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152
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12
RT ICA MID
FIGURE 12-5 Post-stenotic waveform has a delay in upstroke, diminished
amplitude, and marked turbulence. RT ICA MID denotes midportion of right
internal carotid artery.
The pulse repetition frequency (velocity) scale determines the
degree of color saturation and filling of the vessel lumen. The pulse
repetition frequency (radio frequency pulses per second from the
probe) is adjusted so that in a normal vessel, laminar flow appears
as a homogeneous color. The color appearance changes throughout the cardiac cycle. Increasing flow velocity and turbulence in the
region of a stenosis results in production of a high-velocity jet and
an abrupt change in color-flow pattern (
occurs at the site of stenosis when flow velocity exceeds the Nyquist
limit (i.e., when Doppler frequency shift exceeds half the pulse repetition frequency). Aliasing causes the color display to appear as
if there is an abrupt reversal in direction of flow (wraparound).
This suggests a high-velocity flow jet, requiring confirmation by
pulsed-wave Doppler analysis. Color persistence is a continuous
flow signal that is the color of the forward direction only, in contrast to the alternating color in normal arteries. There is loss of early
Fig. 12-6). Color aliasing
diastolic flow reversal. Color persistence corresponds to the monophasic spectral Doppler waveform and is indicative of severe stenosis. Post-stenotic regions display mosaic patterns
indicating
turbulent flow (see Fig. 12-6). A color bruit in the surrounding soft
tissue also indicates flow disturbance. This color artifact is associated with turbulence and occurs with flow disturbances associated
with high-velocity jets. The color bruit is particularly useful in locating postcatheterization arteriovenous fistulae (AVF ).
Assessment of Arterial Stenosis
Characteristic duplex ultrasound features of a stenosis include
elevated systolic velocity, elevated end-diastolic velocity (EDV),
color aliasing, color bruit, spectral broadening of the Doppler
waveform, post-stenotic flow, and post-stenotic turbulence. An
auditory “thump” occurs in the presence of total arterial occlusion.
Doppler velocity measurements are the main tools used to evaluate stenosis severity. When flow rate is constant, a decrease in
vessel cross-sectional area is balanced by an increase in velocity.13
As blood flow turbulence increases, spectral broadening of the
Doppler waveform becomes a clear indicator of turbulent flow
seen in the post-stenotic region. The post-stenotic waveform is
dampened with a delayed upstroke (see
notic turbulence can be identified, inappropriate angle alignment
or a tortuous vessel should be suspected.
Power (or amplitude) Doppler is a complementary imaging
technique that displays the total strength or amplitude of the
returning Doppler signal.
15
In comparison with conventional colorflow imaging, color-flow sensitivity is increased by a factor of 3 to
5 times with power Doppler. This enhanced dynamic range can
depict very slow flow in the area of a subtotal occlusion that may
not be detected by conventional color-flow Doppler. Contrast
agents can also help differentiate between occlusion and highgrade stenosis in carotid and renal arteries, especially in cases
where multiple renal arteries are present.
Fig. 12-3). If no post-ste-
16
A
B
FIGURE 12-6 Aliasing at the site of arterial stenosis. There is an abrupt
change from low-velocity laminar flow (A) to high-velocity flow with aliasing (B)
as velocity exceeds Nyquist limits. An echolucent (dark) plaque is evident at site
of stenosis within superficial femoral artery (SFA) stent.
Carotid Duplex Ultrasound
The standard carotid duplex examination includes assessment of
the carotid arteries as well as the vertebral, subclavian, and brachiocephalic arteries. Indications for this test include a bruit, transient
ischemic attack (TIA), amaurosis fugax, stroke, and surveillance
after revascularization.
survey of the extracranial carotid arteries in transverse and longitudinal views. The operator images the region from the clavicle to the
angle of the jaw, in both anterolateral and posterolateral views.
The common carotid artery (CCA) is typically medial to the internal jugular vein, and the bifurcation is often located near the cricoid cartilage. The ICA is usually posterolateral, with a diameter at
its origin greater than that of the anteromedially located external
carotid artery (ECA).
