presentation on ultrasound elastography-introduction ,techniques,physics,application, interpretation and future prospects.sourced from multiple articles.

1. BY-
DR.SAHIL CHAUDHRY
MODERATOR-
DR.BHARATH SHETTY
AJIMS MANGALORE

2. OUTLINE
• Introduction
• Physics
• Techniques of Elastography and interpretations.
• Clinical Applications
• Conclusion

3. ELASTOGRAPHY
‘PALPATION IMAGING’
• Ultrasonographic elastography (sonoelastography)-
Noninvasive imaging technique used to depict relative
tissue stiffness or displacement (strain) in response to
imparted force.
• Stiff tissues deform less and exhibit less strain than
compliant tissues in response to the same applied
force.Thus, the basis of elastography is analogous to
manual palpation

4. • Like palpation, elastography
aims to characterise tissue
stiffness.
.The application of US elastography for imaging tissues first described in
1987 by Krouskop et al. Since its inception, sonoelastography is used to
evaluate numerous types of tissues, including breast, prostate, liver,
blood vessels, thyroid, and musculoskeletal structures.

5. Aim of elastography
• The aim of elastography is to assess tissue stiffness based on 3
steps:
1. Excitation: transmission of stress in a tissue (mechanical, vibrational,
shear).
2. Acquisition: recording the signal induced by the tissue deformation
due to the stress .
3. Analysis/post-treatment: analysis of tissue strain induced by the
propagation of the stress.

6. PHYSICS
• 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.

7. • On applying a time-varying force to a tissue,
two types of mechanical waves are
propagated –
 Compression waves
 Shear waves

8. Compression Wave
Shear Wave

9. COMPRESSION WAVES SHEAR WAVES
Parallel to the medium displacement Perpendicular to the medium displacement
High velocity (∼ 1500 m/s) Low velocity (∼ 1-50 m/s)
High frequency Low frequency (10 Hz to 2000 Hz)
Depend on Bulk Modulus Depend on Shear Modulus
Used in Ultrasound imaging Used in Shear Wave Elastography

10. PHYSICS
Elasticity
• Tissue stiffness is generally measured by a physical quantity
calledYoung’s modulus and expressed in pressure units - Pascals
or kilo Pascals (kPa).
• TheYoung’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 higherYoung’s modulus than soft ones.

11. • Stress = F/A
• Strain = DL/L0
• E = Stress/Strain
•The harder the tissue, the lesser will
be the strain for a given force.

12. • Advantages of measuringYoung’s modulus –
 Better characterization of tissues.
 Quantitative reproduction of clinician’s
palpation.

13. Typical values of elasticity in different tissues.

14. • Elasticity (E) and shear wave propagation speed (c) are
linked through the formula:
E = 3ρc²
(ρ = density of tissue in kg/m3 ∼ 1000 kg/m3)
• Hence, if the shear wave propagation velocity (c) can
be measured, the elasticity of the tissue can be
determined.

15. TECHNIQUES OF
ELASTOGRAPHY
• Based on type of force applied –
 Quasi-static Elastography
 Dynamic Elastography

16. Type of Force Method
Quasi-Static Strain Elastography
Dynamic ARFI (Acoustic Radiation Forced
Impulse) Imaging
Transient Elastography
Shear Wave Elastography

17. Static Elastography
• First elastography technique, developed by the
Ophir Group at the beginning of the 1990s.
• Uses a uniform compression at the surface of the
body to cause deformation of the tissue.
• Compression is applied by the user and the
ultrasound scanner calculates and displays the
induced deformation.

18. STRAIN ELASTOGRAPHY
Applied Force Mechanical –
a) Active external displacement of tissue surface.
b) Passive internal physiologically induced.
Property displayed Strain (‘ELASTOGRAM’)
Measurement Qualitative
Imaging Full area image; colour image superimposed on a
standard B-mode image
Commercial Siemens (eSieTouch)
Hitachi (Real-timeTissue Elastography”.)

19. STRAIN ELASTOGRAPHY
 Strain Elastography reconstructs a ‘Strain Map’ by
calculating the deformations caused by a static compression
imposed by the operator via the ultrasound array.

20. • eSieTouch

21. STRAIN ELASTOGRAPHY
Advantages - First elastography technique developed; most widely used
and validated.
- Does not require a complex software.
Limitations -Operator dependent.
- Absence of a specific quantification.
- Limited to superficial organs; i.e. breast, thyroid.

