Diagnostic ultrasound ( PDFDrive )

CHAPTER 27 Peripheral Vessels 965
Prior chapters have described details of physics of Doppler
analysis and use of ultrasound in the assessment of the
vasculature supplying the head and neck. In this chapter we
describe assessment of the peripheral arteries and veins, as well
as arteriovenous istula (AVF) and grats. In general, these areas
are readily evaluated by Doppler ultrasound. Because they are
usually located at depths of 6 cm or less, the extremity vessels
are more consistently imaged than those in the abdomen or
thorax. Availability of suicient imaging windows allows the
transducer to be placed over the vascular area of interest with
overlying tissue containing bone or gas. Transducers with frequencies
greater than 5 MHz can typically be used.
Gray-scale sonography is useful for evaluating the presence
of atherosclerotic plaque or conirming extravascular masses.
Color low Doppler imaging allows for a rapid survey of the area
of interest, and then spectral Doppler can be used to characterize
blood low patterns.
Standardized protocols, such as those provided by the American
College of Radiology (ACR), American Institute of Ultrasound
in Medicine, and Society of Radiologists in Ultrasound should
be followed. 1,2 It is recommended that examinations be performed
in an accredited laboratory with participation in one of the
vascular accreditation programs, such as the ACR or the Intersocietal
Commission for the Accreditation of Vascular Laboratories,
in order to achieve a national standard of excellence and
to improve the chance of success of peripheral arterial and venous
ultrasound examinations. 3 In the setting of a dedicated staf and
with physician support, ultrasound can be used to diagnose many
peripheral vascular abnormalities deinitively and avoid the need
for ionizing radiation or intravenous contrasted cross-sectional
studies.
PERIPHERAL ARTERIES
A variety of symptoms and signs can be evaluated by arterial
ultrasound. Sonographic examination is relatively rapid and has
beneits over other modalities, such as real-time technique, lack
of ionizing radiation, and relatively low expense. In the last two
decades, the number of indications for peripheral artery ultrasound
has expanded. he most recent ACR practice parameter
on the topic lists indications for the examination, which include
claudication and/or rest pain in the lower extremities to evaluate
for arterial stenosis or occlusion. 2 Patients with pain, discoloration,
or ulcer formation in the extremities (most commonly lower)
may have tissue ischemia or necrosis from arterial stenosis or
occlusion. Additional symptoms of numbness or cold extremity
may be noted. However, symptomatology may vary depending
on the rapidity of onset and whether collaterals have developed
to decrease the efects of stenosis on the tissues. In some patients,
vascular abnormalities may be subclinical and found incidentally
on imaging for other indications. Once an abnormality has
been identiied, ultrasound can monitor progression of disease,
determine success or failure ater intervention, and identify
acceptable vessels for bypass grat creation.
Other extremity abnormalities can be evaluated sonographically.
Focal masses can be assessed to exclude vascular causes
such as aneurysm or istula with venous enlargement. When
chronic positional upper extremity symptoms are present,
ultrasound can evaluate for thoracic outlet syndrome. More
peripherally, Doppler can document patency of the palmar arch
in surgical planning for bypass grat harvesting, and it can assess
the radial artery before and ater vascular access.
In the acute setting, traumatic injuries can be evaluated to
determine adjacent arterial patency. Pseudoaneurysms and
dissections are visible by ultrasound in these patients. Speciic
levels of embolic disease can also be depicted.
Sonographic Examination Technique
Gray-scale evaluation of the peripheral arteries is important to
determine the amount of atherosclerotic disease or thrombus
present. he highest frequency transducer that allows good
penetration and visualization should be applied, typically a 5- to
12-MHz linear array transducer, with a higher frequency transducer
used in areas where the arteries are more supericial.
Occasionally, a 3- to 5-MHz sector or curved array probe
may be necessary in large patients or those with large amounts
of edema.
Occasionally, atherosclerotic plaque or thrombus is hypoechoic,
and color Doppler is extremely useful to evaluate residual lumen,
with the gain adjusted so color does not overlap into adjacent
tissues. he spectral Doppler gate is adjusted within the lumen
of the artery to allow adequate signal. he scale and gain should
be optimized to show strong low signals that use most of the
scale to display the waveform. Normally, a medium or high wall
ilter is used in arterial evaluation. If there is slow low, a low
wall ilter may be used to improve detection. In general, for
detection of small channels of slow low in areas of near-occlusion,
power Doppler may be more sensitive than color Doppler. 4
However, the advances in color Doppler may have reduced this
diference in recent years.
he components of the sonographic evaluation difer based
on the indication. For example, imaging for suspected arterial
stenosis or occlusion is very diferent from evaluation of a focal
mass or aneurysm. he technical components of the examination
have been recently described in the ACR practice parameters. 2
Stenosis Evaluation
Color and spectral Doppler imaging are key to stenosis evaluation,
using a combination of waveform morphology and velocity
characteristics. On gray-scale imaging, a focal stenosis or occlusion
may be visible, but this should be conirmed by Doppler. Collaterals
should also prompt additional attention with Doppler.
Any areas of visible narrowing or turbulent color Doppler signal
should be further characterized with spectral Doppler. A change
in spectral waveform morphology from one arterial segment to
the next should also be further evaluated with color and spectral
Doppler to locate a point of transition (Fig. 27.1). Spectral Doppler
should be performed in the longitudinal plane and should be
angle corrected 60% or less from the center beam. If a jet at or
downstream from a stenosis is seen, angle correction parallel to
the orientation of the jet should be performed to more accurately
measure peak systolic velocity (PSV). Using this technique,
waveform morphology and peak velocity should be evaluated
at any suspected area of stenosis, as well as the feeding vessel