Edward G. Grant, MD
Carol B. Benson, MD
Gregory L. Moneta, MD
Andrei V. Alexandrov, MD, RVT
J. Dennis Baker, MD
Edward I. Bluth, MD
Barbara A. Carroll, MD
Michael Eliasziw, PhD
John Gocke, MD, MPH, RVT
Barbara S. Hertzberg, MD
Sandra Katanick, RN, RVT
Laurence Needleman, MD
John Pellerito, MD
Joseph F. Polak, MD
Kenneth S. Rholl, MD
Douglas L. Wooster, MD, RVT
Eugene Zierler, MD
Carotid arteries, flow dynamics
Carotid arteries, stenosis or
obstruction, 172.4311, 172.4312,
Carotid arteries, US, 172.12981,
Published online before print
Radiology 2003; 229:340–346
University Hospital, 1500 San Pablo St, Los
Angeles, CA 90033 (E.G.G.); Dept of Radiol-
ogy, Brigham and Women’s Hosp, Harvard
Med School, Boston, Mass (C.B.B., J.F.F.);
Univ, Portland, Ore (G.L.M.); Cerebrovascu-
lar Ultrasound and Stroke Treatment Team,
Univ of Texas Houston Med School (A.V.A.);
Dept of Surgery, West Los Angeles VA Med
Ctr, Calif (J.D.B.); Dept of Radiology,
Ochsner Clinic, New Orleans, La (E.I.B.);
Dept of Radiology, Duke Univ Med School,
tistics, Univ of Calgary, Alberta, Canada
(M.E.); Midwest Heart Specialists Vascular
Lab and La Grange Memorial Vascular Labo-
ratory, Downers Grove, Ill (J.G.); Intersocietal
Accreditation Commission, Columbia, Md
(S.K.); Dept of Radiology, Thomas Jefferson
Univ, Philadelphia, Pa (L.N.); Dept of Radiol-
School of Med, NY (J.P.); Dept of Radiology,
Inova Alexandria Hosp, Va (K.S.R.); Dept of
Surgery, Univ of Toronto, Ontario, Canada
Apr 1, 2003; revision requested May 7; revi-
dress correspondence to E.G.G. (e-mail:
Carotid Artery Stenosis:
Gray-Scale and Doppler US
Radiologists in Ultrasound
The Society of Radiologists in Ultrasound convened a multidisciplinary panel of
experts in the field of vascular ultrasonography (US) to come to a consensus
regarding Doppler US for assistance in the diagnosis of carotid artery stenosis. The
panel’s consensus statement is believed to represent a reasonable position on the
basis of analysis of available literature and panelists’ experience. Key elements of the
statement include the following: (a) All internal carotid artery (ICA) examinations
should be performed with gray-scale, color Doppler, and spectral Doppler US.
(b) The degree of stenosis determined at gray-scale and Doppler US should be
stratified into the categories of normal (no stenosis), ?50% stenosis, 50%–69%
stenosis, ?70% stenosis to near occlusion, near occlusion, and total occlusion.
(c) ICA peak systolic velocity (PSV) and presence of plaque on gray-scale and/or
color Doppler images are primarily used in diagnosis and grading of ICA stenosis;
two additional parameters, ICA-to–common carotid artery PSV ratio and ICA end-
diastolic velocity may also be used when clinical or technical factors raise concern
that ICA PSV may not be representative of the extent of disease. (d) ICA should be
diagnosed as (i) normal when ICA PSV is less than 125 cm/sec and no plaque or
intimal thickening is visible; (ii) ?50% stenosis when ICA PSV is less than 125 cm/sec
and plaque or intimal thickening is visible; (iii) 50%–69% stenosis when ICA PSV is
125–230 cm/sec and plaque is visible; (iv) ?70% stenosis to near occlusion when
ICA PSV is greater than 230 cm/sec and visible plaque and lumen narrowing are
seen; (v) near occlusion when there is a markedly narrowed lumen at color Doppler
US; and (vi) total occlusion when there is no detectable patent lumen at gray-scale
US and no flow at spectral, power, and color Doppler US. (e) The final report should
discuss velocity measurements and gray-scale and color Doppler findings. Study
limitations should be noted when they exist. The conclusion should state an esti-
mated degree of ICA stenosis as reflected in the above categories. The panel also
considered various technical aspects of carotid US and methods for quality assess-
ment and identified several important unanswered questions meriting future re-
A panel of experts from a variety of medical specialties was convened under the auspices
of the Society of Radiologists in Ultrasound to arrive at a consensus about the performance
of Doppler ultrasonography (US) to aid in diagnosis of internal carotid artery (ICA)
stenosis. The panel met in San Francisco, Calif, October 22–23, 2002, and drew up a
consensus statement. Although there are several facets of carotid disease that could be
considered by such a panel, carotid stenosis (and by extension, carotid occlusion) is by far
the most common pathologic process involving carotid arteries. Furthermore, the clinical
suspicion of ICA stenosis is responsible for most of the referrals for carotid imaging.
