Wang H Z, Riederer S J
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710.
Magn Reson Med. 1990 Aug;15(2):175-91. doi: 10.1002/mrm.1910150202.
We present a spoiler sequence which substantially eliminates residual transverse magnetization in rapid magnetic resonance imaging. Such magnetization is due to the repetition time TR being on the order of or shorter than the transverse relaxation time T2. This sequence was designed using computer simulation methods to model the slice profile and signal. The spoiler pulse is applied in the slice-selecting direction and the magnitude of the gradient spoiler is incremented with each repetition as an arithmetic series. A finite number of different spoiler amplitudes is repeated with a cycle time several times greater than the anticipated T2. Each spoiler is shown to nullify the residual transverse magnetization from the just-measured signal of the experiment as well as that from preceding repetitions. It is shown experimentally that the spoiler pulse can be as short as 2 ms. This is considerably shorter than existing methods using constant spoiling or phase-tagged spoiling. This sequence was used to acquire T1-weighted images free of the central line artifact of FLASH imaging. Furthermore, images formed with the new spoiled technique are shown to have contrast-to-noise comparable if not superior to standard T1-weighted spin-echo images while taking only a fifth of the scan time.
我们提出了一种扰相序列，该序列能在快速磁共振成像中大幅消除残余横向磁化。这种磁化是由于重复时间TR约等于或短于横向弛豫时间T2所致。此序列是利用计算机模拟方法设计的，用于模拟切片轮廓和信号。扰相脉冲沿切片选择方向施加，梯度扰相的幅度以算术级数随每次重复递增。有限数量的不同扰相幅度以比预期T2大几倍的周期时间重复。结果表明，每个扰相都能消除实验中刚测量信号以及先前重复信号产生的残余横向磁化。实验表明，扰相脉冲可短至2毫秒。这比使用恒定扰相或相位标记扰相的现有方法要短得多。该序列用于获取无FLASH成像中心线伪影的T1加权图像。此外，结果表明，用新的扰相技术形成的图像，其对比度噪声即使不优于标准T1加权自旋回波图像，也与之相当，而且扫描时间仅为其五分之一。
