ASN Physics Lecture

Question 1

What are 3 acoustic variables

Answer 1

Pressure (Pa), density, distance

Question 2

7 acoustic parameters

Answer 2

period amplitude frequency power intensity wavelength propagation speed

Question 3

Units of amplitude

Answer 3

Any of acoustic variables - pressure density distance

Question 4

What does increasing gain do?

Answer 4

Increases amplitude of output

Question 5

Relationship of power and amplitude

Answer 5

proportionate to amplitude squared

Question 6

Definition of power vs intensity and units

Answer 6

rate of energy transfer (W), intensity concentration of energy in beam (power(w)/area(cm2))

Question 7

What happens to intensity as sound propogates

Answer 7

It changes (decreases)

Question 8

What is wavelength in soft tissue

Answer 8

1.54 mm/us / f(MHz)

Question 9

DEFINITION of propagation speed

Answer 9

Distance traveled by wave in 1s

Question 10

relative speed of sound in solid liquid and gas

Answer 10

Faster in solid than liquid than gas

Question 11

Definition of PI

Answer 11

(PV - EDV)/MV

Question 12

Typical frequency range of diagnostic ultrasound

Answer 12

1-12MHz

Question 13

Time for roundtrip ultrasound signal

Answer 13

8.3 microseconds

Question 14

Why can’t we visualize A2 on carotid doppler

Answer 14

because its at 90 degrees to probe

Question 15

What is gate that alexandrov uses?

Answer 15

10 - 15mm

Question 16

strongest reflector in artery

Answer 16

adventitia

Question 17

Are RBCs strong reflectors?

Answer 17

No weak, but movement lets you pick them up with doppler

Question 18

Why is shadow artifact below calcified plaque?

Answer 18

Bright reflector so little gets through

Question 19

What causes Rayleigh scattering?

Answer 19

When the imaged is much smaller than the wavelength

Question 20

Rayleigh and frequency relationship

Answer 20

Likelihood of Rayleigh scattering increases f^4

Question 21

What degree of refraction do you get with speed of sound in medium 1 vs 2

Answer 21

If speed of sound much faster in medium 2 you get a more oblique refraction

Question 22

What causes refraction artifact

Answer 22

when beam hits bright reflector

Question 23

Definition of aliasing

Answer 23

When doppler shift is greater than 1/2 pRF

Question 24

With doppler what is relationship between 1kHz and cm/s

Answer 24

1kHz = 37 cm/s

Question 25

On spencers curve what does degree of stenosis do to measured velocity? 50% vs 70%

Answer 25

50% - doubles velocity

70% - quadruples velocity

Question 26

Definition of embolic signal?

Answer 26

Greater than 3dB over background and unidirectional

Question 27

How many bubbles is one cardiac cycle that is completely covered with bubbles?

Answer 27

100 bubble

Question 28

Best place to pick up a signal in elderly

Answer 28

Just anterior to pinna of ear

Question 29

Normal values for MCA in alexandrov lab

Answer 29

30 - 100 cm/s

Question 30

How do you do monitoring for bowhunters

Answer 30

Look for signal drop off with head turned when monitoring p1

Question 31

What do hemorrhage, necrosis and lipid deposits look like?

Answer 31

Low attenuation in plaque

Question 32

Why not use color flow doppler to measure degree of stenosis?

Answer 32

It uses average velocity flow and is therefore more subject to aliasing

Question 33

Causes of focal PI elevations

Answer 33

Can be due to mass effect caused by ICH compressing the adjacent vessel, focal intracranial atherosclerosis

Question 34

PSV through stent

Answer 34

150 m/s

Question 35

wHAT are velocities for restenosis post stent compared with usual??

Answer 35

They are elevated

Question 36

If you have bilateral severe carotid stenosis what can you look for to tell you which side is worse and which side has compensatory increased flow?

Answer 36

Look at ICA/CCA ratio. High on side of max stenosis, lower on compensatory side

Question 37

Sign of carotid occlusion on carotid doppler

Answer 37

absent flow in distal ICA
high resistance stump waveform
Drumbeat sound of lesion motion and vessel wall vibration (usually spikes of low frequency)
Delayed systolic flow acceleration in MCA or flow diversion

Question 38

What is initial finding of MCA stenosis >50%,>70

Answer 38

Increase in MFV > 100 cm/s, >130cm/s

Question 39

Whgenb do you apply >30%between homologous contralateral structures rule?

Answer 39

If patient has conditions that would substantially increases or decrease velocity there must be >30% difference between two sides

Question 40

What can you see with near occlusion MCA?

Answer 40

Decreased velocity, Blunted systolic waveform with slow takeoff.

Question 41

Whats similar about waveform in mCA of MCA stenosis and cervical carotid stenosis…

Answer 41

With both you can get decreased velocity and blunted systolic peak.

Question 42

What velocity or side difference incdicates ACA stenosis

Answer 42

30% difference or >80 cm/s

Question 43

What depth are PCA signals. usually found

Answer 43

Between 55-65

Question 44

Where is top of basilar for temporal window location?

Answer 44

70-80mm

Question 45

What is primary finding of BA stenosis?

Answer 45

Focal significant velocity increase > ICA/ACA/MCA.

Question 46

What is primary finding of stenosis in any vessel

Answer 46

> 30?% of other vessels

Question 47

What is primary finding of VA stenosis

Answer 47

MFV VA > BA

Question 48

What is hierarchy of velocities that if disrupted makes you think about arterial stenosis?

Answer 48

MCA>ACA>ICA>PCA>BA>VA 20% disruption.