Magnetic Resonance Elastography

1. MR Elastography
DR MANOJ K S MD RD DNB RD
SENIOR CONSULTANT
Dept. of IMAGING SCIENCES & IR
KIMS HEALTH
Trivandrum, Kerala

2. Akkulam Lake ,Trivandrum
Sincere Thanks to Dr Rijo Mathew , IRIA Kerala,

3. The Story

4. Part I : NCD in Kerala

6. The NAFLD prevalence within this population was 49.8%
which is significantly higher than the global pooled
prevalence of 25%. This highlights the importance of
robust, prospective studies like this to enable collection of
longitudinal data on risk factors, disease progression and to
facilitate future interventional studies.

8. Part II: Mayo Clinic
Rochester ,USA

9. In 2006, Mayo Clinic researchers developed a new imaging technology for accurately measuring the
stiffness or elasticity of the liver with the goal of providing a reliable, painless and less expensive
alternative to a liver biopsy for diagnosing a common abnormality. The technique is called magnetic
resonance elastography (MRE).
In 2007, MRE was adopted into the clinical practice at Mayo Clinic, with patients at all three national
campuses benefitting from the new technology. By 2009, it was introduced as an FDA-cleared product
for patients everywhere by Resoundant Inc., a Mayo Clinic-owned company.
Dr Richard L Ehman .MD ,Mayo Clnic

19. The Technology

20. MRE Definition
MRE is MRI Based measurement of Liver stiffness
Elastography is an imaging technique used to evaluate the
mechanical properties of tissue according to the propagation
of mechanical waves.
Magnetic resonance elastography (MRE) measures stiffness
of the liver by analyzing the propagation of shear waves
through the liver .
MRE is currently regarded as the most accurate non-invasive
diagnostic tool for detection and staging of liver fibrosis

21. Liver parenchymal stiffness is dependent on tissue
composition, organization of the components, vascular
component and interstitial pressure, and the pathological
conditions affecting these factors.
In patients with CLD, destruction of normal hepatic
parenchyma, progressive accumulation, and decreased
remodeling of excessive extracellular matrix (ECM) and
distortion of the parenchymal architecture lead to increased
liver stiffness.
Inflammation, biliary obstruction and cholestasis, passive
congestion, and increased portal venous pressure may also
contribute to increased liver stiffness

22. Active Driver
FDA Cleared : GE 2009 Siemens 2012 Philips 2014

27. In a typical liver MR elastography configuration, an active
pneumatic mechanical wave driver is located outside the
MR elastography room is connected, by way of a flexible
25-ft (7.62-m) polyvinyl chloride tube, to a passive driver
that is fastened onto the abdominal wall over the liver.
The passive driver generates a continuous acoustic
vibration that is transmitted through the entire abdomen,
including the liver,at a fixed frequency, which is typically
60 Hz

28. A phase-contrast pulse sequence with motion encoding
gradients is synchronized to the frequency of mechanical
waves created by the passive driver.
This sequence is then used to image the micron-level cyclic
displacements caused by the propagating shear waves to
create a magnitude image, which provides anatomic
information, and a phase image, which provides wave
motion information

29. After the magnitude and phase images are created, an
inversion algorithm installed in the MRI unit automatically
processes these raw data images to create several additional
images and maps.
The most common output images generated by MRI units from
three major vendors are a color wave image depicting the
propagation of shear waves through the abdomen, a gray-
scale elastogram without a superimposed 95% confidence
map, a gray-scale elastogram with a superimposed 95%
confidence map, a color elastogram without a
superimposed 95% confidence map, and a color elastogram
with a superimposed 95% confidence map

31. The confidence map is a statistical derivation used to
overlay a “checkerboard” on the stiffness map to exclude
regions in the liver that have less reliable (ie, noisy and
discontinuous) stiffness data, so that a high-quality LSM can
be obtained
An inversion algorithm installed in the scanner automatically
processes the information in the magnitude and phase
images and produces gray scale and colored stiffness
maps. The stiffness maps are also known as elastograms

33. Reader can then draw region of interest (ROI) within the confidence
map over the liver, avoiding liver edge, artifacts, fissures, fossa,
and regions of wave interference, to obtain a reliable LSM.
Depending on the vendor specifications, the LSM measurements
can be made either on the gray-scale images or the colored
stiffness maps.
The mechanical property measured with MRE is the magnitude of
the complex shear modulus expressed in kilopascals (kPa). This
mechanical property represents both elasticity and viscosity of the
tissue.
A mean LSM value from the ROIs drawn on the 4 obtained slices is
reported for clinical purposes.

