Balchandani Priti, Pauly John, Spielman Daniel
Department of Electrical Engineering, Stanford University, 1201 Welch Road, Stanford, CA 94305, USA.
Magn Reson Med. 2008 May;59(5):1072-8. doi: 10.1002/mrm.21540.
Adiabatic pulses are useful in achieving uniform excitation profiles in the presence of B(1)-inhomogeneity. At higher fields, this inhomogeneity becomes more severe, further amplifying the need for B(1)-insensitive excitation. Although gradient modulation techniques for slice-selective adiabatic excitation have been introduced, a pulse that falls within the gradient and RF amplifier limits for most commercial human scanners is currently unavailable. In this work, we present an alternative gradient modulated approach for pulse design that achieves adiabatic slice selection with significantly lower RF peak power requirements. The resulting Slice-selective Tunable-flip AdiaBatic Low peak-power Excitation (STABLE) pulse consists of an oscillating gradient in conjunction with a BIR-4-like RF envelope that is sampled by many short spatial subpulses to achieve spatial selectivity. Simulations show that the expected spatial profile as well as the off-resonance behavior of the pulse remain invariant for a range of B(1) values. Phantom and in vivo results demonstrate the adiabaticity and slice selectivity of the STABLE pulse.
在存在B(1)不均匀性的情况下，绝热脉冲对于实现均匀激发分布很有用。在更高场强下，这种不均匀性变得更加严重，进一步凸显了对B(1)不敏感激发的需求。尽管已经引入了用于切片选择性绝热激发的梯度调制技术，但目前还没有一种脉冲能在大多数商用人体扫描仪的梯度和射频放大器限制范围内。在这项工作中，我们提出了一种用于脉冲设计的替代梯度调制方法，该方法能以显著更低的射频峰值功率要求实现绝热切片选择。由此产生的切片选择性可调翻转绝热低峰值功率激发（STABLE）脉冲由一个振荡梯度与一个类似BIR-4的射频包络相结合组成，该包络由许多短空间子脉冲采样以实现空间选择性。模拟表明，对于一系列B(1)值，脉冲的预期空间分布以及失谐行为保持不变。体模和体内实验结果证明了STABLE脉冲的绝热性和切片选择性。