22. DYNAMIC ELASTOGRAPHY
1. Transient Elastography
2. Acoustic Radiation Force ImagingTechnique
3. Supersonic ShearWave Elastography

23. Acoustic Radiation Force Imaging
• It uses a focused ultrasound pulse.
• It provides an estimate of the stiffness of deep tissues,
non-accessible by external compression.
• After identification of the area of interest by USG imaging,
a focused ultrasonic wave is applied.
• This wave leads to tissue displacement & a shear wave.
• The velocity of the shear wave is measured and expressed
in m/s.

25.  Radiation force slightly displaces the tissue at the
focal spot according to Hooke’s law.
 Displacement profile estimated by tracking of the
ultrasound signal (called speckle)
Temporal properties of the displacement profile give
information about the stiffness of the medium.

26. ARFI Imaging
Applied Force Ultrasound induced focused radiation force
impulse at depth
Property
displayed
Displacement
Measurement Qualitative
Imaging Single image in a box
Commercial Siemens

27. Advantages - Less user-dependent.
- Better resolution than SE.
- Better transfer of shear modulus contrast to image
contrast.
Limitations - Absence of a specific quantification.
-Transducer heating limits the frame rate.
- Displacement profile depends on the elasticity of the
medium, but also on many other parameters, such as
geometries of the beam & of the medium.
ARFI IMAGING

28. Transient Elastography
• Probe (3.5 MHz) contains a vibrator and an ultrasound transducer.
• Not imaging guided system -probe is positioned randomly on skin
• Measures are done at a depth between 25 and 65 mm.
• Exam takes 5-10 minutes- consists of 10 measures at same location.
• Principle- mechanical pulse induced at skin surface by an external
vibrator generates a transient shear wave (pulse) that propagates
longitudinally.
• Velocity & amplitude of shear wave are measured in ROI.
• velocityV is converted into kPa, and reflects the tissue stiffness.
• It can also compute wave attenuation in decibels per meter dB / m.

30. TRANSIENT ELASTOGRAPHY
Applied Force Mechanically induced – impulse at tissue surface
Property
displayed
Shear wave speed
Measurement Quantitative
Imaging Single measurement; beam-line average
Commercial Echosens (FibroScan)

31. FIBROSCAN

32. TRANSIENT ELASTOGRAPHY
Advantages - Easy to use.
- Quantification of tissue elasticity.
- Rapid, painless.
- Good reproducibility.
Limitations - Difficult in obese patients & in ascites.
- Lacks 2D image guidance of the measurement.
- Left side of the liver cannot be examined.

34. Ultra-fast shear wave elastography
• This is the technique developed by Supersonic Imaging also based
on transient elastography ultrasound pulse.
• However they allow the generation of multiple shear wave along a
same longitudinal axis (through a compression wave) leading to
the propagation of a plane shear wave.
• This technique also allows the measurement of the velocity of this
plane in each point of the image in real time
• Thus providing a 2D quantitative measure of elasticity E in real
time, usually expressed by a parametric map in kPa

37. SHEARWAVE ELASTOGRAPHY
Applied Force Ultrasound induced - radiation force swept over depth
faster than shear-wave speed to create a Mach cone
Property displayed Shear wave speed
Measurement Quantitative
Imaging Image within a color box; refreshed at up to several per
second (5000 images per second).
Commercial SuperSonic Imagine

38. Advantages - Displayed in real time, like a conventional ultrasound
image.
- Good reproducibility.
- Quantitative value of stiffness.
-Very short acquisition time (∼30 ms).
Limitations - Expensive.
- Requires a complex software.
SHEARWAVE ELASTOGRAPHY

39. ELASTOGRAPHYTECHNIQUES
STRAIN ARFI TRANSIENT SWE
Applied Force Mech Ultra Mech Ultra
(Mach Cone)
Property Strain Strain Shear wave
speed
Shear wave
speed
Measurement Quali Quali Quanti Quanti
Commercial Siemens
(eSieTouch)
Siemens
(VTI)
Echosens
(Fibroscan)
SuperSonic
(Aixplorer)

40. CLINICAL APPLICATIONS

41. APPLICATIONS
• Breast Imaging
• Prostate Imaging
• Thyroid Imaging
• Liver Imaging
• Intravascular Strain Imaging
• Cardiac Elastography
• DeepVeinThrombosis
• KidneyTransplant Monitoring

42. BREAST
• TECHNIQUE
 Pressure applied on the probe should be as low as
possible.
 Locate B-mode image in centre before activating the
elastography mode.
 Surround the lesion with adjacent normal tissue.
 Avoid non-perpendicular angulated scanning.

