Dependency of the IVIM Signal on the First-Order Motion Moment and Encoding Duration in the Liver and Kidneys

Motivation: Characterizing the dependencies of the first-order motion moment (M1) and encoding duration (T) on the intravoxel incoherent motion (IVIM) signal is important for developing accurate biophysical modeling and reproducible quantitative IVIM methods. Goal(s): Evaluate the dependency of M1 and T on the IVIM signal in the liver and kidneys using specially designed gradient waveforms. Approach: IVIM data with 85 unique b-M1-T-TE combinations were acquired in six healthy volunteers. Dependencies of the IVIM signal were evaluated using mixed-effects modeling. Results: In the liver and kidneys, the IVIM signal demonstrated significant dependency on M1 (p<0.001) and non-significant dependency on T (p≥0.26). Impact: In the liver and kidneys, a combined ballistic and pseudo-diffusion IVIM signal model with b and M1 dependence may be valid. IVIM models that depend on T may be inaccurate in these organs for T approximately 11.5-80.5ms.