1. Display of Motion & Doppler Ultrasound
Resident Class

2. Blood Flow Characterization
Hemodynamics
Blood Flow Characterization
Plug
Laminar
Disturbed
Turbulent

3. Plug Flow Type of normal flow Constant fluid speed across tube
Occurs near entrance of flow into tube

4. Laminar Flow also called parabolic flow
fluid layers slide over one another
occurs further from entrance to tube
central portion of fluid moves at maximum speed
flow near vessel wall hardly moves at all
friction with wall

5. Flow Disturbed Flow Turbulent Flow
Normal parallel stream lines disturbed
primarily forward particles still flow
Turbulent Flow
random & chaotic
individual particles flow in all directions
net flow is forward
Often occurs beyond obstruction such as plaque on vessel wall

6. Flow, Pressure & Resistance
pressure difference between ends of tube drives fluid flow
Resistance
more resistance = lower flow rate
resistance affected by
fluid’s viscosity
vessel length
vessel diameter
flow for a given pressure determined by resistance

7. Flow Variations pressure & flow in arteries fluctuate with pulse
pressure & flow in veins much more constant
pulse variations dampened by arterial system

8. Flow Rate Measurements
Volume flow rate
Volume of liquid passing a point per unit time
Example
100 ml / second

9. Flow Rate Measurements
Linear flow rate
Distance liquid moves past a point per unit time
Example
10 cm / second

10. Flow Rate Measurements
Volume Flow Rate = Linear flow rate X Cross Sectional Area

11. Flow Rate Measurements
Volume Flow Rate = Linear flow rate X Cross-sectional Area
High Velocity
Small Cross-section
Low Velocity
Large Cross-section
Same Volume Flow Rate

12. Volume Flow Rates
constant volume flow rate in all parts of closed system
Sure! Any change in flow rate would mean you’re gaining or losing fluid.

13. Stenosis narrowing in a vessel
fluid must speed up in stenosis to maintain constant flow volume
no net gain or loss of flow
turbulent flow common downstream of stenosis

14. Stenosis If narrowing is short in length If narrowing is long
Little increase in overall resistance to flow
Little effect on volume flow rate
If narrowing is long
Resistance to flow increased
Volume flow rate decreased

15. Doppler Shift
difference between received & transmitted frequency
caused by relative motion between sound source & receiver
Frequency shift indicative of reflector speed IN
OUT

16. Doppler Examples
change in pitch of as object approaches & leaves observer
train
Ambulance siren
moving blood cells
motion can be presented as sound or as an image

17. Doppler Angle angle between sound travel & flow 0 degrees 90 degreesq
angle between sound travel & flow
0 degrees
flow in direction of sound travel
90 degrees
flow perpendicular to sound travel

18. Flow perpendicular to sound
Flow Components
Flow vector can be separated into two vectors
Flow parallel to sound
Flow perpendicular to sound

19. Flow perpendicular to sound
Doppler Sensing
Only flow parallel to sound sensed by scanner!!!
Flow parallel to sound
Flow perpendicular to sound

20. Doppler Sensing Sensed flow always < actual flow Actual flow

21. Doppler Sensing
cos(q) = SF / AF
Actual flow
(AF) q
Sensed flow
(SF) q

22. Doppler Equation 2 X fo X v X cosq
f D = fe - fo = c q
where
fD =Doppler Shift in MHz
fe = echo of reflected frequency (MHz)
fo = operating frequency (MHz)
v = reflector speed (m/s)
q = angle between flow & sound propagation
c = speed of sound in soft tissue (m/s)

23. Relationships 2 X fo X v X cosq
f D = fe - fo = c
positive shift when reflector moving toward transducer
echoed frequency > operating frequency
negative shift when reflector moving away from transducer
echoed frequency < operating frequency q q

24. Relationships Doppler angle affects measured Doppler shift
cosq
2 X fo X v X cosq
f D = fe - fo = c q
Doppler angle affects measured Doppler shift q

25. Simplified (?) Equation
2 X fo X v X cosq
f D = fe - fo = c
77 X fD (kHz)
v (cm/s) =
fo (MHz) X cosq
Simplified:
Solve for reflector velocity
Insert speed of sound for soft tissue
Stick in some units

26. Doppler Relationships
77 X fD (kHz)
v (cm/s) =
fo (MHz) X cos 
higher reflector speed results in greater Doppler shift
higher operating frequency results in greater Doppler shift
larger Doppler angle results in lower Doppler shift

27. Continuous Wave Doppler
Audio presentation only
No image
Useful as fetal dose monitor

28. Continuous Wave Doppler
2 transducers used
one continuously transmits
voltage frequency = transducer’s operating frequency
typically 2-10 MHz
one continuously receives
Reception Area
flow detected within overlap of transmit & receive sound beams

29. Continuous Wave Doppler: Receiver Function
receives reflected sound waves
Subtract signals
detects frequency shift
typical shift ~ 1/1000 th of source frequency
usually in audible sound range
Amplify subtracted signal
Play directly on speaker - =

30. Pulse Wave vs. Continuous Wave Doppler
No Image
Image
Sound on continuously
Both imaging & Doppler sound pulses generated

31. Doppler Pulses short pulses required for imaging
minimizes spatial pulse length
optimizes axial resolution
longer pulses required for Doppler analysis
reduces bandwidth
provide purer transmitted frequency
important for accurate measurement of frequency differences needed to calculate speed

32. Color-Flow Display Features
Imaged electronically scanned twice
imaging scan processes echo intensity
Doppler scan calculates Doppler shifts
Reduced frame rates
only 1 pulse required for imaging
additional pulses required when multiple focuses used
several pulses may be required along a scan line to determine Doppler shift

33. Duplex Doppler Gates
operator indicates active Doppler region on display
regions are called gates
only sound in gate analyzed for frequency shift
can be isolated based on delay time after pulse
Gate

34. Spectral Display shows range of frequencies received
amplitude of each frequency indicated by gray shade
can be displayed real time
fast Fourier Transform (FFT) technique
frequency
range
Frequency
Elapsed Time

35. Spectral Broadening display indicates range of frequencies
corresponds to range of speeds of blood cells
range indicative of type of flow
laminar, disturbed, turbulent
frequency
range
Frequency
Time

36. Pulse Wave Doppler Allows range selectivity
monitor Doppler shift (frequency difference) at only selected depth(s)
ability to separate flow from >1 vessel or localize flow within vessel

37. Spectral vs. Color-Flow
spectral Display shows frequency range directly
Color Doppler’s color represents complete spectrum at each pixel
frequency
range
Frequency
Elapsed Time

38. "Color Power Angio" of the Circle of Willis
Power Doppler
AKA
Energy Doppler
Amplitude Doppler
Doppler angiography
Magnitude of color flow output displayed rather than Doppler frequency signal
flow direction or different velocities not displayed
"Color Power Angio" of the Circle of Willis