Quantitative chemical shift-encoded magnetic resonance imaging (CSE-MRI) is an effective, noninvasive way to monitor liver fat levels over time after bariatric surgery, a study published today in Radiology reports.

Common in obese people, nonalcoholic fatty liver disease (NAFLD) can progress to fibrosis, cirrhosis, and cancer. Although weight loss can reduce the extent of NAFLD, biopsy has been the only possible method of assessing the long-term impact of weight loss on hepatic steatosis.

B. Dustin Pooler, MD, an adjunct assistant professor at the University of Wisconsin School of Medicine and Public Health and a radiologist at Madison Radiologists, S.C., in Madison, Wisconsin, and colleagues used the noninvasive MRI technique to measure average liver proton density fat fraction (PDFF) in 50 patients before bariatric surgery and at several points during the year afterward. They compared this MRI biomarker with postsurgical changes in body mass index (BMI), weight, and waist circumference.

The study cohort, which included 43 women and seven men and was recruited from 2010 to 2015 from medical centers at the University of California San Diego and the University of Wisconsin-Madison, had a mean age of 51.0 years and a mean BMI of 44.9 kg/m².

Presurgical preparation entailed a very low-calorie diet of 600 to 900 calories per day, started at a mean of 2.6 weeks before surgery. Bariatric procedures included gastric banding (n = 2), gastric bypass (n = 28), gastric sleeve (n = 19), and gastric plication (n = 1). PDFF was assessed presurgically before and after the diet, and along with anthropomorphic measurements was assessed at 1, 3, and 6 months after surgery.

Liver fat content began to normalize early during the low-calorie diet and soon after surgery, suggesting metabolic disturbances of NAFLD begin to correct rapidly in response to the caloric deficit of the presurgical diet even before substantial weight loss.

Overall, 32 (64%) of 50 study participants saw their liver fat normalized and an estimated 90% reached that goal by 42 weeks. Six to 10 months postsurgery, patients’ mean PDFF had returned to the normal range of < 5%, falling from 18.1% to 4.9%, with a mean estimated time to normalization of 22.5 weeks.

Mean BMI fell to 34.5 kg/m² (mean decrease 10.4), and the cohort’s final mean weight of 91.6 kg represented am overall reduction of 29.9 kg. The final mean waist circumference of 110.9 cm represented a mean decrease of 21.3 cm. All reductions were statistically significant (P < .0001)

Rohit Loomba, MD, director of the NAFLD Research Center at the University of California San Diego and chair of the NAFLD Special Interest Group for the American Association for the Study of Liver Diseases, told Medscape Medical News the findings are an important contribution to the field of liver study.

“Previously the MOZART trial conducted by our group demonstrated the role of MRI-PDFF in assessing treatment response in [nonalcoholic steatohepatitis; NASH] trials. This excellent study clearly extends those findings to examine longitudinal changes in liver fat by MRI-PDFF specifically after bariatric surgery,” said Loomba, who was not involved in the research.

Loomba noted that further studies are needed to examine longitudinal changes that might suggest progressive NAFLD, including biomarkers of fibrosis and inflammation.

Earlier this year, Duke University researchers confirmed MRI’s utility for detecting NAFLD, but concluded it was not sufficiently accurate to replace biopsy in distinguishing between NAFLD and its more advanced relative, nonalcoholic steatohepatitis.

Interestingly, whereas initial PDFF level strongly predicted both rate of liver fat change and time to normalization, body anthropometrics did not predict either outcome. “Decreases in liver fat content were only weakly correlated with starting weight and the amount of overall weight loss, suggesting possible utility in monitoring liver fat with MRI following bariatric surgery, independent of monitoring weight loss,” Pooler and colleagues write.

They suggest that PDFF measurements could also help identify appropriate candidates for bariatric surgery as a result of this robust association between liver fat reduction and pretreatment steatosis levels.

According to the authors, their study is the first longitudinal analysis of changes in liver fat over time in a bariatric surgery population.