FAST PROTON SPECTROSCOPIC IMAGING EMPLOYING K-SPACE WEIGHTING ACHIEVED BY VARIABLE REPETITION TIMES

A k-space weighted spectroscopic imaging (SI) method is presented that allows a reduction in the total data acquisition time by up to 55% co mpared with standard SI. The k-space weighting is achieved by varying the repetition time, thus realizing an inherent apodization that corre sponds to a circularly symmetric generalized Hamming filter. The flip angle is varied with the repetition time to enhance the signal-to-nois e ratio. These techniques were employed using a short echo time of 10 ms. In vivo measurements on healthy rat brain at 4.7 T were conducted, obtaining two-dimensional spectroscopic imaging data from a 25 x 25 c ircularly reduced k-space area in as little as 5 min. The signal-to-no ise ratio is sufficiently high to detect J-coupled resonances such as myo-inositol or glutamate/glutamine, demonstrating the ability to comb ine short acquisition times with comprehensive metabolic information. The T-1 dependency of the apodization and the corresponding point spre ad function was evaluated by computer simulations. The achievable sign al-to-noise ratio per unit time was compared with standard SI giving a parameter-dependent advantage of approximately 20% of the standard SI method.