Iterative reconstruction of single-shot spiral MRI with off resonance

A variety of applications and research directions in magnetic resonance imaging which require fast scan times have recently become popular. In order to satisfy many of the requirements of these applications, snapshot imaging methods, which acquire an entire image in one excitation, are often used. These snapshot techniques are relatively insensitive to motion and can allow rapidly occurring processes to be imaged. However, snapshot imaging techniques acquire data over a relatively long period, during which off-resonance phase can accumulate, leading to image degradation. This degradation often limits the usefulness of the images. Presented here is a method to iteratively reconstruct an image acquired by a spiral snapshot technique and to remove image degradation due to off resonance. This iterative method does not assume that the inhomogeneity is slowly varying within the image, allowing better results than with deblurring techniques which do not take abrupt changes into account. Although presented here with a spiral imaging technique, the iterative algorithm general enough to be applied to a variety of snapshot imaging techniques.