35. The Technique

37. Patient Preparation
Patients should be fasting for 4–6 hours before the MR
elastography examination
The liver stiffness in healthy subjects does not change
significantly with food intake.
However, in persons with chronic liver disease, liver stiffness
may increase for a short time after a meal.

38. Passive Driver Placement
The passive driver should be placed over the right hepatic
lobe, which is usually the largest portion of the liver, as an
LSM obtained from a larger volume of tissue is the most
representative of liver stiffness.
To localize the right lobe, in most patients, the xiphoid
process of the sternum is used for the superior-inferior
position, and the right midclavicular line is used for the right-
left position .

41. Typical parameters used to perform MR
elastography on a 1.5-T MRI system are as follows:
Section thickness : 8–10 mm
Intersection gap : 2–5 mm
Number of sections: Four
Repetition time msec/echo time (TE) msec, 50/18 per
section
Flip angle L 30Åã Bandwidth, 31.25 Hz

46. Section Positioning
In a typical MR elastography examination, four
elastograms are obtained, and each should include
the largest portion of the liver, avoiding the liver
dome and inferior portion of the liver
Images obtained too high over the liver dome can yield
falsely elevated liver stiffness values owing to oblique waves
propagating through the liver while images obtained too
low can create chaotic waves resulting in inaccurate or
nondiagnostic liver stiffness values.

48. Pulse sequence timing. Diagram shows the timeline for performing an
abdominal MRI examination, including MR elastography and liver fat
and liver iron quantification

49. MR elastography section positioning. Top: Coronal T2-weighted MR image shows
the sites (four lines) where the four MR elastography magnitude image sections at
the bottom were obtained. Bottom: Magnitude image sections include the largest
portion of the liver, with the liver dome and inferior aspect of the liver excluded.

50. Passive Driver Frequency
in routine clinical practice, the frequency is generally set at
60 Hz and should not be changed.
This is because most of the LSM references and thresholds
for staging liver fibrosis cited in the literature are based on
imaging at 60 Hz

51. Liver Stiffness
In patients with CLD, destruction of normal hepatic
parenchyma, progressive accumulation, and decreased
remodeling of excessive extracellular matrix (ECM) and
distortion of the parenchymal architecture lead to increased liver
stiffness.
Although liver fibrosis is the predominant factor that causes
increased stiffness in CLD, other pathologic processes often
coexisting with fibrosis, such as inflammation, biliary obstruction
and cholestasis, passive congestion, and increased portal
venous pressure may also contribute to increased liver stiffness

52. Mean liver stiffness (m)
for the ROIs drawn on four images, with each image having an
ROI size
of w pixels:
AMw = (m1w1 + m2w2 + m3w3 + m4w4 )
ÅÄ (w1 + w2 + w3 + w4 ), where m1, m2, m3, and m4
are the mean liver stiffness values measured on
the four elastograms, and w1, w2, w3, and w4 are the sizes of the
ROIs drawn on each of the four elastograms
Liver Stiffness : Generic formula for calculating the
Weighted Arithmetic mean (AMw )

54. Acquisition of LSMs and calculation of the mean liver
stiffness. Four gray-scale elastograms with superimposed
confidence maps show the proper way to obtain LSMs.
Using the freehand ROI tool, the largest portion of the liver is
drawn on each of the four elastogram sections. The outer
margin (white arrows) should be drawn parallel to the liver
margin, 1 cm or more from the liver edge.

55. The inner margin (green arrows) should avoid the 95%
confidence map. For this examination, four measurements
were obtained. The weighted mean LSM was calculated as
follows: [(2.08 3 55.5) + (2.14 3 63.4) + (2.1 3 72.0) + (1.99 3
34.4)] ÷ (55.5 + 63.4 + 72.0 + 34.4) = 2.1 kPa. Therefore, 2.1
kPa was the mean liver stiffness reported for this
examination

56. Quality
Liver MR Elastography Technique and Image Interpretation: Pearls and Pitfalls
Flavius F. Guglielmo, MD Sudhakar K. Venkatesh, MD Donald G. Mitchell, MD
RadioGraphics 2019; 39:1983–2002 https://doi.org/10.1148/rg.2019190034

57. When liver MR elastography is first performed,each image
should be evaluated immediately to ensure its quality so that
corrective steps, if needed, can be taken before the
examination concludes.
MRE Quality Control

58. Step 1: Review the Magnitude
Images

59. Step 2: Review the Phase
Images

60. diffuse signal void
no signal void
no signal void

61. Axial magnitude image obtained at MR elastography shows
a diffuse signal void (arrows) in the subcutaneous tissues in
the right upper quadrant in the abdominal wall, indicating
that the mechanical waves were applied

62. Step 3: Review the Wave
Images

64. excellent wave propagation laterally
excellent wave propagation anteriorly
Low-amplitude waves have distortion,
with chaotic waves that have poor propagation

