Radiolabeled exosomes for theranostics: Personalized tailored therapy through imaging

Table 1 Radiolabeling and imaging strategies for in vivo tracking of exosomes and extracellular vesicle

Imaging modality	Radiolabeling agent	Labeling strategy	Labeling efficiency/purity	Key findings	Ref.
PET	Cu-64, Ga-68	Direct or indirect (chelator-based)	98%	Enables quantitative whole-body tracking of exosome in sentinel lymph nodes	[13]
SPECT/CT	Tc-99m HMPAO	Direct	> 90%	Predominant liver accumulation, no/minimal brain uptake	[10]
SPECT	Tc-99m tricarbonyl	Direct	> 90%	Significant liver and spleen accumulation	[30]
Gamma imaging	Tc-99m	Direct	> 99%	Kupffer-cell-mediated hepatic uptake; liver and spleen accumulation	[31]
SPECT/gamma imaging	I-125, I-131	Direct surface labeling	> 98%	Rapid blood clearance; accumulation in liver, spleen, and lungs	[29,32]
MRI	Gadolinium	Surface modification/cargo loading	90%	Prolonged tumor accumulation of engineered exosomes	[33]
MPI/MRI	Magnetic nanoparticle	Nanoparticle incorporation	-	Visualization of exosome delivery to hypoxic tumors	[34]
CT	Gold nanoparticle	Nanoparticle conjugation	-	Selective accumulation in pathological brain regions and inflammatory sites	[35]
MRI	F-19	Direct membrane incorporation	-	Background-free biodistribution tracking	[36]
SPECT/CT	I-131	Chloramine-T method	50.16%-60.21%	Targeting and tumor growth inhibition	[38]

PET: Positron emission tomography; SPECT: Single-photon emission computed tomography; CT: Computed tomography; MRI: Magnetic resonance imaging; MPI: Magnetic particle imaging; Cu-64: Copper-64; Ga-68: Gallium-68; Tc-99m: Technetium-99m; HMPAO: Hexamethylpropyleneamine oxime; I-125: Iodine-125; I-131: Iodine-131; F-19: Fluorine-19.