Assessment of selective excitation artifacts in spatially localized P-31 spectroscopy

Many spectroscopic spatial localization techniques involve selective excitation (in which a shaped radio-frequency pulse is applied in the presence of a gradient field). These are liable to produce artifacts due both to variations in section shape (similar in general to those found in imaging) and to registration errors that occur because the chemical shift of the individual lines causes different anatomic regions to be selected. Complex methods such as ISIS can result in quite variable effects. Unless adequate spoilers are applied between the 1800 pulses and the 900 pulse, magnetization at the edges of the nominally inverted regions is phase modulate, which results in the excitation of very complex and irregular regions. Analysis has been performed for the P31 spectrum in various tissues (muscle, liver, and brain) and demonstrated for the section imaging techniques described previously