Carotid artery stenosis can be focal, and flow patterns can normalize within a short distance. Therefore, the pulse-wave sample volume should be methodically advanced along the length
of the vessel; color Doppler may be used for guidance in delineating areas of abnormal flow requiring change in position of
the sample volume (
ments should be recorded from the proximal, mid- and distal
CCA. The CCA spectral waveform is a combination of the ECA
and ICA waveforms, with greater diastolic flow than the ECA but
less than the ICA. Atherosclerosis, when present, is usually most
evident at the ICA origin, whereas fibromuscular dysplasia may
be more evident distally. Using spectral Doppler, the sample volume is advanced throughout the entire ICA. At a minimum, PSV
and EDV from the proximal, mid-, and distal ICA segments should
be recorded. The vertebral artery is then located posterior to the
carotid artery. The vertebral artery and vein lie between the spinous processes. The vertebral artery is followed as far cephalad
as possible, sampling the spectral Doppler in the accessible portions of the vertebral artery.
17
The examination begins with a gray-scale
Fig. 12-7). Representative velocity measure-
18
ICA
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ECA
LT bifurcation
RT ECA
153
CCA
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VASCULAR LABORATORY TESTING
RT ICA PROX
FIGURE 12-7 Gray-scale image of right and left carotid bifurcation.
Internal carotid artery (ICA) in each is slightly wider at the origin than external
carotid artery (ECA). Red arrow indicates plaque in proximal right ICA. A branch is
evident arising from left ECA. In the absence of identified branches, waveforms
are necessary to distinguish the ICA from the ECA. CCA, common carotid artery.
Distinguishing between the ICA and ECA is critical to the exami-
nation (
Fig. 12-8). The ECA is usually smaller, more anteromedial,
and has less diastolic flow than the ICA. The ECA will also have
branches in the cervical region, whereas the ICA will not. Direct
comparison of the waveforms from the two vessels is critical.
A velocity waveform obtained from the proximal vessel or the
site of maximal velocity should be obtained while intermittently
tapping on the preauricular branch of the temporal artery. The
intermittent tapping is reflected clearly in the diastolic portion of
the ECA waveform, but not in the ICA waveform (
Fig. 12-9).
Interpretation of the spectral waveforms is based on
parameters such as PSV, EDV, shape, and extent of spectral
broadening
19
(Fig. 12-10). A number of criteria have been
proposed, each having their own strengths and weaknesses
(
Table 12-1). Peak systolic velocity criteria for ICA stenosis
have identified a cut point of 230 cm/sec as the threshold for
detecting greater than 70% stenosis, and 125 cm/sec as the cut
point for identifying greater than 50% stenosis. Criteria that
include EDV use a cut point of greater than 140 cm/sec to identify
greater than 80% stenosis. The ratio of peak ICA systolic velocity
to mid-CCA velocity may be particularly useful in determining
the presence of stenosis in the hemodynamic setting of low
cardiac output or critical aortic stenosis. At a minimum, velocity
criteria must distinguish less than 50% stenosis, 50% to 69% stenosis, and greater than 70% stenosis. Selection of criteria for use in
an individual laboratory requires review of the published parameters and selection of those appropriate to laboratory practice.
Individual vascular laboratories must validate the results of their
own criteria for stenosis against a suitable standard such as
arteriography.
FIGURE 12-8 Color Doppler of internal carotid artery (ICA). Color Doppler
is added to gray-scale picture of right ICA seen in Figure 12-7. Color aliasing
identifies an area of high velocity adjacent to the plaque. This guides placement
of spectral Doppler sample volume, identified by parallel white lines.
FIGURE 12-9 Spectral waveforms of internal and external carotid arteries
(ICA, ECA) during intermittent tapping of ipsilateral temporal artery. A, No
clear “tapping” pattern, and therefore likely ICA. B, High peak systolic velocity
(PSV) of 400 cm/sec. Tapping (asterisk) clearly identified in diastolic component of
waveform identifies the artery as ECA and indicates that the high PSV represents
ECA stenosis. C, Typical ECA waveform is high resistance with low PSV and
obvious tapping pattern of temporal artery during diastole.
154
FIGURE 12-10 Internal carotid artery
(ICA) stenosis. Pulsed-wave sample
volume is placed at the site of aliasing.
There is marked spectral broadening.
Waveform resembles that in Figure 12-9C.
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12
TABLE 12-1 Criteria for Internal Carotid Artery Stenosis
STENOSIS
0 <125 0 <2 <40
1-49 <125 + <2 <40
50-69 >125 + 2-4 40-100
>70 >230 + >4 >100
subtotal VAR. +++ VAR. >0
total 0 +++ 0 0
This table summarizes multiple criteria including PSV alone, PSV and EDV, and ICA/CCA
ratio.