Authors of recent major studies have shown a decrease in stroke risk when carotid
endarterectomy is performed for carotid stenosis (1–4).
The performance of carotid US and the interpretation of US results vary considerably
from laboratory to laboratory (5). Accred-
itation of vascular laboratories has re-
sulted in an increased degree of standard-
ization of the carotid US examination,
but a wide range of practice patterns still
exist. The goal of the conference was to
develop recommendations for the perfor-
mance of Doppler US and interpretation
of the results in the diagnosis of ICA ste-
nosis. The panel limited its discussion to
atherosclerotic stenosis of the ICA at or
just beyond the carotid bifurcation and
to vessels without prior intervention.
METHODS AND CONFERENCE
Prior to the meeting, 30 representative
articles were selected by the moderator
(E.G.G.) and sent to conference partici-
pants, along with a summary spreadsheet
with such information as the purpose of
the research, the statistical methods
used, and the pertinent results and con-
clusions (Tables 1, 2) (6–26). The panel
consisted of a moderator and 16 panelists
from various medical specialties.
Background and Summary of the
Historically, clinical studies of carotid
artery disease have classified patients in
two groups: symptomatic and asymp-
tomatic. The former group of patients
typically has had a neurologic event
(stroke, transient ischemic attack, or am-
aurosis fugax) secondary to cerebral isch-
emia, likely as a result of an embolic
event arising from atherosclerotic disease
at the carotid bifurcation. Patients in this
group have formed the basis for such
well-known studies as the North Ameri-
can Symptomatic Carotid Endarterec-
tomy Trial (1) and the European Symp-
tomatic Carotid Trial (3).
The asymptomatic group includes pa-
tients who have not had a neurologic
event. The seminal investigation in this
population, the Asymptomatic Carotid
Artery Study (2), included patients who,
though they had not had a neurologic
event, typically had clinical markers for
diffuse atherosclerosis. Overall, the prev-
alence of significant (?50%) stenotic dis-
ease in symptomatic patients is stated as
being in the range of 18%–20% (27,28),
while the prevalence in asymptomatic
patients referred for carotid imaging is
14% (29). The prevalence of ICA disease
in the asymptomatic group, therefore,
approaches that found in symptomatic
Doppler US is by far the most common
imaging examination performed world-
wide to aid in the diagnosis of carotid
disease. Given the prevalence of patients
with carotid disease and the frequency
with which patients are referred for ca-
rotid imaging, the number of carotid US
examinations performed annually is con-
siderable (22). This imaging modality is
increasingly becoming the only exami-
nation performed before surgical inter-
vention. It was estimated by the panelists
that as many as 80% of patients in the
United States undergo carotid endarter-
ectomy after a US examination as the
only preoperative imaging study. There-
fore, it is of utmost importance that in-
formation provided by the US examina-
tion be reproducible and reliable.
Considerable gains have been made in
the quality of US examinations of the
carotid arteries over the past 2 decades.
