Reducing off-resonance distortion by echo-time interpolation

Off-resonant spins, produced by chemical shift, tissue-susceptibility differences, or main-field inhomogeneity, can cause blurring or shifts, severely compromising the diagnostic value of magnetic resonance images. To mitigate these off-resonance effects, the authors propose a technique whereby two images are acquired at different echo times (TEs) and interpolated to produce a single image with dramatically-reduced blurring. The phase difference of these two images is not used to produce a field map; instead, the weighted complex-valued average of the two images is used to produce a single image. Previously-described methods reconstruct a set of preliminary images, each at a different off-resonant frequency, and then assemble these into one final image, choosing the best off-resonant frequency for each voxel. Compared to these methods, the proposed technique requires the same or less processing time and is much less sensitive to errors in the field map. This technique was applied to centric-ordered EPI but it can be applied to any imaging trajectory, including one-shot EPI, spiral imaging, projection-reconstruction imaging, and 2D GRASE. Magn Reson Med 45:269-276, 2001.