+, presence of plaque; CCA, common carotid artery; EDV, end-diastolic volume; ICA, internal
carotid artery; PSV, peak systolic velocity; VAR, variable.
*From Grant EG, Benson CB, Moneta GL, et al: Carotid artery stenosis: gray-scale and Doppler US
diagnosis—Society of Radiologists in Ultrasound Consensus Conference. Radiology 229:340, 2003.
ICA PSV
LUMEN
PLAQUE
ICA/CCA
PSV
ICA EDV*
19
Waveform analysis depends on evaluation of acceleration, diastolic flow, direction of flow, and comparison to the contralateral
vessel. If the ICA is totally occluded, there will be absent or severely
diminished diastolic flow in the ipsilateral CCA (
Fig. 12-11). A delay
in the upstroke suggests more proximal stenosis. For example,
severe stenosis of the brachiocephalic artery will result in dampened right CCA waveforms. A step-up in systolic velocity in the
cervical portion of the CCA indicates stenosis, with doubling indicating at least 50% stenosis and tripling indicating at least 75%
stenosis.
Waveform evaluation is particularly valuable in the vertebral
artery because the segments within the bone cannot be directly
evaluated with ultrasound. Specific velocity criteria have not
been developed for vertebral artery stenosis. Velocities greater
than 125 cm/sec and dampened waveforms are two indicators
of vertebral artery stenosis. Absent flow in the vertebral artery
is confirmed when flow is detected in the vertebral vein, but not
in the vertebral artery. Retrograde flow in the vertebral artery is
referred to as subclavian steal (i.e., the subclavian circulation is
stealing from the cerebral circulation). Reverse flow is confirmed
FIGURE 12-11 Absent diastolic flow in common carotid artery (CCA)
suggesting presence of total occlusion of the ipsilateral internal carotid
artery (ICA).
by comparing the direction of vertebral artery flow with that of the
carotid artery (Fig.12-12). Reverse flow typically will have a diminished diastolic component because flow is into the high-resistance
bed of the subclavian artery (Fig. 12-13). If flow is cephalad but
notching is evident in the systolic portion of the wave, subclavian
steal can be elicited by reexamining flow after arm exercise or following deflation of a blood pressure cuff that had been inflated
to suprasystolic pressures on the ipsilateral arm. These maneuvers
will increase demand in the subclavian bed, and vertebral flow will
completely reverse in the setting of subclavian stenosis proximal to
the vertebral origin. The vast majority of these patients with subclavian stenosis are asymptomatic.
The subclavian artery is evaluated as close to the origin as possible. The probe is placed longitudinally above the clavicle and angled
to obtain a scanning plane below the clavicle. Color Doppler surveillance is used to detect nonlaminar flow. The Doppler spectrum
is obtained throughout the vessel.20 Doubling of PSV is consistent
with 50% or greater stenosis.
Plaque and Arterial Wall Characterization
Gray-scale imaging is used to evaluate carotid plaque and arterial wall characteristics. Atherosclerotic plaque is evident on
ultrasound examination as material that thickens the intima and
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LT CCA MID
LT VERT
FIGURE 12-12 Color Doppler of common carotid artery (CCA) and
vertebral arteries (VERT), demonstrating flow in two different directions,
antegrade carotid artery flow and retrograde vertebral artery flow.
B
Left Prox ICA
FIGURE 12-14 Gray-scale image of atherosclerotic plaque. Echolucent
plaque is indicated (arrow A) adjacent to more echobright plaque (arrow B) in
gray-scale image of this internal carotid artery (ICA).
A
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FIGURE 12-13 A, Spectral waveform of normal antegrade vertebral flow
with low-resistance waveform. B, Reversed retrograde vertebral flow with highresistance waveform.
protrudes into the arterial lumen. Plaque surface and echo characteristics can be determined and described. Ulceration refers to an
excavation within the plaque containing flow. Echolucent plaque
is characterized as plaque that is less echogenic than surrounding
muscle (
abnormal color flow (
Fig. 12-14) and is often first detected by the presence of
Fig. 12-15). The volume of plaque is appreci-
ated best in the transverse view and with three-dimensional (3D)
reconstruction.
