Denoise an image using a spatially adaptive filter originally described in J. V. Manjon, P. Coupe, Luis Marti-Bonmati, D. L. Collins, and M. Robles. Adaptive Non-Local Means Denoising of MR Images With Spatially Varying Noise Levels, Journal of Magnetic Resonance Imaging, 31:192-203, June 2010. (doi 10.1002/jmri.22003)