MR imaging of oscillatory magnetic field changes: Progressing from phantom to human.
Detection of ultra-weak oscillatory magnetic field changes using MRI is of great research interest not only for neuronal current MRI of endogenous neuronal oscillations but also for direct visualization of exogenous transcranial currents or iron oxide contrast agent distribution. In this work, we present a novel oscillatory-selective detection (OSD) method that is magnitude-sensitive to the oscillatory magnetic field changes and immune to the main field inhomogeneity. In OSD, a train of 180° pulses with alternating polarity and mirror symmetry are used to refocus and accumulate magnetization changes induced by external oscillatory fields. After taking both the signal change and image signal-to-noise ratio (SNR) into account, a final 90° pulse with a phase offset of 45° is applied to store a combination of the current-induced signal change and background magnetization for the subsequent EPI acquisition. Its performance was demonstrated in phantom and human studies, both of which showed much better detection in the comparison with the recently proposed spin-lock oscillatory excitation (SLOE) method. OSD was further successfully applied in imaging transcranial alternating current stimulation (tACS) induced field changes in the human brain. These promising results suggest that OSD can overcome the limitation of field inhomogeneity impeding previous oscillatory current MRI sensitivity and be a viable tool in future tACS study.
Beijing City Key Lab for Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China; Center for MRI Research, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China.
Yuhui
Y
Chai
Beijing City Key Lab for Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China; Center for MRI Research, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China.
Jingwei
J
Sheng
Beijing City Key Lab for Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China; Center for MRI Research, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China.
Weiwei
W
Men
GE Healthcare MR Research China, Beijing, China.
Yang
Y
Fan
GE Healthcare MR Research China, Beijing, China.
Bing
B
Wu
Beijing City Key Lab for Medical Physics and Engineering, Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China; Center for MRI Research, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China; McGovern Institute for Brain Research, Peking University, Beijing, China. Electronic address: jgao@pku.edu.cn.
Jia-Hong
JH
Gao
D001921:Brain / Q000000981:diagnostic imaging* / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio
Neuronal current; Oscillatory current; fMRI; tACS