论文标题
使用单通道线圈的通用脉冲用于均质激发
Universal pulses for homogeneous excitation using single channel coils
论文作者
论文摘要
目的：通用脉冲（UPS）是激发脉冲，可在没有受试者特异性优化的高场MRI系统中降低翻转角度不均匀性，最初是在7T下为平行传输（PTX）系统开发的。我们研究了UPS对单个通道（SC）的3T传输系统的潜在益处，该系统被广泛用于临床和研究成像，而对于该成像，对于其中，flip角度不均匀性仍然可能是有问题的。 方法：使用螺旋非选择性的K空间轨迹设计SC-UPS在3T处使用发射场图（B1+）（B1+）和非谐波图（B0）在两种不同的扫描仪类型上获取：一种“标准”单通道传输系统和带有PTX主体盘的系统。使用标准系统的数据（200个受试者）研究了训练组规模的效果。 PTX系统用于将SC-UP与PTX-UP进行比较（15个受试者）。在另外两个主题中，研究了使用SC-UP的前瞻性成像。 结果：使用经过50多个受试者训练的SC-UPS，平均翻盖角误差从9.5 +/- 0.5％降至3.0 +/- 0.6％。随着训练组的规模的增加，UPS的性能稳步改善，但在约15名受试者后稳定。在启用PTX的系统上，SC UPS再次优于模拟中的默认激发（分别为4.8 +/- 0.6％的错误，分别为10.6 +/- 0.8％），尽管可以使用PTX-UP（3.9 +/- 0.6％）和个性化脉冲（SC-PPP 3.6 +/- 1.0％，PTX-2.9％）实现更大的均质化。使用SC-UP进行的MP-RAGE成像导致灰质和白质信号强度之间的分离比默认激发更大。 结论：SC-UP可以在不进一步校准的情况下改善标准3T系统中的激发均匀性，而不是在3T时进行非选择性神经影像的默认激发脉冲。
Purpose: Universal Pulses (UPs) are excitation pulses that reduce the flip angle inhomogeneity in high field MRI systems without subject-specific optimization, originally developed for parallel transmit (PTX) systems at 7T. We investigated the potential benefits of UPs for single channel (SC) transmit systems at 3T, which are widely used for clinical and research imaging, and for which flip angle inhomogeneity can still be problematic. Methods: SC-UPs were designed using a spiral nonselective k-space trajectory for brain imaging at 3T using transmit field maps (B1+) and off-resonance maps (B0) acquired on two different scanner types: a 'standard' single channel transmit system and a system with a PTX body coil. The effect of training group size was investigated using data (200 subjects) from the standard system. The PTX system was used to compare SC-UPs to PTX-UPs (15 subjects). In two additional subjects, prospective imaging using SC-UP was studied. Results: Average flip angle error fell from 9.5+/-0.5% for 'default' excitation to 3.0+/-0.6% using SC-UPs trained over 50 subjects. Performance of the UPs was found to steadily improve as training group size increased, but stabilized after ~15 subjects. On the PTX-enabled system, SC-UPs again outperformed default excitation in simulations (4.8+/-0.6% error versus 10.6+/-0.8% respectively) though greater homogenization could be achieved with PTX-UPs (3.9+/-0.6%) and personalized pulses (SC-PP 3.6+/-1.0%, PTX-PP 2.9+/-0.6%). MP-RAGE imaging using SC-UP resulted in greater separation between grey and white matter signal intensities than default excitation. Conclusions: SC-UPs can improve excitation homogeneity in standard 3T systems without further calibration and could be used instead of a default excitation pulse for nonselective neuroimaging at 3T.
