Reducing reconstruction error of classified textural patches by integration of random forests and coupled dictionary nonlinear regressors: with applications to super-resolution of abdominal CT images

Mahdieh Akbari | Amirhossein Foroozan | Yen-Wei Chen | Hongjie Hu

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URL :   http://research.shahed.ac.ir/WSR/WebPages/Report/PaperView.aspx?PaperID=158843
Date :  2021/08/01
Publish in :    International Journal of Computer Assisted Radiology and Surgery
DOI :  https://doi.org/10.1007/s11548-021-02449-3
Link :  http://dx.doi.org/10.1007/s11548-021-02449-3
Keywords : Super-resolution, Random forests, Coupled dictionary learning, Auto-encoders, Abdominal CT images

Abstract :

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Purpose Random forests and dictionary-based statistical regressions have common characteristics, including non-linear mapping and supervised learning. To reduce the reconstruction error of high-resolution images, we integrate random forests and coupled dictionary learning. Methods Textural differences of image blocks are considered by the classification of patches using an Auto-Encoder network. The proposed algorithm partitions an input LR image by 5 × 5 blocks and classifies training patches into six categories. A single random forest regressor is then trained corresponding to each class. The output of an RF is considered as an initial estimate of the HR slice. If a slice’s representation is sparse in the Discrete Cosine Transform domain, the initial reconstructed image is further improved by a coupled dictionary. Results In this study, we applied our method to abdominal CT scans and compared them to conventional and recent researches. We achieved an average improvement of 0.06 (2.37) using the SSIM (PSNR) index compared to the random forest + dictionary learning method. Conclusion The low standard deviation of the results reveals the stability of the proposed method as well. The proposed algorithm depicts the effectiveness of classifying image patches and individual treatment of each class.