Simultaneous Water‐Specific and Fat‐Specific T1 and Fat Fraction Mapping of the Abdomen in Free Breathing Conditions With a Radially Encoded MP2RAGE

The purpose of this study is to enable 3D abdominal imaging and quantitative parameter mapping in free breathing conditions and simultaneously provide proton-density fat fraction (PDFF), water-specific and fat-specific T1 maps. A radially encoded MP2RAGE with alternated fat and water selective pulses was implemented and validated on a phantom containing gadolinium (Gd) and pork fat at different concentrations. Comparison with MR spectroscopy and imaging techniques of reference was performed in vitro. Multiple experiments were carried out on healthy volunteers and individuals with a record of liver disease and benign bone marrow lesions to evaluate the method's repeatability, accuracy and potential for clinical application. In vitro water or fat specific T1 was in agreement with estimates provided by reference methods over a wide range of mixture ratios. PDFF was strongly correlated with spectroscopy (Pearson coefficient of 0.98) and other imaging techniques although underestimated due to the imperfect pulse selectivity profile. Images free of ghosting artefacts were acquired in vivo on seven volunteers. The whole abdomen was imaged, as well as a large part of the spine (from T11 to L5). Parametric maps provided repeatable estimates in the liver, the bone marrow and the subcutaneous fat that were consistent with values reported in literature and other imaging techniques. The acquisition time could be halved without significantly affecting the quantitative values. Overall, high-contrast MP2RAGE abdominal images, water- and fat- specific T1 maps and PDFF maps were achieved in a single 3D acquisition under free breathing.