US Physics Unit 2

Nature of Ultrasound

A wave is a traveling variation in quantities called wave ____

variables

Sound is a traveling variation in quantities called ____ variables

acoustic

Ultrasound is sound with a frequency greater than _____ Hz

20,000

Acoustic variables include _______________ and particle motion

pressure, density

Which of the following frequencies is in the ultrasound range?

15Hz, 15,000Hz, 15kHz, 30,000Hz, 0.004MHz

30,000Hz

Which of the following is not an acoustic variable

propagation speed

frequency is the number of _____ an acoustic variable goes through in a second

cycles

the unit of frequency is ______ which is abbreviated as:

Hertz, Hz

Period is the _____ that it takes for one cycle to occur

time

Period decreases while _____ increases

frequency

Wavelength is the length of ____ over which a cycle occurs

Space

Propagation speed is the speed with which a ___ moves through a medium

wave

Wavelength is equal to _______ __divided by__ ______

propagation speed, frequency

The ____ __and__ ____ of a medium determines propagation speed

density,stiffness

Propagation speed increases if _______ is increased

Stiffness

The average propagation speed in soft tissues is _____ __m/s or__ ______ mm/microsec

1540, 1.54

Propagation speed is determined by the ______

medium

Place the following classifications of matter in order of increasing sound propagation speed

gas, liquid, solid

Propagation speed in bone is _____ that in soft tissues

higher than

Sound travels fastest in ______

steel

Solids have higher propagation speeds than liquids because they have greater ______

stiffness

Sound travels most slowly in ______

gases

Sound is a _______ wave

mechanical, longitudinal

Waves can carry _____ from one place to another

information

from given values for propagation speed and frequency _____ can be calculated

wavelength

If 2 medians have different stiffness, the one with the higher stiffness will have the higher propagation speed. True or false?

True

Speed of sound in air

0\.33

Speed of sound in Fat

1\.45

Speed of sound in water

1\.48

Speed of sound in soft tissue

1\.54

Speed of sound in blood

1\.57

Speed of sound in muscle

1\.58

Speed of sound in bone

4\.0

Speed of sound in PZT

4\.08

Speed of sound in steel

5\.0-6.0

Compression

When a variable reaches its highest value

Rarefraction

when a variable reaches its lowest value

Compression has ___ __pressure and__ ____ density

high, high

Rarefaction has ___ __pressure and__ ___ density

low, low

Amplitude measures…

how far a sound waves moves any acoustic variable.

Longitudinal waves

variations of acoustic variables occur parallel to the direction of sound propagation

in soft tissue

Transverse waves

variations of acoustic variables occur perpendicular to the direction of sound propagation

in bone

Continious wave

constant emission of a sound, always on

does not give us an image

pulsed wave

intermittent emission of sound

a pulse then a gap

all imaging is PW

What is determined by the source of sound? (In CW)

Frequency, Period, Amplitude, Power, IntensityW

What is determined by the source of sound and the medium through which sound propagates

wavelength

determined by the medium through which sound propagates

acoustic velocity

frequency (f)

the number of complete cycles in the unit of time (1sec)

cycle

a complete variation of an acoustic variable

equation of frequency in Hz

\#cycles/ sec

In common Diagnostic Medical Ultrasound frequencies range from

2-20 MHz

Infrasound

less than 20 Hz

Audible sound

20-20,000 Hz (or 20 Hz-20kHz)

Ultrasound

greater than 20,00Hz (20kHz)

Period (T)

the time it takes for one complete cycle to occur

Period and frequency are inversely proporitonal

true

Equation for period

T= 1/f (MHz)

Amplitude (A)

the difference between the max value of an acoustic variable and its normal value

Power (P)

the rate at which work is done, or the rate at which energy is transfered

energy

the ability to do work

Equation for Power

P= work done/time required to do work

or

energy transfered/ time required to transfer energy

Intensity (I)

the rate at which energy passes through a unit area

equation for intensity

I= Power/ area

If power increases, Intensity _____

increases

if area decreases, Intensity ______

increases

Intensity is proportional to the amplitude of the wave squared

true

Wavelength

the length of space over which one complete cycle occurs

equation for wavelength

wavelength- c/f

acoustic velocity (aka propagation speed) (c)

is the speed that a sound wave travels through a MEDIUM

The denser the material, the _____ the velocity of ultrasound

slower

Stiffness (acoustic impedance or bulk modulus) (Z)

the resistance of a material to compression

Compressibility (K)

fractional decrease in volume when pressure is applied

Z= 1/K

Elasticity (e)

the ability of an object to return to its orginal shape and volume after force is removed

Z= /e

The stiffness of a medium has much more affect on velocity of sound than the density

true

acoustic variables (PPDT)

pressure, particle motion, density, temperature

in phase

two waves start from the same point at the same time

different phase

2 waves start from the same point at different times

one complete wavelength

360

one half wavelength

180

one quarter wavelength

90

principle of superposition

the summation of waves to form more complex waves is known

complex wave

waves of different frequencies cause this, no longer sinusoidal

constructive interference

when waves of same frequencies are transmitted in phase. superposition of waves.

makes larger amp

destructive interference

occurs when waves are out of phase.

makes waves smaller

huygens’ principle

all points on a wave can be considered as point sources for the production of 3d spherical waves

linear propagation

speed does not depend on pressure and the shape of the wave does not change with pressure

remains sinusoidal; crests and valleys travel with same velocity

nonlinear propagation

wave propagation in which speed depends on pressure and the shape of the wave changes with pressure

crests advance faster than valleys

Areas of high pressure travel

faster

areas of low pressure travel

slower

linear propagation has a

sinusoidal shape

non linear propagation has a

tooth pattern of propagation, which compressions speed up and rarefractions slow down

fundamental frequency

original frequency

when the speed of sound changes within a pulse, the _____ changes too

frequency

harmonics

the new frequencies are multiples of the original frequency

in ultrasound, the 2nd harmonic of the fundamental frequency can be used to improve ____

image quality

a broadband transducer that emits a 2 MHz pulse will listen selectively for ______MHz echoes

4

Harmonics improve

lateral resolution

eliminate grafting lobe artifacts

reduce artifacts from superficial reverberation

wavelength is soft tissues ______ while frequency increases

decreases

if propagation speed is doubled (a different medium) and frequency is held constant, the wavelength is _______

doubled

if frequency in soft tissue is doubled, propagation speed is ______

unchanged