2012 Proceedings - International Tissue Elasticity Conference

050 SHEAR WAVE DISPERSION MEASURES FAT CONCENTRATION IN A MOUSE LIVER MODEL.
Zaegyoo Hah 1 , Alexander Partin 1 , Gil Zimmerman 1 , Christopher T. Barry 2 , Robert A. Mooney 2 ,
Deborah J. Rubens 2 , Kevin J. Parker 1 .
1 Electrical and Computer Engineering Department, University of Rochester, Rochester, NY, USA;
2 University of Rochester Medical Center, Rochester, NY, USA.
Background: Nonalcoholic fatty liver disease (NAFLD) is characterized by accumulation of fat within the
liver. In the most severe cases, NAFLD can progress to nonalcoholic steatohepatitis (NASH) and
subsequently to liver cirrhosis. Since in many cases NAFLD can be asymptomatic, a non–invasive and
painless method for the measurement of fat concentration within the liver would very beneficial.
Aims: We aim to assess our hypothesis, as illustrated in Figure 1a, that higher fat concentration within a
liver will introduce higher shear speed dispersion, while slightly reducing the shear wave speed. This is a
consequence of adding a viscous component to the liver [1]. Our objective in this study is to compare
experimentally measured shear speed dispersion within liver specimens grouped by measured fat
concentrations.
Methods: A total of 70 mouse liver specimens were scanned ex vivo over a four month period. 35 mice fed
with a regular diet (Lean) and 35 fed with high fat diet (Obese). After hepatectomy, each liver specimen
was embedded in a gelatin phantom and scanned with multiple frequencies between 200 and 350Hz
using the CrW (crawling wave) imaging technique [2]. Using an estimation algorithm, a shear speed
dispersion per 100Hz and shear speed at a reference frequency of 250Hz were obtained for each liver
sample. For the hypothesis assessment, the estimated results are presented on a two parameter plot of
dispersion slope (vertical axis) and shear speed at reference frequency (horizontal axis). The livers were
categorized into two groups, Group 1 containing less than 50% fat and Group 2 with 50% fat or greater.
The data were analyzed using two approaches. In the sample–by–sample approach, each liver specimen’s
estimate is placed in the plot, Figure 1b, where box plot size indicates the standard deviation within each
group. In the group approach, Figure 1c, a linear regression with 95% confidence intervals was used to
obtain the values for dispersion and shear speed of each of two groups. These values, together with the
upper and lower bounds obtained with linear regression, are presented as box plots.
Results: In the sample–by–sample analysis, the dispersion per 100Hz in m/s/Hz and the shear speed in
m/s for the two groups are: (0.13, 2.5) for Group 1 and (0.55, 1.9) for Group 2. The group analysis shows
the following results: (0.12, 2.51) for Group 1 and (0.64, 1.93) for Group 2. Paired t–tests provided the
following p–values: p