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Nanoparticles in magnetic resonance imaging: from simple to dual contrast agents.

Estelrich J, Sánchez-Martín MJ, Busquets MA - Int J Nanomedicine (2015)

Bottom Line: Moreover, the signal-to-noise ratio can be improved with the acquisition of a large number of measurements.They can simultaneously bear both kinds of contrast and can, furthermore, incorporate targeting ligands and chains of polyethylene glycol to enhance the accumulation of nanoparticles at the site of interest and the bioavailability, respectively.Here, we review the most important characteristics of the nanoparticles or complexes used as MRI contrast agents.

View Article: PubMed Central - PubMed

Affiliation: Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Barcelona, Catalonia, Spain ; Institut de Nanociència I Nanotecnologia (IN UB), Barcelona, Catalonia, Spain.

ABSTRACT
Magnetic resonance imaging (MRI) has become one of the most widely used and powerful tools for noninvasive clinical diagnosis owing to its high degree of soft tissue contrast, spatial resolution, and depth of penetration. MRI signal intensity is related to the relaxation times (T 1, spin-lattice relaxation and T 2, spin-spin relaxation) of in vivo water protons. To increase contrast, various inorganic nanoparticles and complexes (the so-called contrast agents) are administered prior to the scanning. Shortening T 1 and T 2 increases the corresponding relaxation rates, 1/T 1 and 1/T 2, producing hyperintense and hypointense signals respectively in shorter times. Moreover, the signal-to-noise ratio can be improved with the acquisition of a large number of measurements. The contrast agents used are generally based on either iron oxide nanoparticles or ferrites, providing negative contrast in T 2-weighted images; or complexes of lanthanide metals (mostly containing gadolinium ions), providing positive contrast in T 1-weighted images. Recently, lanthanide complexes have been immobilized in nanostructured materials in order to develop a new class of contrast agents with functions including blood-pool and organ (or tumor) targeting. Meanwhile, to overcome the limitations of individual imaging modalities, multimodal imaging techniques have been developed. An important challenge is to design all-in-one contrast agents that can be detected by multimodal techniques. Magnetoliposomes are efficient multimodal contrast agents. They can simultaneously bear both kinds of contrast and can, furthermore, incorporate targeting ligands and chains of polyethylene glycol to enhance the accumulation of nanoparticles at the site of interest and the bioavailability, respectively. Here, we review the most important characteristics of the nanoparticles or complexes used as MRI contrast agents.

No MeSH data available.


Related in: MedlinePlus

Schematic image of core–shell-type dual-mode nanoparticle contrast agent [MnFe2O4@SiO2@Gd2(CO3)2].Notes: The T1 contrast material is positioned on the shell to have direct contact with the water for high T1 contrast effects, and the superparamagnetic T2 contrast material is located at the core, inducing a long-range magnetic field for the relaxation of water.
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f4-ijn-10-1727: Schematic image of core–shell-type dual-mode nanoparticle contrast agent [MnFe2O4@SiO2@Gd2(CO3)2].Notes: The T1 contrast material is positioned on the shell to have direct contact with the water for high T1 contrast effects, and the superparamagnetic T2 contrast material is located at the core, inducing a long-range magnetic field for the relaxation of water.

Mentions: USPIONs with a core of less than 10 nm in diameter are capable of producing positive contrast in T1-weighted images when administered in moderate concentrations.75,76 While positive T1 contrast is possible with USPIONs, this benefit is at the expense of their T2 effects.77,78 For this reason, mixing both types of iron oxides, SPIONs and USPIONs, to form a single contrast agent could potentially be a good choice. However, an important problem arises as a consequence of the strong magnetic coupling between the T1 and T2 contrast agents when they are in close proximity: the spin–lattice relaxation process of T1 contrast materials is significantly diminished. One strategy to overcome this phenomenon is the inclusion of a separation layer to modulate the magnetic coupling. To this end, micellar structures incorporating organic block copolymers, inorganic porous materials, and core–shell-type inorganic materials have been considered as possible frameworks.52 For instance, a core–shell-type T1–T2 dual-mode nanoparticle contrast has been described, where the T1 contrast material, Gd2O(CO3)2 of 1.5 nm, is located on the shell so as to come into direct contact with water molecules, for high T1 contrast effects; while the superparamagnetic T2 contrast material, MnFe2O4 of 15 nm, is located at the core, from where it induces a long-range magnetic field for the relaxation of water molecules. The two materials are separated by SiO2. By adjusting the thickness of the SiO2, the magnetic coupling between the T1 and T2 contrast agents is controlled. As the SiO2 becomes thicker, T1 quenching reduces and, concurrently, r1 increases; while the decrease in the T2 effects is relatively weaker. When the SiO2 layer is 16 nm thick, both T1 and T2 contrast effects become larger than the effects of the individual single-mode contrast effects (Figure 4).79


Nanoparticles in magnetic resonance imaging: from simple to dual contrast agents.

