the unit for intensity?

W/cm^2 (watts per length measurement squared)

What is the typical value for Intensity?

.01 - 300 W/cm^2

What does intensity =?

Intensity = Power / Area

How are all 3 "Bigness" Parameters related?

Directly related

Wavelength

the length of one cycle

What is the unit of wavelength?

Millimeters (any unit of length)

What is the typical value for wavelength?

.1mm - .8mm

How are wavelength and frequency related?

Inversely Related

What is the frequency and wavelength in soft tissue?

A frequency of 1MHz has a wavelength of 1.54mm in soft tissue

Why Do We Care about Frequency & Wavelength?

They play a MAJOR role in our image quality.

Frequency (and therefore, wavelength) determines how deep we can scan and how much detail we can see in our image.

Propagation Speed

the rate that sound travels through a medium

What is the unit for propagation speed?

(any distance divided by time) m/s

What is the typical value for propagation speed?

500m/s - 4000m/s (will depend on what tissue it is travelling in)

Propagation speed is not affected by?

wavelength or frequency. If the waves are traveling through the same medium, they will all arrive at the same time.

What is the speed of sound in soft tissue?

1540 m/sec

Sound travels fastest in?

Solids

Sound travels slower in?

Liquids

Sound travels slowest in?

Gases

What is the order of tissue type from slowest to fastest speed?

Lung, fat, soft tissue, liver, blood, muscle, tendon, and bone

what is the formula for wavespeed?

wave speed=frequency x wavvelength

How does stiffness affect speed?

the ability of something to resist compression

How does density affect speed?

relative weight of a material

Bulk Modulus

another way to say stiffness

Elasticity

opposite of stiffness

Compressibility

opposite of stiffness