Physics Chapter 1 and 2

A wave is a traveling variation in quantities called

wave variables

Sound is a traveling variation in quantities called

acoustic variables

Ultrasound is sound with a frequency greater than

20,000 Hz

What are some examples of acoustic variables?

Pressure, density, and particle motion

Frequency is the number of what?

Cycles an acoustic variable goes through in a second

What is the unit of frequency?

Hertz, Hz

What is Period?

The time it takes for one cycle to occur

Period decreases, frequency _____

increases

What is wavelength?

The length of space over which one cycle occurs

What is propagation speed?

The speed with which a wave moves through a medium

Wavelength is equal to _________ divided by _________

Propagation speed, frequency

What determines the medium’s propagation speed?

Density and stiffness

When propagation speed increases, stiffness _______

increases

What is the average propagation speed in soft tissue?

1540 m/s or 1.54mm/ms

What determines the propagation speed?

The medium

Place the classifications of matter of increasing sound propagation speed

Gas, liquid, solid

The wavelength of 7MHz ultrasound in soft tissues is what?

0.22mm

Wavelength in soft tissue decreases while frequency _____

increases

How many ms does it take for ultrasound to travel 1.54cm in soft tissue?

10 ms

True or false propagation speed in bone is higher than that is soft tissues

True

Sound travels fastest in air, helium, water, or steel?

Steel

Why do solids have higher propagation speed than liquids?

They have greater stiffness

Sound is a ____________ wave

mechanical longitudinal

If propagation speed is doubles and frequency is held constant, the wavelength is _____

doubled

If frequency in soft tissue is doubled, propagation speed is ________

unchanged

If wavelength is 2mm and frequency is doubled, the wavelength becomes what?

1mm

Waves carry what from one place to another?

Information

From given values for propagation speed and frequency, what can be calculated?

Wavelength

The second harmonic of 3MHz is what?

6MHz

Odd harmonics of 2MHz are what?

6, 10, 14 MHz

Even harmonics of 2 MHz are what?

4, 8, 12 MHZ

Nonlinear propagation means that _____

the waveform changes shape while it travels

In nonlinear propagation, addition frequencies appear that are odd and even multiples of the fundamental frequency. They are called what?

Harmonics

If the density of a medium is 1000 kg/m³ and the propagation speed is 1540 m/s, what is the impedance?

1,540,000 rayls

True or false: if two media have the same propagation speed but different densities, the one with the higher density will have the higher impedance

True

True or false if two media have the same density but different propagation speeds, the one with higher propagation speed will have the higher impedance

True

Impedance is ______ multiplied by _______

density, propagation speed

What is PRF?

The number of pulses occurring in 1 second

What is PRP?

The time from the beginning of one pulse to the beginning of the next

The PRP decreases while the PRF _______

increases

What is PD?

The time it takes for a pulse to occur

What is SPL?

The length of space that a pulse occurs while it travels

What is duty factor?

The fraction of. time that pulsed ultrasound is actually on

PD equals the number of cycles in the pulse multiplied by what?

period

SPL equals the number of cycles in the pulse multiplied by what?

wavelength

The DF of continuous wave sound is _____

1

If the wavelength is 2mm, the SPL for a three-cycle pulse is what?

6mm

The SPL in soft tissue for a two-cycle pulse of frequency 5MHz is what? For a 1-kHz PRF, the PRP is what? What is the DF?

0.4 ms, 1 ms, 0.0004

How many cycles are there in 1 second of continuous wave 5MHz ultrasound?

5,000,000

How many cycles are there in 1 second of pulsed 5-MHz ultrasound with a DF of 0.01? How many cycles did pulsing eliminate?

50,000 99%

For pulsed ultrasound, the DF is always what?

Less than

What is a typical DF for sonography?

0.1

Amplitude is the maximum what?

Variation that occurs in an acoustic variable

What is intensity?

The power divided by area

What is the unit for intensity?

mW/cm²

What is intensity proportional to?

Amplitude squared

If area is doubled and power remained unchanged, intensity is what?

