Selective maximization of (31)P MR spectroscopic signals of in vivo human brain metabolites at 3T.
OBJECTIVE
To 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.


METHODS
Two 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.


RESULTS
The 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.


CONCLUSIONS
The 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.
Blenman
Rose-Ann M
RA
Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Port
John D
JD
Felmlee
Joel P
JP
D000328:Adult; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D010759:Phosphorus Isotopes; D012016:Reference Values; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors
D010759:Phosphorus Isotopes