Particle Motion and Wave Propagation

Question 1

5 steps of getting an image

Answer 1

1. operator control: decide preset/transdcer
2. transducer activation (sending): electrical current to sound; reverse piezoelectric effect
3. sound interaction: sound waves travel through tissue and produce echoes
4. transducer activation (receiving): sound waves converted to electrical current; piezoelectric effect
5. image display: electrical current processed through machine and converted to image on monitor

Question 2

3 reason why preset is important

Answer 2

1. get you in the neighborhood
2. gives you labels/calculations
3. safety

Question 3

acoustic

Answer 3

refers to sound

Question 4

propagation

Answer 4

refers to travel

Question 5

acoustic propagation

Answer 5

refers to the effects tissue cause on sound

Question 6

bioeffects

Answer 6

refers to the effects of ultrasound on tissue (can be good or bad)

Question 7

acoustic variables

Answer 7

pressure
density (rarefactions/compressions)
particle motion
temperature

Question 8

pressure represented by

Answer 8

sine wave where crests=increased pressure and troughs=decreased pressure

Question 9

density

Answer 9

concentration of particles or mass per unit volume
low=rarefaction
high=compressions

Question 10

what kind of wave is a sound wave

Answer 10

mechanical wave (needs a medium to travel through)

Question 11

what kind of wave is an ultrasound machine using

Answer 11

longitudinal mechanical wave

Question 12

longitudinal vs transverse sound waves

Answer 12

L: back and forth particle motion parallel to wave travel direction
T: perpendicular to wave travel (swinging rope up and down but waves travel sideways)

Question 13

mode conversion

Answer 13

when one type of wave is converted to another form (ex. long waves until hit bone then trans waves)

Question 14

wave terms (6)

Answer 14

frequency
period
wavelength
propagation speed
amplitude
intensity

Question 15

frequency (what/equation)

Answer 15

number of complete variations an acoustic variable goes through in one second (how many cycles per second)

f=1/T

Question 16

period (what/equation)

Answer 16

time it takes for once cycle to occur

T=1/f

Question 17

wavelength

Answer 17

length of space one cycle takes up

λ=C/f

Question 18

speed of sound in tissue

Answer 18

1540 m/s
1.54 mm/microsecond

Question 19

an increase in frequency affects the period and wavelength how

Answer 19

it will result in a decrease in period and wavelength

Question 20

what determines the propagation speed

Answer 20

the medium

Question 21

amplitude

Answer 21

max variation of an acoustic variable

strength of wave determined by the source of sound

Question 22

intensity (what/equation)

Answer 22

power of wave divided by the area

I= P/a

Question 23

power

Answer 23

total energy over the entire cross-sectional area

Question 24

how are intensity and amplitude related

Answer 24

I = Amp^2

this means a small change in amplitude results in a large change in intensity

Question 25

spatial peak (what/where)

Answer 25

greatest intensity found across beam where focus is

Question 26

spatial average (what/where)

Answer 26

average intensity over entire beam right where probe first makes contact

Question 27

SP and SA related by what and what does the equation look like

Answer 27

related by beam uniformity ratio BUR= SP/SA

Question 28

Temporal peak

Answer 28

greatest intensity found in the pulse

Question 29

pulse average

Answer 29

average for all values found in a pulse (average of peak on 3 cycles if pulse has 3 cycles)

Question 30

TP and PA relation

Answer 30

TP always higher than PA but in ultrasound its so close they are used interchangeably

Question 31

temporal average

Answer 31

includes the dead time between pulses where there is no intensity

Question 32

TP and TA related by (equation)

Answer 32

related by duty factor DF=TA/TP

Question 33

highest intensity

Answer 33

SPTP

Question 34

biological considerations intensity

Answer 34

SPTA

Question 35

lowest intesnity

Answer 35

SATA

Question 36

modes of ultrasound from lowest to highest intensity

Answer 36

M mode real time b mode doppler continuous wave (no dead time=SPTP)

Question 37

SPTA values are dependent on

Answer 37

the depth (changes shape of beam=changes SP)

Question 38

propagation speed in air, fat, bone, soft tissue

Answer 38

330m/s 1460m/s 4080m/s 1540m/s

Question 39

range equation

Answer 39

D=Cxt

Question 40

what do we do differently in an equation of we want distance to a reflector (interface) vs G-R

Answer 40

for reflector we divide by 2 for G-R we dont

Question 41

1cm rule

Answer 41

it takes 13 microseconds to travel 1cm to reflector and back to probe (2cm total)

Question 42

If the intensity of the emitted sound is doubled what will happen to the power?

Answer 42

it will also double

Question 43

If you scanned with frequencies of 3 MHz, 5 MHZ, and 7.5 MHZ to scan through the same section of liver tissue, which one would reflect back to the surface first?

Answer 43

all at the same time as speed of sound is constant