Diagnostic ultrasound ( PDFDrive )

930 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
ICA
C
B
A
CCA
ECA
Measurement Methodology
ECST =
B – A
x 100
B
NASCET
ACAS
= 1–
x 100
FIG. 26.21 Comparative Measurement Methodology. Different
methodologies for grading internal carotid artery stenoses, from the
North American Symptomatic Carotid Endarterectomy Trial (NASCET),
Asymptomatic Carotid Atherosclerosis Study (ACAS), and European
Carotid Surgery Trial (ECST). CCA, Common carotid artery; ECA, external
carotid artery; ICA, internal carotid artery.
techniques: the NASCET, the ECST, and a technique comparing
distal CCA measurements with those of ICA stenosis. Researchers
concluded that the ECST and NASCET techniques were similar
in their prognostic value, whereas the CCA/stenosis measurement
was the most reproducible of the three techniques. hey also
concluded that the CCA method, although reproducible, would
be invalidated by the presence of CCA disease. 110 Virtually all
investigators advocate using the NASCET angiographic measurement
technique.
he results of these trials, as well as the more recent ACAS
and moderate NASCET studies, have generated reappraisals of
the Doppler velocity criteria that most accurately deine 70% or
greater stenosis and, more recently, greater than 50% diameter
stenoses. 111 Attempts have been made to determine the Doppler
parameters or combination of parameters that most reliably
identify a certain-diameter stenosis. Most sources agree that the
best parameter is the PSV of the ICA in the region of a stenosis. 108
Using multiple parameters can improve diagnostic conidence,
particularly when combined with color and power Doppler
imaging (see Video 26.19).
he degree of stenosis is best assessed using the gray-scale
and pulsed Doppler parameters, including ICA PSV, ICA end
diastolic velocity (EDV), CCA PSV, CCA EDV, peak systolic
ICA/CCA ratio, and peak end diastolic ICA/CCA ratio
(EDR) 108,109,112 (Videos 26.21 and 26.22). 108,109,112 PSV has proved
accurate for quantifying high-grade stenoses. 98,109 he relationship
of PSV to the degree of luminal narrowing is well deined
and easily measured. 113,114 Although Doppler velocities have
proved reliable for deining 70% or greater stenosis, Grant
et al. 109 showed less favorable results for substenosis classiication
between 50% to 69% using PSV and ICA/CCA PSV ratios. In
A
C
our experience, however, using all four parameters and determining
a correct category for the degree of stenosis is the most
eicacious way to ensure accuracy. Agreement for all four
parameters for a clinical situation is most common. When there
is an outlying parameter, further assessment and careful attention
to technique and detail are required. EDV and EDR are
particularly useful in distinguishing between high grades of
stenosis. Additionally, correlating the visual estimation of the
degree of stenosis and the velocity numbers will help in correctly
grading stenosis, particularly when the degree of stenosis is “near
occlusion” (Figs. 26.22 and 26.23; see also Fig. 26.20D and E).
On rare occasions, alternate imaging methodologies (e.g., MRA,
CTA) may need to be recommended.
No criteria for grading external carotid artery stenoses have
been established. A good general rule is that if the ECA velocities
do not exceed 200 cm/sec, no signiicant stenosis is present.
However, we usually rely on a visible assessment of the degree
of narrowing associated with velocity changes. Occlusive plaque
involving the ECA is less common than in the ICA and is rarely
clinically signiicant.
Similarly, velocity criteria used to grade common carotid
artery stenoses have not been well established. 115,116 However,
if one is able to visualize 2 cm proximal and 2 cm distal to a
visible CCA stenosis, a PSV ratio obtained 2 cm proximal to the
stenosis (vs. in region of greatest visible stenosis) can be used
to grade the “percent diameter stenosis” in a manner similar to
that used in peripheral artery studies. A doubling of the PSV
across a lesion would correspond to at least a 50% diameter
stenosis, and a velocity ratio in excess of 3.5 corresponds to a
greater than 75% stenosis.
One persistent problem with duplex Doppler with gray-scale
ultrasound evaluation of the carotid arteries is that diferent
institutions use PSVs ranging from 130 cm/sec 117 to 325 cm/
sec 111 to diagnose greater than 70% ICA stenosis. 118,119 Factors
adding to these discrepancies include technique and equipment. 120
While there is a strong level of correlation between techniques
and criteria, the choice of criteria has a signiicant impact on
which patients go to surgery. 119 his wide range of PSVs reinforces
the need for individual ultrasound laboratories to determine
which Doppler parameters are most reliable in their own institution.
120 Correlation of the velocity ranges obtained by ultrasound
with angiographic and surgical results is necessary to achieve
accurate, reproducible examinations in a particular ultrasound
laboratory. 121
he Society of Radiologists in Ultrasound, representing
multiple medical and surgical specialties, held a consensus
conference in 2002 to consider carotid Doppler ultrasound. 122
In addition to guidelines for performing and interpreting carotid
ultrasound examinations, panelists devised a set of criteria widely
applicable among vascular laboratories (Table 26.1). 122 Although
the conference did not recommend all established laboratories
with internally validated velocity charts alter their practices, they
suggested physicians establishing new laboratories consider using
the consensus criteria; those with preexisting charts might
consider comparing in-house criteria with those provided by
the consensus conference. Velocity criteria corresponding to
speciic degrees of vascular stenosis are listed in the tables. Our