Sample Shuttling Relaxometry of Contrast Agents: NMRD Profiles above 1 T with a Single Device.

Daniel Henrard,Dimitrios Sakellariou,Zeinab Serhan,Rafael T. M. de Rosales,Thorsten Marquardsen,Fabien Ferrage,Yves Gossuin,Lydia Sandiford

doi:10.1007/s00723-015-0751-7

Abstract

Nuclear magnetic relaxation dispersion (NMRD) profiles are essential tools to evaluate the efficiency and investigate the properties of magnetic compounds used as contrast agents for magnetic resonance imaging (MRI), namely gadolinium chelates and superparamagnetic iron oxide particles. These curves represent the evolution of proton relaxation rates with the magnetic field. NMRD profiles are unparalleled to probe extensively the spectral density function involved in the relaxation of water in the presence of the paramagnetic ion or the magnetic nanoparticles. This makes such profiles an excellent test of the adequacy of a theoretical relaxation model and allow for a predictive approach to the development and optimization of contrast agents. From a practical point of view they also allow to evaluate the efficiency of a contrast agent in a certain range of magnetic fields. Nowadays, these curves are recorded with commercial fast field cycling devices, often limited to a maximum Larmor frequency of 40 MHz (0.94 T). In this article, relaxation data were acquired on a wide range of magnetic fields, from 3.5 × 10−4 to 14 T, for a gadolinium-based contrast agent and for PEGylated iron oxide nanoparticles. We show that the low-field NMRD curves can be completed with high-field data obtained on a shuttle apparatus device using the superconductive magnet of a high-field spectrometer. This allows a better characterization of the contrast agents at relevant magnetic fields for clinical and preclinical MRI, but also refines the experimental data that could be used for the validation of relaxation models.Electronic supplementary materialThe online version of this article (doi:10.1007/s00723-015-0751-7) contains supplementary material, which is available to authorized users.

Highlights

Nuclear magnetic resonance (NMR) relaxometry consists in the measurement of the relaxation times (T1, T2) of a nucleus observable in NMR as a function of the magnetic field
We show that the low-field Nuclear magnetic relaxation dispersion (NMRD) curves can be completed with high-field data obtained on a shuttle apparatus device using the superconductive magnet of a high-field spectrometer
Most new magnetic resonance imaging (MRI) systems operate at 3 T, typical small animal MRI systems operate at 7 T while some new devices reach 21 T. Such fields are not accessible to commercial fast field-cycling (FFC) equipments which are often limited to 1 T, while some recent hybrid systems using a superconducting magnet reach 3 T. We show that both the low-field and high-field NMRD profiles are necessary for the evaluation of contrast agents efficiency as well as for the development of relaxation models for magnetic contrast agents

Summary

Introduction

Nuclear magnetic resonance (NMR) relaxometry consists in the measurement of the relaxation times (T1, T2) of a nucleus observable in NMR as a function of the magnetic field. The dependence of the relaxation rates (R1 = 1/T1 and R2 = 1/T2) with the magnetic field bears important information since it gives access to the spectral density and to the mechanism of relaxation [1, 2] This allows one to probe the molecular dynamics of different systems such as proteins, polymers, and water trapped in porous systems. Relaxometry provides sufficiently extensive experimental datasets so that the relaxation mechanisms can be determined in yet poorly characterized systems containing magnetic entities. This is especially true for water proton relaxation induced by paramagnetic ions [3] and superparamagnetic particles used as contrast agents for magnetic resonance imaging [4]. It necessitates the access to numerous instruments and can be time consuming

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Conclusion