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 MRSI is a useful technique for obtaining spatially localized profiles of metabolites of interest in the breast, brain and prostate. However, MRSI usually suffers from: 1) Inadequate water or lipid suppression; 2) spectral shifts due to B0 inhomogeneity; 3) spatially varying phase profiles and 4) chemical shift artifacts. A pulse sequence has been designed for use at 3T that utilizes a dualband spatial-spectral matched phase 90 -180 pulse pair to excite a thin slice. The dualband spectral profile of these pulses enables complete lipid suppression and partial water suppression so that water may be used as a phase and frequency reference. Using a matched phase 90 -180 pulse pair yields a final echo with a flat phase profile and the higher spatial bandwidth of spatial-spectral compared to standard spatial pulses (3.5 kHz vs. 1.2 kHz) results in less severe chemical shift artifacts. The first set of pulses have been designed for breast MRSI, however it is not difficult to adapt the pulses to the brain or prostate. Methods and Discussion: Initially a linear-phase 180 dualband spatial-spectral pulse that encompassed choline at 3.2 ppm and suppressed all lipid resonances was designed. The partial water band was designed to excite 1% of the water signal at 4.7 ppm. Using the Shinnar Le-Roux (SLR) algorithm [1] for RF pulse design, each RF pulse can be described by a pair of complex polynomials (?(kz,k?), ?(kz,k?)) or just (?, ?). In order to bring the linear 180 pulse below RF peak power limits, the roots of the ? polynomial that fell outside the unit circle were computed and every possible root flipped configuration was traversed to find the one that resulted in the lowest RF peak power [2]. In order to compensate the non-linear phase profile introduced by root flipping, the ? from the 180 pulse was used to create a phase matched ? for the 90 pulse. The final spectral profile had flat phase and successfully passed a 1 ppm band encompassing the metabolites present in the breast (i.e. choline at 3.2 ppm, creatine at 3 ppm) while suppressing all other resonances. References: [1] Pauly J, Le Roux P, Nishimura D, Macovski A. IEEE Trans Med Imaging. 1991; 10: 53-65. [2] Cunningham CH, Vigneron DB, Chen AP, Xu D, Hurd RE, Sailasuta N, Pauly JM. Magn Reson Med. 2004 Jul;52(1):147-53. [3] Cunningham CH, Vigneron DB, Marjanska M, Chen AP, Xu D, Hurd RE, Kurhanewicz J, Garwood M, Pauly JM. Magn Reson Med. 2005 May;53(5):1033-9. [4] Barker PB, Hearshen DO, Boska MD. Magn Reson Med. 2001 May;45(5):765-9. Acknowledgements: Lucas Foundation, NIH RR09784, CA48269
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