Pilot Study on the Use of Rheology and Low Field Nmr to Characterize the Liver of Obese Patients Undergoing Metabolic and Bariatric Surgery

Background and aims. Liver mechanical properties’ (stiffness/viscoelasticity) evaluation is relevant for diagnosing/monitoring liver fibrosis. Due to limitations of the commonly used elastography, we propose the use of rheology and Low Field-Nuclear Magnetic Resonance (LF-NMR). Methods. In 30 liver samples from patients undergoing bariatric surgery and 18 control samples, we evaluated the shear modulus G/critical stress τc (elastic properties) and mean complex modulus Ga* (elastic/viscous properties) by rheology. LF-NMR was used to measure the spin–spin relaxation time (T2m), reflecting iron content. The expression of iron-related proteins and of pro-fibrotic proteins were evaluated by qRT-PCR. Tissue histology was also determined. Results. Ga*/G/τc were higher in pathological samples, which also showed increased expression of pro-fibrotic proteins. Fibrosis determination displayed a correspondence of 4/30 samples for elastography/histology and 17/30 for rheology/histology. T2m was significantly lower in pathological livers, indicating iron accumulation as confirmed by increased expression of iron-related proteins. T2m was more effective than histology in detecting iron. An inverse correlation was observed between T2m and Ga*/G showing that iron accumulation is associated with increased liver elasticity/viscoelasticity, i.e., fibrosis. Additionally, an inverse correlation of Ga*/G with transferrin, was observed. Conclusion. As our patients mostly have mild liver fibrosis, the combined use of rheology/LF-NMR can effectively detect early changes in liver mechanical properties, aiding in staging and diagnosis of fibrosis.