Another potential technique to characterize plaque content
and activity is contrast-enhanced ultrasound to detect ulceration
and inflammation. Activated leukocytes attached to the inflamed
vessel wall may bind the shells of lipid microbubbles, which are
detectable by ultrasound.
the wall/lumen interface (
21
Contrast also can be used to define
Fig. 12-16A). Plaque thickness can be
severely overestimated or underestimated in the longitudinal
image, and is best evaluated in transverse images.
Ultrasound can also evaluate findings such as edema
(
Fig. 12-16B) and dissection of the carotid wall (Fig. 12-16C) .
Dissection can originate in the ICA or extend from the arch into
the CCA. A flap separates the true and false lumen. The flap may
be apparent on gray-scale imaging but generally requires color
or contrast for elucidation. A flutter is occasionally identified in
the downslope of the waveform on the affected side. Evaluation
FIGURE 12-15 Duplex imaging of atherosclerotic plaque. Echolucent
plaque is now clearly evident with addition of color Doppler.
should identify both the proximal and distal extent of dissection,
and flow velocities in the true lumen.
Carotid Intima Media Thickness
Carotid ultrasonography has traditionally been used to evaluate the presence of obstructive atherosclerosis in the setting of
symptomatic cerebrovascular disease or asymptomatic carotid
bruit. More recently, carotid ultrasonography has been performed
in epidemiological studies to detect nonobstructive plaque and
intima media thickness (IMT).
the distance from the intima lumen interface to the media adventitia border. Protocols have measured ICA, CCA, ICA plus CCA, and
carotid bulb IMT. Yield and reproducibility appear to be greatest
for the far-wall CCA IMT measurement. Intima media thickness
measurement is most commonly made from longitudinal images,
with the assistance of semiautomated edge-detection software
(
Fig. 12-17). There is variability in this measurement from systole
to diastole, and by age and gender. A single threshold value for
abnormal IMT has not been determined. Ideally, threshold values
derived from large population-based studies should be used in
evaluation of IMT. Both plaque and IMT correlate with cardiovascular morbidity and mortality.
plaque resulting in 50% stenosis is included in the Adult Treatment
Panel III guidelines as a coronary heart disease equivalent.
22
Intima media thickness refers to
22
Indeed, the presence of carotid
156
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12
ECA
b
a
ICA
RT ICA PROX
AB C
FIGURE 12-16 Arterial wall characteristics. A, Contrast is used to identify lumen/wall interface. Wall thickening is evident between intima lumen interface (a)
and media adventitia interface (b). B, Power Doppler is used to identify lumen/wall interface. Thickened echolucent wall suggests presence of arteritis. C, Dissection
of internal carotid artery (ICA) with flow evident in both true and false lumen.
I
M
FIGURE 12-17 Intima media thickness (IMT). I indicates intima lumen
border, and M indicates media adventitia border. Distance between intima
lumen border and media adventitia border is determined with automated
edge-detection program that averages thickness of wall over region, identified
by blue lines laid over these borders.
LT bifurcation
HEP A
Splenic A
Celiac trunk
FIGURE 12-18 Transverse gray-scale image of splenic and hepatic arteries
arising from celiac trunk. Celiac trunk is first branch from abdominal aorta.
Abdominal Aorta Evaluation
Abdominal ultrasound is used to diagnose and follow abdominal
aortic aneurysms. An ultrasound machine with a low-frequency
transducer (e.g., 2.5 MHz) is used to determine aneurysm size,
shape, location (infrarenal or suprarenal), and distance from other
arterial segments. The patient is required to fast prior to the study
because bowel gas will obscure imaging. Aortic ultrasound scanning begins with the patient supine and the transducer placed
in a subxiphoid position. The aorta is located slightly left of midline. The abdominal aorta from the diaphragm to the bifurcation
is evaluated using three sonographic views: the sagittal plane
(anteroposterior [AP] diameter), transverse plane (AP diameter
and transverse diameters), and coronal plane (longitudinal and
transverse diameters). Diameter is measured from outer wall to
outer wall. If overlying bowel gas obstructs the aorta from view,
patients are instructed to lie in the decubitus position, and the
aorta is visualized via the coronal plane through either flank.23
As the transducer is moved caudally, the celiac trunk will be
evident branching into the common hepatic and splenic arteries (
Fig. 12-18). The superior mesenteric artery (SMA) originates
approximately 1 cm distal to the celiac trunk (Fig. 12-19). Next,
the right renal artery may be seen emerging from the aorta and
traveling under the inferior vena cava. The left renal vein then
crosses over the aorta, and the left renal artery will be seen posterior to the vein. The inferior mesenteric artery (IMA) is the final
branch arising from the aorta before it bifurcates into the iliac
vessels. Spectral Doppler evaluation of the celiac and mesenteric
vessels will demonstrate low-resistance waveforms following a
meal and high resistance waveforms in the normal fasting patient
(
Fig. 12-20). In contrast, evaluation of the normal renal arteries
always demonstrates low-resistance waveforms.
