Ultrasound Elastography is a new imaging technique that allows a noninvasive estimation and imaging of tissue elasticity distribution within biological tissues using conventional, Real Time Ultrasound equipment with modified software. It can be viewed as an electronic palpation of tissues. Introduced by Ophir et al in 1991, it subsequently evolved into a Real Time Imaging tool.

1. Ultrasound Elastography

2. Technology Update
PRINCIPLES AND TECHNICAL ASPECTS
Tissue elasticity is characterized by the amount of tissue
displacement or distortion in response to the application of
an external load. A region of tissue is subjected to a
compression force (called stress) and the degree to which it
distorts (known as strain) is assessed.While in principle any
imaging technique could be used Ultrasound has the
advantage of good resolution in both space and time, is safe,
repeatable, so has emerged as the dominant technique while
MR also has a role. Basically, tissue elasticity imaging
methods based on ultrasound fall into three main groups [1].
(i) Methods where a quasi-static compression is applied
to tissue and the resulting components of displacement
or of the strain is estimated. These methods include
elastography based on a global compression of the
medium and Acoustic Radiation Force Impulse
(ARFI) that uses localized compression.
(ii) Methods based on a monochromatic low frequency,
vibration such as sonoelasticity which uses Doppler
signals to estimate tissue displacement and vibro
acoustography which uses ultrasound stimulated
acoustic emission.
(iii) Transient elastography which relies on the observation
of the propogation of a transient shear wave through
tissues. These propogations are followed by pulse
echo acquisitions and the measured velocity of propo-
gations is directly related to tissue stiffness. (Results
are expressed in kilopascals).
Qualitative and quantitative assessment methods of
tissue elasticity are available. In the qualitative assessment
using Real Time Ultrasound Imaging a baseline B mode
sonographic reference image is obtained. After this an
external mechanical compression force (stress) is exerted
to produce a strain. Depending on its specific stiffness
properties the given tissue will be displaced and the
motion displacement of the tissue is estimated. In
practical terms, RF ultrasonic data before and after the
applied compression is acquired and speckle tracking
technique (e.g.) Cross correlation methods are employed
to calculate the resulting strain. The resulting strain image
is called elastogram [2]. There are two types of
elastograms - gray scale and color. The hard and soft areas
appear in the grey scale elastogram as dark and bright
respectively (Fig.1). In the color increasing tissue
hardness appears in ascending order as red, yellow, green
and blue. These colors represent the relative hardness of
the tissues in the elastography (red - soft tissue, blue-hard
tissue, green and yellow (intermediate).
The color coding might vary in different equipments.
The more recent and quantitative technology shear wave
elastography has emerged usingAcoustic Radiation Force
Impulse Imaging (Figs. 2,3) [3,4].An important benefit of
generating the displacement acoustically in that it
removes the user dependence of strain elastography,
because, no manual compression is applied to the tissues.
It is easy to perform, reproducible and provides numerical
values (wave velocity measurements (m/s) of tissue
stiffness at the precise image based Anatomical Location
Region of Interest (ROI).
Various applications of ultrasound elastography
breast
Various studies indicate that breast elastography has
good sensitivity for differentiation between malignant
ULTRASOUND ELASTOGRAPHY
Meera Krishnakumar
Consultant, Department of Radiology, Apollo Hospitals, Greams Road
(off Greams Lane),Chennai 600 006, India.
E-mail: mikimeera@yahoo.co.in
Ultrasound Elastography is a new imaging technique that allows a noninvasive estimation and imaging of
tissue elasticity distribution within biological tissues using conventional, Real Time Ultrasound equipment with
modified software. It can be viewed as an electronic palpation of tissues. Introduced by Ophir et al in 1991, it
subsequently evolved into a Real Time Imaging tool.
Key words : Elastography, Tissue-elasticity, Acoustic Radiation Force Impulse(ARFI ), Qualitative and
quantitative assessment, Region of Interest (ROI).
Apollo Medicine, Vol. 7, No. 3, September 2010 224

