Table 1.

Imaging modalities for in vivo tracking of immune cells

Heading	Modality	Advantages	Disadvantages
Nuclear medicine imaging	PET	High sensitivity and specificity; no depth limit; clinically applicable; quantitative	Ionizing radiation exposure; expensive; relatively low spatial resolution 5 mm; no standardized cell labeling method
	SPECT	High sensitivity and specificity; no depth limit; clinically applicable; cell tracking at late time points	Ionizing radiation exposure; expensive; long scan times; relatively low spatial resolution 10 mm; no standardized specific cell labeling method
Magnetic Resonance imaging	MRI	High resolution (more than 0.1 mm); no ionizing radiation exposure; clinically applicable; possible quantification (indirect)	Lower sensitivity than PET/SPECT; high costs; contrast agents interference with cells; long scan times
Optical imaging	MI	Visualization of cell processes and interactions; time-lapse imaging	Photobleaching, phototoxicity; diffraction limit of light; no translational potential for in-vivo imaging
	BLI	Short acquisition time; high sensitivity (100 cells); high signal-to-noise ratio (no background signal)	No translational potential for in-vivo imaging; diffraction and absorption of light by tissues; immunogenicity or gene silencing; erroneous readouts; signal quantification; half-life and stability of enzymes; limited penetration depth (3 cm)
	FLI	Low cost; radiation free; easy labeling method; real-time	Tissue autofluorescence and absorption; limited penetration depth (1 cm); poor spatial resolution (photon scattering); limited quantification