Patients with NAFLD undergoing bariatric surgery can expect significant decreases in liver volume and hepatic steatosis at 6 months, with 83.7% of patients achieving resolution of steatosis. Liver volume reduction plateaus 1-month post-bariatric surgery, but PDFF continues to decrease. LSG and LRYGB did not differ in efficacy for inducing regression of hepatosteatosis.

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O besity is a major public health issue in the United States, with over two-thirds of American adults considered overweight or obese (1). Nonalcoholic fatty liver disease, widely considered the hepatic manifestation of metabolic syndrome (2), is an increasingly prevalent condition common in patients with obesity (3). Intracellular accumulation of triglycerides (hepatic steatosis) is the hallmark feature of nonalcoholic fatty liver disease, which can progress to nonalcoholic steatohepatitis and ultimately cirrhosis (4,5) while also increasing the risk of hepatocellular carcinoma (6). Bariatric surgery is an effective weight loss intervention in patients with obesity, reducing liver fat (7,8) and improving other health outcomes (9-11). Furthermore, use of a very low calorie diet (VLCD) prior to bariatric surgery facilitates surgery and may augment the degree of weight loss (12-14). However, the relationship between overall weight loss achieved by these treatments and decreases in liver fat content is not well understood, to our knowledge. A barrier to understanding these relationships has been the lack of reproducible, noninvasive methods to quantify liver fat. Liver biopsy has long been the reference standard for liver fat quantification (15) but is invasive. Traditional imaging methods, including conventional MRI, MR spectroscopy (16), and US (17), are of limited utility due to poor accuracy or technical difficulty (18). Advanced complex-based chemical shift-encoded (CSE) MRI methods for quantifying proton density fat fraction (PDFF) as a fundamental biomarker of liver fat concentration (19) have been developed and validated across multiple vendors

Purpose To assess and compare the accuracy of magnitude-based MRI (MRI-M) and complex-based MRI (MRI-C) for estimating hepatic proton density fat fraction (PDFF) in children, using magnetic resonance spectroscopy (MRS) as the reference standard. A secondary aim was to assess the agreement between MRI-M and MRI-C. Methods This was a HIPAA-compliant, retrospective analysis of data collected in children enrolled in prospective, IRB-approved studies between 2012 and 2014. Informed consent was obtained from 200 children (ages 8–19 years) who subsequently underwent 3T MR exams that included MRI-M, MRI-C, and T1-independent, T2-corrected, single-voxel STEAM MRS. Both MRI methods acquired 6 echoes at low flip angles. T2*-corrected PDFF parametric maps were generated. PDFF values were recorded from regions of interest (ROIs) drawn on the maps in each of the 9 Couinaud segments and 3 ROIs co-localized to the MRS voxel location. Regression analyses assessing agreement with MRS were performed to evaluate accuracy of each MRI method, and Bland-Altman and ICC analyses were performed to assess agreement between the MRI methods. Results MRI-M and MRI-C PDFF were accurate relative to the co-localized MRS reference standard, with regression intercepts of 0.63% and −0.07%, slopes of 0.998 and 0.975, and proportion-of-explained-variance values (R2) of 0.982 and 0.979, respectively. For individual Couinaud segments and for the whole liver averages, Bland-Altman biases between MRI-M and MRI-C were small (ranging from 0.04 to 1.11%) and ICCs were high (≥0.978). Conclusions Both MRI-M and MRI-C accurately estimated hepatic PDFF in children, and high inter-method agreement was observed.