Prato F S, Drost D J, Keys T, Laxon P, Comissiong B, Sestini E
Magn Reson Med. 1986 Feb;3(1):63-75. doi: 10.1002/mrm.1910030109.
A simplified model relating signal intensity in an MR image to spin-lattice relaxation time (T1), repetition time (TR), number of signal averages and the average tip angle (-alpha) of the protons within the slice has been developed. This model has been used to select the optimal repetition times of two spin-echo images for a fixed total imaging time to maximize signal to noise in calculated T1 images. Theoretical predictions of T1 are virtually identical to spectroscopically measured values, and the relative noise (delta T1) in T1 images calculated from two measured spin-echo images is in good agreement with the theoretically predicted values of delta T1/T1. This model predicts that: (a) for a T1 of approximately 500 ms, the least T1 image noise is obtained with one of the spin-echo images collected with a TR of 400-500 ms. The longer the TR of the other spin-echo image, the lower the T1 image noise, but past a TR of approximately 1400 ms, T1 image signal/noise is optimized for the same total imaging time by increasing the number of averages in the shorter TR spin-echo image rather than increasing the TR of the second spin-echo image. (b) The error is reduced and the optimum TR1 is reduced as -alpha is increased from 63 to 90 degrees. (c) For a range of T1, optimal selection of TR1 and TR2 based on an intermediate value of T1, results in relatively little increase over optimal values in delta T1/T1 for the entire T1 range.
已建立一个简化模型，该模型将磁共振图像中的信号强度与自旋晶格弛豫时间（T1）、重复时间（TR）、信号平均次数以及切片内质子的平均翻转角（-α）相关联。此模型已用于在固定的总成像时间内选择两个自旋回波图像的最佳重复时间，以最大化计算出的T1图像中的信噪比。T1的理论预测值与光谱测量值几乎相同，并且从两个测量的自旋回波图像计算出的T1图像中的相对噪声（δT1）与理论预测的δT1/T1值高度吻合。该模型预测：（a）对于约500毫秒的T1，使用重复时间为400 - 500毫秒采集的其中一个自旋回波图像可获得最低的T1图像噪声。另一个自旋回波图像的重复时间越长，T1图像噪声越低，但超过约1400毫秒的重复时间后，对于相同的总成像时间，通过增加较短重复时间自旋回波图像的平均次数而非增加第二个自旋回波图像的重复时间来优化T1图像的信号/噪声。（b）随着-α从63度增加到90度，误差减小且最佳TR1减小。（c）对于一系列T1，基于T1的中间值对TR1和TR2进行最佳选择，在整个T1范围内，δT1/T1的增加相对于最佳值相对较小。
