MR elastography用バルスシーケンスの最適化による弾性波画像上の高波歪み抑制

摘要

Magnetic Resonance Elastography (MRE) is a technique for quantitative and noninvasive assessment of tissue elasticity. MRE is often described as image-based palpation that can be used to characterize disease because the mechanical properties of tissues are often dramatically affected by the presence of disease processes. MRE pulse sequences obtain shear wave images by synchronizing motion sensitized gradients (MSG) with an external vibrator. A quantitative shear modulus map is calculated from the shear wave images. However, the magnitude property of the external vibrator and nonlinearity of the imaged object often induce unwanted higher harmonics that distort the shear wave images and impair the estimation of the elastic modulus. In this study, we optimize the MSGs to minimize the contribution of higher harmonics to the shear wave images and therefore improve the accuracy of shear modulus estimation. Simulation and phantom studies were performed to confirm the performance of the proposed MRE pulse sequence. The results show that the optimized MSG is able to acquire single frequency shear wave images even when large amplitude harmonic waves are present in the imaged object.