Aorta
FIGURE 12-19 Longitudinal gray-scale image of aorta. Superior mesen-
teric artery (SMA) is second branch of abdominal aorta and is seen running
parallel to aorta in this longitudinal image of abdominal aorta.
SMA
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VASCULAR LABORATORY TESTING
A
B
FIGURE 12-20 A, Fasting spectral waveform in superior mesenteric artery (SMA). B, Postprandial spectral waveform in celiac trunk.
An abdominal aortic aneur ysm is defined as an aortic diameter of at least 1.5 times the adjacent normal segment, or a distal
aorta diameter of greater than 3.0 cm (Fig.12-21). Normal abdominal aortic diameters range from 1.4 to 3.0 cm.24 The shape of the
abdominal aortic aneurysm is described as saccular, fusiform, or
cylindrical. The majority of abdominal aortic aneurysms are fusiform in shape, located below the renal arteries, and involve one or
both of the iliac arteries. Atherosclerotic plaque, mural thrombus,
and dissection can be detected in the wall of the aneurysm.
Ultrasound evaluation is also performed after endograft repair of
abdominal aortic aneurysm. Flow within the graft is evaluated with
longitudinal and transverse imaging. Endoleak is diagnosed when
there is flow outside the graft but within the aneurysm. Dissection,
pseudoaneurysm, and thrombus within the graft are other potential
complications
26
that can be detected using ultrasound evaluation.
Renal Artery Duplex Ultrasonography
Atherosclerotic renal artery stenosis is recognized as a cause of
hypertension and may contribute to decline in renal function (see
Chapter 22). Duplex ultrasound of the renal arteries includes spectral Doppler evaluations of the aorta, the renal arteries and renal
parenchyma, and B-mode determination of kidney size (also see
Chapter 41). Abdominal obesity and bowel gas are barriers to adequate renal artery duplex examination.
A longitudinal view of the aorta is obtained with the patient
in the supine position. The origins of the celiac artery and
FIGURE 12-21 Gray-scale image from an abdominal aortic aneurysm
screening examination. This transverse image of abdominal aorta has a
maximum diameter of more than 5.6 cm, indicating aneurysm.
SMA are seen on the anterior aspect of the aorta cephalad to
the renal arteries. Peak systolic velocity in the aorta is then
recorded using a 60-degree Doppler angle. The probe is turned
25
158
Peripheral Arterial Ultrasonography
CH
12
FIGURE 12-22 Doppler image of origin of right renal artery. Turbulent
flow is evident in the renal artery origin, suggesting presence of atherosclerotic
plaque and possibility of stenosis.
R renal artery
Aorta
transverse to localize the renal arteries. The Doppler cursor
is “walked” from the aorta into the ostium of the renal artery
(
Fig. 12-22). The right renal artery is generally seen most easily.
It is followed from the origin to the hilum of the kidney. The left
lateral decubitus position can also be used for examination of
the right renal artery. The left renal artery is best evaluated in
the right lateral decubitus position using a posterolateral transducer position. Ideally, the renal arteries are evaluated from two
views to ensure that stenosis is not missed. Kidney length is
measured from pole to pole with the patient in the decubitus
position.
Color and spectral Doppler are obtained throughout the
course of each renal artery. A low-velocity range and a low wall
filter setting are used in spectral Doppler evaluations of the segmental renal arteries and hilar flow. The renal artery normally
has a low-resistance waveform.
27
A 60% or more renal artery stenosis is characterized by a renal-to-aortic PSV ratio of greater
than 3.5, combined with a PSV within the stenosis of greater
than 200 cm/sec. Elevated EDV 150 cm/sec or more suggests
80% or greater stenosis (Fig. 12-23). The same criteria are used
in native and stented renal arteries.
28
Low systolic flow, post-stenotic turbulence, and a color mosaic appearance indicate subtotal occlusion of the renal artery. Low parenchymal Doppler
velocities support the diagnosis of an occluded renal artery in
those cases where no flow can be detected in the renal artery.
