SPI test 1

Speed of sound in various mediums (slowest-fastest)

Air

Fat

Water

Soft tissue

Blood

Muscle

Bone

PZT

Steel

Wavelength equation

c = wavelength x frequency

Relationship of propagation speed ( c ) and stiffness (Z)

Directly related

Relationship of stiffness (Z) to compressibility (K)

Inversely related

Relationship of stiffness (Z) and elasticity (e)

Inversely related

What aspect has the greatest affect on velocity of sound

Stiffness (Z)

Compression

Crest (highest point of wave)

What kind of wave is a sound wave

Longitudinal (slinky)

Rarefaction

Trough (lowest point of wave)

Frequency unit

Hz (hertz)

Velocity unit

m/s (meters/second)

T (period) unit

Microseconds

Wavelength unit

Meters or millimeters

Intensity unit

Watts/cm²

Acoustic variables

Pressure

Particle motion

Density of medium

Temperature of medium

What type of energy is sound

Mechanical energy

Characteristics of media

Density (p)

Stiffness (Z)

Propagation speed ( c )

Compressibility (K)

Elasticity (e)

Acoustic velocity of soft tissue

1540 m/s

1.54 mm/microsecond

Prefixes with exponents

Giga ^9

Mega ^6

Kilo ³

Hecto ²

Deca ^1

Deci ^-1

Centi ^-2

Milli ^-3

Micro ^-6

Nano ^-9

If wavelength is given in mm and frequency is given in MHz, the answer unit will be

mm/microsecond

If wavelength is given in meters and frequency is given in Hz, the answer unit will be

m/s

Period equation

T=1/f (in microseconds)

What happens to particles when sound passes through them

Particles are pushed together (compressions) and are spread apart (rarefactions)

Compressibility formula

Z=1/K

Elasticity formula

Z=1/e

Acoustic velocity formula

c=Z/rho

How do harmonics improve image quality

Improves lateral resolution

Harmonic beam is narrower

Eliminates grating lobe artifacts

Reduce artifacts from superficial reverberation

What type of waves are harmonics

Non-linear wave propagations

What is sent in and what is received (harmonics)

Send in fundamentals (original frequency), receive harmonics (new frequencies that are multiple of the original)

What kind of harmonic is used in dmu

Second harmonics

What do harmonics do

Improves image quality

Linear propagation

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

Hyugen’s principle

All points on wave can be considered as point sources for the production of three dimensional spherical waves

One complete wavelength degree

360 degrees

“In phase” meaning

Two waves start from the same point at the time

“Different phase” meaning

Two waves start from the same point at different time

Principle of superposition

The summation of waves to form more complex waves

Constructive interference

Occurs when waves with the same frequency are transmitted in phase

Waves combine to form a wave of larger amplitude

Destructive interference

Occurs when waves with same frequency are transmitted 180 degrees out of phase (exactly opposite)

Waves combine (subtract) to form a wave with a smaller amplitude

Intensity unit

Watts/cm²

Types of waves

Electromagnetic and ,echanical

Sinusoidal wave

Oscillations (variations) occur at a constant rate (speed)

Longitudinal wave

Variations of acoustic variables occur parallel to the direction of the sound propogation

Transverse waves

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

Continuous wave (cw)

Constant emission of sound

Pulsed wave (pw)

Intermittent emissions of sound

A few cycles of sound followed by a gap and repeated

Properties of continuous waves are determined by

Source and medium

Source of CW

Frequency

Period

Amplitude

Power

Intensity

Medium of CW

Acoustic velocity

Source and medium of CW

Wavelength

Amplitude (A)

Difference between the maximum value of acoustic variables occur parallel and its normal (undisturbed) value

Amplitude units

MPa, mega pascal

Intensity equations

I = P/Area

I = A²

Wavelength

The distance (mm) covered by one cycle

Acoustic impedance (Z) units

Rayls or Megarayls

Oscillation

Back and forth movement

Sinusoidal wave

Oscillations occurring t a constant rate

Intensity definition

The rate at which energy passes through a unit area

Acoustic impedance

The resistance of a material to compression

Stiffness