CVT 100 #9 Ultrasound

Question 1

Sound is

Answer 1

particles in a medium vibrating around a rest point.

It is energy traveling through a medium.

Question 2

How is sound propagated?

Answer 2

Particles are disturbed by the sound source. This disturbance is transmitted to adjacent particles, and so forth. In this way the sound is propagated.

Question 3

What does sound require to be a sound?

Answer 3

Sound requires a source of disturbance and a medium to travel through (no medium—no sound, e.g., a vacuum)

Question 4

Production of sound:

Answer 4

Source vibrates, disturbs particles, creates ACOUSTIC PRESSURE

Question 5

There is no net movement of the particles in the medium. What moves through the medium?

Answer 5

It is the energy that moves through the medium, leaving the particles where they were

Question 6

Does the water move?

Answer 6

Nope—just the energy.

Question 7

The energy is propagated by?

Answer 7

The region of acoustic pressure is transmitted to adjacent particles in the medium— the energy is propagated.

Question 8

This creates areas in the medium of COMPRESSION AND RAREFACTION

Answer 8

|||||| | | | | | |||||||| | | | | | |||||||| | | | | |||||||||

These are regions of higher and lower acoustic pressure, due to higher and lower concentrations of particles.

Question 9

Wave:

Answer 9

A propagating (i.e., traveling) variation in quantity.

Question 10

Sound is a

Answer 10

propagating variation in acoustic pressure.

Question 11

Two types of waves:

Answer 11

Longitudinal and Transverse

Question 12

Transverse wave:

Answer 12

moves across (90° to) direction of propagation

Question 13

Longitudinal wave:

Answer 13

moves in the direction of (axial to) propagation

Question 14

What type of wave is sound?

Answer 14

Sound is a longitudinal wave. The acoustic variations occur along the direction of travel.

Question 15

The changes in acoustic pressure can be graphed as?

Answer 15

The changes in acoustic pressure can be graphed as a sine wave.

Question 16

Areas of higher pressure that go above the baseline are:

Answer 16

compression

Question 17

Areas that go below the baseline are:

Answer 17

rarefaction

Question 18

What does zero represent?

Answer 18

the rest point of the particles in the medium

Question 19

In that sine-wave graphical depiction of sound, the positive peak represents _______________, the negative peak represents ___________, and the zero represents the rest point.

Answer 19

Compression

Rarefaction

Question 20

Waves move in cycles:

Answer 20

Repetitions of the physical changes in the medium. One cycle of sound would be one compression/rarefaction in the medium.

Question 21

Frequency =

Answer 21

number of cycles in one second

Question 22

Hertz (Hz) =

Answer 22

Cycles per second

Question 23

****test
Sound that humans can hear:
Below this:
Above this:

Answer 23

20 to 20,000 Hz
infrasound (think of elephants)
ultrasound (think of bats)

Question 24

Medical diagnostic ultrasound uses very high frequencies:
vascular:
echo:
Therapeutic ultrasound:

Answer 24

3.5–10 MHz for vascular
2.5–5 MHz for echo (possibly higher for pediatric echo)
Therapeutic ultrasound is in the hundreds of thousands of Hz

Question 25

Commonly used units: How many Hz and how to write it in scientific notation? KHz = MHz =

Answer 25

``` KHz = 1,000 Hz = 1 x 3 10 Hz MHz = 1,000,000 Hz = 1 x 106 Hz ```

Question 26

Period:

Answer 26

Time it takes to complete one cycle

Question 27

Period and frequency are reciprocal:

Answer 27

f= 1 = cycles --- P second P = 1 = seconds --- f cycle

Question 28

A shorter period means a | A longer period means a

Answer 28

higher frequency— you can fit more cycles into a second. | lower frequency— you can’t fit as many cycles into a second.

Question 29

``` Example: 5 cycles/sec or 5 Hz = 4 Hz (cycle/sec)= 400 cycle/sec= 4 MHz = ```

Answer 29

1/5 seconds/cycle (0.2 sec) OR 1/5 Hz 1/4 sec/cycle 1/400 sec/cycle 4 cycles/msec OR .25 msec/cycle

Question 30

If the period is 0.5 msec, what is the frequency?

Answer 30

f=1/P f=1/0.5ms=2MHz OR f=1/0.5x10^-6s = 2,000,000MHz

Question 31

If the frequency is 3.5 MHz, what is the period?

Answer 31

P=1/f P=1/3.5MHz = 1/3.5x10^6Hz = .0000002857 s/c or .286x10^-6s or .286ms/c

Question 32

Source of ultrasound: crystals

Answer 32

lead zirconate titanate (PZT)

Question 33

************test | The piezolelectric effect:

Answer 33

Voltage in, sound out and sound in, voltage out More on this later.

