DSB seminar Elastography and Use of a Tissue Model for Discrimination

Sverre Holm will go through a paper which is relevant for elastography

Use of a tissue model for discrimination:

Ralph Sinkus, Simon Lambert, Khaled Z. Abd‐Elmoniem, Caryn Morse, Theo Heller, Christian Guenthner, Ahmed M. Ghanem, Sverre Holm, Ahmed M. Gharib, Rheological determinants for simultaneous staging of hepatic fibrosis and inflammation in patients with chronic liver disease, NMR in Biomedicine, 2018.

The tissue model, which was my contribution in the paper, is the fractional Kelvin-Voigt model from S. Holm, R. Sinkus, A unifying fractional wave equation for compressional and shear waves, J. Acoustical Soc. America, 2010.

Abstract of first paper:

The purpose of this study is to investigate the use of fundamental rheological parameters as quantified by MR elastography (MRE) to measure liver fibrosis and inflammation simultaneously in humans.

MRE was performed on 45 patients at 3 T using a vibration frequency of 56 Hz. Fibrosis and inflammation scores were obtained from liver biopsies. Biomechanical properties were quantified in terms of complex shear modulus G* as well as shear wave phase velocity c and shear wave attenuation α. A rheological fractional derivative order model was used to investigate the linear dependence of the free model parameters (dispersion slope y, intrinsic speed c0, and intrinsic relaxation time τ) on histopathology. Leave‐one‐out cross‐validation was then utilized to demonstrate the effectiveness of the model.

The intrinsic speed c0 increases with hepatic fibrosis, while an increased relaxation time τ is reflective of more inflammation of the liver parenchyma. The dispersion slope y does not depend either on fibrosis or on inflammation. The proposed rheological model, given this specific parameterization, establishes the functional dependences of biomechanical parameters on histological fibrosis and inflammation. The leave‐one‐out cross‐validation demonstrates that the model allows identification, from the MRE measurements, of the histology scores when grouped into low−/high‐grade fibrosis and low−/high‐grade inflammation with significance levels of P = 0.0004 (fibrosis) and P = 0.035 (inflammation).

The functional dependences of intrinsic speed and relaxation time on fibrosis and inflammation, respectively, shed new light onto the impact hepatic pathological changes on liver tissue biomechanics in humans. The dispersion slope y appears to represent a structural parameter of liver parenchyma not impacted by the severity of fibrosis/inflammation present in this patient cohort. This specific parametrization of the well‐established rheological fractional order model is valuable for the clinical assessment of both fibrosis and inflammation scores, going beyond the capability of the plain shear modulus measurement commonly used for MRE.

Published Nov. 6, 2018 12:12 PM - Last modified Nov. 6, 2018 12:16 PM