3. Technology Update
225 Apollo Medicine, Vol. 7, No. 3, September 2010
Benign tumours reduce in size on mechanical
compression while malignant tumours being stiff stay the
same size or appear bit larger. A qualitative assessment of
the tumoral pattern and an Elasticity score 1-5 has been
developed for breast lesions; the higher score (4 or 5), the
stiffer the tissue and higher probability of malignant
lesion.
Thyroid
It is a potentially adjunctive tool in identifying thyroid
cancer and useful in diagnosis of metastatic cervical
nodes. In the case of multiple nodules it can help to target
biopsies. [6].
Prostate
Can accurately locate prostate tumour foci, determine
extent and take targeted biopsies.
Skin
It can detect dermatological malignancies and
identifies at times tissue indurations and abscesses not
seen on B mode imaging.
EUS
It is an useful add-on to endoscopic ultrasound for
differentiation between benign and malignant pancreatic
lesions and lymph nodes can be useful in differentiating
the benign or malignant GIST located in the wall of the
gastro intestinal tract.
Vascular imaging
Cardiological applications are also under review
especially regarding functioning of cardiac muscles.
Studies on quantifying the elasticity of carotid plaques
which might predict the risk of stroke are also under
progress. Evaluation of blood vessel wall and venous
thrombi also shows great potential.
Liver [1,2]
TheARFI imaging (Virtual Touch Tissue Qualification
mode provided by Siemens Acuson S2000) is a highly
promising method for assessing liver fibrosis.
Comparative studies with transient elastography and liver
biopsy are underway. The shear wave velocity
measurements strongly correlate with the fibrosis stage of
the liver and predict cirrhosis. It can be considered as a
virtual biopsy of the liver and found useful to:
(a) Differentiate focal lesions.
(b) Identify malignant lesions in a cirrhotic liver.
Fig.1. Colour and grey scale elastography of a malignant
lesion.
Fig.2. Schematic diagram of ARFI imaging.
Fig.3. ARFI imaging of a malignant liver neoplasm.
and benign tissue, thus reducing the number of
unnecessary biopsies performed. It can be used as next
line imaging technique when mammography detects a
suspicious lesion [5].

4. Apollo Medicine, Vol. 7, No. 3, September 2010 226
Technology Update
(c) Identify metastasis.
(d) Diagnose fatty liver.
(e) Grade fibrosis and help in early referral for liver
transplant.
(f) Help in target biopsies.
(g) Post liver transplant assessment.
(h) Follow up in alcoholic liver and hepatitis under
treatment.
(i) Follow up of post radiofrequency ablation cases.
Pancreas
ARFI is helpful in detecting adenocarcinomas and in
cystic lesions of pancreas (serous vs mucinous
cystadenomas).
Others
Various studied are underway for numerous other
applications of elastography viz.in acute appendicitis,
musculoskeletal pathology (shoulder, ankle, plantar
fascitis), assessing the severity of lymphedema or
evaluating the kidneys and spleen.
In conclusion, with the fast paced advancement in
technology and research and availability of accurate,
practical quantitative and /qualitative or (focal/regional)
elastographic assessments, ELASTOGRAPHY promises
to make an important contribution to ultrasound practice
by improving specificity. It is definitely a new
revolutionary method and shows potential as a reliable and
non invasive way to assess lesions.
REFERENCES
1. Liana Gheorghe, et al. Real Time Sonoelastography – A
New Application. Clinical Imaging 2008; 17.
2. Ultrasound Elastography Seminar LUT 2 University of
Kuopio, Finland (Joseph Jaros).
3. Roee S. Lazabnik. Tissue Strain Analytics, Virtual Touch
Tissue Imaging and Quantification. Siemens Medical
Solutions, USA.
4. Farzana Alam, Kumiho Naito, et al.
5. Barbara Dowell. Applications Ultrasound 2008; 16:123-
127.
6. Accuracy of Sonographic Elastography in the different
diagnosis of enlarged cervical lymphnodes.