Two-dimensional excitation short echo time chemical shift imaging at 0.5 tesla

Detection of short T2 metabolites such as glutamate and glutamine (glx) in the brain can be improved by minimizing the echo time (TE) of the pulse sequence. By combining two dimensions of localization during a single radiofrequency (RF) pulse, an elliptic excitation chemical shift imaging sequence (EECSI) that further reduces TE by a factor of 2 relative to a TE-optimized point resolved spectroscopy sequence chemical shift imaging sequence was developed. An additional set of outer volume saturation pulses is included to minimize the contamination from scalp and marrow space lipids. The sequence runs with conventional gradient hardware (1 G/cm, 17 T/m/s slew rate) at 0.5 T. The increase in the fitted areas of beta,gamma multiplet of glutamate and glx in a brain-mimicking phantom was by a factor of 1.66. In the thalamus of healthy volunteers, glx was increased by 1.44. Combined with the field strength-related improvements in glutamate and glx detection previously demonstrated at 0.5 T, EECSI offers further improvements for imaging glutamate and glx in vivo.