In addition, the ipsilateral kidney is often small, less than 9 cm
in length. Overall sensitivity of duplex ultrasonography for renal
artery stenosis is 98%, and specificity is 98% compared with
arteriography.
29
Measurement of the resistive index (RI) is used to evaluate renal parenchymal disease. Spectral Doppler waveforms
are obtained from at least three regions of each kidney. The
RI is calculated using the formula: RI = [1 − (V
where V
peak systolic velocity. In severe renal artery stenosis where
denotes end-diastolic velocity, and V
min
min
÷ V
there is significant renal parenchymal disease, the EDV is often
low. An RI above 0.80 suggests significant parenchymal renal
30
disease
of therapy. Similarly, the PSV and EDV can be used to monitor
renal transplants.
and may have implications regarding the outcome
31
)] × 100,
max
denotes
max
Ultrasound of the lower extremities is used to diagnose PAD in the
setting of claudication, limb pain, or ulcers.
12
It is also indicated
following lower-extremity revascularization and in planning therapy for known PAD. The goal of the examination is to elucidate
the location and severity of limb arterial stenoses.
32
The study is
tailored to individual requirements and can be limited to a given
arterial segment, extended to evaluate both lower extremities in
their entirety, or to evaluate the upper extremity.
Color Doppler is used initially to detect normal or abnormal
flow states throughout the arterial segments or bypass grafts
being evaluated.
ease (
Fig. 12-24A), whereas turbulence and aliasing are present
33
Laminar flow is visible in the absence of dis-
at the sites of disease. When an abnormal flow pattern is detected
by color Doppler, pulsed (spectral) Doppler sampling is used to
characterize the degree of stenosis. The pulse Doppler signal is
acquired throughout the arterial segments. Peak systolic velocity
determination and waveform analyses are the primary parameters used to quantify and localize disease. Peak systolic velocity
measurements are obtained at the level of the lesion and from
vascular segments proximal and distal to the lesion. Aneurysmal
dilation is another etiology for abnormal color flow. Velocities will
decrease as diameter doubles at the site of the aneurysm. The iliac,
superficial femoral, and popliteal arteries are all sites of aneurysm
(
Fig. 12-25).
Peripheral arterial stenosis is categorized by pulsed-wave
Doppler examination as percentage reduction of luminal
diameter that is mild (0%-19%), moderate (20%-49%), or severe
(≥50%).
12
With mild stenosis, there is some spectral broadening and a slight increase in PSV. With moderate stenosis, there is
increased spectral broadening and a rise in PSV less than double
that of the proximally sampled segment. Pulsed Doppler interrogation at the level of a severe stenosis reveals marked spectral
broadening and a monophasic waveform. The waveform loses
its normal diastolic reverse flow component, and flow is forward
throughout the cardiac cycle. Also, the PSV is more than double the velocity measured in the proximal segment. An occlusion is present when flow is absent within an arterial segment.
If there are no collateral vessels, high-resistance waveforms are
present in the artery proximal to the occlusion. Antegrade diastolic flow is present in the proximal artery if there are collateral
vessels. The reconstituted distal artery will have the characteristic post-stenotic tardus et parvus waveform. This Doppler waveform is particularly important to recognize because it signifies a
proximal high-grade lesion.
Duplex ultrasound examination is accurate for diagnosing PAD.
The comparison of duplex ultrasound evaluation with arteriography to detect significant stenoses in patients with symptomatic aortoiliac and femoropopliteal disease reveals high sensitivity (82%)
and specificity (92%) for identifying significant stenoses.
33
Ratios
of PSV between the stenosis and the proximal artery are preferred
over absolute PSV measurements for classification of peripheral
arterial stenosis because a wide range of absolute PSV measurements is obtained in normal and abnormal patients. There is a
stronger correlation between PSV ratio and degree of stenosis than
between absolute PSV and degree of stenosis. Peak systolic velocity ratios of 2 and 7 correspond to stenoses of 50% or more and 90%
or more, respectively. There are conflicting data regarding precision
of duplex ultrasound examination in determining stenosis severity
when serial stenoses are present.
Extremity Arterial Ultrasound Following
Revascularization
Ultrasound evaluation following endovascular procedures is performed to detect recurrence of stenoses at sites of intervention. The
concept is similar to that for graft surveillance (i.e., early detection of lesions assists in identifying the need for reintervention
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FIGURE 12-23 Color Doppler demonstrates right renal artery originating from aorta, with right renal vein (blue) running parallel. Elevated systolic and
diastolic velocities in spectral Doppler are consistent with renal artery stenosis.
to maintain arterial patency).
