WIMP: SELF-NAVIGATING MAGNETIZATION TRANSFER POOL MAPPING WITH STIMULATED ECHOES

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。简介：磁化转移（MT）提供了有关交换速率以及存在于组织中的结合大分子的相对数量的信息。MT已被证明可用于检测早期白质变性，如多发性硬化症[6]。然而，定量MT序列需要复杂的多参数拟合。因此，序列通常只与简单的开或关共振预脉冲结合，从中可以计算半定量参数，如MTR。然而，这些MT序列的变体不能映射纯生物物理参数，并且可能被几个因素混淆。结合池和自由池的转移速率和相对分数大小有望提供更多关于组织成分的定量信息[4]，但目前需要复杂的多参数模型和超长的成像时间[3-5]。最近，Ropele等人提出了一种新的方法，可以直接测量结合的大分子含水量，该方法基于受激回波（STE）制备方案，该方案可以调节水自旋的相分布。这些标记的自旋然后用作本征指示剂，由于与大分子质子的磁化交换而被稀释。目前，该方法仅限于单次采集，因为在序列的制备阶段应用了小磁场梯度，使得序列对整体生理运动敏感。在这项工作中，我们将利用可变密度螺旋轨迹[2]的自导航能力来精确补偿运动和相位积累，从而实现更准确的BPF计算和更高的空间分辨率。参考文献：[1]Ropele等。MRM(49), 864 - 871年,2003年。刘，等。MRM(52), 1388 - 1396年,2004年。b[3] Sled等。MRM(46), 923 - 931年,2001年。[10]刘建军，陈建军，2003。[10]杨建军，刘建军，刘建军，2002。[b] Tozer等。科学通报，2003。[2] [j] .中华核磁共振杂志，2002(10):721- 331。]刘志强，刘志强(5),2005。致谢：工作得到了美国国立卫生研究院（1R01EB002771）、斯坦福大学高级磁共振技术中心（P41RR09784）、卢卡斯和橡树基金会的部分支持

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Magnetization transfer (MT) provides information on the rate of exchange as well as relative amount of bound macromolecules present in tissue. MT has been shown useful in detecting early white matter degeneration, such as with multiple sclerosis [6]. However, quantitative MT sequences require complex multi-parametric fits. Therefore, sequences were normally only combined with simple on or off-resonant pre-pulses, from which semi-quantitative parameters, such as MTR, can be computed. However, these variants of MT sequences do not map pure bio-physical parameters and can be confounded by several factors. Transfer rate and relative fraction sizes of bound and free water pools are expected to provide more quantitative information on tissue composition [4] but presently require complicated multi-parametric models and prohibitively long imaging times [3-5]. Recently, Ropele et al. [1] introduced a novel method that provides direct measurement of bound macromolecular water content, which is based on a stimulated echo (STE) preparation scheme that modulates the phase distribution of water spins. These labeled spins are then used as an intrinsic indicator, which dilutes due to magnetization exchange with macromolecular protons. Currently, this method is limited to single-shot acquisitions due to the application of small magnetic field gradients in the preparation phase of the sequence that renders the sequence sensitive to bulk physiologic motion. In this work, we will capitalize on the self-navigating capabilities of variable density spiral trajectories [2] to accurately compensate for motion and phase accumulation, which in turn allows a more accurate BPF calculation and higher spatial resolution. References: [1] Ropele, et al. MRM (49),864-871,2003. [2] Liu, et al. MRM (52),1388-1396,2004. [3] Sled et al. MRM (46),923-931,2001. [4] Henkelman, MRM (29),759-766,1993. [5] Yarnykh, MRM (47),929-939,2002. [6] Tozer et al. MRM 5:83-91, 2003. [7] Ramani, MRI, 20(10), 721-31, 2002. [8] Liu, MRM (54), 2005. Acknowledgements: Work was supported in part by the NIH (1R01EB002771), Center of Advanced MR Technology at Stanford (P41RR09784), Lucas and Oak Foundations