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Shear wave elastography and liver pulp elastometry (methodical aspects).

O.B. Dynnik, A.V. Linskya, N.N. Kobyliak

The clinical significance of fibrosis staging in chronic diffused liver diseases (CDLD) and limitations imposed on biopsy motivated by development of noninvasive methods of assessment of liver fibrosis. Transient elastography (TE) became the leading and recognized tool methods for this purpose in Europe.

The pioneer in the elastomery of liver stiffness measurements (LSM) is Fibroscan® Co (Echosence, France Designers showed for the first time that there is a close correlation of parenchyma stiffness and liver fibrosis stages on the METAVIR scale. This found the confirmation in numerous publications and meta-analyzes. The principle of transient elastomery method is in the LSM measurement as a function of speed distribution in liver of elastic shear wave reproduced by mechanical shock. The transient elastography (TE) key limitation in clinic practice has come to high level of results (20%), that are evaded interpretation. The method makes it impossible to visualize the radiation zone that reduces reliability results for specific patient.

Compression (static) elastography integrated as a module into the high level ultrasound equipment uses sensor-induced or natural (i.e. respiratory or cardiac) displacements in a body for producing images of stiffness color mapping (SCM) on the liver slice. As stress force value in this ethod is not known, it is possible only qualitative relative assessment of tissue stiffness but not a quantitative one.

The real-time shear wave elastography (SWE) represents a new noninvasive method for assessment of liver fibrosis based on the LSM quantitative measurement. The device family that uses the shear wave (SW) method in the ultrasound elastography and liver parenchyma elastometry are currently presented by three manufacturers: Aixplorer® (Supersonic Imaging S.A., Aix-en-Provence, France), Ultima PA Expert® (Radmir, Ukraine), Acuson S3000® (Siemens, Germany) and manufacturer Epiq® (Philips, Hoolland ) that uses the same method of side wave. Supersonic Imaging Co. proposed to call method as Real-Time Shear Wave Elastography™ (SWE™) Imaging.

The SWE method is based on the ultrasound beam property to induce mechanical shear waves in the direction lateral to their distribution. Their track speed through the tissue depends on its stiffness or gluey-and-elastic properties. The tissue space covered by probing ultrasound beam depends on Mach cone shaped with the support of the SW several excitation focuses. Besides, the SWE imaging is built up at high image frequency in the B-mode. This method made it possible to evaluate fibrosis stage with greater accuracy as compared to transient elastography (TE) owing to navigation in the B-mode. Close to the SWE method, but a single-focused method for the LSM assessment is the Acoustic Radiation Forсe Imaging (ARFI) technology. It is presented by apparatus samples Acuson S2000® (Siemens) and IU 22® (Philips, Holland).

O.B. Dynnik, A.V. Linskya, N.N. Kobyliak
Radiodiagnosis, radiotherapy. – 2014. – №1-2. – P. 73-82.

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