Comparison of 2- and 3-Point Dixon Techniques in RF- and Readout-Shifted FSE Sequences

Introduction Different implementations of the Dixon technique (1) have been used to quantify fat and water in various parts of the human body. In most applications, the 3-point Dixon technique with Bo correction is preferred over simple suppression methods because of its robustness in the presence of Bo inhomogeneities (2). It is also superior to the saturation techniques from an SNR standpoint, offering an equivalent of 2-2.7 signal averages. More recently, a 2D FSE version of the Dixon technique has been described (3), where it was suggested that shifting the acquisition window may be preferred to shifting the RF pulses, in order to meet the CPMG criterion. Although generally less robust than the 3-point counterpart, the 2-point Dixon technique with phase unwrapping (4,5) has the advantage of shorter scan time, and with fewer acquisitions, can be less susceptible to misregistration artifacts in the fat/water component images. The purpose of this work is to compare the 2and 3-point Dixon techniques in both RFand readout (RO)-shifted versions of the 2D FSE sequence, and to evaluate the effects of transverse relaxation on measurement accuracy. Fat (proton density) fractions are compared in several regions of the calcaneus (heel bone), where T2* varies considerably (6).