Diagnostic ultrasound ( PDFDrive )

924 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
A
B
FIG. 26.11 Plaque Ulceration and Abnormal Flow. (A) Longitudinal image of the proximal right internal carotid artery (ICA) demonstrates
heterogeneous plaque with an associated area of reversed low-velocity eddy low within an ulcer (arrow). (B) Pulsed Doppler waveforms in this
ulcer crater demonstrate the extremely dampened low-velocity reversed low, not characteristic of that seen within the main vessel lumen of the
ICA.
B
A
A
B
FIG. 26.12 Measurement of Carotid Artery Diameter. (A) Power Doppler transverse image shows a less than 50% diameter stenosis
(cursors). (B) Transverse B-mode low image of the right carotid bifurcation shows measurement of stenosis (B) in area of internal carotid artery
(ICA). A, Outer ICA area.
to measure plaque volume with good intraobserver and interobserver
variability as well as plaque characterization. 95,96
As the severity of a stenosis increases, the quality of the realtime
image deteriorates. 93,97 Several factors work against successful
image assessment of high-grade stenosis. Plaque calciication
and irregularity produce shadowing, which obscures the vessel
lumen. Heterogeneous plaque oten has acoustic properties similar
to lowing blood, producing anechoic plaques or thrombi that
are diicult to visualize on gray-scale images. In the most extreme
cases, vessels can show little visible plaque yet be totally occluded
(see Fig. 26.9E and F). Color Doppler sonography readily identiies
such phenomena. For these reasons, real-time gray-scale ultrasound
is best suited for the evaluation of nonrate-limiting lesions
and not for quantifying high-grade stenoses, which are more
accurately determined by spectral analysis. 98,99 he gray-scale
indings and Doppler spectral analysis values must be integrated
and correlated for a complete ultrasound assessment of the carotid
vessels (Video 26.14).
It is probably unnecessary to make a quantitative assessment
of the amount of plaque. Rather, a qualitative assessment of the
amount of plaque should be made and compared to the Doppler
spectral indings to ensure accuracy in grading stenoses. A
mismatch between the qualitative assessment of the amount of
plaque and the Doppler indings should alert the examiner to a
possible technical error. If these cannot be resolved, further
assessment with CTA or MRA should be considered.