33,34
Duplex ultrasonography is performed following the intervention, prior to discharge; 1, 3, and
6 months postintervention; then yearly. The color Doppler and
pulsed-wave Doppler evaluations focus on the vessel proximal to
the site of intervention, at the site of intervention, and distal to the
site of intervention. Waveform analysis is used to categorize stenosis in a manner similar to that used in native vessels.
35
A doubling
of PSV is consistent with hemodynamically significant stenosis
(see
Fig. 12-24B). Increases in velocity measurements and change
in waveform shape from triphasic to monophasic on serial examinations suggest developing stenosis and warrant close-interval follow-up and consideration for revision.
Graft surveillance is extremely useful in efforts to preserve
patency of peripheral arterial bypass grafts.
36
Graft failure in the
first month is usually caused by technical factors. Between 1 month
and 2 years postoperatively, it is often due to intimal hyperplasia. Graft failure after 2 years is likely the result of progression of
atherosclerotic disease. The 5-year primary patency rate for an
infrainguinal vein bypass graft ranges from 60% to 85%. Surgical
revision of these stenoses identified with ultrasound surveillance
improves the 5-year patency rate to 82% to 93%. By contrast, segmental pressure measurements have not proved useful to predict
bypass graft thrombosis. To detect graft abnormalities before frank
graft failure, standard graft surveillance protocols recommend
duplex ultrasound evaluation at 1, 3, and 6 months during the first
postoperative year, and 12 months thereafter.
37
Location and type of graft are identified before performing ultra-
sound examination. Scanning techniques in the supine patient
are similar to native arterial examinations. Color Doppler is used
initially to scan the entire graft. Color pulse repetition frequency
is adjusted so focal stenoses or AVF appear as regions of aliasing,
persistence, or bruit color flash artifact. Based on color Doppler
findings, pulsed Doppler interrogation is used to determine the
PSV. Sampling is done routinely at the proximal native artery, proximal anastomosis, throughout the graft, distal anastomosis, distal
native vessel, and throughout sites of flow disturbance. These measurements are used also for serial comparison during subsequent
examinations.
Pulsed Doppler is used to determine PSV ratios within the graft,
similar to its use in the native arterial examination (
Fig. 12-26). A
segment distal (rather than proximal) to the lesion may be chosen for the ratio when there is a diameter mismatch in the graft
or there are tandem lesions proximal to the flow disturbance.
Doubling of the velocity ratio indicates a significant graft stenosis
(>50% diameter reduction) with a sensitivity of 95% and specificity of 100%. Vein graft lesions also have been classified using
PSV: (1) a minimal stenosis (<20%) has PSV ratio up to 1.4 with
a PSV of less than 125 cm/sec; (2) a moderate stenosis (20%-50%)
has a PSV ratio of 1.5 to 2.4 with a PSV up to 180 cm/sec; (3) a
severe stenosis (50%-75%) has a PSV ratio of 2.5 to 4 with a PSV
of more than 180 cm/sec; and (4) a high-grade stenosis (>75%)
has a PSV ratio greater than 4 with a PSV greater than 300 cm/sec.
Intervention is recommended for lesions categorized as severe
or high grade.
38
Detection of low-flow velocities within the graft
with pulsed Doppler suggests either proximal or distal stenosis.
Low velocity flow can also be caused by large graft diameter or
160
CH
12
LT SFA MID Thigh
A
LT PROX / MID Stent
B
FIGURE 12-24 Duplex ultrasound of a superficial femoral artery (SFA) stent.
A, Laminar flow is evident in longitudinal image of proximal stent. B, Color
aliasing and elevated velocity are present at site of stenosis within distal SFA stent.
poor arterial inflow. Nonetheless, velocities within a functioning
graft that are less than 45 cm/sec indicate that subsequent graft
failure is likely to occur. Other worrisome findings are a significant
decrease or increase in PSV on serial examination.
Pseudoaneurysm
A pseudoaneurysm is a contained arterial rupture. A hole through
all layers of the arterial wall results in extravasation of blood, which
is then enclosed by surrounding soft tissues.
undergone an arterial puncture for arteriography and experiences
sudden pain at the access site, or is found to have pulsatile mass or
a bruit on auscultation over the access site, should be evaluated
for the presence of pseudoaneurysm.
