2012 Proceedings - International Tissue Elasticity Conference

032 ANALYSIS OF THE INFLUENCE OF INFLAMMATION, IRON AND WATER DIFFUSIVITY ON
LIVER VISCOELASTIC PARAMETERS IN FIBROSIS.
H Leitao 1,2,3 , S Doblas 1,2 , P Garteiser 1,2 , G D’Assignies 1,2 , F Mouri 1,2 , V Vilgrain 1,2 , R Sinkus 1,2 ,
BE Van Beers 1,2 .
1 INSERM, U773, F–75205, Paris, FRANCE; 2 University Paris Diderot, Sorbonne Paris Cité,
UMRS773, F–75205, Paris, FRANCE; 3 University of Coimbra, Coimbra, PORTUGAL.
Background: Increased liver steatosis, inflammation and iron are often observed in patients with liver
fibrosis [1,2]. Moreover, the apparent diffusion coefficient (ADC) is associated with water content and the
collagen matrix, and restricted diffusion is found with higher stages of fibrosis [3]. Yet, the influence of
these factors on liver viscoelastic parameters determined by MR elastography is not fully understood.
Aims: The purpose of our study was to assess the relationship between hepatic viscoelasticity and
steatosis, inflammation, iron and ADC.
Methods: All patient studies were performed under informed consent and within the agreement of local
ethical guidelines. Thirty–seven patients with chronic viral hepatitis B (n=11) and C (n=26) underwent MR
elastography (MRE), diffusion–weighted imaging (DWI) and multiecho imaging (ME) at 1.5T. Liver
inflammation, fibrosis, inflammation and steatosis were assessed on percutaneous liver biopsies taken
within a maximum delay of two months (mean 29 days). For MRE, we used a spin–echo EPI sequence
(TR/TE=320ms/40ms, 4mm in–plane resolution, 3–directional encoding). Mechanical waves (50Hz) were
coupled into the liver by an electromechanical actuator. DWI was performed with a spin echo EPI
sequence (TR/TE=300/56, 4mm in–plane resolution, 11 b–values from 10 to 500s/mm 2 ). ME with an EPI
readout (TR/TE=120/n×2.3ms; n=1;10) was used to quantify iron and fat. The following viscoelastic
parameters were calculated by local inversion of the complex linear viscoelastic 3D wave equation:
storage modulus, G’ (kPa), loss modulus G’’ (kPa), absolute value of the shear modulus, Gabs
(Gabs 2 =G’ 2 +G’’ 2 ), propagation coefficient β (2π over the wavelength, mm -1 ) and attenuation, α (mm -1 ). The
ADC was obtained by fitting a monoexponential function to the pixel intensities obtained at increasing
diffusion sensitizing gradient strengths. Fat content was assessed by fitting separate monoexponential
functions to the pixel intensities as a function of echo time on in–phase (water + fat) and out of phase
(water – fat) echo images, subtracting the respective values predicted by the fit at zero echo time and
dividing by two. The iron content was determined by mapping of the T2* MR relaxation coefficient
according to the method exposed by Wood et al. [4]. Spearman rank correlation (r) and multiple
regressions coefficients (RC) were calculated.
Results: A positive correlation was found between liver fibrosis
and all the viscoelastic parameters, with the exception of α (G’:
r=0.59, P