66. Liver has normal appearance in the anatomic image, and the wave
image shows that shear waves at 60 Hz have a short wavelength,
consistent with the normally soft mechanical characteristics of normal
liver tissue.
The elastogram shows a mean stiffness value of 2.1 kPa, well below the
upper limit of normal (2.9 kPa), indicating the absence of hepatic fibrosis.
Middle row: This patient also has a normalappearing liver, but the wave
images show relative prolongation of the visualized shear waves. The
elastogram shows an abnormally high mean stiffness value of 4.8 kPa,
consistent with moderate hepatic fibrosis
The wave image shows marked lengthening of the visualized shear
waves. The elastogram shows that liver stiffness is markedly
heterogeneous, with many confluent areas measuring more than 8 kPa in
stiffness.

67. Step 4: Evaluate the
Elastogram Quality

68. Causes of Low-Quality and Nondiagnostic Elastograms
Low-quality elastograms
Poor shear wave delivery to liver
Too high or too low active driver
power
output setting
Liver parenchymal causes
Interfering paramagnetic materials
Motion artifact
Nondiagnostic
elastograms
Significant iron overload
Nonfunctioning active
driver
Disconnected or kinked
tube connecting
active and passive drivers

69. A common cause of poor shear wave delivery is the passive driver
improperly secured to the abdominal wall because it loosened after
application. Alternatively, the passive driver may have been
inadvertently applied during inspiration rather than end expiration.
Another reason is that the location of the elastogram section may
not match the location of the passive driver, which may be
positioned too high or too low. Even if the elastogram section
location matches the driver location, the driver still may have been
applied too high or too low.
Structures interposed over the liver, such as the lung base or
colon, also can interfere with shear wave delivery.
Finally, a leak in the connecting tube between the active and
passive drivers may be the reason for the poor shear wave delivery.

74. https://radreport.org/home/50792
https://radreport.org/home/
50792/2019-10-15%2011:27:44

80. MRE & NASH
One of the major gaps in clinical practice is the lack of safe
and accurate methods that distinguish between patients
with NASH, who are at risk of progression to advanced
disease, from those who have simple steatosis and are less
likely to develop liver-related complications
. Timely identification of NASH before the onset of fibrosis
would allow early intervention to avoid development of end-
stage liver disease. Several biomarkers of inflammation have
been evaluated, but they lack the accuracy and reliability
necessary to eliminate the need for liver biopsy

81. Accuracy
MRE has emerged as the most accurate tool to predict
hepatic fibrosis, with an AUROC above 0.90 for all fibrosis
stages

82. MRE Advantages
MRE has several advantages over ultrasound-based
elastography, because it samples a much larger volume of
the liver, it is not affected by body mass index, degree of
steatosis, it is not operator dependent , it has favorable
test-retest repeatability, and a high success rate

85. MRE liver of a 37-year-old normal healthy male. Axial magnitude image (a), wave image (b), and stiffness map (c)
of one slice from the MRE sequence. The liver is outlined in the wave image and stiffness map. Three ROIs placed in the right
lobe of the liver avoiding liver edge, vessels, and any areas of wave interference. The mean 6 SD of liver stiffness from this
slice was 2.1 6 0.18 kPa. The mean 6 SD stiffness from all four slices was 2.05 6 0.20 kPa.

86. Magnetic Resonance Imaging/Elastography Is Superior to Transient Elastography for
Detection of Liver Fibrosis and Fat in Nonalcoholic Fatty Liver Disease
https://www.gastrojournal.org/article/s0016-5085%2816%2900083-4/fulltext

91. MRE charges
INR 10-20,000 in India
INR
18000+

92. Whats New

93. 3D MRE

97. NEW PARAMETERS

98. NEW PARAMETERS WITH 3DMRE

101. Next steps

102. Imaging Biomarkers for evaluation of liver fibrosis
Liver stiffness with ultrasound - LSM with SWE
Liver stiffness with MRE - LSM with MRE
Restricted diffusion with diffusion weighted imaging (DWI), intra-voxel
incoherent motion (IVIM) imaging
T1-relaxation on MRI, extracellular space estimation with CT or MRI
Relative liver function estimation with gadoxetate-enhanced MRI
Surface nodularity index on CT or MRI
Attenuation differences with dual energy CT.
Artificial intelligence and deep learning methods, including texture analysis

103. https://youtu.be/ZjPXskHrZeI

104. https://youtu.be/B8a9k4jvfPA

110. https://youtu.be/fI9d619uEPU

112. IN 2020 MRE has emerged as most valuable tool :
In initial evaluation and establishing the stage
assessing progression, or regression and in treatment response

116. Thank You ALL