On the field strength dependence of bi- and triexponential intravoxel incoherent motion (IVIM) parameters in the liver

TL;DR

This study examines how IVIM parameters in liver imaging depend on magnetic field strength, comparing bi- and triexponential models at 1.5T and 3T to inform cross-study comparisons.

Contribution

It demonstrates the B0 dependence of certain IVIM parameters and suggests the triexponential model's parameters are more comparable across different field strengths.

Findings

Triexponential model fits data better at low b-values.

Biexponential pseudo-diffusion coefficient varies significantly with field strength.

Triexponential parameters are more consistent across field strengths.

Abstract

Background: Studies on intravoxel incoherent motion (IVIM) imaging are carried out with different acquisition protocols. Purpose: Investigate the dependence of IVIM parameters on the B_0field strength when using a bi- or triexponential model. Field Strength/Sequence: 20 volunteers were examined at two field strengths (1.5 and 3T). Diffusion-weighted images of the abdomen were acquired at 24 b-values ranging from 0.2 to 500 s/mm2. Assessment: ROIs were manually drawn in the liver. Data were fitted with a bi- and a triexponential IVIM model. Resulting parameters were compared between both field strengths. Results: At b-values below 6s/mm2, the triexponential model provided better agreement with the data than the biexponential model. The average tissue diffusivity was D=1.22/1.00 um/ms at 1.5/3T. The average pseudo-diffusion coefficients for the biexponential model were D*=308/260um/ms at 1.5/3T; and for the triexponential model D1*=81.3/65.9um/ms , D2*=2453/2333um/ms at 1.5/3T. The average perfusion fractions for the biexponential model were f=0.286/0.303 at 1.5/3T; and for the triexponential model f1=0.161/0.174 and f2=0.152/0.159 at 1.5/3T. A significant B0 dependence was only found for the biexponential pseudo-diffusion coefficient (ANOVA/KW p=0.037/0.0453) and tissue diffusivity (ANOVA/KW: p<0.001). Conclusion: Our experimental results suggest that triexponential pseudo-diffusion coefficients and perfusion fractions obtained at different field strengths could be compared across different studies using different B0. However, it is recommendable to take the field strength into account when comparing tissue diffusivities or using the biexponential IVIM model. Considering published values for oxygenation-dependent transversal relaxation times of blood, it is unlikely that the two blood compartments of the triexponential model represent venous and arterial blood.