Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
Institute of Neuroscience and Medicine-4, Forschungszentrum Juelich GmbH, Wilhelm-Johnen-Strasse, Juelich, Germany.
Magn Reson Med. 2017 Dec;78(6):2216-2225. doi: 10.1002/mrm.26624. Epub 2017 Feb 28.
In order to benefit from the increased spectral bandwidth at ultrahigh field (UHF), the use of parallel transmission (pTx) to mitigate flip-angle inhomogeneity in chemical exchange saturation transfer (CEST) imaging is investigated.
A pTx basis pulse is homogenised by magnitude least-squares (MLS) optimization and expanded to form a frequency-selective saturation pulse for CEST. The pTx saturation pulse was simulated with a three-pool Bloch-McConnell equation to evaluate the impact of pTx on CEST contrast. In vivo CEST imaging performance (7 T) of the pTx saturation pulse and the standard Gaussian saturation in circularly polarized mode were compared. Two-spokes pTx homogeneous excitation was used in all in vivo experiments to ensure fair comparison of the two saturation pulses. Magnetization transfer ratio and inverse Z-spectrum analyses were used as metrics in evaluating the data from 3 healthy volunteers.
Bloch-McConnell simulations showed that side bands of the pTx saturation pulse at ±20 ppm did not affect any CEST contrast. Improved homogeneity in contrasts and relaxation-compensated CEST metrics were observed in our in vivo data when the pTx saturation pulse was used.
A pTx-based pulsed CEST presaturation scheme is proposed and validated by simulations and 7T in vivo imaging. Magn Reson Med 78:2216-2225, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
为了受益于超高场（UHF）下增加的光谱带宽，研究了使用并行传输（pTx）来减轻化学交换饱和转移（CEST）成像中翻转角不均匀性。
通过幅度最小二乘（MLS）优化来均匀化 pTx 基脉冲，并将其扩展为形成用于 CEST 的频率选择饱和脉冲。使用三池 Bloch-McConnell 方程模拟 pTx 饱和脉冲，以评估 pTx 对 CEST 对比度的影响。比较了 pTx 饱和脉冲和圆形偏振模式下标准高斯饱和在 7T 下的体内 CEST 成像性能。在所有体内实验中都使用两束 pTx 均匀激发，以确保两种饱和脉冲的公平比较。使用磁化转移比和逆 Z 谱分析作为评估来自 3 名健康志愿者的数据的指标。
Bloch-McConnell 模拟表明，pTx 饱和脉冲的 ±20ppm 边带不会影响任何 CEST 对比度。当使用 pTx 饱和脉冲时，我们的体内数据显示对比度和弛豫补偿的 CEST 指标的均匀性得到了改善。
提出了一种基于 pTx 的脉冲 CEST 预饱和方案，并通过模拟和 7T 体内成像进行了验证。磁共振医学 78:2216-2225, 2017。©2017 年国际磁共振学会。
