SHORT ECHO TIME DUALBAND SPATIAL-SPECTRAL PULSE SEQUENCE FOR BRAIN MRSI 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: 1H Magnetic resonance spectroscopic imaging (1H MRSI) is a useful technique for measuring brain metabolites. Dualband spatial-spectral (SPSP) pulses have been designed at 3T for fully exciting the metabolites of interest, partially exciting water, while suppressing lipids. However, in these sequences, the 180¿ SPSP pulses must have nonlinear phase (along the spectral direction) in order to stay below RF peak power limits and consequently both 180¿ pulses in the PRESS excitation are relatively long. This limits TE to a minimum of 90 ms for the brain. In this study, the use of a PRESS sequence with only one dualband spatial-spectral linear phase 90¿ pulse and two standard spatial 180¿ pulses is proposed for brain MRSI. This sequence provides spectral selectivity while allowing significantly shorter echo times than existing SPSP PRESS sequences for the brain. Methods and Discussion: A linear phase 90¿ dualband SPSP pulse was designed using twenty one linear phase subpulses that could excite a slice as thin as 5 mm. The passband for the pulse encompassed choline at 3.2 ppm to NAA at 2.0 ppm while suppressing the lipids at 1.3 ppm and below. The partial water band was designed to excite 2% of the water signal at 4.7 ppm. The final pulse duration was 24 ms resulting in TE=60 ms. The dualband SPSP 90¿ pulse had very low ripple in the metabolite passband but considerable ripple in the partial water passband. However, since we are only using water as a frequency reference and not concerned with its magnitude, this ripple is tolerable. Phantom and in vivo studies demonstrate the new pulse sequence achieved the targeted design parameters. References: [1] Star-Lack JM, et al. Magn Reson Med 2000; 43:325-330. [2] Cunningham CH, et al. Magn Reson Med. 2005 May; 53(5):1033-9. [3] Barker PB, et al. Magn Reson Med. 2001 May;45(5):765-9. Acknowledgements: Lucas Foundation, NIH RR09784,