An update on clinical applications of magnetic nanoparticles for increasing the resolution of magnetic resonance imaging

Figures & data

Table I. Comparison of several imaging modalities (Cheon and Lee 2008, Hachani et al. 2011, Massoud and Gambhir 2003).

	Source of imaging	Spatial resolution	Tissue penetrating depth	Sensitivity	Types of probe
MRI	Radiowave	25–100 mm	No limit	mM to µM (low)	Para-(Gd^3+) or superparamagnetic(Fe3O4) materials
PET	γ-ray	1–2 mm	No limit	pM (high)	Radionuclides (^18F, ^11C, ^13N, ^15O, ^124I, ^64 Cu)
CT	X-ray	50–200 mm	No limit	Not well characterized	High atomic number atoms (iodine, barium sulfate)

Figure 1. An MRI (gradient echo, TR/TE = 100/4 ms, flip angle 30°, FOV = 5.5 × 2.5 cm, 256 × 256) of a mouse liver obtained at 9.4 T (A) before and (B) after injection of iron oxide (Nano-Ocean, Springdale, AR). The decrease of MR signal within the liver (yellow arrow) is visible (Blasiak et al. 2013).

Figure 2. Effect of magnetic particle internalization in cells on $T_2^{*}$ relaxation times: (A) the protons in cells tagged by magnetic particles have a shorter $T_2^{*}$ relaxation time than those in (B) untagged cells (Pankhurst et al. 2003, Yang et al. 2010).

Table II. Comparison of some nanoparticles with high transverse relaxivity for T₂ MRI (Benyettou et al. 2011, Hachani et al. 2011, Huang et al. 2011, Jung and Jacobs 1995, Ruiz et al. 2006).

Nanoparticle	Core size (nm)	Hydrodynamic diameter (nm)	R1 (mM^-1 s^-1)	R2 (mM^−1 s^−1)
Ferumoxide (feridex)  γFe2O3,Fe3O4–dextran	4.96	160	10.1	120
Fe3O4–PEG–(NH2)2	12	49	22 (1.5 T)	191 (1.5 T)
γFe2O3–alendronate	10	32.5	_	287 (4.7 T)
Fe3O4–casein	15	30	_	273 (3 T)

Figure 3. Schematic representations of (A) the structure of functional magnetic nanoparticles (MNPs) for MRI applications and (B) a colloidal nanoparticle suspended in biological media.

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