Lee J N, Riederer S J
Magn Reson Med. 1986 Aug;3(4):634-8. doi: 10.1002/mrm.1910030416.
Spin-echo images can be synthesized at arbitrary values of echo time TEs if two images are acquired at the same repetition time and two different echo times TE1 and TE2. Depending on the value of TEs, the noise in the synthetic images can either be greater or less than the acquisition noise. This note shows that if the time between the acquired echoes TE2 - TE1 is equal to T2, the noise level in the synthetic images is no larger than the acquisition noise for TEs greater than or equal to TE1. This is the lowest possible noise bound for two-echo acquisition. Also, the noise bound for images synthesized with O less than or equal to TEs less than or equal to TE1 is minimized by making TE1 as short as possible.
如果在相同的重复时间以及两个不同的回波时间TE1和TE2采集两幅图像，那么自旋回波图像可以在任意回波时间TE值下进行合成。根据TE值的不同，合成图像中的噪声可能大于或小于采集噪声。本说明表明，如果采集回波之间的时间TE2 - TE1等于T2，那么对于大于或等于TE1的TE值，合成图像中的噪声水平不大于采集噪声。这是双回波采集可能的最低噪声界限。此外，通过使TE1尽可能短，可以将在0≤TE≤TE1范围内合成的图像的噪声界限最小化。
