Ultrasound Elastography Applications

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                <p>Ultrasound elastography is the use of ultrasound to
produce measurements or images of tissue stiffness. Several different
approaches are used, but all rely on creating some form of displacement
of the tissue and measuring the response. Ultrasound elastography can be
implemented in a number of ways; from simple add-ons for conventional
ultrasound scanners, to dedicated ultrasound elastography units.
Different techniques are used to generate the results, depending on the
particular approach and clinical application.</p>
<p>Ultrasound elastography is a new ultrasonic imaging technique
introduced to produce images of the Young's modulus distribution of
compliant tissue. This Young's modulus distribution is derived from the
ultrasonically estimated longitudinal internal strains induced by an
external compression of the tissue. The displayed two-dimensional images
are called elastograms.</p>
<p>Tissue strain analytics could represent the most important development
in ultrasound technology since the advent of Doppler imaging. Tissue
Strain applications provide a new dimension of diagnostic information
through either qualitative assessment or quantitative measurement of the
mechanical stiffness of tissue. Tissue strain analytics compliments
conventional ultrasound exams by providing an extra dimension of
information - mechanical stiffness. This additional information can be
combined with anatomical (B-mode) as well as vascular (Doppler)
information such that the actual diagnosis is contained by the
intersection of three dimensions of information.</p>
<p>In order to produce ultrasound elastography images or measurements,
the tissue to be assessed are stressed by the application of a force.
This force may be applied by the operator, an external mechanical device,
physiological motion, or by the ultrasound probe itself in the form of
acoustic waves. The response of underlying tissue structures to such
stress varies according to tissue stiffness. Perhaps the simplest form of
ultrasound elastography is to acquire data before a stress is applied. By
comparing these two sets of data, it is possible to derive a 'stiffness'
measure. A stiff object will tend to move as a whole, whereas soft tissue
compresses more unevenly, with tissue closer to the applied force
compressing more than those further away.</p>
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<p>Ultrasound elastography has been most frequently used in the
assessment of liver fibrosis in a non-imaging, quantitative capacity, but
in recent years the technique has been investigated in a broad array of
clinical applications. Of particular note is the potential of ultrasound
elastography in the assessment of liver fibrosis and in breast imaging.
These subjects have been the subject of a significant body of research
and were the primary focus of this review. Other clinical applications
for which the ultrasound elastography technique has been investigated
include: endoscopic, vascular and prostate imaging, which were briefly
reviewed for this evaluation, as well as thyroid, skin and brain tumors,
which were outside the scope of this review.</p>
<p>Clinical research has shown very promising results in differentiation
between benign and malignant tissue in thyroid gland, breast, and
prostate and to assess liver fibrosis.</p>
<p>Also, endoscopic ultrasound elastography is a new application in the
field of the endosonography and seems to be able to differentiate benign
from the malignant nodes and pancreatic lesions with a high-sensitivity
specificity and accuracy. Ultrasound elastography is superior compared to
conventional B-mode imaging and the interobserver reproducibility is
satisfying.</p>
<p>Intravascular ultrasound elastography is a promising tool for studying
atherosclerotic plaque composition and assessing plaque vulnerability.
Current ultrasound elastography techniques can measure the 1D or 2D
strain of the vessel wall using various motion tracking algorithms. Since
biological soft tissue tends to deform non-uniformly in 3D, measurement
of the complete 3D strain tensor is desirable for more rigorous analysis
of arterial wall mechanics. Atherosclerotic plaque rupture is the major
cause of acute coronary syndromes. Currently, there are no reliable
diagnostic tools to predict plaque rupture. Knowledge of plaque
mechanical properties based on local artery wall strain measurements
would be useful for characterizing its composition and predicting its
vulnerability.</p>
<p>Currently, a quiet revolution is occurring in diagnostic ultrasound,
the results of which are benefiting all ultrasound practitioners.
Smaller, portable machines are becoming available, image quality is
dramatically improved, real-time imaging is now possible, and solutions
are being found for those patients that were previously difficult to
image.</p>                 <!--INFOLINKS_OFF-->
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posted:10/19/2011
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