1. A method of determining a k-space convolution kernel in GRAPPA reconstruction of magnetic resonance imaging, comprising: acquiring plural frames of 2-D images or 3-D images at a same slice location (2-D) or slab location (3-D); acquiring k-space data of the plural frames of 2-D images or 3-D images; providing at least two sets of ACS lines from the acquired k-space data; and utilizing a number of linear equations estimate the k-space convolution kernel that is greater than a number of linear equations that could be derived from one set of ACS lines.