Radiologists and clinicians with an interest in pancreatic fat quantification. Elevated pancreatic fat has been associated with increased insulin resistance, type 2 diabetes, and pancreatic cancer.^1,2 A recent study demonstrated that patients undergoing bariatric weight loss surgery experience a concomitant decrease in both pancreatic ectopic fat and hepatic steatosis as measured by ¹H MRS;² that study assessed only two time points (baseline, six-months post-surgery) and so did not examine in detail the time course of pancreatic fat reduction. The primary purpose of this pilot study was to explore in greater detail the time course of pancreatic fat reduction during weight loss in initially obese adults in a surgical weight loss program. The secondary purpose was to explore the relationship between rates of change in pancreatic PDFF, hepatic PDFF, and anthropometric measures. Pancreatic and hepatic fat was measured at multiple time points (baseline, 1 month, 2 months, 4 months, and 7 months). We used MRI rather than MRS to measure pancreatic fat because, as suggested in other work being submitted as a scientific abstract to this meeting, MRI may provide more repeatable measurements of pancreatic fat than MRS. Nine obese adults (7 female, 2 male, mean age 49.6 years) scheduled for weight loss surgery were prospectively recruited to undergo non-contrast MR examinations on a 3T scanner (GE Signa EXCITE HDxt, GE Healthcare, Waukesha, WI) at multiple time points before and after surgery. Hepatic and pancreatic fat quantification were performed using complex-based MRI (C-MRI) methods.³ The C-MRI technique originally developed for liver imaging was optimized to quantify pancreatic fat by eliminating parallel imaging to boost signal to noise ratio, and adjusting voxel size to minimize volume-averaging effects around the pancreas (Table 1). The entire pancreas was covered in 2-3 overlapping single breath-hold acquisitions. A specialized reconstruction algorithm⁴ automatically generated T2* corrected multi-fat-peak model PDFF maps, which were then transferred off line for further analysis. Regions of interest (ROIs) with areas of 100mm² were placed in the head, body, and tail of the pancreas, with care to include only pancreatic parenchyma and to exclude vasculature and surrounding adipose tissue. Each ROI was co-localized to the first visit. Monthly rate of change of pancreatic PDFF, waist circumference, hepatic PDFF, and BMI were computed for each subject as a slope of a linear regression line over the first three study visits where the change is usually linear and most acute. T-test was used to test significance of slopes. Spearman’s rank-order correlation (ρ) was used to test the association between pancreatic PDFF waist circumference, hepatic PDFF, and BMI slopes.At their first visit, the 9 subjects had an average BMI of 44.1 kg/m² and pancreatic PDFF value of 15.5% (range 5.0 – 32.2%), and at 7 months an average BMI of 32.9 kg/m² and pancreatic PDFF value of 8.6% (range 3.7 - 16.4 %). All 9 subjects had lower pancreatic PDFF at the last visit than at the first visit (range of reduction 0.77% - 17.7%). Figure 1 illustrates the longitudinal changes in a representative subject. Figure 2 plots the longitudinal change of pancreatic PDFF values for all 9 subjects. Over all, patients lost an average absolute PDFF of 2.8% in the first two months and 4.1% in the last five months. Rate of change of pancreatic PDFF was significant (p=0.006). As shown in Figure 3, the rate of change in pancreatic PDFF was not significantly correlated with the rate of change in waist circumference, hepatic PDFF or BMI. Our study was limited by small sample size. While the associations between slopes of pancreatic PDFF and BMI, waist circumference, and hepatic PDFF did not reach statistical significance, ρ=037 suggests a potential relationship between pancreatic PDFF and waist circumference, changes that will need to be confirmed with a larger sample size. Another limitation was that although a high spatial resolution technique was used, we could not resolve intracellular fat from extracellular fat (adipose tissue) within the intercalations of the pancreatic parenchyma.Pancreatic PDFF declines with weight loss. This pilot study offers a descriptive exploration of how C-MRI measured pancreatic fat content changes longitudinally in obese adults who undergo weight loss. Further research in larger cohorts is needed to confirm our findings and to understand the clinical and biological relevance of pancreatic PDFF reduction.