Mori S, Hurd R E, van Zijl P C
Johns Hopkins University Medical School-Department of Radiology & Biophysics, Baltimore, Maryland 21205, USA.
Magn Reson Med. 1997 Mar;37(3):336-40. doi: 10.1002/mrm.1910370305.
It is shown that a repetitive pulse sequence consisting of two 90 degrees pulses and gradients in a 1:2 ratio around the second 90 degrees pulse generates interscan shifted stimulated echoes (SSTEs) and intrascan multiple spin echoes (MSEs). Separation of these two types of signals is accomplished using specific gradient crusher schemes. The intensity of the SSTEs is an order of magnitude larger than that of the MSEs and determines the signal contrast if both effects are selected simultaneously. The SSTE sequence generates improved contrast between gray and white matter, even at high field, which is explained in terms of increased inverse T1-weighting for the interscan echo. The MSE image has low signal to noise and no detectable contrast. The effect of interscan diffusion weighting is also discussed.
结果表明，由两个90度脉冲以及围绕第二个90度脉冲以1:2比例的梯度组成的重复脉冲序列会产生扫描间移位的受激回波（SSTE）和扫描内多自旋回波（MSE）。使用特定的梯度去相位方案可实现这两种信号的分离。SSTE的强度比MSE大一个数量级，并且如果同时选择这两种效应，SSTE将决定信号对比度。即使在高场强下，SSTE序列也能改善灰质和白质之间的对比度，这可以通过扫描间回波的反T1加权增加来解释。MSE图像的信噪比很低，且没有可检测到的对比度。文中还讨论了扫描间扩散加权的影响。
