Burst imaging: Rotation artifacts and how to correct them

The effect of coherent rotational motion on images acquired with the ultraf ast single-shot spin-echo Burst sequence has been analyzed. Previous experi ence has demonstrated that sample rotation during Burst experiments has the potential to cause severe image artifacts. In this paper we show that no d istortions are visible when the readout gradient is parallel to the rotatio n axis, but that there is a very distinctive behavior for the case of the r otation axis orthogonal to the imaging plane. The mathematical expression t hat describes the resulting signal is presented and is used as a basis for a method of correcting the k-space data. The conditions under which undisto rted images may be recovered are discussed. It is shown that there is an as ymmetry, dependent on the rotation direction, in both the manifestation of the artifact and the range of angular velocities over which one can correct the images. Data from an agar gel phantom rotating at a known rate are use d to show how the theory is successful at reconstructing images, with no fr ee parameters. The range of angular velocities over which correction is pos sible depends on the timing parameters of the pulse sequence, but for these data was -0.016 < omega less than or similar to 0.1 revolutions/s, Volunte er experiments have confirmed that the theory is applicable to patient moti on and can correct motional distortion even when the exact rate is not know n a priori. By optimizing the reconstruction to restore a known sample geom etry/aspect ratio, an estimate of the rotation angular frequency is obtaine d with a precision of +/-10%. (C) 2000 Academic Press.