IMPROVEMENTS OF NUCLEAR-MAGNETIC-RESONANCE IMAGE QUALITY USING ITERATIONS OF ADAPTIVE NONLINEAR FILTERING

To improve NMR image quality, a method using iterations of adaptive nonlinear filtering is presented. The method utilizes the properties of an NMR image's noises which are spike-like in the local region. An NMR image is iteratively filtered by a mode-change-type nonlinear filter which has two modes. The first mode reduces small amplitude noises in the NMR image, so that the SN ratio of the image is improved, and then the residual noises become more spike-like. The second mode mainly reduces large amplitude spike-like noises of the image improved by the first mode, which cannot reduce spike-like noises. Using the proposed iterative filter, it is found by simulations that the SN ratio of the NMR image is improved by as much as a factor of 2.7. A significant improvement in the image quality when this filter is used is demonstrated by applying it to an NMR image of a human head obtained from an actual NMR imaging apparatus.