Elastography is a noninvasive imaging technique that uses ultrasound to image the elasticity or stiffness of tissues. It works by applying slight pressure and tracking how tissues deform. Stiffer tissues will deform less than softer tissues. There are different elastography techniques that vary by how tissue excitation is achieved and measured. Elastography provides objective quantification of tissue stiffness and has applications in imaging the breast, thyroid, prostate, liver and lymph nodes to help distinguish between benign and malignant lesions. It provides quantitative measurements of tissue elasticity in kilopascals and qualitative color maps of relative stiffness.

1. ELASTOGRAPHY

2. PHYSICS OF ELASTOGRAPHY
• Elastography is a noninvasive technique of
imaging stiffness or elasticity of tissues by
measuring movement or transformation of
tissue in response to a small applied
pressure.
• ‘VIRTUAL PALPATION’ which can
overcome the subjectivity flaw and provide
objective as well as quantitative measure of
tissue stiffness.

3. Going back to school days….
•Stress: It is defined as force per unit
area. Unit- Pascal.
•Stress can due to: Compression - which
acts Perpendicular to the surface and
causes shortening of an object
: Shear stress which
acts parallel to the surface and causes
deformation.

5. DEFINITIONS…..(cont…)
• Strain: When subjected to stress an object
tends to undergo deformation of its original
size and shape; the amount of deformation is
known as strain. Unit less - expressed as
change in length per unit length of the object.
• Elasticity: It is the property of the materials to
return back to its original form after stress is
removed

6. The Basics of Human Tissue Elasticity
• Tissue stiffness is generally measured by a
physical quantity called Young’s modulus and
expressed in pressure units - Pascals or kilo
Pascals (kPa).
• The Young’s modulus is defined simply as the
ratio between the applied stress and the
induced strain.
• Young’s modulus, or elasticity E, quantifies
tissue stiffness. Hard tissues have a higher
Young’s modulus than soft ones.

7. TYPE OF SOFT TISSUE YOUNG’S MODULUS –
E = s (in kPa)
e
BREAST NORMAL FAT 18 – 24
NORMAL
GLANDULAR
28 – 66
FIBROUS TISSUE 96 – 244
CARCINOMA 22 – 560
PROSTATE NORMAL 55 – 71
BPH 36 – 41
CARCINOMA 96 – 241
LIVER NORMAL 0.4 – 6

8. HOW EXACTLY DOES THIS WORK??
Three step methodology:
1. Generate a low frequency vibration in tissue to
induce shear stress
2. Image the tissue with the goal of analyzing the
resulting stress
3. Deduce from this analysis a parameter related to
tissue stiffness
• If the Young’s modulus, or elasticity of the tissue,
can be determined directly from the analysis, the
technique is considered quantitative.

9. TYPES OF ELASTOGRAPHY
•Elastography techniques vary
depending upon:
 Method used for tissue excitement
(either mechanical or ultrasonic force)
 By response of tissue to compression
i.e. Static, where single compression is
applied or Dynamic, where response to
rapid compressions or vibration is used.

10. COMPRESSION ELASTOGRAPHY
• Most widely used
• Evaluate elastic property of tissues by analyzing
radiofrequency pulses generated by a structure in
response to external compression
• Compression causes deformation of the tissue
that varies as a function of the elastic coefficient
expressed by Young’s modulus of elasticity
• RF waveform before and after compression are
windowed and the signals in the same segment
are compared to calculate the displacement.

11. LIMITATIONS
 Tissue strain dependent on the amount of
compression applied making it operator
dependent
 Qualitative imaging of relative stiffness, so actual
strain values cannot be compared with next
image
 Because it shows only changes in strain from
one area to other in same image, suitable for
detection and evaluation of small focal lesions
and not diffuse disease process that produces
same stiffness all over in one image

12. ACOUSTIC RADIATION FORCE IMPULSE
(ARFI)
• Short duration acoustic force k/a Pushing Pulses are used to
cause displacements.
• Pushing pulses can be applied by US transducer array that
are similar to power doppler except that they are much longer
in duration (200 cycles v/s 10 cycles)
• Ultrasound pulses track these displacements by locating
change in the peak along multiple tacking lines.
• Peak displacement, time taken to reach it & recovery time are
utilize to characterize tissue response.
• Tissue recoil also generate shear waves whose velocity can
be used to calculate Shear modulus for quantitative
measurement

13. ADVANTAGES
Images are more homogeneous and have better contrast
than compression elastography
Deeper tissue not accessible by superficial external
compression elastography, can be evaluated.
DISADVANTAGES
Physiological (respiration, pulsation) and transducer
motion can degrade image quality as 1 – 3 ms is required
per tracking line pair.
Tissues at a depth of more than 10 cm cannot be
assessed accurately due to attenuation of radiation force
at greater depths.

