Quantifying Pancreatic Fat Using a Free-Breathing Acquisition in Adults With Obesity Undergoing Diet-Induced Weight Loss-Results From the LION Study.

A free-breathing six-echo radial stack-of-stars acquisition is evaluated as an alternative to Cartesian breath-hold scans for pancreatic fat quantification at 3T. Pancreatic fat deposition was assessed in 18 participants with obesity enrolled in a randomized controlled lifestyle intervention study (LION) using both a Cartesian breath-hold scan and a free-breathing high-resolution stack-of-stars sequence (scan times: 16 s vs. 2 min 55 s). Pancreatic segmentations were initially generated using the VibeSegmentator and subsequently refined manually to reduce the amount of included visceral fat. The Intra-observer reproducibility of the manual refinement was assessed after 3 months using Dice similarity score. SNR for both scan methods was quantified using a large water phantom. Mean segmented volume and mean pancreatic proton density fat fraction (PDFF) values between radial and Cartesian scans were compared. PDFF and volume changes between baseline and post-intervention were investigated for both techniques. Segmented pancreatic volumes and PDFF measurements demonstrated excellent agreement between the radial and Cartesian sequences (Volume: R2 = 0.97, ICC = 0.96; PDFF: R2 = 0.98, ICC = 0.98). Compared to the Cartesian scans, the radial scans exhibited a minor positive volume bias at higher pancreatic volumes (linear regression: 0.85x + 9.4 cm3; mean volume bias: 5.8 cm3, 95% LoA: -7.1 to 18.7 cm3), alongside a proportional PDFF bias leading to slight overestimation at lower values and underestimation at higher values (linear regression: 0.88x + 2.1%; mean PDFF bias -0.2%, 95% LoA: -3.0 to 2.7%). Post-intervention, both datasets captured significant decreases in pancreatic PDFF (mean loss 2.3% ± 2.1%, Cartesian p < 0.001, radial p < 0.01) and volume (mean loss 8.4 cm3 ± 7.7 cm3; both p < 0.001). The present study demonstrates the feasibility of a free-breathing radial stack-of-stars sequence for pancreatic fat quantification at 3T and its application in adults with obesity undergoing diet-induced weight loss.