Noise estimation in MR GRAPPA reconstructed data

A new method to estimate the variance of noise from the composite magnitude signal of GRAPPA reconstructed images is presented. Parallel imaging methods allow to increase the acquisition rate via subsampled acquisitions of the k-space. However, the reconstruction process yields to a variance of noise value which is dependent on the position within the image. The proposed method uses information of the GRAPPA reconstruction coefficients and assumes a final non-central chi distribution to recover the spatial pattern of noise.