The technology has experienced great ad-
vances in equipment, ranging from con-
tinued improvements in gray-scale reso-
lution to landmark advances in Doppler
methods, including color Doppler imag-
ing. The imaging community has gained
expertise in performance of carotid US
and interpretation of the results through
widespread use of technology, research,
and continuing medical education. In
addition, various accrediting bodies have
been established by groups such as the
Intersocietal Commission for Accredita-
tion of Vascular Laboratories, the Ameri-
can Institute of Ultrasound in Medicine,
and the American College of Radiology
in an attempt to improve and standard-
ize the quality of vascular US examina-
Despite improvements and advances,
Literature Review of Doppler US Thresholds and Performance in Diagnosis of ICA Stenosis
Study and Year
Huston et al (6), 200050
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
Grant et al (7), 1999
Abu Rahma et al (8), 1998
Carpenter et al (9), 1996
Hood et al (10), 1996
Carpenter et al (11), 1995
Browerman et al (12), 1995
Moneta et al (13), 1995
Neale et al (14), 1994
Moneta et al (15), 1993
. . .
. . .
Note.—EDV ? end diastolic velocity in ICA, NPV ? negative predictive value, PPV ? positive predictive value, PSV ? peak systolic velocity in ICA. Ratio
is ICA PSV to distal common carotid artery (CCA) PSV.
* AP ? asymptomatic patients, SP ? symptomatic patients. Thresholds based on outcome ? sensitivity/specificity ? accuracy.
Volume 229 ? Number 2Society of Radiologists in Ultrasound Consensus Conference ? 341
the consensus panel agreed that, overall,
carotid US is often performed inconsis-
tently within a given laboratory, and
there is nonuniformity in practice from
one laboratory to the next. In many set-
tings, interpretive criteria for carotid ste-
nosis are either indiscriminately applied
or the interpreters are uncertain about
exactly how to make the diagnosis of ca-
The results of the consensus conference
regarding performance of carotid US and
interpretation of the results and the diag-
nosis of ICA stenosis can be summarized
into six key areas: (a) technical consider-
ations, (b) diagnostic strata, (c) imaging
and Doppler parameters, (d) Doppler di-
agnostic thresholds; (e) the final report of
the gray-scale and Doppler US examina-
tions, and (f) quality assessment. The
panel identified a number of issues re-
lated to performance of carotid US and
interpretation of the results and made
recommendations to address these issues.
Issue.—The performance of carotid US
examinations is not standardized from
laboratory to laboratory. Even within a
given laboratory, there is often a failure
to follow a consistent protocol.
Recommendation.—Examinations of the
ICA should be performed with gray-scale,
color Doppler, and spectral Doppler US in
a standardized fashion, according to a rig-
idly applied laboratory protocol, in accor-
dance with the standards of one of the
accrediting bodies. The panel encourages
all sonographers performing carotid US to
become credentialed as vascular technolo-
Positioning and Angulation
Issue.—Errors in positioning the Dopp-
ler gate and in accounting for the Dopp-
ler angle are common in current clinical
practices. Since interpretative criteria for
carotid stenosis are heavily based on
Doppler velocities, errors in Doppler po-
sition and angle correction will lead to
serious errors in diagnosis.
Recommendation.—The Doppler wave-
form should be obtained with an angle of
insonation less than or equal to 60°, as
measurements obtained with an angle of
insonation greater than 60° are likely to
be inaccurate, even with appropriate an-
gle adjustment, because of the physical
properties of Doppler.
that maintaining a constant angle of in-
sonation of exactly 60° would provide
greater consistency. Other panelists did
not agree that a fixed angle of insonation
for all carotid US examinations is re-
quired and instead expressed that it is
necessary only to maintain an angle of
less than or equal to 60°. It was thought
that further investigation on this matter
Sample Volume Position
Issue.—Other common technical short-
comings in ICA examinations include in-
correct positioning of the sample volume,
incomplete sampling through an area of
of a carotid plaque.
Recommendation.—Care should be taken
to position the sample volume within the
area of greatest stenosis. The ICA must be
sampled through the region of stenosis
completely until the distal end of the
plaque is visualized, to ensure that the site
of highest velocity has been located.
Issue.—Several errors may result from
problems inherent to the patient, such as
extensive plaque calcification, severe ICA
tortuosity, and tandem lesions.
