SUSCEPTIBILITY ARTIFACTS IN 2DFT SPIN-ECHO AND GRADIENT-ECHO IMAGING - THE CYLINDER MODEL REVISITED

Susceptibility-induced geometry and intensity distortions are a famili ar observation in MR imaging. In the past few years several attempts h ave been made to aid in the understanding of susceptibility artifacts by means of simulation studies. Although these studies, which were mos tly carried out with simple test objects, have produced some qualitati ve insight into chi-artifacts, the results lacked precision in describ ing finer details. In this paper we show the discrepancy between theor y and experiment in previous work to be the result of an inadequate th eoretical approach. In most studies so far, DELTAB0 effects are taken into account in the frequency domain, that is, after Fourier transform ation of the data. In our view the simulation should follow the actual sequence of events in an imaging experiment and deal with the effect of error fields in the time domain (k-space) already. The correctness of this view is demonstrated here by comparing the results of time and frequency domain simulation against experimental observation f or a c oaxial cylinder phantom, a widely used model in this type of work. Hav ing established the superiority of the time domain simulation, we demo nstrate its use in predicting chi-artifacts under various experimental conditions, for example, in spin-echo and gradient-echo imaging with a reduced number of phase-encoding steps.