Neggers Sebastiaan F W, Hermans Erno J, Ramsey Nick F
Rudolf Magnus Institute of Neuroscience, Division of Neuroscience, University Medical Center Utrecht, The Netherlands.
NMR Biomed. 2008 Aug;21(7):663-76. doi: 10.1002/nbm.1235.
A major impetus in functional MRI development is to enhance sensitivity to changes in neural activity. One way to improve sensitivity is to enhance contrast to noise ratio, for instance by increasing field strength or the number of receiving coils. If these parameters are fixed, there is still the possibility to optimize scans by altering speed or signal strength [signal-to-noise ratio (SNR)]. We here demonstrate a very fast whole-brain scan, by combining a three-dimensional (3D)-PRESTO (principle of echo shifting with a train of observations) pulse sequence with a commercial eight-channel head coil and sensitivity encoding (SENSE). 3D-PRESTO uses time optimally by means of echo shifting. Moreover, 3D scans can accommodate SENSE in two directions, reducing scan time proportionally. The present PRESTO-SENSE sequence achieves full brain coverage within 500 ms. We compared this with a two-dimensional (2D) echo planar imaging (EPI) scan with identical brain coverage on 10 volunteers. Resting-state temporal SNR in the blood-oxygen-level-dependent (BOLD) frequency range and T-statistics for thumb movement and visual checkerboard activations were compared. Results show improved temporal SNR across the brain for PRESTO-SENSE compared with EPI. The percentage signal change and relative standard deviation of the noise were smaller for PRESTO-SENSE. Sensitivity for brain activation, as reflected by T-values, was consistently higher for PRESTO, and this seemed to be mainly due to the increased number of observations within a fixed time period. We conclude that PRESTO accelerated with SENSE in two directions can be more sensitive to BOLD signal changes than the widely used 2D-EPI, when a fixed amount of time is available for functional MRI scanning.
功能磁共振成像（fMRI）发展的一个主要推动力是提高对神经活动变化的敏感性。提高敏感性的一种方法是提高对比度与噪声比，例如通过增加场强或接收线圈的数量。如果这些参数固定，仍然有可能通过改变速度或信号强度[信噪比（SNR）]来优化扫描。我们在此展示了一种非常快速的全脑扫描，通过将三维（3D）-快速成像稳态采集（PRESTO，基于一系列观测的回波移位原理）脉冲序列与商用八通道头部线圈及灵敏度编码（SENSE）相结合。3D-PRESTO通过回波移位来优化时间利用。此外，3D扫描可以在两个方向上应用SENSE，从而按比例减少扫描时间。当前的PRESTO-SENSE序列在500毫秒内实现全脑覆盖。我们将其与对10名志愿者进行的具有相同脑覆盖范围的二维（2D）回波平面成像（EPI）扫描进行了比较。比较了血氧水平依赖（BOLD）频率范围内的静息态时间SNR以及拇指运动和视觉棋盘格激活的T统计量。结果表明，与EPI相比PRESTO-SENSE在全脑范围内的时间SNR有所提高。PRESTO-SENSE的信号变化百分比和噪声的相对标准差更小。PRESTO的T值所反映的脑激活敏感性始终更高，这似乎主要是由于在固定时间段内观测次数增加所致。我们得出结论，当有固定时间用于功能磁共振成像扫描时，在两个方向上采用SENSE加速的PRESTO对BOLD信号变化可能比广泛使用的2D-EPI更敏感。
