String-averaging expectation-maximization for maximum likelihood estimation in emission tomography - Helou, Elias Salomão; Censor, Yair; Chen, Tai-Been; Chern, I-Liang; Pierro, Álvaro Rodolfo De; Jiang, Ming; Shing Lu, Henry Horng (Inverse Problems : An International Journal of Inverse Problems, Inverse Methods and Computerised Inversion of Data, 2014)