Halved

If both power and area are doubled, intensity is ____

unchanged

If amplitude is doubled, intensity is _____

quadrupled

If a sound beam has a power of 10mW and a beam area of 2cm², what is the spatial average intensity?

5 mW/cm²

Attenuation is the reduction in what?

Amplitude and intensity as a wave travels through a medium

Attenuation consists of what?

Absorption, reflection, and scattering

The attenuation coefficient is attenuation per ____

cm

What are the units for attenuation and the attenuation coefficient?

dB, dB/cm/MHZ

For soft tissues, there is approximately ______ of attenuation per cm for each MHz

0.5 dB

For soft tissues, the attenuation coefficient at 3MHZ is what?

1.5 dB/cm

When the attenuation coefficient in soft tissue increases, frequency

increases

For soft tissue, if frequency is doubled, attenuation is:

If path length is doubled, attenuation is:

If both frequency and path length are doubled, attenuation is:

doubled

doubled

quadrupled

If frequency is doubled and path length is halved, attenuation is:

unchanged

What is absorption?

The conversion of sound to heat

True or false absorption can be greater than attenuation in a given medium at a given frequency

False

True or false attenuation is higher in bone than in soft tissue

True

The imaging depth (penetration) decreases while frequency

increases

If the intensity of 4MHz ultrasound entering soft tissue is 2W/cm², the intensity at a depth of 4cm is what?

0.32

If the intensity of 40MHz ultrasound entering soft tissue is 2 W/cm², the intensity at a depth of 4cm is what?

0.00000002

The depth at which half-intensity occurs in soft tissues at 7.5MHz is what?

0.8cm

When ultrasound encounters a boundary with perpendicular incidence, the ______ of the tissues must be different to produce a reflection (echo)

impedances

With perpendicular incidence, two media _______ and the incident _______ must be known to calculate the reflected intensity

Impedances, intensity

With perpendicular incidence, two media ________ must be known to calculate the intensity reflection coefficient

impedances

For an incident intensity of 2mW/cm² and impedances of 49 and 51 rayls, the reflected intensity is ______ mW/cm², and the transmitted intensity is mW/cm²

0.0008, 1.9992

True or false if the impedances of the media are equal, there is no reflection

True

With perpendicular incidence, the reflected intensity depends on what?

Impedance difference and impedance sum

Refraction is a change in _______ of a sound when it crosses a boundary. Refraction is caused by a change in _____________ at the boundary.

direction, propagation speed

Under what two conditions does refraction not occur?

Perpendicular incidence or equal media propagation speeds

The low speed of sound in fat is a source of image degradations because of refraction. If the incidence angle at a boundary between fat (1.45mm/ms) and kidney (1.56mm/ms) is 30 degrees, what is the transmission angle?

32 degrees

Reflection of sound in many directions white it encounters rough media junctions or particle suspensions (heterogeneous media) is called what?

Scattering

True or false backscatter helps make echo reception less dependent on incident angle

True

What must be known to calculate the distance to a reflector?

Travel time and speed

No reflection will occur with perpendicular incidence if the media impedances are ______

equal

True or false scattering occurs at smooth boundaries and within homogeneous media

False

Axial resolution is the minimum reflector separation required along the direction of the _______ to produce separate ________

scan lines, echoes

Axial resolution depends directly on what?

Spatial pulse length

True or false smaller axial resolution is better

True

If there are 3 cycles of a 1mm wavelength in a pulse, the axial resolution is what?

1.5mm

For pulse traveling through soft tissue in which the frequency is 3 MHz and there are 4 cycles per pulse, what is the axial resolution?

1mm

If there are two cycles per pulse, the axial resolutions is equal to the _______. At 5MHz in soft tissue, this is _______.

wavelength, 0.3

Doubling the frequency causes axial resolution to be _____-

halved

Doubling the number of cycles per pulse causes axial resolution to be ________

doubled

True or false when studying an obese subject, a higher frequency will be required

False

True or false if better resolution is desired, a lower frequency will be required

False