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Elastography

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Elastography

  1. 1. ELASTICITY FOR ME
  2. 2. THEY SPOILED MY CHILDHOOD..
  3. 3. 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.
  4. 4. 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. 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. 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. 7. TYPE OF SOFT TISSUE YOUNG’S MODULUS –(E = s (in kPa) e) 18-24 28-66 FIBROUS TISSUE 96-244 CARCINOMA PROSTATE NORMAL FAT NORMAL GLANDULAR BREAST 22-560 NORMAL 55-71 BPH 36-41 CARCINOMA LIVER 96-241 NORMAL 0.4-6 CIRRHOSIS 15-100
  8. 8. HOW EXACTLY DOES THIS CRAP 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. 9. TYPES OF ELASTOGRAPHY  Elastography techniques are commonly classified according to the type of vibration applied to the tissue. There are three classes of Elastography :  Static  Dynamic and  Shear wave based
  10. 10. STATIC ELASTOGRAPHY  Static elastography uses a uniform compression at the surface of the body to cause deformation of the tissue.  The compression is applied by the user and the ultrasound scanner calculates and displays the induced deformation in the imaging plane.  Young’s modulus cannot be reconstructed as the stress within the tissues induced is unknown.
  11. 11. STRESS Static Elastography. Bmode (left) and elastogram (right). On the elastogram, less deformed tissue appears darker
  12. 12. DYNAMIC ELASTOGRAPHY  Dynamic elastography utilizes a continuous (monochromatic) vibration.  Stationary waves induced in the body are analyzed to deduce tissue elasticity.  Dynamic elastography is well suited for MR systems as the vibration pattern is not time dependent but must be assessed in a volume.  It is a quantitative approach but suffers from the usual MR drawbacks: high cost, limited availability, and lack of real time imaging.
  13. 13. Dynamic elastography images from MRI .Displacements @ 50Hz . Elasticity map (bottom right).
  14. 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 approach able to provide quantitative and local elastic information in real time
  15. 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. 16. A shear wave induced by an ultrasound beam focused in the center of the image
  17. 17. ADVANCES IN SHEAR WAVE IMAGING  SPATIALLY MODULATED ULTRASOUND RADIATION FORCE (SMURFS)  SUPERSONIC SHEAR WAVE IMAGING  AXIAL SHEAR STRAIN IMAGING
  18. 18. APPLICATIONS  Breast Imaging  Prostate Imaging  Thyroid Imaging  Liver Imaging  Treatment Monitoring  Intravascular Strain Imaging  Cardiac Elastography  Deep Vein Thrombosis  Kidney Transplant Monitoring
  19. 19. 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.
  20. 20. Heterogeneous echo texture , irregular shape and stiff color elastogram, which appears larger than the gray scale image. The color scale is a measure of stiffness. In these images, red indicates very stiff tissue, green/yellow indicates intermediate stiffness and blue indicates low stiffness IDC
  21. 21. Benign lesions demonstrating : homogenoeus oval shape and very soft elastogram, which also appears the same size on both gray-scale and shearwave elastography.. Clustered microcysts
  22. 22. FIBROADENOMA
  23. 23. 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
  24. 24. Large simple cyst which shows no elasticity within the lesion and hence black
  25. 25. COMPLICATED CYST- HOMOGENEOUSLY BLUE
  26. 26. 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
  27. 27. 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.
  28. 28. ADVANTAGE Oval circumscribed hypoechoic mass on gray-scale imaging, which has benign ultrasound features. However, elastography demonstrates a
  29. 29. 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 low 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
  30. 30. On compression elastography, hard tissue appears blue and soft tissue appears red to green.
  31. 31. 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.
  32. 32. 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
  33. 33. 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
  34. 34. Liver stiffness cut-offs in chronic liver diseases Matavir F0-F1 Fibrosis Mild F2 F3 Sign Severe F4 Cirrhosis LSM 2.5 – 7 kPa → Mild or absent fibrosis is likely LSM > 12.5 kPa → Cirrhosis is likely
  35. 35. MR elastography Conventional MR Wave images at 60 Hz MR elastography Shorter wavelength Normal: 1.7 kPa Longer wavelength Cirrhosis: 18.83 kPa .
  36. 36. LSM According to different etiologies of CLD
  37. 37. FOCAL LIVER LESIONS Hemangioma, elastic score (ES) =17.31kPa.
  38. 38. Malignant tumor, V= 3.73m/sec, elastic score = 41.76kPa.
  39. 39. LIMITATIONS OF US ELASTOGRAPHY OF LIVER  Uninterpretable results  Acute liver injury  Extrahepatic cholestasis  Increased CVP  Ascites  Narrow intercostal spaces
  40. 40. 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
  41. 41. 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.
  42. 42. Elastography image on left shows pattern 1, absent or small hard area. B-mode sonographic image on right shows score of 5, reactive. Final diagnosis from clinical and serologic findings was reactive lymph node.
  43. 43. 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. B-mode sonographic image on right shows score 7, metastatic
  44. 44. PROSTATE  TO DIAGNOSE PRIMARY  TO GUIDE FOR CORE BIOPSY  TO SEE EXTRA CAPSULAR EXTENSION
  45. 45. ROTATOR CUFF TEAR
  46. 46. BURSITIS
  47. 47. BAKER’S CYST
  48. 48. PITFALLS  LARGE LESIONS CAN BE UNDER ASSESSED WITH PORTIONS OF LESION LYING OUT OF THE VIEW  PAINFULL LESIONS MAYBE UNDER REPRESENTED BECAUSE OF INCREASED DISCOMFORT  TECHNICALLY CHALLENGING IN ORGANS LIKE SALIVARY GLANDS AND OBEESE PEOPLE. INSPITE OF THE FEW SHORT COMINGS, IT’S A BIG RADIOLOGICAL FIND OF THIS CEENTURY AS AN ADJUNCT TO THE OTHER MODALITIES

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