Influence of cardiac motion on diffusion-weighted magnetic resonance imaging of the liver

To assess cardiac motion-induced signal loss in diffusion-weighted magnetic resonance imaging (DWI) of the liver using dynamic DWI. Three volunteers underwent dynamic coronal DWI of the liver under breathholding, in the diastolic (DWI(diast)) or systolic (DWI(syst)) cardiac phase, and with motion probing gradients (MPGs) in phase encoding (P, left-right), frequency encoding (M, superior-inferior), or slice select (S, anterior-posterior) direction. Liver-to-background contrasts (LBCs) of DWI(syst) were compared to those of DWI(diast), for both the left and right liver lobes, using nonparametric tests. Signal decrease ratios (SDRs) were calculated as (1-(LBCDWI(syst)/LBCDWI(diast))) x 100%. DWI(syst) was further analyzed to determine which direction of MPGs was most affected by cardiac motion. In the left liver lobe, LBCs of DWI(syst) (median 3.35) were significantly lower (P < 0.0001) than those of DWI(diast) (median 4.84). In the right liver lobe, LBCs of DWI(syst) (median 4.17) were also significantly lower (P < 0.0001) than those of DWI(diast) (median 5.35 ). SDRs of the left and right liver lobes were 25.5% and 17.3%, respectively. In DWI(syst), the significantly lowest (P < 0.05) LBCs were observed in the M direction (left liver lobe) and P direction (right liver lobe) of MPGs. Signal intensity of both liver lobes are affected by cardiac motion in DWI. In the left liver lobe, signal loss especially occurs in the superior-inferior direction of MPGs, whereas in the right lobe, signal loss especially occurs in the left-right direction of MPGs.