1. Diagnostic Medical Sonography Program
Chapter 19: Carotid Duplex Scanning and Color Flow Imaging
Part A
Holdorf

2. Carotid Duplex/Color Flow Imaging
Capabilities
Localize lesion in extra-cranial carotid arteries
Differentiate occlusion from stenosis
Document progression of disease
Identify surface characteristics
Evaluate pulsatile mass

3. Limitations Poor visualization secondary to:
Presence of dressings, skin staples, or sutures
Size or contour of neck
Depth or course of vessel
Acoustic shadowing from calcification

4. Over-estimation of the disease process from:
Accelerated flow mistakenly attributed to stenosis instead of
Cardiac output
Tortuous vessel
Compensatory flow
Inappropriate Doppler angle

5. Under-estimation of the disease process:
Accelerated flow not present and or detected:
Jet of accelerated flow missed
Long, smooth plaque formation
Stenosis at area of dilatation, i.e., carotid bulb
Inappropriate Doppler angle

6. Patient Positioning: Patient in comfortable supine position, neck slightly hyperextended, and head turned slightly

7. Physical Principles Spectral analysis
Information displayed electronically on a monitor
Utilizes Fast Fourier Transform (FFT) method: individual frequencies/velocities displayed with time on horizontal axis and various frequency shifts/ velocities on vertical axis
Displays true frequency / velocity shifts
Commonly used with imaging modalities

8. Continuous Wave Doppler (CW)
Two piezo-electric crystals: one constantly sending ultrasound, one constantly receiving reflected waves
No range resolution
Fixed sample size

9. Pulsed Doppler Crystals send then receive the reflected ultrasound
Has range resolution
Variable sample size
Well-defined spectrum

10. Normal Spectral Analysis

11. Color Doppler
Assigns color to display average frequencies (e.g., hue, brightness of color) and direction (phase) of moving blood
Pulsed Doppler beams evaluate multiple sample sites throughout a specific area
Scan rates are slower because of multiple transmit / received pulse cycles in each “color line of site”
Several processing methods exist to produce color duplex.

12. Pulsed Doppler Technique
Sagittal / Longitudinal View
Vessels followed from clavicle to mandible using anterior, oblique, lateral and or posterior oblique views
Evaluate flow patterns of CCA, ICA, and ECA
Evaluate vertebral arteries
Use posterior-lateral approach
Identify artery by vertical shadows running through it (from transverse processes of vertebrae)
Evaluate direction of flow

14. Transverse / Cross-Sectional View
Vessels followed from clavicle to mandible
Document plaque formation
Percent stenosis may be calculated

15. Interpretation B-mode: Normal Vessel
Absence of wall irregularities or soft tissue abnormalities

16. B-mode: Abnormal Vessel
Hypoechoic and homogeneous: low level echoes of similar appearance, i.e., fatty streaks, found in persons of all ages.

17. B-mode: Abnormal Vessel
Homogeneous: low-to-medium level echoes of similar appearance, i.e., fibrous plaque

18. B-mode: Abnormal Vessel
Echo and heterogeneous: all levels of echoes (soft and dense areas), i.e., complex plaque or intra-plaque hemorrhage (sonolucent area inside plaque).

19. B-mode: Abnormal Vessel
Hyperechoic: very bright/highly reflective echoes; acoustic shadow form calcium deposit may result in erroneous calculation of % of stenosis
Thrombosis: same echogenicity of flowing blood on B-mode
Surface characteristics: Smooth, Slightly irregular, or grossly irregular surface
Stenosis should be visible form at least 2 projections

20. Occluded artery Varying degrees of echogenic material
Vessel completely filled with echoes
Vessel motion: horizontally or piston-like

21. Occluded ICA

22. Normal Doppler Signals
ICA
More high-pitched and continuous than ECA
Wave form has rapid upstroke and down stroke with a high diastolic component

23. Normal Doppler Signals
ECA
Signal more pulsatile; very similar to peripheral vessels
Rapid upstroke and down stroke with low flow diastole

24. Normal Doppler Signals
Dicrotic notch. A small, downward deflection observed on the downstroke of an arterial pressure waveform. It represents closure of the aortic or pulmonic valve at the onset of ventricular diastole. (S2)

25. Dicrotic Notch and oscillations in waveform seen with tapping of Superior Temporal artery (Arrow)

26. Normal Doppler Signals:
CCA: Flow Characteristics of both ICA and ECA

27. Abnormal Doppler Signals
Stenosis
Characterized by higher pitched sound and waveform with higher velocity (from elevated frequencies)
Spectral broadening evident (representing turbulence)
Loss of spectral window also represents loss of laminar flow

28. Loss of spectral window

29. Distal to a stenosis: disturbed flow patterns e. g
Distal to a stenosis: disturbed flow patterns e.g. turbulent, bi-directional; then can become dampened and monophasic.
Consider disease at carotid siphon when high resistant flow patterns are evident in the ICA

30. Diminished CCA velocities bilaterally may indicate poor cardiac output or stroke volume
Diminished CCA velocities unilaterally suggests proximal disease, e.g., innominate or common carotid artery

31. Categorizing Disease Based on a 60 degree angle of insonation
Based mainly upon criteria developed by D.E. Strandness MD, University of Washington

32. Peak Systolic Velocity End Diastolic Velocity
% Stenosis
Peak Systolic Velocity
End Diastolic Velocity
Normal
< 125 cm/sec NA
Less than 50
<125 cm/sec
50-79
>125 cm/sec
<140 cm/sec
80-99
>125cm/sec
>140cm/sec
Occluded
Absent

33. Criteria Critical in Determining an Occlusion
CCA may have a very low or absent diastolic component
Evidence of collateralization, e.g., ECA may exhibit high flow in end diastole
Absent ICA Doppler signal or pre-occlusive thump
NOTE: Although an absent signal may indicate occlusion, a tight stenosis (also termed a “String sign”, cannot be ruled out.