Table 2 Stem cell tracking strategies for cardiovascular applications in vivo

Tissue contrast based

Magnetic field change

CMR

• Iron oxides

• High spatial resolution

• Low sensitivity

• Gad-chelates

• Signal not linked to cell viability

• Microcapsules

• High anatomic detail

• Reporter genes (enzyme-based, transporter-based)

• Lack of CMR-compatible devices for interactivity

• No ionizing radiation

• Post-processing capabilities

• Not compatible for patients with implants

• Permits medium-term tracking

• Expensive

• Acoustic noise

Electron density change

X-Ray/CT

• Gold Nanoparticles

• High sensitivity

• Ionizing radiation

• Microcapsules

• High potential of real-time interactivity

• Limited spatial resolution

• Lacks soft tissue detail

Echogenicity change

US

• Liposomes

• High potential of real-time interactivity

• Difficultly with thin/obese patients

• Microbubbles

• Microcapsules

• Highly operator dependent

• Perfluorocarbons

• No ionizing radiation

• Interpretation has high learning curve

• Inexpensive

• Highly portable

• Limited resolution

• Acoustic artifacts may compromise image

Photon emission based

Radionuclide imaging (High energy ionizing radiation)

PET

• Reporter genes, e.g. HSV-tk, hNIS

• High sensitivity

• Poor anatomic detail

• High translational capacity

• Poor interactivity

• Radionuclides, e.g. ¹⁸ F-FHBG, ¹²⁴I FIAU, and ¹⁸ F-FDG

• Ionizing radiation

• Temporal limitations (due to radioactive decay)

SPECT

• Radionuclides, e.g. ¹¹¹In oxine, ^99mTc and¹⁸ F FDG

• Concerns for label-induced cellular toxicity

• Biohazardous labels

• Expensive

Optical imaging (Low energy radiation)

BLI

• Reporter genes, e.g. luciferase

• Permits longitudinal monitoring

• Limited spatial resolution

• Lacks clinical relevance

• Low background

• No excitation light required

• Biohazardous labels

Fluorescence

• Fluorophores, e.g. GFP

• High sensitivity

• Photon attenuation w/cell division

• Multiplexing

• Near-infrared probes

• No ionizing radiation

• Autofluorescence yields high background

• Quantum dots

• Low cost

• Small depth of high-resolution

• Permits short-term tracking

• Biohazardous labels