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

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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