“…This last category is probably the most studied in image reconstruction. Such methods are often improved by using ordered subsets (Erdoǧan and Fessler, 1999b;Hudson and Larkin, 1994) or Nesterov momentum (Nesterov, 1983;Kim et al, 2014;Xu, Yang, Tan, Sawatzky, and Anastasio, 2016;Choi, Wang, Zhu, Suh, Boyd, and Xing, 2010;Jensen, Jørgensen, Hansen, and Jensen, 2012). Recently, problem-splitting and proximal approaches have been proposed in the context of sparse reconstruction (Sidky, Jørgensen, and Pan, 2013;Nien and Fessler, 2015;Xu et al, 2016).…”