Fig. 1. Overall structure block diagram of imaging system

Fig. 2. (a) Structure of digital lock-in demodulator; (b) phase characteristics of lock-in in square mode

Fig. 3. Structural diagram of lock-in photon counting hardware logic implementation

Fig. 4. Linearity assessments of the system

Fig. 5. Ability of the system to overcome ambient light

Fig. 6. Crosstalk ratio between channels at different frequency spaces. (a) Frequency space of 50 Hz; (b) frequency space of 200 Hz; (c) frequency space of 252 Hz

Fig. 7. Schematics of solid-state phantom in experiment. (a) Three-dimensional structure; (b) top view

Fig. 8. Scan schemes

Fig. 9. DOT reconstruction under 7-time excitation