Image acquisition for intravoxel incoherent motion imaging of kidneys should be triggered at the instant of maximum blood velocity: evidence obtained with simulations and in vivo experiments

摘要

Purpose To demonstrate that diffusion‐weighted images should be acquired at the instant of maximum blood velocity in kidneys to extract the perfusion fraction (PF) by the bi‐exponential intravoxel incoherent motion model. Methods The PF values were measured in Monte‐Carlo simulations corresponding to different blood velocities with a constant known PF. The distribution of the measured PF values (PF‐distribution) was characterized quantitatively by 3 markers highlighting the deviation of the measurement from the true PF. Diffusion‐weighted images of kidneys were acquired in 10 healthy volunteers at the instant of maximal respectively minimal blood velocity in the renal artery (V max versus V min acquisition). The PF‐distributions measured from the V max and V min acquisitions were compared mutually and with simulated PF‐distributions using the 3 markers. A radiologist evaluated the quality of the PF maps. Results The PF‐distributions measured in the simulations were spread around the true PF value, and spreading was reduced as blood velocity increased. A comparison between simulated and in vivo PF‐distributions suggests that a similar phenomenon is plausible in vivo. The quality of the PF maps of the V max ‐acquisition was scored higher by the radiologist than those of the V min ‐acquisition in 95% of cases (19 of 20). Conclusions The PF maps are of better quality when the V max ‐acquisition is used. We show evidence supporting the hypothesis that the variation of PF along the cardiac cycle is due to oscillations between a poor estimation when the blood velocity is low, and a better estimation when blood velocity is higher.