Simple method for RF pulse measurement using gradient reversal.
Simple method for RF pulse measurement using gradient reversal.
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DOI：
10.1002/mrm.26920
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发表时间：
2018-05
影响因子：
3.3
通讯作者：
Nayak KS
中科院分区：
文献类型：
--
作者：
Landes VL;Nayak KS
开发和评估一种简单的方法，用于测量 MRI 中小尖端射频激励波形的包络，无需额外的硬件或同步。评估 RF 的梯度反转方法 (GRATER) 涉及以恒定梯度进行 RF 激励，并在信号接收期间反转该梯度，以获取 RF 包络的时间反转版本。可选地使用外部体积抑制（OVS）预脉冲来预选择均匀体积。 GRATER 在模型和体内实验中进行了评估。将其与编程波形和传统拾波线圈方法进行比较。在均匀体模实验中，对于翻转角≤30°、时间带宽乘积2至8和2至5个激励频带的真实射频脉冲，拾波线圈、GRATER和OVS+GRATER将编程波形分别匹配<2.1%、<6.1%和<2.4%归一化均方根误差(NRMSE)。对于翻转角 >30°，如 Bloch 模拟预测的那样，测量误差会增加。 OVS+GRATER 的脂肪-水模型和体内实验证明 <6.4% NRMSE。 GRATER 序列可测量小尖端 RF 包络，无需额外硬件或同步，只需两倍于 RF 持续时间。 GRATER 可用于预扫描校准以及射频放大器非线性的测量和预补偿。
To develop and evaluate a simple method for measuring the envelope of small-tip RF excitation waveforms in MRI, without extra hardware or synchronization. Gradient Reversal Approach to Evaluate RF (GRATER) involves RF excitation with a constant gradient and reversal of that gradient during signal reception to acquire the time-reversed version of an RF envelope. An outer-volume suppression (OVS) pre-pulse is optionally used to pre-select a uniform volume. GRATER was evaluated in phantom and in-vivo experiments. It was compared to the programmed waveform and the traditional pick-up coil method. In uniform phantom experiments, pick-up coil, GRATER, and OVS+GRATER matched the programmed waveforms to <2.1%, <6.1% and <2.4% normalized root mean square error (NRMSE), respectively, for real RF pulses with flip angle ≤30°, time-bandwidth product 2 to 8, and 2 to 5 excitation bands. For flip angles >30°, GRATER measurement error increased as predicted by Bloch simulation. Fat-water phantom and in-vivo experiments with OVS+GRATER demonstrated <6.4% NRMSE. GRATER sequence measures small-tip RF envelopes without extra hardware or synchronization in just over two times the RF duration. GRATER may be useful in pre-scan calibration and for measurement and pre-compensation of RF amplifier nonlinearity.
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影响因子：
10.6
作者：
PAULY, J;LEROUX, P;MACOVSKI, A
通讯作者：
MACOVSKI, A
影响因子：
3.3
作者：
Smith, Travis B.;Nayak, Krishna S.
通讯作者：
Nayak, Krishna S.
影响因子：
10.6
作者：
Zanchi, Marta G.;Stang, Pascal;Scott, Greig C.
通讯作者：
Scott, Greig C.
影响因子：
3.3
作者：
CHAN, F;PAULY, J;MACOVSKI, A
通讯作者：
MACOVSKI, A
影响因子：
2.2
作者：
Hoult, DI;Kolansky, G;King, SB
通讯作者：
King, SB