ROBUST LIPID SUPPRESSION USING MULTIPLE FREQUENCY PULSES FOR BRAIN MRS AT 3T

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。脑光谱成像在神经疾病的诊断和治疗中应用越来越广泛。脂质抑制对研究的成功至关重要，为了实现全脑覆盖，尽管有显著的代谢物信号丢失，但经常使用反转恢复。在3T时，频率选择性反转恢复技术已经实现，以避免这些信号损失。然而，由于B1和T1的变化，抑制往往是不完全的。为了解决这些问题，一种强大的脂质抑制技术被提出并用于3T脑mri。方法与讨论：采用Shinnar-Le Roux算法设计了一个20 ms长的最小相位脂质选择性反转脉冲。为了考虑到B1的不均匀性和脂质自旋的不同T1s，我们使用了四个这样的脉冲，间隔10ms，具有不同的翻转角度。在三种不同的T1s， 170/260/280 ms和¿10% B1不均匀性下，通过最小化激发时残余纵向脂质磁化的最大绝对值，找到了四种不同的翻转角度。仿真和实验结果表明，该系统具有良好的性能。使用优化算法发现的四个翻转角度为110/74/67/162度，使用多个脉冲明显优于单脉冲实现。多个脂质选择脉冲在靶向T1s上实现了更好的脂质抑制，并且在B1不均匀性下具有鲁棒性。特别是，单次反转脉冲对体内脂质抑制约为10，多次翻转角脉冲对体内脂质抑制约为20。致谢：Lucas基金会，NIH RR 09784, CA 48269

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: Brain spectroscopic imaging has been increasingly used in diagnosis and treatment of neuropathologies. Lipid suppression is critical for a successful study, and to achieve whole brain coverage, inversion recovery is often used, despite significant metabolite signal loss. At 3T, frequency selective inversion recovery technique has been implemented to avoid these signal losses. However, suppression is often incomplete due to B1 and T1 variations. To address these issues, a robust lipid suppression technique has been proposed and implemented for brain MRSI at 3T. Methods and Discussion: A 20 ms long minimum phase lipid-selective inversion pulse was designed using the Shinnar-Le Roux algorithm. To account for B1 inhomogeneity and different T1s of lipid spins, four such pulses, 10ms apart, with different flip angles were used. The four different flip angles were found by minimizing the maximum absolute value of residue longitudinal lipid magnetization at the time of excitation for three different T1s, 170/260/280 ms, and ¿10 percent B1 inhomogeneity. Simulations and experimental results showed excellent performance. The four flip angles found using the optimization algorithm are 110/74/67/162 degrees, and the use of multiple pulses clearly outperformed single pulse implementations. The multiple lipid selective pulses achieved much better lipid suppression at targeted T1s and were robust under B1 inhomogeniety. In particular, in vivo lipid suppression was on the order of 10 for a single inversion pulse and higher than 20 for multiple flip angle pulses. Acknowledgements: Lucas foundation, NIH RR 09784, CA 48269