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% compared with standard SI. The k ‐space weighting is achieved by varying the repetition time, thus realizing an inherent apodization that corresponds to a circularly symmetric generalized Hamming filter. The flip angle is varied with the repetition time to enhance the signal‐to‐noise 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 × 25 circularly reduced k ‐space area in as little as 5 min. The signal‐to‐noise ratio is sufficiently high to detect J ‐coupled resonances such as myo ‐inositol or glutamate/glutamine, demonstrating the ability to combine short acquisition times with comprehensive metabolic information. The T 1 dependency of the apodization and the corresponding point spread function was evaluated by computer simulations. The achievable signal‐to‐noise ratio per unit time was compared with standard SI giving a parameter‐dependent advantage of approximately 20% of the standard SI method.