43. • APPLICATIONS IN BREAST
 Characterization of Benign/Malignant solid lesions.
 Characterization of micro-calcification clusters.
 Elastography of lymph nodes.
 Monitoring treatment response to neo- adjuvant
chemotherapy in Ca Breast patients.

44. Characterization of Benign/Malignant solid lesions.
- Can improve specificity of BIRADS score.
- Reclassify BIRADS 3 & 4a lesions.
- Useful for malignant lesions presenting as benign
on B-mode.

45. • Most important elastographic characteristics in evaluating breast lesions -
size and stiffness criteria.
• Size criterion: Difference in the measurement of the longest diameter on
the corresponding B-mode image and the elastogram.
• Structures that are less compressible than surrounding tissues measure
larger on the elastogram than they do on the corresponding B-mode
image.Therefore, cancers will be larger on the elastogram than on the
conventional US image.
• This phenomenon is attributed to the incited by
many malignant breast neoplasms.

46. Normal BreastTissue
• Biomechanical testing has shown normal fibro-glandular
breast tissue to be markedly stiffer than normal fatty
breast tissue by as much as two orders of magnitude.
Therefore, at elastography, fatty tissue will appear bright
with respect to the adjacent glandular tissue, and normal
fibrous parenchyma appears darker.

47. • Normal breast tissue. (a) B-mode US image of the breast shows that a lobule
of normal fatty tissue (f) is hypoechoic with respect to the surrounding
glandular tissue (g). (b) US elastogram shows that the fatty tissue (f)
surrounded by dense breast tissue appears bright because it is appreciably
“softer” than the surrounding glandular tissue.

49. Features on Strain Elastography
Benign Malignant
Softer Harder
Brighter on strain image Darker on strain image
Color red/green (soft) (vendor specific) Color blue (hard) (vendor specific)
Tumor diameter<B-mode diameter Tumor diameter>B-mode diameter

50. Tsukuba Scoring
-Semi- quantitative
- Risk of malignancy
increases from 1 to 5.
STRAIN ELASTOGRAPHY

51. • Category 1
• lesions demonstrate a uniform
pattern of high strain, marked by an
evenly distributed green color
throughout the lesion.
• Ex.- LIPOMA

52. • Category 2
• lesions show a heterogeneous but
mostly green color signature,
indicating a predominantly high
strain pattern of the lesion.
• Ex. FIBROADENOMAS

53. Category3
• lesions show a pattern of high peripheral strain with
central low strain pattern, and they produce a small
central blue area that is surrounded by a green
peripheral color.
Ex. -FIBROADENOMA

54. • Category 4
• lesions produce a low strain pattern and a
uniformly blue color signature confined to
the visible margin of the lesion
• Ex.- Lobular carcinoma

55. • Category 5
• lesions show a similar blue signature
that extends beyond the lesion into
the adjacent tissues
• Ex.- invasive ductal carcinoma

56. SWE

57. False Positive False Negative
Old/ Calcified / large fibro adenoma Mucinous Ca
Breast Implants Inflammatory Ca
Medullary / Papillary Ca
Cystic Ca
Deep lesions (>4-5 cm)

60. Elastography of lymph nodes.
- Normal lymph nodes are reniform in shape and
contain a hyperechoic fatty hilum on B-mode US
images.At elastography, these features translate
into relative softness of the lymph node, with a
slightly lower elastogram-to-B-mode size ratio .
- Lymph node that contain metastases tend to
appear stiffer and disproportionately larger at
elastography

61.  Monitoring treatment response to
neoadjuvant chemotherapy in Ca Breast
patients.
- Changes in stiffness during treatment could be
a potential marker for response.
- Elasticity heterogeneity is lost in responders.

