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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

Influence of the r2/r1 ratio on the efficiency of a contrast agent.Notes: High values of r2/r1 are characteristic of T2 contrast agents, which produce a hypointense signal in T2-weighted images, and thus organs appear darker in the image. Low values of r2/r1 define T1 contrast agents, and the associated images are clearer and brighter.
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f1-ijn-10-1727: Influence of the r2/r1 ratio on the efficiency of a contrast agent.Notes: High values of r2/r1 are characteristic of T2 contrast agents, which produce a hypointense signal in T2-weighted images, and thus organs appear darker in the image. Low values of r2/r1 define T1 contrast agents, and the associated images are clearer and brighter.

Mentions: Although nearly all MRI contrast agents affect both T1 and T2, the effects of contrast agents are usually more pronounced for either T1 or T2, leading to their categorization as either T1 or T2 contrast agents. Contrast enhancement is measured by the relaxation rate Ri =1/Ti (s−1), where i =1 or 2. The most important parameter for defining the efficiency of a contrast agent is its relaxivity, ri (ri = Ri/cCA(mM−1 s−1), where cCA is the analytical concentration of ion responsible for the contrast). The r2/r1 ratio is also used to indicate the contrast efficiency; the higher the ratio, the greater the efficiency of a T2 contrast agent and vice versa for a T1 contrast agent (Figure 1).


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

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

Influence of the r2/r1 ratio on the efficiency of a contrast agent.Notes: High values of r2/r1 are characteristic of T2 contrast agents, which produce a hypointense signal in T2-weighted images, and thus organs appear darker in the image. Low values of r2/r1 define T1 contrast agents, and the associated images are clearer and brighter.
© Copyright Policy
Related In: Results  -  Collection

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

f1-ijn-10-1727: Influence of the r2/r1 ratio on the efficiency of a contrast agent.Notes: High values of r2/r1 are characteristic of T2 contrast agents, which produce a hypointense signal in T2-weighted images, and thus organs appear darker in the image. Low values of r2/r1 define T1 contrast agents, and the associated images are clearer and brighter.
Mentions: Although nearly all MRI contrast agents affect both T1 and T2, the effects of contrast agents are usually more pronounced for either T1 or T2, leading to their categorization as either T1 or T2 contrast agents. Contrast enhancement is measured by the relaxation rate Ri =1/Ti (s−1), where i =1 or 2. The most important parameter for defining the efficiency of a contrast agent is its relaxivity, ri (ri = Ri/cCA(mM−1 s−1), where cCA is the analytical concentration of ion responsible for the contrast). The r2/r1 ratio is also used to indicate the contrast efficiency; the higher the ratio, the greater the efficiency of a T2 contrast agent and vice versa for a T1 contrast agent (Figure 1).

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