Recommendation.—It is important to
recognize these patient conditions and
understand that, in such cases, the exam-
ination may be limited.
Other Pertinent Literature on ICA Stenosis
Study and Year
Assessment and ResultsStenosis (%)PSV (cm/sec)Ratio†
Umemura and Yamada
Perkins et al (17), 2000
NA NANA Evaluated results of B-flow imaging without Doppler
NANA NASurvey results show that laboratories use inconsistent
Doppler US cannot be used to estimate a single degree of
stenosis but is better for differentiating less than or
more than a single degree of stenosis
Color and gray scale perform well alone; Doppler helps
for midrange lesions
Ratio of ICA PSV at and distal to stenosis performs better
than ICA/CCA ratio
Ratio of ICA PSV at stenosis to that distal to stenosis:
sensitivity, 97%, specificity, 98%
Evaluation of cost-effectiveness of asymptomatic screening
Grant et al (18), 2000 NA NANA
Beebe et al (19), 1999 NANA NA
Soulez et al (20), 1999 70, 60NA 3.4, 2.9
Ranke et al (21), 199970NA NA
Derdeyn and Powers
Griewig et al (23), 1996
Srinivasan et al (24),
Hunink et al (25), 1993
Bluth et al (26), 1988
Power Doppler better than color Doppler (not quantified)
Doppler poor for differentiating degree of ?50% stenosis
PSV best parameter for predicting ?70% stenosis
EDV best Doppler parameter; did not use NASCET
* NA ? not applicable.
†Ratio is ICA PSV to distal CCA PSV.
‡NASCET ? North American Symptomatic Carotid Endarterectomy Trial.
342 ? Radiology ? November 2003 Grant et al
Issue.—There is substantial variability
in equipment from machine to machine,
from manufacturer to manufacturer, and
between older and newer equipment
(30–33). This variability in equipment
may explain, in part, the lack of agree-
ment and inconsistency in the literature
concerning Doppler thresholds for the
diagnosis of carotid stenosis.
US equipment manufacturers to mini-
mize equipment variability by establish-
ing industry-wide standards for Doppler
measurement and calibration and the de-
velopment of a reliable Doppler phan-
tom that can be made readily available to
industry and to vascular laboratories.
Methods of Reporting
Issue.—Methods by which the degree
of ICA stenosis is reported vary from lab-
oratory to laboratory, as well as within
some laboratories. Some report an esti-
mate of the specific percentage of steno-
sis, others stratify their estimates into five
or six diagnostic categories or gradations
Recommendation.—Doppler US cannot
be used to predict a single percentage of
stenosis. Therefore, the consensus panel-
ists strongly recommend the use of de-
should establish protocols for stratifying
the degree of ICA stenosis, and, once es-
tablished, these criteria should be consis-
Doppler Measurement Variability
Although investigators have confirmed
that the average Doppler velocity rises in
direct proportion to the degree of steno-
sis as determined
(18,26), there are very wide ranges of
Doppler values around those means,
which makes it impossible to classify le-
sions into gradations as narrow as 10%
(Figure) (18,34). Even in evaluations of
the ability of Doppler US to help estimate
the degree of stenosis by using more ex-
panded strata (eg, ?50%, 50%–69%, and
?70% stenosis), the findings have been
disappointing. US is most accurate when
lesions are classified as being above or
below a single level, such as 60% stenosis
or 70% stenosis (18).
Stenosis of Less than 50%
Issue.—In many laboratories, stratifica-
tion or diagnosis of minor (?50%) de-
grees of ICA stenosis is based on Doppler
Recommendation.—Because Doppler is
inaccurate for subcategorizing stenoses
less than 50%, these stenoses should be
reported under a single category as
“?50% stenosis.” Subcategories for mi-
nor degrees of stenosis should not be
Stratification of Stenoses
Issue.—How should reporting of ICA
stenosis be stratified?
Recommendation.—The consensus panel
recommends stratification of the degree
of stenosis on the basis of gray-scale and
Doppler US results into the following
strata: normal (no stenosis), ?50% steno-
sis, 50%–69% stenosis, ?70% stenosis
but less than near occlusion, near occlu-
sion, and total occlusion.
