Table 1.

Summary of the merits and drawbacks of different optical modalities

Classification	Merits	Drawbacks	Ref.
PA imaging	Deep tissue penetration; high imaging resolution, low scattering and dissipation in biological tissue	Low signal-to-noise ratio; diminished image contrast due to strong optical attenuation; a lower-bound on spatial resolution in deep tissue	24-26
FL imaging	Excellent sensitivity and selectivity; high spatiotemporal resolution; real-time detection; non-invasiveness; and low cost	Limited tissue penetration depth; severe interference from tissue absorption, scattering, and spontaneous fluorescence	27-29
BL imaging	No autofluorescence and phototoxicity; without external light excitation	Bioluminescence signal is relatively low and bioluminescence imaging rely on enzyme-initiated redox reactions to trigger luminescence	30-32
CL imaging	Effectively avoids light scattering; high sensitivity and signal-to-noise ratio, without external light excitation, no phototoxicity	Chemiluminescence signal is relatively weak and chemiluminescence signals are easily perturbed by internal stimuli such as redox microenvironment	33-36
Afterglow luminescence imaging	Effectively eliminated autofluorescence; no particular chemical mediator or exogenous enzyme	Luminescence decays with time, poor quantitative ability	37-39