Atalar E, McVeigh E R
Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Magn Reson Med. 1994 Dec;32(6):773-7. doi: 10.1002/mrm.1910320613.
With the advent of breath-hold MR cardiac imaging techniques, the minimization of TR and TE for oblique planes has become a critical issue. The slew rates and maximum currents of gradient amplifiers limit the minimum possible TR and TE by adding dead-periods to the pulse sequences. We propose a method of designing gradient waveforms that will be applied to the amplifiers instead of the slice, readout, and phase encoding waveforms. Because this method ensures that the gradient amplifiers will always switch at their maximum slew rate, it results in the minimum possible dead-period for given imaging parameters and scan plane position. A GRASS pulse sequence has been designed and ultra-short TR and TE values have been obtained with standard gradient amplifiers and coils. For some oblique slices, we have achieved shorter TR and TE values than those for nonoblique slices.
随着屏气磁共振心脏成像技术的出现，对于斜平面而言，使重复时间（TR）和回波时间（TE）最小化已成为一个关键问题。梯度放大器的 slew 率和最大电流通过在脉冲序列中增加死时间来限制可能的最小 TR 和 TE。我们提出一种设计梯度波形的方法，该方法将应用于放大器，而不是层面选择、读出和相位编码波形。由于此方法确保梯度放大器始终以其最大 slew 率切换，所以对于给定的成像参数和扫描平面位置，可得到可能的最小死时间。已设计出一种稳态进动快速成像（GRASS）脉冲序列，并使用标准梯度放大器和线圈获得了超短的 TR 和 TE 值。对于一些斜层面，我们获得了比非斜层面更短的 TR 和 TE 值。