Discussion.—The threshold of 70% ste-
nosis was chosen because it was believed
to be the threshold currently used by
most major vascular centers for surgical
intervention. The panel agreed, however,
that in some laboratories, there may be a
compelling reason to choose a different
stratification scheme. The diagnoses of
near occlusion and total occlusion are
usually not based primarily on the Dopp-
ler measurement of velocity but rather on
gray-scale and color and/or power Dopp-
Imaging and Doppler Parameters
Key Components of ICA
Issue.—What are the key components
of the US examination of the ICA?
Recommendation.—The ICA US exami-
nation should consist of gray-scale imag-
ing, color Doppler imaging, and spectral
Doppler velocity determination. Because
stenosis is typically an area of narrowing
caused by plaque, with a focal area of
increased velocity and a poststenotic dis-
turbed flow, the location and character-
istics of plaque in the ICA should be de-
termined. The color Doppler appearance
of the lumen should also be assessed.
Primary US Parameters
Issue.—Numerous imaging and Dopp-
ler parameters are currently used at vari-
ous laboratories for the evaluation of ICA
stenosis, including ICA PSV, ICA EDV
and ICA/CCA PSV ratio, CCA EDV, and
ICA/CCA EDV ratio. The application of
these parameters for diagnosis of ICA ste-
nosis varies from laboratory to laboratory
and sometimes within a given labora-
Recommendation.—The panel suggested
that the ICA PSV and the presence of
plaque on gray-scale and/or color Dopp-
ler US images are the parameters that
should be used when diagnosing and
grading ICA stenosis.
Discussion.—The ICA PSV is easy to ob-
tain and has good reproducibility and
should be used in conjunction with avail-
able gray-scale and color Doppler informa-
tion to ensure concordance of diagnostic
information. The degree of stenosis esti-
mated by using ICA PSV and the degree
of narrowing of the ICA lumen on gray-
scale and color Doppler images should be
Graph demonstrates the relationship between mean PSV and percent-
age of stenosis as measured arteriographically. PSV increases with
increasing severity of stenosis. Note marked overlap in adjacent cat-
egories of stenosis. Error bars ? 1 SD about the mean. (Reprinted, with
permission, from reference 18.)
Volume 229 ? Number 2 Society of Radiologists in Ultrasound Consensus Conference ? 343
Additional US Parameters
Issue.—Should other Doppler parame-
ters be used and, if so, when?
Recommendation.—Two additional pa-
rameters, ICA/CCA PSV ratio and ICA
EDV, are useful for internal checks or
may be used when ICA PSV may not be
representative of the extent of disease
owing to technical or clinical factors such
as in the presence of tandem lesions, con-
tralateral high-grade stenosis, discrep-
plaque and ICA PSV, elevated CCA veloc-
ity, hyperdynamic cardiac state, or low
cardiac output. For example, in a patient
with low cardiac output, the ICA PSV
may be disproportionately low when
compared with the ICA/CCA PSV ratio.
This discrepancy should prompt the in-
terpreter to consider all gray-scale and
Doppler information when stratifying
the degree of ICA stenosis. In particular
in such cases, the interpretation should
be based more heavily on the ICA/CCA
PSV ratio than on absolute values such as
the ICA PSV or ICA EDV. The panel be-
lieved that outlining the reasons for mak-
ing diagnostic choices that are not in
keeping with usual practice should be in-
cluded in the final report.
Doppler Diagnostic Thresholds
Issue.—Published literature is replete
with velocity thresholds for categorizing
ICA stenosis (Table 1). Tremendous vari-
ation exists among these studies in the
methods used to assess individual Dopp-
ler parameters and in the thresholds rec-
ommended for diagnosing ICA stenosis
Recommendation.—The consensus panel
developed recommendations for diagnosis
and stratification of ICA stenosis (Table 3).