Estelrich J, Sánchez-Martín MJ, Busquets MA - Int J Nanomedicine (2015)

Schematic image of core–shell-type dual-mode nanoparticle contrast agent [MnFe2O4@SiO2@Gd2(CO3)2].Notes: The T1 contrast material is positioned on the shell to have direct contact with the water for high T1 contrast effects, and the superparamagnetic T2 contrast material is located at the core, inducing a long-range magnetic field for the relaxation of water.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358688&req=5

f4-ijn-10-1727: Schematic image of core–shell-type dual-mode nanoparticle contrast agent [MnFe2O4@SiO2@Gd2(CO3)2].Notes: The T1 contrast material is positioned on the shell to have direct contact with the water for high T1 contrast effects, and the superparamagnetic T2 contrast material is located at the core, inducing a long-range magnetic field for the relaxation of water.
Mentions: USPIONs with a core of less than 10 nm in diameter are capable of producing positive contrast in T1-weighted images when administered in moderate concentrations.75,76 While positive T1 contrast is possible with USPIONs, this benefit is at the expense of their T2 effects.77,78 For this reason, mixing both types of iron oxides, SPIONs and USPIONs, to form a single contrast agent could potentially be a good choice. However, an important problem arises as a consequence of the strong magnetic coupling between the T1 and T2 contrast agents when they are in close proximity: the spin–lattice relaxation process of T1 contrast materials is significantly diminished. One strategy to overcome this phenomenon is the inclusion of a separation layer to modulate the magnetic coupling. To this end, micellar structures incorporating organic block copolymers, inorganic porous materials, and core–shell-type inorganic materials have been considered as possible frameworks.52 For instance, a core–shell-type T1–T2 dual-mode nanoparticle contrast has been described, where the T1 contrast material, Gd2O(CO3)2 of 1.5 nm, is located on the shell so as to come into direct contact with water molecules, for high T1 contrast effects; while the superparamagnetic T2 contrast material, MnFe2O4 of 15 nm, is located at the core, from where it induces a long-range magnetic field for the relaxation of water molecules. The two materials are separated by SiO2. By adjusting the thickness of the SiO2, the magnetic coupling between the T1 and T2 contrast agents is controlled. As the SiO2 becomes thicker, T1 quenching reduces and, concurrently, r1 increases; while the decrease in the T2 effects is relatively weaker. When the SiO2 layer is 16 nm thick, both T1 and T2 contrast effects become larger than the effects of the individual single-mode contrast effects (Figure 4).79

Bottom Line: Moreover, the signal-to-noise ratio can be improved with the acquisition of a large number of measurements.They can simultaneously bear both kinds of contrast and can, furthermore, incorporate targeting ligands and chains of polyethylene glycol to enhance the accumulation of nanoparticles at the site of interest and the bioavailability, respectively.Here, we review the most important characteristics of the nanoparticles or complexes used as MRI contrast agents.

View Article: PubMed Central - PubMed

Affiliation: Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Barcelona, Catalonia, Spain ; Institut de Nanociència I Nanotecnologia (IN UB), Barcelona, Catalonia, Spain.

ABSTRACT
Magnetic resonance imaging (MRI) has become one of the most widely used and powerful tools for noninvasive clinical diagnosis owing to its high degree of soft tissue contrast, spatial resolution, and depth of penetration. MRI signal intensity is related to the relaxation times (T 1, spin-lattice relaxation and T 2, spin-spin relaxation) of in vivo water protons. To increase contrast, various inorganic nanoparticles and complexes (the so-called contrast agents) are administered prior to the scanning. Shortening T 1 and T 2 increases the corresponding relaxation rates, 1/T 1 and 1/T 2, producing hyperintense and hypointense signals respectively in shorter times. Moreover, the signal-to-noise ratio can be improved with the acquisition of a large number of measurements. The contrast agents used are generally based on either iron oxide nanoparticles or ferrites, providing negative contrast in T 2-weighted images; or complexes of lanthanide metals (mostly containing gadolinium ions), providing positive contrast in T 1-weighted images. Recently, lanthanide complexes have been immobilized in nanostructured materials in order to develop a new class of contrast agents with functions including blood-pool and organ (or tumor) targeting. Meanwhile, to overcome the limitations of individual imaging modalities, multimodal imaging techniques have been developed. An important challenge is to design all-in-one contrast agents that can be detected by multimodal techniques. Magnetoliposomes are efficient multimodal contrast agents. They can simultaneously bear both kinds of contrast and can, furthermore, incorporate targeting ligands and chains of polyethylene glycol to enhance the accumulation of nanoparticles at the site of interest and the bioavailability, respectively. Here, we review the most important characteristics of the nanoparticles or complexes used as MRI contrast agents.

No MeSH data available.


Related in: MedlinePlus