Chinese Journal of Magnetic Resonance ›› 2018, Vol. 35 ›› Issue (2): 162-169.doi: 10.11938/cjmr20172582

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Rotation Invariant Non-Local Means for Noise Reduction in Magnetic Resonance Images

ZHANG Bo1, XIE Hai-bin1,2, YAN Xu3, LI Wen-jing1, YANG Guang1,2   

  1. 1. Shanghai Key Laboratory of Magnetic Resonance, Department of Physics, East China Normal University, Shanghai 200062, China;
    2. Shanghai Colorful Magnetic Resonance Technology Co., Ltd., Shanghai 200062, China;
    3. MR Collaboration NE Asia, Siemens Healthcare, Shanghai 201318, China
  • Received:2017-05-26 Online:2018-06-05 Published:2018-05-29

Abstract: Averaging of multiple scans is often used in magnetic resonance imaging (MRI) to increase the signal-to-noise ratio (SNR). However, image averaging often results in movement-induced blurs of the edges and tissue details. A matched and weighted averaging (MWA) method has been proposed by our group to obtain images with reduced blurring effects in signal averaging. Here a rotation-invariant non-local means (RINLM) algorithm was proposed, which used circular patches consisted of series of rings with equal area, instead of square patches, to search for similar patches in the images. Compared with the non-local means (NLM) algorithm, the RINLM algorithm was capable of finding more similar patches in the images containing many rotated local structure. This method was used to process noisy images to improve the SNR, and validated using both phantom images and in vivo MR images. The results demonstrated that the method could improve the SNR, while better preserving the edges and details of the images.

Key words: magnetic resonance imaging (MRI), non-local means (NLM), rotation invariance, image denoising

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