Ultrasound evaluation is performed in the region of the puncture. Spectral waveforms are obtained in the native artery proximal
and distal to the site of puncture, and in the femoral vein proximal and distal to the site of puncture. Color Doppler evaluation
should focus on detecting an extravascular collection of flowing
blood, most commonly anterior to the native artery (
Posterior extravasation is less common. The neck is the connection between the native artery and the pseudoaneurysm sac. The
neck is identified by a “to-and-fro” pattern of the Doppler waveform
that is pathognomonic for pseudoaneurysm (
waveform results from systolic flow out of the native artery into the
contained rupture, and diastolic flow back into the native artery. In
addition to the to-and-fro signal in the neck, the segment of native
artery proximal to the origin of the pseudoaneurysm may have a
lower-resistance waveform when compared with that found in the
artery distal to the pseudoaneurysm.
39
Any patient who has
Fig. 12-27A-B).
Fig. 12-27C). This
A
1.1 cm
2.5 cm
B
FIGURE 12-25 A, Transverse gray-scale image of right common iliac
artery (CIA) aneurysm with dissection. Arrow indicates dissection flap.
B, Longitudinal gray-scale image of right CIA aneurysm. Aneurysm is defined
by a 1.5× or greater increase in arterial diameter compared with proximal
segment. Thrombus develops in these aneurysms and can result in occlusion
or distal embolization.
JUMP GRFT
Distal to mid calf
FIGURE 12-26 Duplex ultrasound of peripheral bypass graft. Proximal
velocity is 155 cm/sec and increases to 495 cm/sec at site of stenosis. Aliasing of
the Doppler is also evident at site of stenosis.
There are several options for treatment of pseudoaneurysms,
including observation, surgical repair, manual compression, ultrasound-guided compression, or thrombin injection.
guided compression is performed with visualization of the
pseudoaneurysm neck while compressing until flow is absent in
the neck. Pressure is applied for 20 minutes and may have to be
maintained for much longer before thrombosis of the pseudoaneurysm sac is achieved. Reported success rate of compression
varies from 60% to 80%. Ultrasound-guided thrombin injection
is best suited for those pseudoaneurysms with a long, narrow
40
Ultrasound-
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PSA
RT PSA
CH
Neck
CFV
CFA
RT groin
A
CFA
B
12
VASCULAR LABORATORY TESTING
C
FIGURE 12-27 Doppler evaluations of a pseudoaneurysm (PSA). “Yin-yang” appearance of PSA cavity is evident in longitudinal (A) and transverse (B) images.
Whereas artery lengthens in longitudinal image, the contained PSA rupture sac retains its saccular shape. C, Pulsed Doppler placed in neck of pseudoaneurysm
demonstrates pathognomonic “to-and-fro” pattern of bidirectional flow into and out of the contained rupture.
41,42
neck.
Thrombin injection is contraindicated in those with
allergy to bovine thrombin, those with overlying skin infections,
in the presence of ipsilateral AVF, and in those with active limb
ischemia. The injection is performed under sterile conditions
using a syringe equipped with a three-way stopcock. The needle
is placed into the sac while drawing back gently on the syringe.
The tip of the needle is seen in the cavity, and blood return is
noted. The stopcock is then switched to a position open to the
thrombin, and 0.1 to 0.2 mL of thrombin are injected. The duplex
ultrasound examination should include final pictures documenting thrombosis of the pseudoaneurysm and a patent artery of origin. Complications of thrombin injection include limb ischemia
A
(if thrombin enters the native artery and causes a thrombus to
form) and anaphylaxis.
Arteriovenous Fistulae
Arteriovenous fistulae occur secondary to trauma, including catheterization,
ultrasound findings include turbulent and pulsatile venous flow.
Turbulence may result in a “color bruit” adjacent to the vein, caused
by vibration of the surrounding soft tissue. Arterial flow proximal to
the fistula will have a low-resistance pattern, rather than the typical high-resistance peripheral waveform (
distal to the fistula will have a high-resistance waveform. Venous
flow pattern at the connection will resemble an arterial waveform.
43
or are created intentionally for dialysis.44 Duplex
Fig. 12-28). Arterial flow
B
FIGURE 12-28 Spectral Doppler evaluation of peripheral artery proximal
(A) and distal (B) to an arteriovenous (AV) connection. Low-resistance
pattern in A occurs because artery is flowing into high-capacitance venous bed.
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