Intravoxel incoherent motion diffusion-weighted imaging in the liver: comparison of mono-, bi- and tri-exponential modelling at 3.0-T

To determine whether a mono-, bi- or tri-exponential model best fits the intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) signal of normal livers. The pilot and validation studies were conducted in 38 and 36 patients with normal livers, respectively. The DWI sequence was performed using single-shot echoplanar imaging with 11 (pilot study) and 16 (validation study) b values. In each study, data from all patients were used to model the IVIM signal of normal liver. Diffusion coefficients (D-i +/- standard deviations) and their fractions (f(i) +/- standard deviations) were determined from each model. The models were compared using the extra sum-of-squares test and information criteria. The tri-exponential model provided a better fit than both the bi- and mono-exponential models. The tri-exponential IVIM model determined three diffusion compartments: a slow (D-1 = 1.35 +/- 0.03 x 10(-3) mm(2)/s; f(1) = 72.7 +/- 0.9 %), a fast (D-2 = 26.50 +/- 2.49 x 10(-3) mm(2)/s; f(2) = 13.7 +/- 0.6 %) and a very fast (D-3 = 404.00 +/- 43.7 x 10(-3) mm(2)/s; f(3) = 13.5 +/- 0.8 %) diffusion compartment [results from the validation study]. The very fast compartment contributed to the IVIM signal only for b values a parts per thousand currency sign15 s/mm(2) The tri-exponential model provided the best fit for IVIM signal decay in the liver over the 0-800 s/mm(2) range. In IVIM analysis of normal liver, a third very fast (pseudo)diffusion component might be relevant.