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MR ELASTOGRAPHY: Imaging of Tissue Elastic Properties ByDr. Inas M. ElfikiLecturer of Radiodiagnosis, Zagazig University

ElastographyPhysicians have used palpation to detect differences in tissue stiffness as an aid to diagnosis based on the fact that the mechanical properties of tissues are often dramatically affected by the presence of disease processes such as cancer, inflammation, and fibrosis.

Elastography depends on the same differences in mechanical properties between healthy and abnormal tissues using imaging to detect these differences at depths not reachable by manual palpation and presents data in color-coded display, can be performed with ultrasound, using manual pressure or low frequency sonic waves, or by MR Elastography imaging.

MR Elastography obtains information about the stiffness of tissue by assessing the propagation of mechanical waves through the tissue with a special magnetic resonance imaging (MRI) technique. The technique essentially involves three steps: 1. Generating shear waves in the tissue2. Acquiring MR images depicting the propagation of the induced shear waves 3. Processing the images of the shear waves to generate quantitative maps of tissue stiffness, called Elastograms.

Clinical Applications

Studying The Elastic Properties Of The LIVER

MRE Score for liver stiffnessTop row: Conventional MR images. Middle row: Elastographic wave image. Bottom row: Wave images are processed to generate quantitative images showing stiffness of tissue (elastograms) (normal value 2 kPa seen).

Malignant liver tumors had significantly greater mean shear stiffness than benign tumors with cut off value of 5 Kpa (kilo-pascals). In the absence of focal mass, fibrotic and cirrhotic liver has a high shear stiffness more than 5 Kpa.

MR elastography of HCV-related fibrosis. MR elastographic wave images (left) and color-coded elastograms (right), obtained at 3 T in 3 patients with chronic HCV infection, show biopsy-proved stage F1 (a), F2 (b) and F4 (c).

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Patient with hepatic adenoma:A, T2-weighted MRI shows hyperintense 8-cm adenoma (arrow) in right lobe of liver.B, Gadolinium-enhanced MRI shows intense arterial phase enhancement (arrow).C, Axial MR elastographic wave image shows good illumination of tumor (circle). Waves in tumor have slightly longer wavelength than those in surrounding normal liver parenchyma.D, Elastogram with region of interest corresponding to tumor shows shear stiffness value of tumor is 3.1 kPa and of surrounding liver is 2.4 kPa.

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51-year-old woman with hemangioma in liver: A and B, T1-weighted images during arterial (A) and delayed (B) phases show enhancement pattern typical of hemangioma (arrow).C, Stiffness map shows stiffness of hemangioma (circle) is 3.2 kPa, whereas that of surrounding liver parenchyma is 2.3 kPa.

Patient with liver cirrhosis & biopsy-proven hepatocellular carcinoma:a & b, Dynamic gadolinium-enhanced T1-W MRI show enhanced tumor (arrow) in right lobe of liver during arterial phase (a) with washout during portal venous phase (b). c, MR elastographic wave image shows shear waves with long wavelength (arrow) within tumor. Waves in surrounding liver also have longer wavelength than normal. d, Elastogram shows mean stiffness of tumor (arrow) is about 8 kPa.

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77-year-old man with cholangiocarcinoma. A, Gadolinium-enhanced T1-weighted MR image shows enhanced tumor (arrow) involving left hepatic duct and invading surrounding left lobe of liver.B, Elastogram shows mean stiffness of tumor (arrow) is 15.5 kPa and that of liver parenchyma is 4.3 kPa.

Patient with metastatic colon cancer: A, T2-weighted image shows single hyperintense lesion (arrow) in periphery of right lobe of liver. B, Wave image shows prolongation of shear wave through tumor (arrow) compared with surrounding normal liver parenchyma.C, Elastogram shows tumor (arrow) as hot spot with stiffness value of 8 kPa, suggestive of malignant tumor. Finding was confirmed at surgery to be metastasis from colon cancer.

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Studying The Elastic Properties Of The Breast

Drawing shows device used for MR elastography of breast. Electro-mechanical drivers, integrated into radiofrequency coil unit, are used to generate acoustic shear waves in breast tissues via contact plates on medial and lateral aspects of breast. both breasts gently compressed in the craniocaudal direction via transducer plates. The plates vibrate in the feet-head direction .

