MULTI-EXCITATION NON-CPMG WITH LOW FLIP ANGLES FOR HYPERPOLARIZED 13C MRS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We report a new MR spectroscopic imaging sequence that utilizes non-CPMG1,2 FSE echo trains with quadratic phase modulation of the refocusing pulses to catalyze the stability of longitudinal magnetization while keeping the transverse magnetization refocused during the echo train. Other alternative phase modulation schemes (XY, MLEV ) are useful only over a very restricted range, close to ¿, of the refocusing pulse rotation angle (nutation)1. The non-CPMG phase scheme performs well for nutations as low as 160¿ and with a proper design of RF pulses of wide bandwidth, this technique can be quite suitable for fast spectroscopic imaging. Because non-CPMG allows us to obtain a full magnitude signal even in the presence of initial phase variation, we can perform multiple low flip-angle excitations with FSE readouts without waiting for the longitudinal signal to recover via T1 relaxation, a condition ideal for spectroscopic imaging of hyperpolarized nuclei. In this report, we show preliminary test results of multi-excitation non-CPMG with low flip angles (MENLO) and one of its potential applications for mapping T2 relaxation time. The tests were performed on a 13C-enriched phantom, with imaging parameters suitable for future hyperpolarized 13C applications. To read about other projects ongoing at the Lucas Center, please visit http://rsl.stanford.edu/ (Lucas Annual Report and ISMRM 2011 Abstracts)