Dataset description: Accompanying data for manuscript “Multi-Site,Multi-Vendor Validation of the Accuracy and Reproducibility ofProton-Density Fat-Fraction Quantification at 1.5T and 3T using aFat-Water Phantom”, submitted for publication in Magnetic Resonance inMedicine in January 2016. Details: The 'datasets' folder contains multiple MATLAB MAT-filesfiles with chemical shift-encoded (CSE) MRI data for validation of fatquantification techniques in a fat-water phantom. Data was acquired atsix sites with different MRI vendors, two field strengths (1.5T and3T) per site, and two protocols per field strength. The goal of thesetechniques is to measure proton-density fat-fraction (PDFF) accuratelyand reproducibly. Data from site 1 was acquired both at the beginning(October 2014) and at the end (December 2015) of this study, in orderto evaluate the integrity of the phantom. Details on the vendors, platforms and protocols are described in thefile 'vendors_platforms_protocols.pdf' in this same folder. The phantom consists of 11 vials with different fat concentrations(PDFF = 0%, 2.6%, 5.3%, 7.9%, 10.5%, 15.7%, 20.9%, 31.2%, 20.9%,31.2%, 41.3%, 51.4% and 100%, respectively). At each magnet, the vialswere arranged horizontally along the B0 field and scanned with axialslices using a 3D multi-echo spoiled gradient echo pulse sequence. Each of the MAT-files contains the acquired complex-valued images overthe three central slices within the phantom vials. The structure'imDataAll' contains the acquired data, with the following fields:'TE' (echo times), 'FieldStrength' (in Tesla), 'PrecessionIsClockwise'(describing whether water has higher resonance frequency than fataccording to the reconstruction convention), 'echo_polarity' (relativepolarity of the acquired echoes, ie: monopolar vs bipolar readouts),'images' (five-dimensional array containing the complex valued images,coil-combined in datasets received with multiple channels, withdimensions X x Y x Slices x Coils x Echoes). Additionally, the MAT-files contain reconstruction results asdescribed in the manuscript, in the arrays 'fwmc_*' of size X x Y xSlices. Note that the nomenclature 'fwmc' stands for 'Fat-Waterseparated with Magnitude fitting (performed after complex fitting inorder to obtain full 0-100% range of PDFF while avoiding errorsrelated to phase shifts in the data), and a Common initial phase forthe water and fat signals. The specific arrays are 'fwmc_ff' (PDFFmap), 'fwmc_r2star' (R2*=1/T2* decay rate), 'fwmc_w' (water image),'fwmc_f' (fat image).