Ngo Giang Chau, Sutton Bradley P
Annu Int Conf IEEE Eng Med Biol Soc. 2014;2014:1537-40. doi: 10.1109/EMBC.2014.6943895.
T()2 mapping or R()2 mapping for brain function offers advantages such as providing quantitative measurements independent of the MRI acquisition parameters (e.g. echo time TE). However, magnetic field susceptibility in the human brain can prevent an accurate estimation of R()2, which in turn impacts the ability to study brain function. The present work investigates the effects of in-plane magnetic susceptibility-induced magnetic field gradients on R()2 decay. An iterative method is developed for R(*)2 estimation with an increased robustness to field inhomogeneity. The new method is further tested in a visual fMRI experiment with and without magnetic field gradients and its performance is compared to a standard BOLD fMRI and a BOLD fMRI based on echo summation. Reduced sensitivity in fMRI to in-plane magnetic gradients is obtained with the present methodology.
用于脑功能的 T()2 映射或 R()2 映射具有诸多优势，比如能提供独立于 MRI 采集参数（如回波时间 TE）的定量测量。然而，人脑的磁场敏感性会妨碍对 R()2 的准确估计，进而影响研究脑功能的能力。本研究探讨了平面内磁化率诱导的磁场梯度对 R()2 衰减的影响。开发了一种迭代方法用于 R(*)2 估计，该方法对场不均匀性具有更高的稳健性。在有和没有磁场梯度的视觉 fMRI 实验中对新方法进行了进一步测试，并将其性能与标准 BOLD fMRI 以及基于回波求和的 BOLD fMRI 进行了比较。采用本方法可降低 fMRI 对平面内磁场梯度的敏感性。
