*3.4. Magnetic Resonance Imaging in NASH and NAFLD*

Magnetic resonance imaging (MRI) provides another possibility to quantify hepatic fat content with high spatial resolution. Like the other imaging techniques mentioned before, MRI scans do not require or emit ionizing radiation. However, the generation of meaningful MRI images in high resolution requires long imaging times that can be shortened by intravenous administration of gadolinium(III)-based contrast agents [11]. Advanced MRI techniques such as MRI proton density fat fraction (MRI-PDFF) were developed to specifically detect the presence of hepatic steatosis and to assess liver fat over the entire liver [118]. In this analysis, the PDFF is given as an absolute percentage ranging from 0% to 100% and defined as the ratio of density of mobile protons from fat (i.e., triglycerides) and the total density of protons from mobile triglycerides and mobile water [119]. Based on its robustness, practicability, reproducibility PDFF was proposed as the best-suited quantitative MR-based quantitative MR-based biomarker of tissue fat concentration for large-scale research endeavors and widespread clinical implementation [120]. Several independent studies analyzing NAFLD patients showed that MRP-PDFF performed better than CAP for diagnosing all stages of steatosis and had an overall better diagnostic accuracy [121–123].
