Estimation of pseudo-diffusion coefficient D* using different settings of low b-values in liver IVIM imaging

The purpose of this study was to investigate the effects of low b-value settings on the estimation of pseudo-diffusion coefficient D* in human liver IVIM MR imaging. In this IRB approved study, 14 subjects (M/F 6/8, mean age 26.81±4.62 y) underwent IVIM diffusion-weighted magnetic resonance imaging on a Philip 3T scanner using sixteen b values (0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 400, 800 s/mm2) with navigator to reduce influences from respiratory motion. Signals as a function of b-value were used to derive three parameters in IVIM equation by nonlinear least squared (NLLS) fitting. All data processing was carried out by self-designed Matlab scripts in bi-exponential decay equation. The results showed that using different number of low b values would obtain different calculated IVIM parameters. The reason of unstable results in calculated IVIM parameters may be caused by low signal to noise ratio (SNR), respiration control method, or other uncertain factors. Simulation results showed that D* were not stable if SNR is under 50. The improvement of SNR and breathing control could be further discussed to obtain more reproducible IVIM parameters.