63. BULL’S EYE ARTIFACT

67. FIBROADENOMA

69. LIVER
• TECHNIQUE
 Patient must be lying in a dorsal decubitus
position, with the right arm in maximal abduction.

70. • Measurements are taken in the right lobe of the
liver through an inter-costal space.
• The SWE box must be placed at least 2 cm away
from Glisson’s capsule, away from the vessels.
• Breath hold for at least 4 seconds to allow filling
of SWE box but, no deep inspiration before
breath hold. (No breath hold for FibroScan)

72. • APPLICATIONS IN LIVER
 Assessment of fibrosis.
 Prediction of cirrhosis-linked complications.
 Assessment of response to Anti-viral treatment.
 Characterization of LiverTumors.

73. LIVER STIFFNESS
• 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

74. Liver Fibrosis
METAVIR SCORE HISTOLOGY
F0 No Fibrosis
F1 Portal fibrosis without septa; minimal fibrosis
F2 Portal fibrosis with a few septa; moderate fibrosis
F3 Septal fibrosis with many septae but no cirrhosis; severe fibrosis
F4 Cirrhosis

76. Cut-off values vary depending on etiology and among
different studies.
 Cut-off values for FibroScan (kPa)
Study ≥ F2 ≥ F3 ≥ F4
Ziol et al 8.8 9.6 14.6
Kim et al 6.2 - 11
Nitta et al 7.1 9.6 11.6

77.  Cut-off values for ARFI (m/s)
Study ≥ F2 ≥ F3 ≥ F4
Takahashi et al 1.35 1.55 1.77
Lupsor et al 1.34 1.61 2
Sporea et al 1.34 1.55 1.8

78. • Various stages of liver fibrosis on
SWE.

79.  Prediction of cirrhosis-linked complications.
– Correlation between FibroScan values &
development of esophageal varices.
– Higher elasticity values predict a higher risk for HCC.
Assessment of response to Anti-viral
treatment.
- Liver elasticity values fall in parallel with response.

80.  Characterization of LiverTumors.
- Among benign tumors, hepatic adenoma has
greatest stiffness.
- Hemangioma – less shear stiffness than fibrotic
liver.
- Cholangiocarcinoma - most stiff.
- HCC less stiffer than cholangiocarcinoma.

82. 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

83. LIMITATIONS OF US
ELASTOGRAPHY OF LIVER
 Obesity
 Acute liver injury
 Extrahepatic cholestasis
 Increase CVP
 Ascites
 Narrow intercostal spaces

84. Thyroid
• Performed with a superficial linear probe, during the conventional
examination.
• Main indication of elastography in thyroid disease is the nodule
characterization, in addition to B-mode which it does not replace.
• Thyroid cancers behave differently according to histology:
• Papillary cancer is hard;
• Follicular cancers do not increase stiffness.
• The presence of calcification can cause false positives.
• Metastatic LNs have a higher stiffness.

85. • INTERPRETATION
 Strain Elastography –Visual comparison of
differences in color – Rago/Asteria Scoring.
 ShearWave Elastography –
- Cut-off values beyond which cancer should be
suspected.
STIFFNESS 50 kPa

89. PROSTATE
• TECHNIQUE
 No specific preparation required.
 Conducted after complete, high qualityTRUS
examination in the transverse & sagittal planes.
 Quasi-static elastography requires slight
compressions & decompressions, which are induced
by transrectal probe.

90. • INTERPRETATION
 Normal prostate – Homogenous appearance
with elasticity values below 30 kPa.
 BPH – Central & transition zones become
heterogeneous & hard, with increased values of
elasticity.
 Carcinoma – Peripheral zone cancer nodules
with elasticity values >35 kPa.

91. Prostate adenocarcinoma with Gleason score of 6/10. (a) Sagittal endorectal US image with the
prostate gland outlined shows no discrete lesion (arrow). (b) Sagittal US elastogram shows strong
vibration in the normal prostate tissue and also an area of no vibration (arrow) anteriorly from the
midportion of the gland to the base.(c) Photomicrograph (hematoxylineosin stain) of a transverse
histologic section that included the corresponding lesion (arrow) at the base shows good correlation,
with the deficit noted anteriorly on the elastogram through the selected plane of section (dashed line
in a and b) in the midportion of the gland.The smaller lesion outlined in blue in c is outside the plane of
the elastogram.

