Non-Invasive Electrical Impedance Tomography for Multi-Scale Detection of Liver Fat Content

Abstract

Introduction: Obesity is associated with an increased risk of nonalcoholic fatty liver disease (NAFLD). While Magnetic Resonance Imaging (MRI) is a non-invasive gold standard to detect fatty liver, we demonstrate a low-cost and portable electrical impedance tomography (EIT) approach with circumferential abdominal electrodes for liver conductivity measurements.Methods and Results: A finite element model (FEM) was established to simulate decremental liver conductivity in response to incremental liver lipid content. To validate the FEM simulation, we performed EIT imaging on an ex vivo porcine liver in a non-conductive tank with 32 circumferentially-embedded electrodes, demonstrating a high-resolution output given a priori information on location and geometry. To further examine EIT capacity in fatty liver detection, we performed EIT measurements in age- and gender-matched New Zealand White rabbits (3 on normal, 3 on high-fat diets). Liver conductivity values were significantly distinct following the high-fat diet (p = 0.003 vs. normal diet, n=3), accompanied by histopathological evidence of hepatic fat accumulation. We further assessed EIT imaging in human subjects with MRI quantification for fat volume fraction based on Dixon procedures, demonstrating average liver conductivity of 0.331 S/m for subjects with low Body-Mass Index (BMI < 25 kg/m²) and 0.286 S/m for high BMI (> 25 kg/m²).Conclusion: We provide both the theoretical and experimental framework for a multi-scale EIT strategy to detect liver lipid content. Our preliminary studies pave the way to enhance the spatial resolution of EIT as a marker for fatty liver disease and metabolic syndrome.

Ultrasonic Tomographic Technique and Its Applications

“…EIT is an inverse problem to reconstruct the admittivity at each space point and a frequency from Neumann-to-Dirichlet or Dirichlet-to-Neumann type data. Consult [4] for the review of EIT technique and [5], for example, for an application of EIT for medical imaging.…”

“…is the velocity vector, u(x, θ, t) is the density of photon at (x, t) in the direction θ ∈ S 2 , µ a is the absorption constant and µ s is the scattering constant. The right hand side of Equation (5) represents the effect of scattering, the last term in the right hand side represents the effect of absorption and the second term in the right hand side represents the advection effect.…”

Free fatty acid-based low-impedance liver image: a characteristic appearance in nonalcoholic steatohepatitis (NASH)

“…Recent development of digital technologies has widened the application of novel imaging tools for NAFLD, such as the xenon computed tomography [7] and multi-scale electrical impedance tomography [8]. Against the background, ultrasound (US) is the most frequently used modality for the diagnosis of liver diseases because of the simplicity and non-invasiveness.…”

Liver Electrical Impedance Tomography for Early Identification of Fatty Infiltrate in Obesity

“…To this end, we demonstrated in prior study the theoretical and experimental basis of electrical impedance tomography (EIT) for measuring liver fat content in the New Zealand White Rabbit model of atherosclerosis and fatty liver disease 11 . By virtue of tissue-specific electrical conductivity, fatty infiltrate in the liver was characterized by its frequency-dependent electrical impedance (Z) in response to applied alternating current (AC) 11 . At low frequencies, the cell membranes impede the current flow, resulting in high conductivity, whereas at high frequency, they serve as the imperfect capacitors, resulting in tissue-and fluid-dependent impedance.…”

“…In this context, we reconstructed liver frequency-dependent conductivity distribution with the multi-electrode array-acquired voltage data to demonstrate liver EIT. 11 Applying the multielectrode array, we performed EIT voltage measurements by biasing electrical currents (at 2-4 mA and 50-250 kHz) to the upper abdomen. The currents penetrated the body to varying depths, and the resulting boundary voltages were acquired by the electrodes.…”