Keltner J R, Wong S T, Roos M S
Center for Functional Imaging, Lawrence Berkeley Laboratory, Berkeley, California 94720.
J Magn Reson B. 1994 Jul;104(3):219-29. doi: 10.1006/jmrb.1994.1079.
The gradient-selected triple-quantum-filtered (GS3Q) experiment, developed to improve the contrast in NMR imaging of sodium-23 (23Na) in the human brain, is limited by low signal-to-noise ratio (SNR). We have analyzed the GS3Q experiment and show here that the improvement in GS3Q-filtered 23Na SNR as the repetition time (TR) decreases is accompanied by the appearance of spurious one-quantum (1Q) 23Na signals. An improved filter with better suppression of spurious 1Q 23Na signals is obtained by adding a preparatory crusher gradient and two-step phase cycling to a conventional GS3Q filter. The relative contributions of 3Q coherence and spurious 1Q coherences to the conventional and modified-GS3Q-filtered signals are calculated, providing a measure of the effectiveness of each GS3Q filter. The filters were implemented on a 2.35 T medium-bore spectrometer and their predicted properties verified. SNR measurements from GS3Q-filtered three-dimensional images of an agarose gel phantom indicate that 0.012 M 23Na images in the human brain can be acquired with 8 cm3 voxels and SNR of 10 in 30 minutes at 2.35 T, assuming similar relaxation times.
梯度选择三量子滤波（GS3Q）实验旨在提高人脑23钠（23Na）核磁共振成像的对比度，但受限于低信噪比（SNR）。我们分析了GS3Q实验，在此表明，随着重复时间（TR）的缩短，GS3Q滤波后的23Na信噪比的提高伴随着伪单量子（1Q）23Na信号的出现。通过在传统GS3Q滤波器中添加一个预脉冲去耦梯度和两步相位循环，可得到一种对伪1Q 23Na信号有更好抑制效果的改进滤波器。计算了3Q相干和伪1Q相干对传统和改进型GS3Q滤波信号的相对贡献，以此衡量每个GS3Q滤波器的有效性。这些滤波器在一台2.35 T的中孔径光谱仪上实现，并验证了其预测特性。对琼脂糖凝胶模型的GS3Q滤波三维图像进行的信噪比测量表明，假设弛豫时间相似，在2.35 T下，可以在30分钟内以8 cm3的体素和10的信噪比获取人脑0.012 M 23Na图像。
