Effect of Carr-Purcell Refocusing Pulse Trains on Transverse Relaxation Times of Metabolites in Rat Brain at 9.4 Tesla

PurposeTo investigate the effect of Carr-Purcell (CP) pulse trains on transverse relaxation times, T-2, of tissue water and metabolites (both noncoupled and J-coupled spins) in the rat brain at 9.4 Tesla (T) using LASER, CP-LASER, and T-2-LASER sequences. MethodsProton NMR spectra were measured in rat brain in vivo at 9.4T. Spectra were acquired at multiple echo times ranging from 18 to 402 ms. All spectra were analyzed using LCModel with simulated basis sets. Signals of metabolites as a function of echo time were fitted using a mono-exponential function to determine their T-2 relaxation times. ResultsMeasured T(2)s for tissue water and all metabolites were significantly longer with CP-LASER and T-2-LASER compared with LASER. The T-2 increased by a factor of approximate to 1.3 for noncoupled and weakly coupled spins (e.g., N-acetylaspartate and total creatine) and by a factor of approximate to 2 (e.g., glutamine and taurine) to approximate to 4 (e.g., glutamate and myo-inositol) for strongly coupled spins. ConclusionApplication of a CP pulse train results in a larger increase in T-2 relaxation times for strongly coupled spins than for noncoupled (singlet) and weakly coupled spins. This needs to be taken into account when correcting for T-2 relaxation in CP-like sequences such as LASER. Magn Reson Med 73:13-20, 2015. (c) 2014 Wiley Periodicals, Inc.