Ch3 describing sound waves

Acoustic variables include:

pressure, density, distance

acoustic parameters

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

The source of a sound wave is the

ultrasound system and transducer

Photographer can adjust the level of some of these parameters and others cannot be changed

Medium

Other parameters determined by tissue through which the sound is traveling called medium

Period

The time required to complete a single cycle time from start of one cycle to the start of the next example. The period of the moon circling earth is 28 days the period of class in high school.

What does one cycle consist of?

One compression and one rare fraction

Period is reported in what units?

time microseconds

Is period adjustable?

-No. The sonographer cannot change the period while using a basic ultrasound system with a particular transducer.

What is frequency?

Number of certain events that occurred in a specific duration example how many waves occur in a second

Does frequency change speed

No

What is the unit of frequency?

Hertz (Hz), which is equivalent to cycles per second.

Can frequency be changed by the sonographer?

No. Frequency cannot be changed by the Sonographer determined by sound source machine

9MHz said as

9,000,000 cps

More cycles per second mean

Higher frequency

frequency vs wavelength

As frequency increases, wavelength decreases.

Ultrasound

Sound waves with frequencies above 20,000 Hz. 20Khz

audible sound range

20-20,000 Hz

infrasound range

less than 20 Hz

Period And frequencies are

Reciprocals

What happens if frequency does not change

Period does not change

period

How often an event happens during an amount of time seconds

bigness parameters

amplitude, power, intensity

amplitude

Height of a wave

in one direction

-amount of energy the sound carries

amplitude units

decibels (dB)

as amplitude increases

so does intensity and pressure

Can amplitude be changed by the sonographer?

Yes, can be changed by sonographer by adjusting overall output or overall gain

peak to peak amplitude

The difference between maximum and minimum values of an acoustic variable

power

The rate at which work is done or energy is transferred.

power changed by sonographer?

yes

power units

Watts (W)

power decreases as

sound propagates through the body

Power and amplitude relationship

power is proportional to amplitude squared

power increases amp increases

power decreases amp decrease

Power and Intensity Relationship

Power is proportional to intensity

anything you do to power is done ^2 to what

amplitude or intensity

amplitude changes by 3, how does the power change

factor of 9

amplitude is halfed how does power change

1/2^2 is factor of 1/4

Intesity

concentration of energy in a sound beam

what does intensity depend on

-Power in the beam

-Area over which the power is applied

intensity equation

power/area

watts/cm^2

power is the kool aid packet

area is the pitcher

how does changing the power and area change intensity

if you increase power (kool aid packet) intensity increases

if you increase area (pitcher) intensity decreases and vice versa

Intensity determined by

sound source (initially)

can sonographer change the intensity

yes

wavelenth

length/distance of a single cycle

-units meter, mm

wavelength symbol

λ (lambda)

Wavelength is determined by

Both the source and the medium

can wavelength be change by sonographer

no

Wavelength and frequency relationship

inversely related

-lower the frequency the longer wavelength

wavelength formula

lamda= v/f

speed/frequency

what is the speed of soft tissue

1,540 m/s

1.54 mm/microsec

what is wavelength of 1MHz sound in soft tissue

-formula lambda = v/f

1.54mm/microsec/ 1

so it is 1.54mm

wavelength plays an important role in

image quality

-shorter wavelengths are created by higher frequency creating a more detailed image

propagation speed

units

speed at which a wave moves through a medium

-meter per second or mm/µs

Propagation speed is determined by

medium only

can propagation speed be changed by sonographer

NO

speed only changes if

medium changes

how fast sound travels through body

lung << fat << soft tissue << bone

gas slowest < liquid slower < solid fastest

air/gas speed

330

lung 🫁 speed sound travels

300-1200

fat - sound speed travels

1450

soft tissue - sound speed travels

1540

tendon sound speed travels

1850

bone sound speed travels

2000-4000

speed and wavelength are

Directly related.- sound in a slow medium has a short wavelength, sound in a fast medium has a long wavelength

speed formula

v=fλ

2 factors affect speed of sound

stiffness and density

stiffness

ability of a tissue to resist compression

think ping pong balls

density

relative weight of material

think steel vs aluminum

how does stiffness affect speed

Stiffness and speed are directly related. As materials become stiffer, the speed of sound in the material increases.

how does density affect speed

Speed and density are inversely related. As materials become more dense, the speed of sound in the material decreases. Therefore, sound travels faster in media with low density.

if 2 medium are equally stiff but b is stiffer which one will sound travel faster in

the one with low density

does stiffness or density have a greater influence on speed?

stiffness

whats opposite of stiffness

Compressibility and elasticity

bulk modulus is the same as

stiffness. So when bulk modulus increases, speed increases.

-how resistant to compression something is