ultrasound physics chapter 3- describing sound waves

define parameters

features of a sound wave

what values are needed to completely characterize a sound wave?

the seven parameters

What are the seven parameters?

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

what is the source of a sound wave

ultrasound system and transducer

What is tissue also referred as

the medium

What is the definition of period in relation to waves?

The time it takes a wave to vibrate a single cycle.

How is period defined in terms of wave cycles?

The time from the start of one cycle to the start of the next cycle.

what are the units for period

time, such as microsecond

what are the typical values for period

0.06 to 0.5 microseconds

what is period determined by

Period is determined by the sound source only, not by the medium.

Is the period adjustable by the sonographer?

No, the sonographer cannot change the period.

define frequency of a wave

the number of cycles that occurs in one second

what are the units for frequency

Hertz (Hz)
1 cycle/second = 1Hz

what are the typical values of frequency

2-15 MHz

what is frequency determined by

Sound source only

is frequency adjustable

No

what are frequencies with low sound waves defined as

infrasonic or infrasound

if a frequency is infrasonic what is its value

less than 20 Hz

if a frequency is considered audible what is its value

between 20 Hz and 20 kHz (20,000 Hz)

is a frequency is considered ultrasonic or ultrasound what is its value

greater than 20kHz

Why is frequency important in diagnostic sonography?

it affects penetration and image quality

what is the relationship between frequency and period?

period and frequency are INVERSELY related

As frequency increases, period?

decreases

As frequency decreases, period?

increases

If frequency or period remains constant, the other.....

remains unchanged

what is the special relationship between frequency and period called?

reciprocal

what is the two step process in which we should think about hertz?

1. hertz means events per second
2. to which event are we referring?

What is the meaning of a sound wave with a frequency of 100Hz?

1. 100 events occur each second
2. 100 Hz means 100 cycles per second

Which of the following waves is infrasonic?

D. 2Hz

Identify the wave that is ultrasonic.

B. 4 MHz

Which of these waves is ultrasonic and most useful in diagnostic sonography?

B. 4 MHz

Which of the following waves has the longest period?

C. 6Hz

Which has the highest frequency

B. 8 microseconds

which has the shortest period?

A. 12 kHz

which has the lowest frequency

C. 8 Ms

what are the three big parameters

amplitude, power, intensity

define amplitude

it is the difference between the max value and the average or undisturbed value of an acoustic variable

what are the units for amplitude

dB
pressure -- pascals
density -- g/cm^3
partical motion -- cm, in, etc

what are the typical values of amplitude

1 MPa to 3 MPa

what is amplitude determine by

Sound source only

Is amplitude adjustable by the sonographer?

yes

Define peak to peak amplitude.

Measured from min to max and is twice that of amplitude

define power

The rate at which work is done or energy is transferred

what are the units of power

Watts (W)

what are the typical values of power

0.004 - 0.009watts ( 4 to 90 milliwatts)

what is power determined by

the sound source only

is power adjustable

Yes

how are amplitude and power related?

directly related

mathematically, how are amplitude and power related

power is proportional to amplitude squared

define intensity

concentration of energy in a sound beam

what are the units of intensity

watts/cm2

what are the typical values of intensity

0.01 - 300 W/cm2

what is intensity determined by

sound source

is intensity adjustable

yes

How are amplitude, power, and intensity related?

directly related

mathematically how are intensity and power related

intensity is proportional to power

mathematically how are intensity and amplitude related

intensity is proportional to amplitude squared

define wavelength

the distance or length for one complete cycle

what are the units for wavelength

any unit of length

what are the typical values of wavelength

0.1-0.8mm in soft tissue

what is wavelength determined by

Both the source and the medium

Is wavelength adjustable?

no

how do you find wavelength in soft tissue

wavelength = 1.54 / frequency

define propagation speed

the rate at which a sound wave travels through a medium

what are the units for speed

any distance divided by time

what are the typical values of speed

500 m/s- 4000 ms, depending on the tissue that it is traveling through

what is speed determined by

the medium

is speed adjustable

no

what is the speed of sound in soft tissue

1540 m/s or 1.54 mm/μs or 1.54 km/s. (A mile a second).

what is the speed of sound in a lung

500 m/s

what is the speed of sound in fat

1450 m/s

what is the speed of sound in the liver

1560 m/s

what is the speed of sound in blood

1,560 m/s

what is the speed of sound in muscle

1600 m/s

what is the speed of sound in a tendon

1700 m/s

what is the speed of sound in bone

3,500 m/s

what is the speed of sound through air

330 m/s

what is the speed of sound through water

1480 m/s

what is the speed of sound through metals

2000 to 7000 m/s

what is the formula for speed

speed = frequency x wavelength

define stiffness

the ability of an object to resist compression

How are stiffness and speed related?

directly

what is another term for stiffness

bulk modulus

what is the opposite of stiffness

elasticity and compressibility

define density

the relative weight of a material

how are density and speed related

inversely

Speed is determined by the ______ and ______ of the medium.

density and stiffness

If the stiffness of the medium increases, the propagation speed will:

increase

If the density of the medium increases, the speed of sound will:

decrease

which factor is more important: density or stiffness

stiffness

True/False - A wave with a frequency of 15,000 MHz is ultrasonic

true

true/false- if the amplitude of a wave is increased to 3 times its original value, the intensity is increased 6 times.

false

true/false - if the power of a wave is halved, the intensity is reduced to one-fourth its original value

false

True of False. Propagation speed increases as frequency increases.

false

Medium 1 has a density of 9 and a stiffness of 6. Medium 2 has a density of 8 and a stiffness of 6. In which medium will sound travel slower?

medium 1

which of the following characteristics will create the fastest speed of sound

B. low density, high stiffness

which of the following characteristics will create the slowest speed of sound

C. high density, low stiffness

if intensity remains the same while power is doubled, what has happened to the beam area?

B. doubled

true/false- propagation speed increases as frequency decreases

false

true/false- propagation speed does not change as frequency increases

true