14. SHEAR WAVE ELASTOGRAPHY
• Shear wave based elastography makes
use of transient pulses to generate shear
waves in the body.
• The tissue’s elasticity is directly deduced by
measuring the speed of wave propagation.
• Shear wave based elastography is the only
approachable to provide quantitative and
local elastic information in real time

15. • Shear Wave Elastography uses the
acoustic radiation force induced by
ultrasound beams to perturb underlying
tissues. This pressure or “acoustic wind”
pushes the tissue in the direction of
propagation.
• An elastic medium such as human tissue
will react to this push by a restoring force.
This force induces mechanical waves and,
more importantly, shear waves which
propagate transversely in the tissue.

16. • Shear waves propagate perpendicular to the
axial displacement caused by ultrasound
pulse and attenuate 10,000 times more
rapidly then compression waves
• This high attenuation enables induction of
oscillations within a very limited area of
tissue
• Shear wave is created and tracked by
parallel tracking method
• Velocity of shear waves V (in cm/s) is
measured
• Young’s modulus is calculated by E = 3V2

17. ADVANTAGES
 More objective measurement (due to lack of
compression)
 Direct measurement of elasticity
 Quantitative measurement
DISADVANTAGES
 Assessment of superficial structure is difficult
as certain depth of ultrasound penetration is
needed for shear waves to be produced

18.  On the grey scale elastogram, less deformed
tissue appears darker
 On the color elastogram, the color scale is a
measure of stiffness.
 RED indicates very stiff tissue
 GREEN / YELLOW indicates intermediate
stiffness and
 BLUE indicates low stiffness
SHEAR WAVE ELASTOGRAM

19. ADVANCES IN SHEAR WAVE
IMAGING
• SPATIALLY MODULATED ULTRASOUND
RADIATION FORCE (SMURF)
• SUPERSONIC SHEAR WAVE IMAGING
• AXIAL SHEAR STRAIN IMAGING

20. APPLICATIONS
• Breast Imaging
• Prostate Imaging
• Thyroid Imaging
• Liver Imaging
• Treatment Monitoring
• Intravascular Strain Imaging
• Cardiac Elastography
• Deep Vein Thrombosis
• Kidney Transplant Monitoring

21. OTHER TYPES OF IMAGING
• HARMONIC – MOTION IMAGING : Oscillations produced by low
frequency (10-300 Hz) US are measured at centre. One large
aperture transducer generate radiation and a small phased array
transducer placed through a hole in larger transducer detects
motion. Used in high intensity focused ultrasound (HIFU) therapy
where larger transducer is also used for thermal lesions.
• SHEAR – DISPERSION ULTRASOUND VIBROMETERY: Multiple
pushing waves are transmitted at a particular frequency and
motion stimulated by harmonic frequency is detected by
ultrasound. It measures visco-elastic properties of tissue.
• MECHANICAL IMAGING: Stress patterns of internal structures of
tissue are measured by ultrasound probe which detects temporal
and spatial changes giving information about viscosity and porosity
of tissue. Used to diff. malig. from benign.

22. BREAST IMAGING
• Compared to gray-scale ultrasound,
malignant lesions tend to be larger and
more irregular on elastography likely
secondary to stiff peripheral desmoplastic
reaction.
• When measuring lesion size on
elastography, the lesion should be
measured in the exact position on both the
elastogram and B-mode image.

23. IDC: Heterogeneous echo texture, irregular shape and stiff
color elastogram, which appears larger than the gray scale
image.

24. Benign lesions demonstrating : homogenoeus oval shape and very
soft elastogram, which also appears the same size on both gray-
scale and shear-wave elastography.. Clustered microcysts

25. FIBROADENOMA

26. COMPLEX CYST v/s SOLID LESIONS
• Elastography has the potential to
differentiate complicated cysts form solid
masses.
• Shear-wave propagation does not occur in
cysts and therefore cysts should have
elastography values of zero and will appear
mostly black or homogeneously blue on the
color overlay elastogram

27. Large simple cyst which shows no elasticity within the
lesion and hence black

28. COMPLICATED CYST- HOMOGENEOUSLY BLUE

29. A bull’s eye artifact has also been described as a characteristic
feature present in benign breast cysts, where central fluid may
appear bright with a surrounding dark ring

30. PROBLEM SOLVING
• Elastography has the potential to downgrade BI-
RADS 4a lesions to BI-RADS 3, using qualitative
shear-wave elastography and color assessment of
lesion stiffness, oval shape and a maximum
elasticity value of less than 80 kPa without a
significant loss in sensitivity.
• Elastography may also be used to identify oval
circumscribed cancers detected on ultrasound and
may be used to upgrade a BI-RADS 3 lesion to BI-
RADS 4.
• Furthermore, elastography feature analysis also
has the potential to downgrade BI-RADS 3 lesion to
BI-RADS 2 lesions.

31. ADVANTAGE
Oval circumscribed hypoechoic mass on gray-scale imaging shows
benign ultrasound features. However, elastography demonstrates a
heterogeneous, large and stiff elastogram.