These recommendations were derived
from analysis of numerous studies and
do not represent the results of any one
laboratory or study. For a particular lab-
oratory setting, internal validation is en-
couraged when possible. This may yield
alternative diagnostic criteria that can be
used successfully at that facility. How-
ever, each laboratory should have a sin-
gle set of diagnostic criteria that is ap-
plied uniformly. The following points are
included in Table 3 and should be con-
sidered in the diagnosis of ICA stenosis:
1. The ICA is considered normal when
ICA PSV is less than 125 cm/sec and no
plaque or intimal thickening is visible
sonographically. Additional criteria in-
clude ICA/CCA PSV ratio ? 2.0 and ICA
EDV ? 40 cm/sec.
2. A <50% ICA stenosis is diagnosed
when ICA PSV is less than 125 cm/sec
and plaque or intimal thickening is visi-
ble sonographically. Additional criteria
include ICA/CCA PSV ratio ? 2.0 and
ICA EDV ? 40 cm/sec.
3. A 50%–69% ICA stenosis is diag-
nosed when ICA PSV is 125–230 cm/sec
and plaque is visible sonographically. Ad-
ditional criteria include ICA/CCA PSV ra-
tio of 2.0–4.0 and ICA EDV of 40–100
4. A >70% ICA stenosis but less than
near occlusion of the ICA is diagnosed
when the ICA PSV is greater than 230
cm/sec and visible plaque and luminal
narrowing are seen at gray-scale and
color Doppler US. Additional criteria in-
clude ICA/CCA PSV ratio ? 4 and ICA
EDV ? 100 cm/sec. The higher the Dopp-
ler parameter lies above the threshold of
230 cm/sec, the greater the likelihood of
5. In cases of near occlusion of the
ICA, the velocity parameters may not ap-
ply, since velocities may be high, low, or
undetectable. This diagnosis is estab-
lished primarily by demonstrating a
markedly narrowed lumen at color or
power Doppler US (35).
6. Total occlusion of the ICA should
be suspected when there is no detectable
patent lumen at gray-scale US and no
flow with spectral, power, and color
Doppler US. Magnetic resonance (MR)
angiography, computed tomographic (CT)
angiography, or conventional angiogra-
phy may be used for confirmation in this
Final Report of the Gray-Scale and
Doppler US Examination
Issue.—The structure and content of fi-
nal reports of carotid US examinations
vary greatly from laboratory to labora-
tory, as well as within given laboratories.
Recommendation.—The final report of
the gray-scale and Doppler US interpreta-
tion of the ICA examination should in-
clude the following:
Body of the report.—(a) Pertinent US
findings, including velocity measure-
ments and gray-scale findings (presence,
plaque), as well as color Doppler findings
when appropriate; (b) comments about
limitations of the study or deviations
from usual interpretive criteria due to
technical factors or hemodynamic con-
siderations; and (c) comparison with re-
sults of prior studies.
degree of ICA stenosis, categorized by the
laboratory’s established diagnostic crite-
ria (modified, as appropriate, by techni-
cal factors or hemodynamic consider-
Need for Quality Assessment
Issue.—Should every laboratory have a
system for quality assessment?
Recommendation.—All laboratories should
institute a program of quality assessment.
Internal Validation of Doppler
Issue.—Development of internally val-
idated Doppler thresholds may be diffi-
cult given the infrequency of correlative
angiograms at most institutions.
that it may not always be feasible to ob-
tain angiographic or clinical correlation
for quality assessment of US studies at
Consensus Panel Gray-Scale and Doppler US Criteria for Diagnosis
of ICA Stenosis
Primary Parameters Additional Parameters
?70 but less than
High, low, or
Total occlusionVisible, no
Not applicableNot applicable
* Plaque estimate (diameter reduction) with gray-scale and color Doppler US.
