The non-local means (NLM) noise reduction algorithm is well known as an excellent technique for removing noise from a magnetic resonance (MR) image to improve the diagnostic accuracy. In this study, we undertook a systematic review to determine the effectiveness of the NLM noise reduction algorithm in MR imaging. A systematic literature search was conducted of three databases of publications dating from January 2000 to March 2020; of the 82 publications reviewed, 25 were included in this study. The subjects were categorized into four major frameworks and analyzed for each research result. Research in NLM noise reduction for MR images has been increasing worldwide; however, it was found to have slightly decreased since 2016. It was found that the NLM technique was most frequently used on brain images taken using the general MR imaging technique; these were most frequently performed during simultaneous real and simulated experimental studies. In particular, comparison parameters were frequently used to evaluate the effectiveness of the algorithm on MR images. The ultimate goal is to provide an accurate method for the diagnosis of disease, and our conclusion is that the NLM noise reduction algorithm is a promising method of achieving this goal.

Purpose To investigate the therapeutic effect of local photothermal (PT) heating on suppression of stent-induced granulation tissue formation in mouse colon. Materials and methods A gold nanoparticle (GNP)-coated self-expandable metallic stent (SEMS) was prepared using a two-step synthesis process for local PT heating under near-infrared laser irradiation. Twenty-four mice were randomly divided into two groups of 12 and subjected to SEMS placement in the colon. Group A received a GNP-coated SEMS without local heating and Group B received a GNP-coated SEMS and underwent local heating at 55°C after SEMS placement. The therapeutic effect of local heating was assessed by comparing the histopathological, immunohistochemical, and endoscopic results. Results Four mice were excluded because of stent migration (n = 3, group B) or death (n = 1, group A). Stent-induced granulation tissue-related variables were significantly lower in group B than in group A (p < 0.001). In vivo endoscopic images, 4 weeks after stent placement, showed granulation tissue formation over the wire mesh in group A and relatively good patency of the stented colon with no definite irregularities in group B. There was more vascular endothelial growth factor (VEGF) positivity in group A than in group B. Conclusion Local PT heating suppresses granulation tissue formation after stent placement in mouse colon.

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