Evaluation of a rapid, multiphase MRE sequence in a heart-simulating phantom

The aims of this study were to validate stiffness estimates of a phantom undergoing cyclic deformation obtained using a multiphase magnetic resonance elastography (MRE) imaging sequence by comparison with those obtained using a single-phase MRE sequence and to quantify the stability of the multiphase-derived stiffness estimates as a function of deformation frequency and imaging parameters. A spherical rubber shell of 10 cm diameter and 1 cm thickness was connected to a computerized flow pump to produce cyclic pressure variations within the phantom. The phantom was imaged at cyclic pressures between 18-72 bpm using single-phase and multiphase MRE acquisitions. The shear stiffness of the phantom was resolved using a spherical shell wave inversion algorithm. Shear stiffness was averaged over the slice of interest and plotted against pressure within the phantom. A linear correlation was observed between stiffness and pressure. Good correlation (R² = 0.98) was observed between the stiffness estimates obtained using the standard single-phase and the multiphase pulse sequences. Stiffness estimates obtained using multiphase MRE were stable when the fraction of the deformation period required for acquisition of a single image was not greater than 42%. The results demonstrate the potential of multiphase MRE technique for imaging dynamic organs, such as the heart.