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Table 1 An overview of the optimal stem cell tracking characteristics, the probes used to achieve this, and the appropriate imaging modalities with their advantages and disadvantages

From: Functional imaging for regenerative medicine

Optimal stem cell tracking probe characteristic

Optimal cellular probe

Examples

Probe disadvantages

Imaging modality

Absorbance/emission spectra within “optical window”

Fluorescence

Reporter genes (e.g. iRFP), quantum dots, exogenous probes (e.g. PKH26)

Requires genetic modification and excitation light, high background due to autofluorescence, signal loss with cell division, low depth of imaging, limited spatial resolution

FLI

Bioluminescence

Reporter genes (e.g. fLuc)

Requires genetic modification and exogenous substrate administration

BLI

Photoacoustic

Reporter genes (e.g. LacZ, iRFP), endogenous labels (e.g. Hb, melanin)

Requires excitation light and may require genetic modification, expensive equipment

PAI

High signal sensitivity/intensity

Radionuclide

Reporter genes (e.g. hNIS), 99mTc, 111In, 18F FDG

Ionizing radiation, poor anatomical detail (but can be combined with magnetic resonance or x-ray), radioactive decay limits imaging time, cellular toxicity, may require genetic modification, expensive

SPECT, PET

Electron density

Gold nanoparticles

Limited spatial/soft tissue resolution, ionizing, not indicative of cell viability, expensive

x-ray, CT

Fluorescence

As described above

As described above

FLI

Bioluminescence

As described above

As described above

BLI

Photoacoustic

As described above

As described above

PAI

High spatial resolution

Magnetic resonance

Iron oxides, microcapsules

Low signal intensity, not indicative of cell viability, expensive

MRI

High temporal resolution/real time tracking

Echography

Microbubbles, perfluorocarbons

Low resolution, acoustic artefacts, subject to user bias

US

Fluorescence

As described above

As described above

FLI

Bioluminescence

As described above

As described above

BLI

Photoacoustic

As described above

As described above

PAI

Radionuclide

As described above

As described above

SPECT, PET

High imaging depth

Photoacoustic

As described above

As described above

PAI

Echography

As described above

As described above

US

Radionuclide

As described above

As described above

SPECT, PET

High cellular retention/signal retention upon cell division

Fluorescence

Reporter genes (e.g. iRFP)

As described above

FLI

Bioluminescence

As described above

As described above

BLI

Photoacoustic

As described above

As described above

PAI

High anatomical detail

Magnetic resonance

As described above

As described above

MRI

Electron density

As described above

As described above

x-ray, CT

Multimodal systems which include MRI or x-ray

Low cellular toxicity/non-ionizing

Echography

As described above

As described above

US

Magnetic resonance

As described above

As described above

MRI

Fluorescence

As described above

As described above

FLI

Bioluminescence

As described above

As described above

BLI

Quantifiable signal

Fluorescence

As described above

As described above

FLI

Bioluminescence

As described above

As described above

BLI

No cellular genetic modification

Echography

As described above

As described above

US

Radionuclide

99mTc, 111In, 18F FDG

As described above

SPECT, PET

  1. BLI bioluminescence imaging, CT computed tomography, FLI fluorescence imaging, 18 F FDG fluoro-2-deoxy-d-glucose, Hb haemoglobin, 111 In indium, MRI magnetic resonance imaging, PAI photoacoustic imaging, PET positron emission tomography, SPECT single photon emission computed tomography, 99m Tc technetium, US ultrasound