Biexponential analysis of intravoxel incoherent motion in calf muscle before and after exercise: Comparisons with arterial spin labeling perfusion and T2

Purpose: This study aimed to clarify exercise-induced changes in intravoxel incoherent motion (IVIM) parameters obtained from diffusion-weighted imaging (DWI) of the calf muscle, as well as the relationships between IVIM parameters, perfusion, and water content in muscle tissue. Materials and methods: Thirteen healthy volunteers underwent IVIM-DWI, arterial spin labeling (ASL), and multi-echo spin-echo T-2 mapping of the right calf on a 3.0-T magnetic resonance imaging scanner before and after performing dorsiflexion exercise. From the data, we derived the perfusion-related diffusion coefficient (D*), perfusion component fraction (F), blood flow parameter (FD*), and restricted diffusion coefficient (D) in the tibialis anterior muscle. The muscle blood flow (MBF) and transverse relaxation time (T-2) were also calculated from the ASL and multi-echo spin-echo data, respectively. We compared the parameters measured before and after exercise and assessed the relationship of each IVIM-derived perfusion parameter (D*, F, and FD*) with MBF and each diffusion parameter (D and ADC) or F with T-2. Results: Notably, all these parameters were significantly increased after exercise. Before exercise, the FD* exhibited a significant positive correlation with the MBF, whereas no significant correlation was observed between D* or F and MBF. After exercise, both D* and FD* exhibited significant positive correlations with MBF, whereas F was not significantly correlated with MBF. Additionally, D was significantly correlated with T-2 after exercise, but not before exercise. No significant correlations were found between ADC and T-2 either before or after exercise. Conclusions: The IVIM analyses before and after exercise enable the simultaneous evaluation of exercise-induced changes in perfusion and water diffusion in the muscle and increases the body of information on muscle physiology.