Schröder Christoph, Börnert Peter, Aldefeld Bernd
Philips Research Laboratories, Sector Technical Systems, Hamburg, Germany.
J Magn Reson Imaging. 2003 Jul;18(1):136-41. doi: 10.1002/jmri.10334.
To examine the usefulness of variable-density k-space trajectories for the design of multi-dimensional spatially selective RF pulses.
Experimental phantom and in vivo studies were performed and confirmed by simulations. Two-dimensional spatially selective magnetization patterns were excited using variable-density spiral trajectories and analyzed with respect to the signal excitation outside the excitation field of view (FOX).
By using variable-density trajectories, signal excitation outside the FOX was drastically reduced compared to trajectories with a uniform density, while maintaining fairly short pulse durations.
A main advantage of the method is that unwanted signal excitation outside the nominal FOX can be reduced without significantly increasing the duration of the RF excitation pulse. The variable-density approach is useful for all applications that require a well-defined spatial excitation profile, e.g., to perform imaging in a reduced field of view (FOV), for spatial saturation pulses, for curved slice imaging or in MR spectroscopy.
研究可变密度k空间轨迹在多维空间选择性射频脉冲设计中的实用性。
进行了实验体模和体内研究，并通过模拟进行了验证。使用可变密度螺旋轨迹激发二维空间选择性磁化模式，并分析了激发视野（FOX）之外的信号激发情况。
与均匀密度轨迹相比，使用可变密度轨迹时，FOX之外的信号激发显著减少，同时保持了相当短的脉冲持续时间。
该方法的一个主要优点是，在不显著增加射频激发脉冲持续时间的情况下，可以减少标称FOX之外的不必要信号激发。可变密度方法适用于所有需要明确空间激发轮廓的应用，例如在缩小的视野（FOV）中进行成像、用于空间饱和脉冲、用于曲面切片成像或磁共振波谱分析。