Question 34

**********test | The piezoelectric effect was discovered by

Answer 34

Pierre Curie (with brother Jacques Curie): electric potential created by distorting crystal.

Question 35

**********test | Gabriel Lipmann predicted

Answer 35

the reverse effect mathematically and the brothers confirmed it experimentally.

Question 36

``` *********test Paul Langevin (France): developed? ```

Answer 36

sonar (he studied under Pierre Curie and had an affair with Marie Curie, the cad)

Question 37

``` ********test Ian Donald (Scotland): ```

Answer 37

first efforts at medical use of ultrasound

Question 38

********test The resonant frequency of a piezoelectric crystal is dependent on ___________. What frequency is Thin: What frequency is Thick:

Answer 38

its thickness. Thin: higher frequency Thick: lower frequency

Question 39

The source of sound determines:

Answer 39

1. Frequency 2. Period 3. Amplitude 4. Intensity

Question 40

The medium determines:

Answer 40

Propagation speed (how fast sound travels through the medium) Usually given as c (constant) for ultrasound calculations

Question 41

Propagation speed depends on:

Answer 41

the medium. c = the square root of B/p (if B/p goes down, c goes down) B=bulk modulus: stiffness p = density of medium

Question 42

Density is the concentration of matter:

Answer 42

mass per unit volume g/cm3 kg/m3

Question 43

What does and does not carry sound very well?

Answer 43

Gases don’t carry sound very well: not dense, but too elastic Liquids do much better (whales use it) Solids do very much better: listen to train tracks...

Question 44

Aluminum carries sound better than lead. Why? Which one has a high propagation speed?

Answer 44

Both are pretty stiff, but lead is more dense; this slows down the travel of sound. aluminum

Question 45

Propagation speed Increases with: Decreases with:

Answer 45

Increases with greater stiffness of the medium. Decreases with greater density of the medium. (Density and stiffness aren’t necessarily related.)

Question 46

Greater stiffness means Greater density means

Answer 46

less particle motion, so faster travel. more particles to move, so slower travel.

Question 47

************test Average speed in soft tissue: What is range gating?

Answer 47

c = 1540 m/sec The scanner knows this, and knows time of travel, so it knows distance (depth) d=r x t This is range-gating.

Question 48

Speed of sound in soft tissue:

Answer 48

1540 m/sec or 1.54 mm/μsec Transit time for 1 cm: ~ 6.5 μsec Round trip: 13 μsec 4 cm: 52 μsec 10 cm: 130 μsec 15 cm: 195 μsec

Question 49

**********test | Wavelength is:

Answer 49

Distance of one cycle. **propagation speed frequency(They are not directly related) The formula is c=y*f, y=c/f, f=c/y (y is upside down in the formula) (Don’t confuse it with period—time of one cycle) So wavelength depends on both the source of sound AND the medium.

Question 50

Note the inverse relationship between wavelength and frequency:

Answer 50

Longer wavelength means lower frequency, shorter wavelength means

Question 51

Trick question: What happens to frequency if you double the propagation speed?

Answer 51

NOTHING. The SOURCE governs frequency, not the medium. The MEDIUM governs propagation speed, not the source.

Question 52

**********TEST The source determines The medium determines

Answer 52

how many cycles per second get generated. | how fast the sound can travel. The medium offers some degree of acoustic impedance— we’ll get to that shortly.

Question 53

What happens to wavelength if frequency is doubled?

Answer 53

HALFED

Question 54

What happens to wavelength if propagation speed is doubled?

Answer 54

DOUBLED

Question 55

Next concept: Acoustic impedance

Answer 55

Opposition of the medium to sound travel Greater acoustic impedance means stronger echo SYMBOL: Z

Question 56

Propagation speed of bone: 4080 m/sec Propagation speed of tissue: 1540 m/sec If bone is so fast, why does it make such crummy-looking echoes?

Answer 56

the differences in acoustic impedance It creates a huge change in acoustic impedance. All the ultrasound is bounced back, none gets through.

Question 57

Echoes are created by

Answer 57

changes of acoustic impedance When the sound reaches an interface between tissues having different acoustic impedances, some of the sound is reflected, and the rest travels on.

Question 58

Units of acoustic impedance:

Answer 58

Rayls (remember that)

Question 59

Interface: Two media create a boundary that reflects some of the ultrasound. The bigger the ∆Z, __________________.

Answer 59

the more sound is reflected (the stronger the echo).

Question 60

What is ∆Z?

Answer 60

acoustic impedance