Doppler ultrasound in peripheral arterial disease

Dr. Naveed AshrafRadiologic Pictorial Review
Doppler Ultrasound In
Peripheral Arterial Disease
Dr. Naveed Ashraf
1

Understanding Various Waveforms
2

Cardiac phasicity creates a phasic cycle, which is composed of phases as determined by the
number of times blood flows in each direction at the baseline. The baseline (x = 0) separates
one direction from another.
Moving from left to right along the x-axis corresponds to moving forward in time. Moving
away from the baseline vertically along the y-axis in either direction corresponds to increasing
velocities.
Any given point on the waveform corresponds to a specific velocity. The slope of the curve
corresponds to acceleration (ie, a change in velocity per unit time).
A bend in the curve, or inflection point, corresponds to a change in acceleration. When these
turns are abrupt, they generate audible sounds at Doppler US.
3

Antegrade versus retrograde flow.
Flow towards the transducer is displayed above the baseline and flow away
from the transducer is displayed below the base line.
Antegrade flow may be either toward the transducer ( as in hepatic artery) or
away from the transducer (as in hepatic vein).
Thus antegrade and retorgrade flow correspond to the vessel of interrogation
and not to the transducer.
4

Phasicity.
Note that pulsatile, phasic, and nonphasic flow waveforms all have phasicity.
Pulsatile flow is exaggerated phasicity, which is normally seen in arteries but
can also be seen in diseased veins.
Nonphasic flow does in fact have a phase (of 1); however, the phase has no
velocity variation (nonphasic could be thought of as meaning “nonvariation”).
The term aphasic literally means “without phase,” which is the case when
there is no flow.
5

Directionality and phase quantification.
When phase is defined as a component of phasic flow direction,
waveforms may be described in terms of the number of phases.
All monophasic waveforms are unidirectional;
Bidirectional waveforms may be either biphasic, triphasic, or tetraphasic.
6

High- versus low-resistance arteries.
Schematics illustrate that a high-resistance artery (left) allows less blood flow
during end diastole (the trough is lower) than does a low-resistance artery
(right).
These visual findings are confirmed by calculating an RI. High-resistance
arteries normally have RIs over 0.7, whereas low-resistance arteries have RIs
ranging from 0.55 to 0.7.
7

Dr. Naveed AshrafRadiologic Pictorial Review8

In the proximal aorta, plug flow results in a thin waveform and a clear
spectral window. Note the actual windows (yellow) superimposed on the
first two spectral windows.
9
“Spectral window” and spectral broadening.

In vessels smaller than the aorta, blood flow is laminar. In large and
medium-sized vessel, the waveform is thick, but there is still a spectral
window (middle right).
10

In small or compressed vessels, there is significant spectral broadening,
which obscures the spectral window. Diseased vessels with turbulent
flow (bottom left) also cause spectral broadening (bottom right).
11

Diagram illustrates how the direction of a “stream” is determined by
the direction of flow.
Upstream refers to blood that has not yet passed a reference point,
whereas downstream refers to blood that has already passed the
reference point.
Transducer A is located upstream of the stenosis and transducer B is
located downstream.
13

Flow dynamics in high-grade stenosis.
Note that velocities are increased within a stenotic portion of a vessel, and
that the RI is increased when the stenosis is downstream but decreased when
the stenosis is upstream.
A waveform whose contour is affected by an upstream stenosis is often
described as a tardus-parvus waveform.
14

Diagram illustrates upstream stenosis (tardus-parvus waveform).
When it is apparent that the peak is too late (tardus) and too low
(parvus), use of the term is appropriate. This finding occurs only
downstream from a stenosis (ie, due to upstream stenosis).
15

Initial assessment is done with ABI
16

Dr. Naveed Ashraf
Teaching Points
Radiologic Pictorial Review17
The ankle brachial index is important way to diagnose peripheral vascular disease. The
index compares the systolic blood pressures of the arms and legs to give a ratio that can
suggest various severity of peripheral vascular disease.
An ABI less than 0.90 is diagnostic for PAD in patients with claudication or other signs of
ischemia, with 95% sensitivity and 100% specificity.
•A proximal-to-distal decrease in sequential pressures greater than 20 mm Hg or a
decrease in segmental-brachial index greater than 0.15 indicates occlusive disease and
correlates with the level of the lesion. •
A normal lower extremity arterial Doppler velocity tracing is triphasic, with a sharp
upstroke and peaked systolic component, an early diastolic component with reversal of
flow, and a late diastolic component with forward flow. A biphasic signal is considered
abnormal if there is a clear transition from triphasic signal along the vascular tree.
Monophasic waveforms are always considered abnormal. •

ABI > 1, Normal
ABI > 0.5, Single segment
disease
ABI < 0.5, Multi-segment
disease
ABI <0.35, Concern about
tissue loss.
18
Ankle Bracheal Index is high indicator of PVD

Classification of chronic limb ischemia
19

Normal diameters of lower limb vessels.

Normal velocites in lower limb arteries

Duplex Ultrasound Criteria for diagnosing occlusive disease

Bifurcation Points.
Aortic bifurcation
Common femoral
bifurcation
Popliteal trifurcation
Distal superficial femoral
artery
Tibial arteries.
23
Common sites for atherosclerotic disease

Triphasic Waveform.
Initial high velocity forward flow
component indicating systole.
Early diastolic reverse flow
component due to peripheral
resistance.
Late diastolic forward component
due to elastic recoil.
Narrow systolic window
Normal velocity range.
24
Normal Peripheral Arterial Waveform

Waveform Shape
Peak systolic velocity
Spectral window
25
Components to look for in stenosis

Criteria for the classification of peripheral arterial stenosis
1-19% diameter reduction minimal disease
20-49% diameter reduction moderate disease
50-99% diameter reduction significant disease
Occlusion
26

Grading by Doppler Ultrasound

Mild spectral broadening
1-29 % increase in peak
systolic velocity
Normal waveform.
28
1-19% Diameter reduction. Minimal Disease

Spectral broadening
30-99 % increase in peak
systolic velocity
Reverse flow component
present
29
20-49% Diameter reduction. Moderate Disease

Loss of reverse flow
component (Mono-phasic flow)
Marked spectral broadening
100% increase in systolic
velocity
Monophasic waveform
Post-stenotic turbulence.
30
50-99% Diameter reduction. Significant Disease

Absence of flow in occlusion
Proximal flow is high
resistance
Distal flow is low resistance
with tardus pattern
Collateral flow
31
Occlusion

Low velocity monophasic
waveforms
Lose triphasic character
Tardus parvus appearance
Low resistance related to
degree of ischemia.
32
Collateral flow

Focal color flow change at the
side of stenosis (Aliasing).
Color bruit due to peri-vascular
tissue vibration
Color mosaic pattern due to post
stenotic turbulence.
33
Color flow findings in peripheral arterial disease

tissue vibration
stenotic turbulence.
34

tissue vibration
stenotic turbulence in collateral
vessel.
35

Elevated peak systolic
velocites in stenosis
Loss of diastolic reversal in
stenosis
Bruit
Tardus parvus waveforms
distal to high grade stenosis.
36
Pulse Doppler findings in peripheral arterial disease

Spectrum at and below the level of stenosis
High peak systolic velicity
Tardus Parvus waveform

Doppler ultrasound in peripheral arterial disease

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