T1-weighted MR image shows normal breast color-coded elastograms modestly heterogeneous pattern of shear stiffness ranging from 2 to 14 kPa.

Breast MRE(a) An axial MR magnitude image of the right breast of a patient volunteer is shown. A large adenocarcinoma is shown as the outlined, mildly hyperintense region on the lateral side of the breast. (b) A single wave image from MRE performed at 100 Hz is shown along with the corresponding elastogram (c). (d) An overlay image of the elastogram and the magnitude image shows good correlation between the tumor and the stiff region detected by MRE.

Invasive Carcinoma

Invasive Ductal Breast Carcinoma

Invasive lobular Carcinoma

Studying The Elastic Properties Of The Prostate

A spot of increased stiffness while the surrounding tissue peripheral zone is less stiff. biopsy taken from this area and 12 systemic posterior peripheral biopsy were performed .cancer seen in the targeted stiff area.

Studying The Elastic Properties Of The Muscles

Skeletal muscle MRE(a) A sagittal MR image of the calf soleus muscle with the location of the driver indicated by the arrow is shown. 100-Hz MRE wave images of the muscle are shown while exerting 0 (b), 5 (c) and 10 N/m (d) of force. The increase in the wavelength (and thus stiffness) with the increase in muscle force is easily visible and is indicated by the double sided arrows.

Studying The Elastic Properties Of The Brain

Brain MRE(a) Shown is an axial MR magnitude image of the brain showing white matter, gray matter, and cerebrospinal fluid.(b) A single wave image from MRE performed at 60 Hz.(c) The corresponding elastogram is shown and a good correlation between the magnitude image and the stiffness estimate is evident.

Studying The Elastic Properties Of The Myocardium

Pathologically altered mechanical properties of the heart

Typical shear stiffness values of various tissuesTissueShear stiffness (kPs)Frequency of operation (Hz)Ocular Vitreous Humor0.0110Lung0.9540Liver:HealthyCirrhotic2.28.960Prostatic:CentralPeripheral2.23.365Breast:Adipose tissueFibroglandular tissueTumor3.37.525100

Typical shear stiffness values of various tissues (cont.)TissueShear stiffness (kPs)Frequency of operation (Hz)Brain:Gray matterWhite matter5.213.6100Muscle:HealthyNeuromuscular disease16.635.4150Cartilage20005000Bone0.8 x 1061500

MRE is a recently developed noninvasive imaging technique that can directly visualize and quantitatively measure tissue elasticity.MRE can replace tissue biopsy especially in patients undergoing repeated biopsies, determine smaller lesions in larger population.A number of other applications of MRE for determining tissue properties, structure, and function are being investigated which could offer valuable information to clinicians and researchers in the future and interest in the field continues to grow rapidly.Conclusions

ReferencesMariappan YK, Glaser KJ, Ehman RL. Magnetic Resonance Elastography: A Review. Clin Anat.; 2010, 23(5):497-511.Venkatesh SK, Yin M, Glockner JF, Ehman RL. MR Elastography of Liver Tumors: Preliminary Results. AJR 2008; 190:1534-1540.Binkovitz LA, El-Youssef M, Glaser KJ, Yin M, Binkovitz AK, Ehman RL. Pediatric MR elastography of hepatic fibrosis: principles, technique and early clinical experience.Pediatr Radiol. 2011 Nov 27. Berzigotti A, Ashkenazi E, Reverter E, Abraldes JG, Bosch J. Non-invasive diagnostic and prognostic evaluation of liver cirrhosis and portal hypertension.Dis Markers. 2011; 31(3):129-38. Review.Wuerfel J, Paul F, Beierbach B, et al. MR-elastography reveals degradation of tissue integrity in multiple sclerosis. NeuroImage; 2010, 49:2525-2525.Streitberger KJ, Sack I, Krefting D, Pfller C, Braun J, Paul F, Wuerfel J. Brain viscoelasticity alteration in chronic-progressive multiple sclerosis. PLoS One. 2012; 7(1): e29888.