Lee J N, Riederer S J, Bobman S A, Johnson J P, Farzaneh F
Med Phys. 1986 Mar-Apr;13(2):170-6. doi: 10.1118/1.595954.
We present a model of noise propagation from acquired magnetic resonance (MR) images to TR-extrapolated synthetic images. This model assumes that images acquired at two repetition times TR1 and TR2 are used to generate synthetic images at arbitrary repetition times TR. The predictions of the model are compared with experimentally acquired phantom data, and show excellent agreement. The model is utilized in an analysis of two applications of MR image synthesis: scan time reduction and multiple-image synthesis. Scan time is reduced by acquiring data at two short repetition times, and synthesizing at a longer repetition time, with TR1 + TR2 less than TR. For T1 = 800 ms, a reduction of 20% in scan time results in a 45% reduction in signal-to-noise ratio SNR, when compared to direct acquisition. Reducing scan time by much more than 20% produces large noise levels in the synthetic image, and is unlikely to be useful. In multiple-image synthesis, images are synthesized at any repetition time in the range 0 to TR1 + TR2, for contrast optimization. If T1 = 800 ms, and TR1 + TR2 = 2000 ms, the optimum combination of TR1, TR2 results in synthetic images whose SNR is at worst 22% less than the SNR of directly acquired images. For many values of TR, the synthetic images have SNR superior to that obtainable by direct acquisition.
我们提出了一种从采集的磁共振（MR）图像到TR外推合成图像的噪声传播模型。该模型假设在两个重复时间TR1和TR2采集的图像用于生成任意重复时间TR的合成图像。将该模型的预测结果与实验获取的体模数据进行比较，结果显示出极佳的一致性。该模型被用于分析MR图像合成的两个应用：扫描时间缩短和多图像合成。通过在两个短重复时间采集数据，并在更长的重复时间进行合成来缩短扫描时间，其中TR1 + TR2小于TR。对于T1 = 800 ms，与直接采集相比，扫描时间减少20%会导致信噪比（SNR）降低45%。扫描时间减少超过20%会在合成图像中产生较大的噪声水平，不太可能有用。在多图像合成中，为了优化对比度，在0到TR1 + TR2范围内的任何重复时间合成图像。如果T1 = 800 ms且TR1 + TR2 = 2000 ms，TR1、TR2的最佳组合会得到合成图像，其SNR最差比直接采集图像的SNR低22%。对于许多TR值，合成图像的SNR优于直接采集可获得的SNR。
