Electrical Impedance Tomography in Fatty Liver Detection

Fatty liver disease is a condition where the hepatocytes (liver cells) contain more than 5% fat. This condition is becoming increasingly common due to unhealthy food habits and sedentary lifestyle. Since NAFLD is a silent disease with symptoms arising only at the later stages (e.g., fibrosis), many patients would be diagnosed at the advanced stages when fat accumulation, scarring and liver cell damage are irreversible. Therefore, early diagnosis of silent fatty liver disease during its reversible stages is important to prevent cell damage, liver transplantation and allow better long-term prognosis.

Currently, liver biopsy is the gold standard in diagnosis and prognosis of fatty liver disease. However, biopsies are invasive, expensive and involve risks of internal bleeding and high sampling error. Non-invasive diagnostic tests include blood tests, FibroScan® and MRI. FibroScan® (Echosens, Paris, France) is a quick 10 minutes non-invasive test which measures the fatty change. Normal liver fat amount has controlled attenuation parameter (CAP) <248 dB/m which is S0, while mild fatty liver has CAP 248-267 dB/m or S1. Moderate fatty liver has CAP 268-279 dB/m or S2 and lastly severe fatty liver has CAP >279 dB/m or S3 (Karlas et al., 2017). The device is known to have reduced reliability for patients who are morbidly obese or have ascites. It also heavily relies on the operator experience. Another liver fat quantification method is MRI-based proton density fat fraction (MRI-PDFF). MRI-PDFF is a noninvasive imaging tool which can accurately and precisely calculate the percentage of liver fat over the whole liver. Nevertheless, MRI-PDFF takes a long time (~30 minutes), is expensive, not portable and not routinely accessible.

EIT could be an alternative low cost, noninvasive imaging technique that does not involve radiation and is routinely accessible. Existing EIT commercial devices are at present being deployed in some clinical settings. EIT technology has been in use since more than a decade, although so far it has mostly been used to assist mechanically ventilated patients in intensive care units to prevent lung damage caused by artificial ventilation.

Within the past few years, non-clinical research studies on applying EIT for fatty liver detection in animal and human models have been performed. The electrical conductivity of biological tissues varies according to the tissue type and frequency of AC current. On one hand, fat tissue conductivity is known to be substantially stable across the EIT current injection frequency spectrum. On the other hand, liver tissue conductivity significantly increases over frequency change. Hence, biological tissues can potentially be differentiated using EIT frequency spectrum analysis.