Reduction of T2* dephasing in gradient field-echo imaging.

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Abstract
Fast gradient field-echo imaging is becoming more common in morphologic studies but is not as widespread as might be hoped because of its susceptibility to local field inhomogeneities that lead to spin dephasing (reducing T2 to T2*) and geometric distortion (frequency misregistration). These problems are manifested in both the in-plane and section-select directions. The authors show that reversal of many of these adverse effects is possible through the acquistion of the gradient field echo in a three- and four-dimensional mode for a fixed echo time (TF), since phase-encoding leads to the capture of the echo within the sampling window. This echo centering is shown to be equivalent to the reduction of dephasing across a pixel. Improvements are also obtained by reducing TE to as short a value as possible.