Abstract
Gadoxetic acid-enhanced magnetic resonance imaging has become a useful tool for quantitative evaluation of liver capacity. We report on the importance of intrahepatic fat on gadoxetic acid-supported T1 mapping for estimation of liver maximum capacity, assessed by the realtime 13C-methacetin breathing test (13C-MBT). For T1 relaxometry, we used a respective T1-weighted sequence with two-point Dixon water-fat separation and various flip angles. Both T1 maps of the in-phase component without fat separation (T1_in) and T1 maps merely based on the water component (T1_W) were generated, and respective reduction rates of the T1 relaxation time (rrT1) were evaluated. A steady considerable decline in rrT1 with progressive reduction of liver function could be observed for both T1_in and T1_W (p < 0.001). When patients were subdivided into 3 different categories of 13C-MBT readouts, the groups could be significantly differentiated by their rrT1_in and rrT1_W values (p < 0.005). In a simple correlation model of 13C-MBT values with T1_inpost (r = 0.556; p < 0.001), T1_Wpost (r = 0.557; p < 0.001), rrT1_in (r = 0.711; p < 0.001) and rrT1_W (r = 0.751; p < 0.001), a log-linear correlation has been shown. Liver maximum capacity measured with 13C-MBT can be determined more precisely from gadoxetic acid-supported T1 mapping when intrahepatic fat is taken into account. Here, T1_W maps are shown to be significantly superior to T1_in maps without separation of fat.
Highlights
For evaluation of liver function, medical professionals rely on a variety of diagnostic tools
In Gd-EOB-DTPA-supported T1 mapping, it still remains unclear to what extent the reduction of T1 relaxation time is induced by the presence of intrahepatic fat
It might be assumed that the reduction rate and liver function are overestimated in patients suffering from non-alcoholic steatohepatitis (NASH) or fatty liver disease, as the T1 relaxation time is expected to decrease with increasing fat fraction and the relative voxel-specific uptake of contrast agent is diminished when intrahepatic fat is present
Summary
For evaluation of liver function, medical professionals rely on a variety of diagnostic tools. Due to the paramagnetic properties of gadolinium, accumulation and increasing concentration of Gd-EOB-DTPA shortens T1 and to a lesser extent the T2 relaxation time, that of water molecules and protons, allowing for the quantitative evaluation of liver function[6,11]. MRI signals in the human body are caused by hydrogen protons of water, triglycerides and fatty acids[14] Due to their characteristic chemical structure and properties, fatty acids exhibit a relatively short T1 relaxation time[15]; Gd-EOB-DTPA shortens the T1 relaxation time in interacting molecules. It might be assumed that the reduction rate and liver function are overestimated in patients suffering from non-alcoholic steatohepatitis (NASH) or fatty liver disease, as the T1 relaxation time is expected to decrease with increasing fat fraction and the relative voxel-specific uptake of contrast agent is diminished when intrahepatic fat is present
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