Assessment of phase and amplitude effects due to susceptibility variations in MR imaging of the brain

Susceptibility effects due to the presence of hemorrhage have been observed in a substantial number of patients and are a potential source of artifact in in vivo spectroscopy. The studies so far have concentrated on observations of phase differences, but amplitude variations also exist. This article reviews the degree to which the two are independent and suggests that at least three different pulse sequences are necessary to characterize effects due to local field inhomogeneities arising in clinical studies.