1. Resident Categorical Course
Doppler Ultrasound
Resident Categorical Course

2. Laminar Flow also called parabolic flow
fluid layers slide over one another
central portion of fluid moves at maximum speed
flow near vessel wall hardly moves at all
friction with wall

3. Turbulent Flow random & chaotic
individual particles flow in all directions
net flow is forward
Often occurs beyond obstruction such as plaque on vessel wall

4. Flow, Pressure & Resistance
Quantity of flow is function of
Pressure
Resistance
Heart provides pulsating pressure

5. Flow and Pressure
Low Pressure
Low Flow
High Pressure
High Flow

6. Resistance to Flow more resistance = lower flow rate
resistance affected by
fluid’s viscosity
vessel length
vessel diameter

7. Resistance to Flow
Less Viscosity
More Flow
More Viscosity
Less Flow

8. Resistance to Flow
Shorter Vessel
More Flow
Longer Vessel
Less Flow

9. Resistance to Flow Larger Diameter More Flow Smaller Diameter
Less Flow

10. Flow Variations
Large fluctuation in pressure & flow in arteries with pulse
Less fluctuation in pressure & flow in veins
pulse variations dampened by arterial system

11. Normal Vessel Distensible Vessel expands during systole
Expands & contracts with
pressure changes
Changes over cardiac cycle
Vessel expands during systole
Vessel contracts during diastole

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

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

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

15. 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

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

17. 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

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

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

20. 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

21. Doppler Angle
Angle between direction of sound and direction of fluid flow q

22. Flow perpendicular to sound
Doppler Sensing
Flow vector can be separated into two vectors
Only flow parallel to sound sensed by scanner!!!
Sensed flow always < actual flow
Flow parallel to sound
Flow perpendicular to sound

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

24. Doppler Equation 2 X fo X v X cosq
f D = fe - fo = c q
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) v

25. Relationships Positive Doppler shift Negative Doppler shift
2 X fo X v X cosq
f D = fe - fo = c
Positive Doppler shift
reflector moving toward transducer
echoed frequency > operating frequency
Negative Doppler shift
reflector moving away from transducer
echoed frequency < operating frequency q q

26. 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
Larger angle
Smaller cosine
Small Doppler shift q

27. 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

28. Doppler Relationships
Constant
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

29. Continuous Wave Doppler
Audio presentation
2 transducers used
one continuously transmits
one continuously receives

30. 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 - =

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

32. Doppler Pulses Different Imaging & Doppler pulses
short pulses required for imaging
Accurate echo timing
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

33. 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

34. Duplex Doppler Gates operator defines active Doppler region (gate)
only sound in gate analyzed

35. Spectral Display Displays real-time range of frequencies received
amplitude of each frequency indicated by brightness
display indicates range of frequencies received
corresponds to range of speeds of blood cells
indicative of type of flow
laminar, turbulent

36. Absolute Speed Measurement
Absolute speed measurements must include Doppler angle
angle between flow & sound propagation
Indicated by operator
Accuracy affects flow speed accuracy

37. Relative Speed Measurement
relative measurements can be useful
Doppler angle not required
indications of spectral broadening do not require absolute measurements
ratio of peak-systolic to end-diastolic relative flows independent of angle

38. Color Doppler User defines window superimposed on gray scale image
For each location in window scanner determines
flow direction
mean value
Variance
window size affects frame rate
larger window = slower scanning
more Doppler pulses required

39. Spectral vs. Color-Flow
spectral Display shows detailed frequency data for single location
Color Doppler’s color represents complete spectrum at each location in window

40. "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