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Unbiased Nonlinear Filtering of Fast Spin Echo MRI Images

Introduction: The design of filtering methods for denoising the magnitude MRI images is traditionally fulfilled assuming that that image noise is zero-mean Gaussian, as Rician properties of magnitude MRI image noise usually complicates a method both algorithmically and computationally [1]. This widely used assumption leads to the biased filtering results, the bias increases as local signal-to-noise ratio (SNR) decreases. This systematic error might present a serious problem in studies where contrast-to-noise ratio (CNR) in low SNR areas is essential (i.e. black-blood angiography), or in quantitative evaluations of T1/T2 maps. In this paper, we present a novel scheme for unbiased denoising of fast spin echo (FSE) images and its application to black-blood angiography images. Our method uses phase smoothness property of the spin-echo MRI images for unbiased image filtering. The new method is based on an anisotropic diffusing filter [2] and retains all its attractive properties such as edge-preserving denoising, simplicity, and computational efficiency.