• Rose-Ann M Blenman, John D Port, and Joel P Felmlee.
• Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
• J Magn Reson Imaging. 2007 Mar 1; 25 (3): 628-34.

PurposeTo develop a short TR, short TE, large flip angle (LFA), in vivo (31)P MR spectroscopy (MRS) technique at 3T that selectively maximizes the signal-to-noise ratio (SNR) of long T(1) human brain metabolites implicated in bipolar disorder.Materials And MethodsTwo pulse sequences were evaluated for efficiency. Slice profiles acquired with the scaled, sinc-shaped, radiofrequency (RF) LFA pulses were compared to those acquired with Shinnar-Le Roux (SLR) RF LFA pulses. The SLR-based LFA pulse sequence was used to maximize the inorganic phosphate signal in a phantom, after which volunteer metabolite signals were selectively maximized and compared to their correlates acquired with conventional spin-echo methods.ResultsThe comparison of slice profiles acquired with sinc-shaped RF LFA pulses vs. SLR RF LFA pulses showed that SLR-based pulse sequences, with their improved excitation and slice profiles, yield significantly better results. In vivo LFA spin-echo MRS implemented with SLR pulses selectively increased the (31)P MRS signal, by as much as 93%, of human brain metabolites that have T(1) times longer than the TR of the acquisition.ConclusionThe data show that the LFA technique can be employed in vivo to maximize the signal of long T(1) (31)P brain metabolites at a given TE and TR. LFAs ranging between 120 degrees and 150 degrees are shown to maximize the (31)P signal of human brain metabolites at 3T.

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