. 2015 Aug 31;88(1054):20150375. doi: 10.1259/bjr.20150375

Table 1.

Most commonly used types of contrast agents (probes) for MRI-based cell tracking

Probe	Basic imaging principle	Main advantage	Main disadvantage	Detection sensitivity (number of cells)^f	Used for cell tracking in human subjects
Iron oxide nanoparticles	Shortening T2 relaxation of surrounding water protons	High sensitivity	Lack of specific signal; i.e. signal loss	1 cell^a^,18,19	Yes^20–29
Gd-based nanoparticles	Shortening T1 relaxation of surrounding water molecules	Giving rise to signal enhancement	Issues regarding toxicity	300–3000 cells^b^,30–32	No
Manganese-based nanoparticles	Shortening T1 relaxation of surrounding water molecules	Natural body mineral	Issues regarding toxicity	1000–100,000 cells^c^,33–35	No
Chemical exchange saturation transfer agents	Transfer of selectively saturated, exchangeable spins to surrounding bulk water via chemical exchange	Multispectral imaging	Requires specialized imaging techniques	10,000 cells^d^,36	No
¹⁹F-based nanoparticles	Magnetic spin of ¹⁹F nuclei	Not naturally present in body, therefore providing unique signal	Requires specialized imaging techniques	2000–9000 cells^e^,37,38	Yes³⁹

¹⁹F, fluorine-19.

^{^a}

at intracellular concentrations of 9–50 pg/cell; voxel size 0.26–1 × 10⁻³ mm³.

^{^b}

at intracellular Gd concentrations of 0.05–70 pg/cell; voxel size 2.24–10.3 × 10⁻³ mm³.

^{^c}

at intracellular Mn concentrations of 0.35–0.7 pg/cell; voxel size 160 × 10^−-3 mm³ (only specified by Letourneau et al.³⁵).

^{^d}

at intracellular CEST agent concentrations of 3–4 mM/cell; voxel size 24–73 × 10⁻³ mm³.

^{^e}

at intracellular ¹⁹F concentrations of 0.35–0.7 pg/cell; voxel size 660–2000 × 10⁻³ mm³.

^{^f}

Detection sensitivity is highly dependent of various conditions, such as the cell type, intracellular loading, imaging parameters including voxel size, and magnetic field strength.