Algorithm 1. SR SPECT reconstruction

1: At each sampling angle φ as the LR detector rotates around the object, R2 LR projections $\left\{{\overrightarrow{p}}_{L\phi r}\right\}$ are obtained by our projection acquisition method. 2: for φ = 1 … all angles 3:     The initial estimated SR projection $p_{H\phi (k=0)}$ is generated at each sampling angle φ. 4:     loop k = 1 … maximum iteration number 5:       for m = 1 …R2 6:           The r-th estimated LR projection $p_{L\phi rk}=W_r{p}_{H\phi rk}$ at each sampling angle φ is computed by Formula (1). 7:          The new estimate of $p_{H\phi (r+1)k}$ is computed by Formula (5). 8:       end 9:       if $\left|\right|{\overrightarrow{p}}_{L\phi r}-p_{L\phi rk}|{|}_2< \mathrm{threshold}$ or the maximum iteration number is reached then 10:      terminate 11:      loop 12:      end 13:   end 14: end 15: The SR image is reconstructed from the SR projection via MLEM reconstruction algorithm.