Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6100, United States.
Magn Reson Med. 2012 Aug;68(2):588-94. doi: 10.1002/mrm.23250. Epub 2011 Dec 27.
The sensitivity of chemical exchange saturation transfer (CEST) on glycosaminoglycans (GAGs) in human knee cartilage (gagCEST) in vivo was evaluated at 3 and 7 T field strengths. Calculated gagCEST values without accounting for B(0) inhomogeneity (~0.6 ppm) were >20%. After B(0) inhomogeneity correction, calculated gagCEST values were negligible at 3 T and ~6% at 7 T. These results suggest that accurate B(0) correction is a prerequisite for observing reliable gagCEST. Results obtained with varying saturation pulse durations and amplitudes as well as the consistency between numerical simulations and our experimental results indicate that the negligible gagCEST observed at 3 T is due to direct saturation effects and fast exchange rate. As GAG loss from cartilage is expected to result in a further reduction in gagCEST, gagCEST method is not expected to be clinically useful at 3 T. At high fields such as 7 T, this method holds promise as a viable clinical technique.
在 3T 和 7T 场强下，评估了活体人膝关节软骨中糖胺聚糖（GAG）的化学交换饱和传递（CEST）的灵敏度（gagCEST）。未考虑 B0 不均匀性（约 0.6ppm）时，计算的 gagCEST 值>20%。在进行 B0 不均匀性校正后，在 3T 时计算的 gagCEST 值可忽略不计，在 7T 时约为 6%。这些结果表明，准确的 B0 校正对于观察可靠的 gagCEST 是必要的。通过改变饱和脉冲持续时间和幅度获得的结果以及数值模拟与实验结果之间的一致性表明，在 3T 时观察到的可忽略不计的 gagCEST 是由于直接饱和效应和快速交换率。由于软骨中 GAG 的损失预计会导致 gagCEST 的进一步降低，因此在 3T 时，gagCEST 方法预计不会在临床上有用。在 7T 等较高场强下，该方法有望成为一种可行的临床技术。
