Some methods from different authors to estimate the level of noise out of a MR image. Methods assume an underlying Rician or noncentral chi model.
Most Methods do not require a previous segmentation of the background.
All methods proposed by several author until 2009, and reviewed in
Santiago Aja-Fernández, Antonio Tristán-Vega, Carlos Alberola-López, Noise estimation in single- and multiple-coil magnetic resonance data based on statistical models, Magnetic Resonance Imaging, Volume 27, Issue 10, Pages 1397-1409
Toolbox includes folder with LocalStat toolbox (local statistics processing toolbox). It includes "localmean", "localvar" and mode calculation.