32. QUANTITATIVE ASSESMENT
• Lesion stiffness can also be measured quantitatively
with shear wave elastography.
• Stiffness of malignant lesions is generally greater
than 80–100 kPa), while fat has relatively lower
elasticity values near 7 kPa and breast parenchyma
have elasticity values ranging from 30-50 kPa.
• However, one must be careful when using kPa in
lesion evaluation, as some soft cancers may have
low kPA values between 20-80 kPa, similar to
benign lesions

33. On compression elastography, hard tissue appears blue
and soft tissue appears red to green.

34. THE DOWNFALL….
• Some cancers lack a significant
desmoplastic reaction and may be soft,
resulting in a false negative elastogram.
• With shear-wave elastography, some
cancers may have a mean stiffness of less
than 50 kPa .
• Similarly, some benign lesions may appear
stiff including hyalinized fibroadenomas, fat
necrosis and fibrosis.

35. A heterogeneous mass with indistinct margins on grayscale ultrasound
appears stiff, heterogeneous, large and suspicious on shearwave
elstography.
Biopsy demonstrated benign breast tissue with stromal fibrosis

36. LIVER STIFFNESS
• Assessed by US & more recently by MRI
• Evaluates velocity of propagation of a shock wave
within liver tissue (examines a physical parameter of
liver tissue which is related to its elasticity)
• Rationale : Normal liver is viscous
Not favorable to wave propagation
Fibrosis increases hardness of tissue
Favors more rapid propagation

37. Liver stiffness cut-offs in chronic liver diseases
Stage 1: PORTAL FIBROSIS – Fibrosis around portal triads
but limited to these areas
Stage 2: PERIPORTAL FIBROSIS – Fibrosis extends to
periportal space but do not connect with other portal triads
Stage 3: SEPTAL FIBROSIS – Fibrous connective tissues links
neighbouring portal triads and begins to extend to central veins
Stage 4: CIRRHOSIS – Most portal triads are connected with
fibrous tissue. Some portal triads and central veins are also
connected

38. LSM According to different etiologies of CLD

39. FOCAL LIVER LESIONS
Hemangioma, elastic score (ES) =17.31 kPa

40. Malignant tumor, V= 3.73m/sec, elastic score = 41.76 kPa

41. LIMITATIONS OF US ELASTOGRAPHY
OF LIVER
 Uninterpretable results
 Acute liver injury
 Extrahepatic cholestasis
 Ascites
 Narrow intercostal spaces

42. OTHER APPLICATIONS IN LIVER
• Decreased stiffness post anti-viral
treatment and increased stiffness in
relapse.
• Splenic stiffness > 9kPa correlates with
portal hypertension.
• To d/d between HCV and non HCV
infections in liver transplant recipients.
• Biopsy site from the stiffest region.
• Much larger liver volume assessed then
biopsy

43. LYMPH NODES
•Mainly to d/d between benign and
malignant nodes esp. in axillary and
cervical nodes.
•Score of metastatic nodes in axilla are
> 3.5
•Scores of metastatic nodes in neck > 2
•Sensitivity of > 85 % but less
specificity.

45. Elastography image on left shows pattern 1, absent or
small hard area. Final diagnosis from clinical and
serologic findings was reactive lymph node.

46. Longitudinal sonogram of level 5 lymph node in 52-
year-old man with nasopharyngeal carcinoma.
Elastography image on left shows pattern 4, peripheral
hard and central soft areas , metastatic.

47. OTHER USES
PROSTATE
•To diagnose primary
•To guide for core biopsy
•To see extra capsular extension

48. THYROID
•To differentiate benign v/s malignant
nodules
•Pitfalls:
 Shape of neck with sloping contour
cause lateral shift
 Pulsation from adjoining carotid
artery interfere

49. GYNECOLOGY
•To monitor cervical ripening
•Cervical cancer
•Fibroids
•Fibroids (blue) v/s Adenomyosis
(green with red core)

50. MUSCULOSKELETAL
• Compression ultrasonography is most
commonly used.
• To diff b/w rheumatoid nodule & tophi
• To diff. b/w synovitis d/t Rh. Arthritis from that
d/t Infection (e.g. TB)
• Soft tissue masses: Lipoma and low flow VM-
soft; Dermoid neurogenic tumors, sebaceous
cyst-stiff
• Myofascial pain: To identify active trigger point
• Hyaline cartilage: To evaluate prior to
arthroscopy and in monitoring treatment

51. RENAL TRANSPLANT
• To find patient who really needs biopsy.
SKIN & SOFT TISSUE
• To find out failure of therapy to abscess and
its progression to more invasive infection

52. CARDIOVASCULAR APPLICATIONS
• Myocardial evaluation: Areas of ischemia,
infarction and scarring
• Arterial elasticity evaluation: Detection of
vulnerable plaque and estimation of arterial
wall compliance
• Venous thrombosis: to gauge the age of
thrombus

53. CONCLUSION
There are many shortcomings like-
• Large lesions can be under assessed with portions
of lesion lying out of the view
• Painful lesions maybe under represented because
of increased discomfort
• Technically challenging in organs like salivary glands
and obese people.
Inspite of the few short comings, it’s a big
radiological find of this century as an ADJUNCT
to the other modalities