Semiautomatic off-resonance correction in spiral imaging.

Spiral scanning is a promising MRI method, but one limitation is that off-resonance effects can cause image blurring. Most current off-resonance correction methods for spiral imaging require an accurate field map, which is difficult to obtain in many applications. Automatic methods can perform off-resonance correction without acquiring a field map. However, these methods are computationally inefficient and relatively prone to estimation error. This study describes a new semiautomatic off-resonance correction method that combines an automatic method with a low resolution field map acquisition for off-resonance correction in spiral scanning. Experiments demonstrate that this method is more robust than conventional automatic off-resonance correction and can provide more accurate off-resonance correction than conventional field map based methods. The proposed method is also computationally efficient and has been implemented for online reconstruction. (c) 2008 Wiley-Liss, Inc.