3t imager

Swine were anesthetized, intubated, and monitored as described above for imaging. Animals were scanned in a lateral decubitus position with the rear legs bolstered in an extended position (S1 Fig). A custom 8 channel surface coil was wrapped around both rear legs in a 3T imager (GE Healthcare). Fat-saturated proton density images (TE 18, TR 2000, ETL 4,384 x 256 matrix, 3 mm slice thickness, 0.5 mm spacing, 3 NEX) were performed in sagittal, axial (perpendicular to the patellofemoral joint), and coronal (parallel to the patellofemoral joint) planes. A 3D SPGR acquisition was also obtained (flip angle 10, 320 x 192, 1.5 NEX, slice thickness 1 mm). S2 Fig outlines the MRI time points obtained for each animal.

MR examinations were performed with a 3-T imager (GE Healthcare, Milwaukee, WI). The PDFF was measured using the Dixon method with advanced processing, called IDEAL-IQ (Iterative decomposition of water and fat with echo asymmetry and the least squares estimation quantification sequence, GE Healthcare). The Dixon method using 6 echoes was employed to measure the fat fraction using the following imaging parameters: repetition time/echo space: 6.6 ms/0.78 ms; maximum TE 4.8; minimum TE 0.9; NEX 0.50; location per slab 28; number of shots 2; echo train length 3; flip angle: 3 degrees; matrix: 160 x 160; axial imaging plane; section thickness: 8 mm; FOV: 44 cm; phase FOV: 0.8 cm; bandwidth: 111.11 kHz; imaging time, single breath-hold (19 seconds). After setting the ROIs in the organs of interest, the PDFF calculation was performed by a hybrid multipoint water-fat separation approach, where a T2*-corrected, spectrally modeled ‘‘complex based” water-fat separation method (T2*-IDEAL) is followed by a fitting algorithm based on magnitude multi-echo signals as reported previously [13 (link)].