Table 1.
Tracer agents currently available for tracking stem cells in stroke.
| Tracer agent | Imaging modality | Labeled cell type | Route of administration | Results |
|---|---|---|---|---|
| Radiotracer | ||||
| 111In oxine | SPECT | hUTC | IV | Approximately 1% of transplanted cells migrate to the site of injury, increasing vascular and synaptic densities in the IBZ [38] |
| Nanoparticles | ||||
| SPIOs | 3.0T MRI | MSCs | IA | Safe and feasible; ipsilateral MCA conditions and infarction volume affected the number of cells grafted [119] |
| 4.7T MRI | NSCs | IC | The majority of contralaterally grafted NSCs migrated to the peri-infarct area [76] | |
| MRI, BLI | hNSCs | IC | Tracking the fate and function of implanted cells in real time for 2 months [41] | |
| MPIOs | MRI | eNSCs/NPCs | IC | Immediate, cell-independent MPIO accumulation at the site of injury [136] |
| MRI | hMSCs | IC | Good label stability, did not affect hMSC viability [112] | |
| FMNC | MRI | MSCs | IC | Safe and high efficiency for cell labeling, migration, and accumulation in the ischemic region [118] |
| fmSIO4@SPIONs | 3.0T MRI | NPCs | IC/IA | High MR sensitivity and cell labeling efficiency [117] |
| AIE NPs | FLI | BMSCs | IC | Low cytotoxicity and feasible [137] |
| GRMNBs | PA, 7.0T MRI, IVIS | MSCs | IV | Enhanced stem cell homing and reduced infarct volume, allowed short- and long-term monitoring [135] |
| MGIO | 1.5T MRI | hfMSCs | IV | Low toxicity and feasible [138] |
| Gd-DTPA | MRI | BMSCs | IC | Safe and high efficiency [139] |
| Report gene | ||||
| D-luciferin | BLI | BMSC | IP | Higher signal intensity of luciferase-expressing BMSCs 2 h after transplantation and migration to the IBZ [140] |
| Fluc and eGFP condition lentiviral vectors (Cre-Flex-LVs) | BLI, MRI | eNSCs | IC | A significant increase in eNSC proliferation and migration, and 21% of cells differentiated into astrocytes and neurons [134] |
| GFP and Luc2 double fusion reporter gene | BLI | ECFC | IA | Functional recovery, improved angiogenesis, neurogenesis, and increased apoptosis [133] |
SPECT: single photon emission computed tomography; hUTC: human umbilical tissue-derived cells; IV: intravenous; IBZ: the ischemic boundary zone; SPIOs: superparamagnetic iron oxide; MRI: magnetic resonance imaging; MSCs: mesenchymal stem cells; IA: intra-arterial; MCA: middle cerebral artery; NSCs: endogenous neural stem cells; IC: intracerebral; BLI: bioluminescence imaging; hMSCs: human MSCs; MPIO: micron-sized superparamagnetic iron oxide; eNSCs: endogenous NSCs; NPS: neural progenitor cell; FMNC: fluorescent magnetite nano cluster; fmSIO4@SPIONs: fluorescent mesoporous silica-coated superparamagnetic iron oxide nanoparticles; AIE NPs: fluorescent nanoparticles with aggregation-induced emission; FLI: fluorescent imaging; BMSCs: bone marrow-derived MSCs; GRMNBs: multigold nanorod (multiGNR) crystal-seeded magnetic mesoporous silica nanobeads; PAI: photoacoustic imaging; IVIS: interactive video information system; MGIO: microgel iron oxide; hfMSCs: human fetal MSCs; IP: intraperitoneal; Fluc: firefly luciferase; eGFP: enhanced green fluorescent protein; eNSCs: endogenous NSCs; ECFC: endothelial colony-forming cell.