Fast Hadamard spectroscopic imaging techniques

Fast Hadamard spectroscopic imaging (HSI) techniques are presented. These techniques combine transverse and longitudinal encoding to obtain multiple-volume localization. The fast techniques are optimized for nuclei with short T2 and long T1 relaxation times and are therefore suitable for in vivo 31P spectroscopy. When volume coils are used in fast HSI techniques, the signal-to-noise ratio per unit time (SNRT) is equal to the SNRT in regular HSI techniques. When surface coils are used, fast HSI techniques give significant improvement of SNRT over conventional HSI. Several fast techniques which are different in total experimental time and pulse demands are presented. When the number of acquisitions in a single repetition time is not higher than two, fast HSI techniques can be used with surface coils and the B1 inhomogeneity does not affect the localization. Surface-coil experiments on phantoms and on human calf muscles in vivo are presented. In addition, it is shown that the localization obtained by the HSI techniques are independent of the repetition times.