Method for efficient fast spin echo Dixon imaging

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Abstract
In order to satisfy the Carr-Purcell-Meiboom-Gill (CPMG) condition, echo shift as dictated in fast-spin-echo (FSE)-based Dixon imaging was previously achieved by applying a time shift to the readout gradient and the data acquisition window. Accordingly, interecho spacing is increased, which entails increased image blurring and, in multislice imaging, a significant reduction in the slice coverage for a given imaging time. In this work, a new method is developed by which the echo shift is induced by “sandwiching” in time the readout gradient with a pair of small gradients of equal area and of opposite polarity. While data with non-zero phase shifts between water and fat signals are collected as fractional echoes, no increase in echo spacing is necessary with the modified acquisition strategy, and increased time efficiency is therefore achieved. In order to generate separate water-only and fat-only images in data processing, a set of low-resolution images are first reconstructed from the central symmetric portion (either 128 × 128 or 64 × 64) of the acquired multipoint Dixon data. High-resolution images using all the acquired data, including some partial Fourier-reconstructed images, are then phase demodulated using the phase errors determined from the low-resolution images. The feasibility of the technique is demonstrated using a water and fat phantom as well as in clinical patient imaging. Magn Reson Med 48:1021–1027, 2002.