Diagnostic ultrasound ( PDFDrive )

772 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
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FIG. 21.17 Color Doppler Flow Patterns and Special Waveforms Help Distinguish Between Metastatic and Inlammatory Etiologies of
Mild Lymphadenopathy. (A) Benign reactive lymph node is usually fed by a single hilar artery (arrow). (B) Lymph nodes that bear metastasis
often develop transcapsular feeding vessels (arrows) in addition to having a normal hilar artery (H). (C) Pulsed Doppler spectral waveforms obtained
from benign reactive nodes tend to have low resistive index (RI) and low peak systolic velocity (PSV) with rounded systolic peaks. (D) Waveforms
obtained from metastasis-bearing lymph nodes tend to have high RI, high PSV, and sharp systolic peaks.
pattern of blood vessels within lymph nodes can also be helpful.
Inlamed or reactive lymph nodes tend to be fed by a single hilar
artery that arborizes to various degrees within the mediastinum
of the lymph nodes (Fig. 21.17A). Well-diferentiated and lowgrade
lymphomas can have a similar pattern. Metastases to lymph
nodes can stimulate development of transcapsular tumor neovascularity
(Fig. 21.17B).
Doppler sonography can also be useful for diagnosing vascular
conditions such as arteriovenous malformations, arteriovenous
istulas, venous malformations, and supericial venous thrombosis
(Mondor disease). Along these lines, Doppler can help
identify blood vessels that should be avoided during interventional
procedures.
When assessing blood low in the breast, it is critical to use
exceedingly light compression. Tumor vessels have no muscle
or elastic to prop them open and are very sot. he transducer
is hard, the chest wall is irm, and even the weight of the sonographer’s
arm on the transducer can compress a lesion between
the probe and chest wall enough to decrease or even completely
ablate low within breast lesions (Fig. 21.18; see Videos 21.1 and
21.2). As a result, Doppler sonography must be performed with
such light scan pressure that the transducer barely contacts the
skin. In some cases, using a standof of acoustic gel may be
necessary so that Doppler ultrasound–detectable blood low will
not be afected.
Elastography
Elastography is a technique that uses the lesion’s stifness to
inform the likelihood of malignancy. his phenomenon is captured
quantitatively by Young’s modulus, which measures stifness,
wherein E (elasticity) = stress/strain. Stress is the force that is
applied to the mass during the imaging evaluation and strain is
the amount of tissue displacement that occurs in response to
this force. A less compressible mass has a higher Young’s modulus
and a greater likelihood of malignancy. here are two methods
of performing elastography: strain and shear wave. Strain
elastography requires the operator to provide gentle repetitive
compression to the breast tissue either via repetitive motion or
using the patient’s own breathing or heartbeat. he strain of the
tissue is measured through longitudinal displacement of the tissue
before and ater compression. Because the delivered force is
variable, Young’s modulus cannot be calculated. he result is
predominantly qualitative information. he strain of the mass
and surrounding normal tissue can be compared to create a
strain ratio (Fig. 21.19). Shear wave elastography employs a
force automatically applied by the transducer to the targeted
mass, making it less operator dependent. Horizontal shear waves
are then produced at variable speeds based on the mass’s hardness,
and the elasticity of the mass can be calculated. 24,25
Stifness measures for both strain and shear wave elastography
are typically color-coded for quick interpretation. Although red