“…These reconstruction algorithms are generally in the state-of-the-art compressive sensing (CS) framework, utilizing prior knowledge effectively and permitting accurate and stable reconstruction from a more limited amount of raw data than requested by the classic Shannon sampling theory. CS-inspired reconstruction algorithms can be roughly categorized into the following stages (Wang et al , 2011): (1) The 1st stage: Candes’ total variation (TV) minimization method and variants (initially used for MRI and later on tried out for CT) (Li and Santosa, ’96; Jonsson et al , ’98; Candes and Tao, 2005; Landi and Piccolomini, 2005; Yu et al , 2005; Candes et al , 2006, 2008; Block et al , 2007; Landi et al , 2008; Sidky and Pan, 2008; Yu and Wang, 2009); (2) the 2nd stage: Soft-thresholding method adapted for X-ray CT to guarantee the convergence (Daubechies et al , 2004; Yu and Wang, 2010; Liu et al , 2011; Yu et al , 2011); and (3) the 3rd stage: Dictionary learning (DL) and non-local mean methods being actively developed by our group and others (Kreutz-Delgado et al , 2003; Gao et al , 2011; Lu et al , 2012; Xu et al , 2012; Zhao et al , 2012a,b). …”