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

Authors Estelrich J, Sánchez-Martín MJ, Busquets MA

Received 28 October 2014

Accepted for publication 7 December 2014

Published 6 March 2015 Volume 2015:10(1) Pages 1727—1741

DOI https://doi.org/10.2147/IJN.S76501

Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 4

Editor who approved publication: Dr Thomas J Webster

Joan Estelrich,1,2 María Jesús Sánchez-Martín,1 Maria Antònia Busquets1,2

1Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, Barcelona, Catalonia, Spain; 2Institut de Nanociència I Nanotecnologia (IN2UB), 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 (T1, spin–lattice relaxation and T2, 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 T1 and T2 increases the corresponding relaxation rates, 1/T1 and 1/T2, 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 T2-weighted images; or complexes of lanthanide metals (mostly containing gadolinium ions), providing positive contrast in T1-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.

Keywords: gadolinium, iron oxide nanoparticles, magnetoliposomes, paramagnetic nanoparticles, superparamagnetic nanoparticles, relaxivity

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