Diagnostic ultrasound ( PDFDrive )

950 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
By using spectral analysis, various parameters are determined,
including mean velocity, PSV, EDV, and the pulsatility and resistive
indices of the blood vessels. Color or power Doppler ultrasound
can improve velocity determination by providing better angle
theta determination and localizing the course of vessels. 222 TCD
applications include (1) evaluation of intracranial stenoses and
collateral circulation, (2) detection and follow-up of vasoconstriction
from subarachnoid hemorrhage, (3) determination of brain
death, (4) evaluation of patients with sickle cell disease, and (5)
identiication of arteriovenous malformation. 219-223,226,227 TCD is
FIG. 26.45 Pseudoaneurysm of the Common Carotid Artery
(CCA). Transverse image of the right CCA demonstrates a jet of low
into a pseudoaneurysm, which resulted from an attempted central venous
line placement.
most reliable in diagnosing stenoses of the middle cerebral artery,
with sensitivities as high as 91% reported. TCD is less reliable
for detecting stenoses of the intracranial vertebrobasilar system,
anterior and posterior cerebral arteries, and terminal ICA.
However, TCD is helpful in assessing vertebral artery patency
and low direction when no low is detected in the extracranial
vertebral artery (Fig. 26.46). Diagnosis of an intracranial stenosis
is based on an increase in the mean velocity of blood low in
the afected vessel compared to that of the contralateral vessel
at the same location. 223-225
Advantages of TCD ultrasound also include its availability
for monitoring patients in the operating room or angiographic
suite for potential cerebrovascular complications. 225 Intraoperative
TCD monitoring can be performed with the transducer strapped
over the transtemporal window, allowing evaluation of blood
low in the middle cerebral artery during CEA. he adequacy
of cerebral perfusion can be assessed while the carotid artery is
clamped. 225,228 TCD is also capable of detecting intraoperative
microembolization, which produces high-amplitude spikes
(high-intensity transient signals [“HITS”]) on the Doppler
spectrum. 223,224,227,229-231 he technique can be used for the serial
evaluation of vasospasms. his diagnosis is usually based on
serial examinations of the relative increase in blood low velocity
and resistive index changes resulting from a decrease in the
lumen of the vessel caused by vasospasms. 225 More description
of transcranial Doppler is in Chapter 47.
VERTEBRAL ARTERY
he vertebral arteries supply the majority of the posterior brain
circulation. hrough the circle of Willis, the vertebral arteries
also provide collateral circulation to other portions of the brain
A
B
FIG. 26.46 Transcranial Doppler Imaging. (A) Transcranial duplex scan of the posterior fossa in a patient with an incomplete left subclavian
steal syndrome demonstrates retrograde systolic low (arrow) and antegrade diastolic low (curved arrow). The scan is obtained in a transverse
projection from the region of the foramen magnum (open arrowhead). (B) Color Doppler image obtained in the same patient demonstrates that
there is retrograde low not only within the left vertebral artery but also within the basilar artery (arrow).