Payne G S, Leach M O
CRC Clinical Magnetic Resonance Research Group, Royal Marsden Hospital, Sutton, Surrey, UK.
NMR Biomed. 1992 May-Jun;5(3):142-4. doi: 10.1002/nbm.1940050307.
Spin inversion produced by hyperbolic secant RF pulses is independent of pulse amplitude once a threshold value is exceeded. A semi-empirical formula for these pulses has been derived by application of analytical solutions to the Bloch equations. This predicts the required coil voltages for inversion as a function of inversion bandwidth and side-to-width parameter mu, based on knowledge of a reference voltage for the loaded coil. The voltage required is shown to increase linearly with bandwidth but to fall with the mu, approximately as (1/mu)0.4. Experimental confirmation is presented, and factors affecting choice of pulse parameters are discussed.
一旦超过阈值，双曲正割射频脉冲产生的自旋反转就与脉冲幅度无关。通过将解析解应用于布洛赫方程，推导了这些脉冲的半经验公式。基于对加载线圈参考电压的了解，该公式预测了反转所需的线圈电压与反转带宽和边宽参数μ的函数关系。结果表明，所需电压随带宽线性增加，但随μ下降，近似为(1/μ)^0.4。给出了实验验证，并讨论了影响脉冲参数选择的因素。
