A Semi_LASER 1H MRS Sequence Designed with High Bandwidth RF Pulses for Use at 4.0 T

Hui Liu^1,2, Gerald B. Matson^1,3

Although in vivo MRS at high magnetic field has the potential to better quantitate metabolites exhibiting J-coupled resonances such as glutamate, glutamine and myo-Inositol, which are all of clinical interest, the four-compartment artifact exhibited by J-coupled resonances is exacerbated because of the increased spectral dispersion. The four-compartment artifact can be alleviated by higher RF pulse bandwidth or short echo-time acquisition. However, short echo-time sequences such as STEAM acquires only half of the S/N, while the SPECIAL sequence is susceptible to motion artifacts due to its subtraction scheme. The LASER sequence can be used with higher RF bandwidth pulses; however, its relatively high SAR hinders its use. In this study, a single voxel semi-LASER localization scheme suitable for use on commercial MRI instruments was implemented at 4T at a relatively long echo time (57 ms) with new, high bandwidth RF pulses, designed by our optimization routine incorporated into MatPulse. The higher bandwidth RF pulses combined with the semi-LASER localization scheme helped to suppress the four-compartment artifact, and enabled J-coupled resonances to be acquired with relatively high S/N at the relatively long TE time of 57 ms without major baseline artifacts.