MRI protocol and post processing
Ten participants were scanned on one 1.5 T scanner and one 3 T scanner and twenty participants were scanned on one 1.5 T scanner and on two 3 T scanners. The resulting number of data points (1.5 T and 3 T paired data) was 50. All participants had fasted for 3–5 h before each scan and for each participant all scans were performed on the same day.Three major scanner vendors were represented (Siemens, Philips and General Electric (GE)) and a variety of models were used. The scanner models are shown in Table Scanner vendor, model, field strength and number of scans per scannerOn each scanner a multi-echo gradient echo sequence was used to acquire data for R2* mapping. The corresponding parameters are shown in Table Sequence parameters, range/approximation due to slight variation between scannersAt 1.5 T and 3 T the sequence involved acquiring, respectively, 7 and 12 repeated slices (at the same location). Having multiple repeats improves the signal to noise ratio (SNR) and allows sub-selection to avoid including data impacted by artifacts such as those due to motion. The algorithm used for processing the raw echoes first involves the generation of T2* maps for each repeat, then the automatic sub-selection of the most similar repeats (4 for 1.5 T and 7 for 3 T). This is followed by averaging of the raw echoes of that subset of repeats, and the generation of a T2* map from those averages.The MAGO method was used to obtain T2* [Once T2* maps were obtained trained analysts placed three circular ROIs, each 15 mm in diameter, in representative areas of the liver parenchyma, so as to avoid artifacts, large blood vessels and bile ducts. A median T2* of the pixels included in each ROI was calculated. The median T2* (units: ms) was then converted to R2* in s