Robust Phase Unwraping Using Grid-fit Method

In MRI, field map estimation techniques using 3 point multi-echo acquisitions have been developed for reliable water fat separation. Among the various techniques, Iterative Decomposition of water and fat with Echo Asymmetry and Leastsquares estimation (IDEAL) has gained considerable popularity as a iterative method for acquiring high quality water and fat images. A core of IDEAL is to have an initial estimate of field map, to ensure that algorithm will converge to correct solution which is close to the true value. However, due to the worsened B0 inhomogeneity at high field, IDEAL could not adjust for the meaningful field map estimation, particularly for a large field of view. Previously, to improve the robustness of this estimation, a region-growing (RG) technique was developed to take advantage of the 2D linear extrapolation procedure through the seed point set by median value in target object. There are some limitations with this approach, such as the dependence on the initial seed point, like a number, intensity and position of seed point. In this work, we introduce the simplest and robust method called Gridfit that does not need to considering some parameters relate with accuracy. Keywords-component; MRI, Grid-fit, Least square fit, Phase unwrapping, K-sapce