344 ? Radiology ? November 2003 Grant et al
each laboratory. For this reason, the con-
sensus panel developed the table of rec-
ommended Doppler thresholds for diag-
nosis of ICA stenosis (Table 3), which can
be applied at laboratories that cannot val-
idate their own Doppler thresholds on
the basis of correlative imaging or clinical
Discussion: Although angiography has
historically been considered the “gold
standard” for assessing Doppler thresh-
olds for various degrees of ICA stenosis,
few angiographic examinations are still
performed. Those that are performed at a
given institution are probably not repre-
sentative cases, but rather those cases in
which the US results were equivocal or
otherwise problematic. The use of CT an-
giography and MR angiography for cor-
relation has not, as yet, been fully vali-
Issue.—When angiography is used as
the reference standard for assessment of
Doppler criteria for ICA stenosis, differ-
ent techniques for measuring ICA steno-
sis have been used.
Recommendation.—The panel recom-
mended that the NASCET method of ca-
rotid stenosis measurement should be
employed when angiography is used to
correlate the US findings.
Discussion.—In this method, the nar-
rowest portion of the vascular lumen was
compared with the “normalized lumen
distally” (37). In the European Symptom-
atic Carotid Trial study and studies per-
formed prior to the NASCET study, the
degree of stenosis was determined by
comparing the narrowest diameter of the
residual lumen to an estimate of the orig-
inal lumen in the same area. Because the
original lumen cannot be depicted on the
angiogram, exact measurement is impos-
sible. While the NASCET method of mea-
surement may not reflect the burden of
atherosclerosis in the proximal ICA, it
does minimize the amount of interob-
The panel discussed the issue of appro-
priate follow-up of asymptomatic pa-
tients with known ICA stenosis, as well as
of patients at high risk for ICA stenosis or
stroke. The panelists agreed that patients
with a ?50% stenosis of the ICA who do
not undergo carotid endarterectomy and
who may be candidates for prophylactic
carotid endarterectomy should be fol-
lowed up at 6–12-month intervals, and
high-risk patients with visible plaque and
?50% stenosis should be evaluated every
1–2 years. Patients who have normal ca-
rotid US studies but marked risk factors
might be evaluated every 3–5 years. In all
cases of follow-up or surveillance, a com-
plete examination should be performed.
Follow-up studies should be compared
with results from prior examinations.
The panel identified several important
unanswered questions that merit future
1. What is the role of ICA plaque char-
acterization in carotid disease?
2. What is the role of the ICA intimal-
medial thickness? There are several ongo-
ing large clinical trials in which the inti-
mal-medial thickness is being evaluated
as a marker of atherosclerotic disease, but
there are not yet enough data to establish
the role of this measurement in the as-
sessment of carotid disease in individual
much of a change in estimated ICA ste-
nosis or ICA PSV should be considered
4. What criteria should be used to as-
sess patients after ICA surgery or stent
5. Should US be used to screen for ca-
Other issues that need to be addressed
include the following:
1. There is considerable variation in
Doppler measurements from machine to
machine and manufacturer to manufac-
ture. This should be rectified, because
such variation leads to inconsistencies
and inaccuracies in diagnosing ICA ste-
2. Phantoms for Doppler US need to
be developed to facilitate calibration of
Doppler US equipment.
3. Improved methods for calculating
velocity with angle correction should be
developed to eliminate or minimize the
inconsistency in velocity measurements
as the Doppler angle of insonation is
4. Reliable quality assessment meth-
ods should be developed so that labora-
tories can assess their performance of the
carotid US examination. This should lead
to greater consistency in the performance
of carotid US within each laboratory, as
well as from laboratory to laboratory.
1. North American Symptomatic Carotid
Endarterectomy Trial collaborators. Bene-
ficial effect of carotid endarterectomy in
symptomatic patients with high-grade ca-
rotid stenosis. N Engl J Med 1991; 325:
Executive Committee for the Asymptom-
atic Carotid Atherosclerosis Study. Endar-
terectomy for asymptomatic carotid ar-
tery stenosis. JAMA 1995; 273:1421–
European Carotid Surgery Trialists’ Collab-
orative Group. MRC European Carotid Sur-
gery Trial: interim results for symptomatic
patients with severe (70–99%) or with mild
(0–29%) carotid stenosis. Lancet 1991; 337:
Barnett HJM, Taylor DW, Eliasziw M, et
al. Benefit of carotid endarterectomy in
patients with symptomatic moderate or
severe stenosis. N Engl J Med 1998; 339:
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