Kose Ryoichi, Kose Katsumi, Fujimoto Koji, Okada Tomohisa, Tamada Daiki, Motosugi Utaroh
MRI simulations Inc.
Human Brain Research Center, Graduate School of Medicine, Kyoto University.
Magn Reson Med Sci. 2024 Oct 1;23(4):525-536. doi: 10.2463/mrms.tn.2023-0063. Epub 2023 Sep 9.
Recent high-performance gradient coils are fabricated mainly at the expense of spatial linearity. In this study, we measured the spatial nonlinearity of the magnetic field generated by the gradient coils of two MRI systems with high-performance gradient coils. The nonlinearity of the gradient fields was measured using 3D gradient echo sequences and a spherical phantom with a built-in lattice structure. The spatial variation of the gradient field was approximated to the 3rd order polynomials. The coefficients of the polynomials were calculated using the steepest descent method. The geometric distortion of the acquired 3D MR images was corrected using the polynomials and compared with the 3D images corrected using the harmonic functions provided by the MRI venders. As a result, it was found that the nonlinearity correction formulae provided by the vendors were insufficient and needed to be verified or corrected using a geometric phantom such as used in this study.
近期的高性能梯度线圈主要是以牺牲空间线性度为代价制造的。在本研究中，我们测量了两台配备高性能梯度线圈的MRI系统的梯度线圈所产生磁场的空间非线性。使用三维梯度回波序列和带有内置晶格结构的球形体模来测量梯度场的非线性。梯度场的空间变化近似为三阶多项式。使用最速下降法计算多项式的系数。利用这些多项式对采集到的三维MR图像的几何失真进行校正，并与使用MRI供应商提供的谐波函数校正后的三维图像进行比较。结果发现，供应商提供的非线性校正公式并不充分，需要使用本研究中使用的几何体模进行验证或校正。
