Chung Jun-Young, Yoon Hyo Woon, Kim Young-Bo, Park Hyun Wook, Cho Zang-Hee
Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Republic of Korea.
J Magn Reson Imaging. 2009 Jan;29(1):221-8. doi: 10.1002/jmri.21397.
To implement a method using a tailored radiofrequency (TRF) pulse with a quadratic phase profile to recover susceptibility-induced signal losses in gradient-recalled echo-planar images (EPI).
A functional magnetic resonance imaging (fMRI) experiment for compensation of susceptibility artifacts, known as the TRF pulse EPI sequence (TRF-EPI), was used. TRF pulse compensates the susceptibility effect with a reduced signal-to-noise ratio (SNR) to one-half when the maximum phase distribution is 2pi. We demonstrate theoretically that the maximum phase distribution can also be reduced to pi rather than 2pi, improving the SNR accordingly. An analysis was conducted comparing this newly proposed strategy using a standard RF excitation with a linear phase distribution and a quadratic TRF excitation with a pi phase distribution.
Thorough experimental comparisons were also made between the TRF quadratic excitation with a pi phase profile and conventional EPI with a standard excitation in human subjects during ventral brain activation.
With reduced maximum phase distribution in the TRF pulse, signals in the susceptibility-affected areas, such as the orbitofrontal and inferior temporal cortex, were increased, suggesting that the technique could be a useful adjunct to fMRI.
实施一种使用具有二次相位轮廓的定制射频（TRF）脉冲来恢复梯度回波平面成像（EPI）中由磁化率引起的信号损失的方法。
使用了一种用于补偿磁化率伪影的功能磁共振成像（fMRI）实验，即TRF脉冲EPI序列（TRF-EPI）。当最大相位分布为2π时，TRF脉冲以将信噪比（SNR）降低至二分之一的方式补偿磁化率效应。我们从理论上证明，最大相位分布也可以减小到π而不是2π，从而相应地提高SNR。对这种新提出的使用具有线性相位分布的标准射频激发策略和具有π相位分布的二次TRF激发进行了分析比较。
还在人类受试者大脑腹侧激活期间，对具有π相位轮廓的TRF二次激发与具有标准激发的传统EPI进行了全面的实验比较。
随着TRF脉冲中最大相位分布的减小，受磁化率影响区域（如眶额皮质和颞下回皮质）的信号增加，表明该技术可能是fMRI的有用辅助手段。
