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

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

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

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

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

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

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

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

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

Normal Spectral Analysis

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.

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

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

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

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

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

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).

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

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

Occluded ICA

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

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

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)

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

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

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

Loss of spectral window

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

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

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

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

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.