Test 1 Flashcards by Victoria Milne

Define sound

Sound is a travelling pressure / density variation

Compressions and rarefactions

How well did you know this?

Not at all

Perfectly

What are acoustic variables? Give examples

Quantities that vary in a sound wave

Pressure
Density
Particle motion/vibration

How well did you know this?

Not at all

Perfectly

Compression

Regions of high pressure / density

How well did you know this?

Not at all

Perfectly

Rarefaction

Regions of low pressure / density

How well did you know this?

Not at all

Perfectly

Longitudinal wave

Vibration parallel to direction of wave

How well did you know this?

Not at all

Perfectly

Frequency

Cycles per second
Hz
KHz
MHz

How well did you know this?

Not at all

Perfectly

Audible sound

20Hz - 20 KHz

How well did you know this?

Not at all

Perfectly

Ultrasound range

20 KHz - 160 KHz

How well did you know this?

Not at all

Perfectly

Period

Seconds per cycle

Unit: us (microsecond)

How well did you know this?

Not at all

Perfectly

Wavelength

Cycle length

Unit: mm

How well did you know this?

Not at all

Perfectly

Acoustic velocity /

Prop speed

The speed at which a wave moves through a medium

Unit:
m/s
mm/us

How well did you know this?

Not at all

Perfectly

Propagation speed is dependent on

The medium through which the wave travels

How well did you know this?

Not at all

Perfectly

Wavelength formula

Lambda = c/f

c= mm/us
f= MHz

How well did you know this?

Not at all

Perfectly

Propagation speed units

mm/us

How well did you know this?

Not at all

Perfectly

What is stiffness

Resistance of a material to compression

AKA Bulk modulus (B)

How well did you know this?

Not at all

Perfectly

Propagation speed formula

Square root of :

Bulk modulus (N/m^2)
/
Density (kg/m^3)

How well did you know this?

Not at all

Perfectly

Propagation speed through solid liquid gas - what is the order

Solid is highest

Gas is lowest

How well did you know this?

Not at all

Perfectly

Acoustic velocity in soft tissue

1540 m/s

1.54 mm/us

How well did you know this?

Not at all

Perfectly

Propagation speed in:
bone
Fat

Bone: 3-5 times higher
Fat: slightly lower than ST

How well did you know this?

Not at all

Perfectly

Compressibility and elasticity are related how?

How are they related to stiffness

They represent the same thing. Both inversely related to stiffness

How well did you know this?

Not at all

Perfectly

Stiffness is ____ to propagation speed

Directly related to

How well did you know this?

Not at all

Perfectly

How is stiffness related to bulk modulus

Directly proportional

How well did you know this?

Not at all

Perfectly

Describe pulse echo technique in the use of ultrasound

Pulse separated by a gap because ultrasound needs to receive and process the information

How well did you know this?

Not at all

Perfectly

Describe harmonics production

You send out one frequency, and you get back several higher frequencies.
Therefore harmonics allows us to achieve higher frequency waves and which allows for better image quality

How well did you know this?

Not at all

Perfectly

Continuous wave

Sinusodal waveform where cycles repeat indefinitely

Pulse repetition frequency

Number of pulses per second | Unit: KHz

What does PRF depend on?

Pulse repetition frequency depends on the instrument

Pulse repetition period

Time from beginning of one pulse to beginning of next Unit: ms

If PRF increases, what happens to PRP

Inversely proportional, so PRP decreases

What is pulse duration and it’s unit

Time for one pulse to occur | Unit: us

Typical numbers of cycles in an ultrasound pulse

2-3 cycles long

Typical number of cycles in a Doppler pulse

5-30 pulses

If frequency increases, what happens to PD? Why?

Frequency increases Period decreases because inversely proportional Therefore pulse duration decreases because period and PD are directly proportional : PD = n x T

PD units

us (because T is us)

What is the advantage of shorter PD?

Improves the quality of images

What is DF? It’s unit? It’s equation?

Fraction of time the pulsed ultrasound is ON Unit is a decimal or % DF = PD (us) / PRP (us)

If pulse duration increases what happens to DF?

Increases because the sound is on more % of the time DF = PD (us) / PRP (us)

What is SPL? Unit? Significance?

SPL is the length of the pulse Unit: mm SPL(mm) = n x wavelength (mm)

If frequency increases, what happens to SPL?

Frequency increases therefore wavelength decreases (because wavelength is inversely proportionate). So if wavelength decreases SPL decreases

Anechoic

Without internal echoes

Echogenic

With internal echoes

Heterogeneous

Not smooth

Homogeneous

Smooth

Hyperechoic

Brighter echoes than surrounding tissue

Hypoechoic

Darker echoes than surrounding tissues

Isoechoic

Similar echoes to surrounding tissues

Grey scale US

Pulse-echo technique

Doppler US

Pulse-echo + Doppler effect

Bandwidth

Range of frequencies produced by a transducer

Bandwidth is seen only in

Pulsed ultrasound

What happens to bandwidth with a shorter pulse?

Larger bandwidth Thus lower Q factor All of these improve image quality

What is the range of fractional bandwidth in most transducers

50-100%

What happens to quality factor if fractional bandwidth goes down

It increases

Amplitude is

The strength of a sound wave | Unit: pressure (N/m^2) or voltage

Power is

The rate at which energy is transferred | Unit: W or mW

Intensity is

The rate at which energy passes through a unit area Unit: mW/cm^2 Power/area

What is the relationship between intensity and amplitude

``` I = Amp^2 Amp = 1/I^2 ```

What is the relationship between power and amplitude

``` P = Amp^2 Amp = 1/P^2 ```

Waves

Transfer energy from one location to another | Cyclical

Amplitude units

Pressure - N/m2 Density - kg/m^3 Voltage - V

Nonlinear propagation

Propagation in which speed depEnds on pressure and the shape of the wave changes