Fig. 1. Nested MURA coding boards

Fig. 2. Collimator thickness determination model

Fig. 3. Architecture simulation of gamma camera detection system

Fig. 4. System response matrix is constructed by Monte Carlo calculation

Fig. 5. Central point source reconstruction of MLEM algorithm with different iterations: (a) iterate once to decode; (b) iterate 10 times to decode; (c) iterate 50 times to decode; (d) iterate 100 times to decode

Fig. 6. Convolutional neural network structure

Fig. 7. Single point source images obtained by different reconstruction algorithm: (a)、(b) δ decode; (c)、(d) fine sampling balanced decoding; (e)、(f) CNN；(g)、(h) MLEM

Fig. 8. Reconstruction effect of different algorithms under multi-point source radiation: (a) δ decode; (b) fine sampling balanced decoding; (c) CNN; (d) MLEM

Fig. 9. Reconstruction of a line source: (a) δ decode; (b) fine sampling balanced decoding; (c) CNN; (d) MLEM

Fig. 10. Reconstruction effect of diamond surface source: (a) δ decode; (b) fine sampling balanced decoding; (c) CNN; (d) MLEM