Physics Mod 5

Question 1

Cosine of basic angles

Answer 1

0 = 1
30 = 0.86
45 = 0.707
60 = 0.5
90 = 0
180 = -1

Question 2

Doppler equation

Answer 2

fDop = 2f0vCos(theta) / c

fDop = doppler shifted frequency relative to transmit frequency
f0 = transmit frequency
v = velocity of target through medium
c = speed of beam through medium 1540 m/s for soft tissue
theta = insonification angle (angle to flow)

Question 3

Fast Fourier Transform (FFT)

Answer 3

Process used to separate the sum of frequency shifts into individual frequency bins

Question 4

When is blood more likely to be visualized on US

Answer 4

1) higher frequency
2) superficial
3) harmonics on
4) TEE
5) slow flow (stasis)
6) poor LV function
7) atrial fib
8) higher hematocrit

Question 5

Amplitude depends on

Answer 5

1) intensity of transmit signal
2) total attenuation
3) number and concentration of scatterers
4) wavelength relative to RBCs cross-sectional area
5) wavelength relative to aggregate cross-sectional area
6) acoustic mismatch of RBC’s relative to plasma

Question 6

Nyquist criterior

Answer 6

Aliasing occurs when Doppler frequency shift is > PRF/2

Question 7

Factors that increase aliasing

Answer 7

1) higher operating frequency
2) higher velocity
3) angles closer to 0 or 180
4) increasing doppler gate depth

Question 8

Wall filter saturation

Answer 8

Bright white signals symmetric above baseline

Wall filter setting too low

Question 9

Typical wall filter settings for each application

Answer 9

Venous < 25-50Hz
Arterial 50-100 Hz
Adult Echo 200-600 Hz
Pediatric Echo 600-800 Hz