92. Benign Prostatic Hyperplasia
• Endorectal US - heterogeneous hypoechoic area or areas in the transitional
zone.
• Foci of benign prostatic hyperplasia have elastic moduli (stiffness) that are
an order of magnitude greater than those of normal prostate tissues but
are less than those of prostate carcinomas.
• On elastograms, benign prostatic hyperplasia will appear darker than
normal prostate tissue.
• However, the difference between benign prostatic hyperplasia and
prostate carcinoma can be difficult to discern because benign prostatic
hyperplasia also appears darker than the background tissues.

93. Benign prostatic hyperplasia. (a)Transverse B-mode US image demonstrates a mildly prominent
isoechoic area (arrow) in the central zone of the prostate gland. (b) Corresponding transverse
elastogram shows that the area of benign prostatic hyperplasia (arrow) is more conspicuous.The
lesion demonstrates greater stiffness than the surrounding normal prostate
tissue. (c) Photomicrograph (hematoxylineosin stain) shows that there is good correlation
between the extent of the lesion (arrow) on the histologic section and the lesion extent on the
elastogram.

94. • The best stiffness cut-off value to differentiate benign from
malignant lesions was found to be 35 and 37 kPa in two
independent studies.
• The shear wave elasticity ratio between the nodule and the
adjacent peripheral gland tissue for benign and malignant
lesions were 1.5 ± 0.9 and 4.0 ± 1.9 (p < 0,002), respectively

95. Value of Elastrography for Staging Prostrate
Cancer :
Allows excellent visualization of prostatic
capsule as soft rim artefact.

98. • APPLICATIONS
 Characterization of abnormal regions
detected by B-mode imaging or Doppler.
 Detection of lesions not seen with any
other imaging.
Targeting of biopsies.

99. RENAL APPLICATIONS
• Assessment of renal fibrosis
- Native kidneys
- Evaluation of transplants
• Characterization of renal tumors.

101. TESTICULAR DISEASES
• Ideal tissue to be explored by elastography.
• Normal testis – Homogenous, medium level of
elasticity.
• Improves discovery of testicular nodules.
• Ability to distinguish between testicular lesions
& inflammatory changes based on elasticity.

103. ENDOSCOPIC ELASTOGRAPHY
• No special probe required
• Use in hepatobiliary, pancreatic masses
• Also to d/f malignant from benign lymph
nodes.
• Limitations :
- inability to control compression.
- adjacent aorta, spine, vessels.
- difficult to d/f pancreatic tumour from
chronic pancreatitis.

106. PREGNANT CERVIX
• Assess the biomechanical properties of cervix.
• Applied to transvaginal ultrasound probe.
• ‘Elastography Index’ – Larger strain in internal os
correlates with successful induction.
• No correlation with Bishop score nor cervical length.
• Might help identifying women who will have
successful induction of labor.

107. MUSCULOSKELETAL
APPLICATIONS
• Achilles tendinopathy –The asymptomatic Achilles
tendons are usually hard (86-93%) or may contain
small areas of mild softening. Distinct softening is
found in 50% of tendons with Achilles tendinopathy.
• Grade 1 ,blue (hardest tissue) to green (hard tissue);
• Grade 2, yellow (soft tissue);
• Grade 3, red (softest tissue).

108. Achilles tendinopathy

109. RODENT ULCER
CUTANEOUS MALIGNANCIES

110. USG Elastography for muscles:
• Normal relaxed muscle appears as an inhomogeneous
mosaic of intermediate or increased stiffness with scattered
softer areas especially at the periphery or near boundaries.
• In inflammatory myopathies USE can show changes in
muscle elasticity in correlation with elevated serum
markers(increased stiffness due to fibrosis or as reduced
stiffness, secondary to fatty infiltration)

112. PICTURESARECOPYRIGHT PROTECTED

128. NEW APPROACHES
POROELASTOGRAPHY
– Evaluates Fluid Movement in the Interstitium
OverTime Using Poisson’s Ratio Images
AXIAL SHEAR STRAIN ELASTOGRAPHY
–Visually Displays the Shear Strain at a Lesion
Boundary
– Estimates the Degree toWhich a Mass is Bonded
to the SurroundingTissue

130. CONCLUSION
• Elastography – A new modality of ultrasound imaging.
• Characterizes tissue stiffness.
• Types – Quasi-static & Dynamic.
• Complementary to B-mode imaging.
• Well established diagnostic role in breast & liver
pathologies.
• Vast scope in future.

131. REFERRENCES