Transverse relaxivity of particulate MRI contrast media: From theories to experiments

Müller, Robert N.; Gillis, Pierre; Moiny, Francis; Roch, Alain

doi:10.1002/mrm.1910220203

Cited by 159 publications

(128 citation statements)

References 4 publications

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“…In the presence of stoichiometric quantities of polyvalent biotin-dextran, uncomplexed SA-MACS showed a pronounced increase in hydrodynamic radius and a 2-to 3-fold decrease in T2 relaxivity (data not shown). An inverse relationship between iron oxide cluster size and T2 relaxation rates has been described previously (21) and explained by the extensive theoretical work of Gillis and colleagues (22)(23)(24). For colloidal suspensions of fixed iron oxide volume fraction, the particle size-dependence of T2 relaxivity depends on the quantity ␦ R 2 ͞D, where ␦ is the change in (angular) NMR frequency at the particle equator, R is the radius of the cluster, and D is the self-diffusion coefficient.…”

Section: Mri Signal Changes In Response Tomentioning

confidence: 72%

Calcium-sensitive MRI contrast agents based on superparamagnetic iron oxide nanoparticles and calmodulin

Atanasijević¹,

Shusteff

Fam

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

231

169

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We describe a family of calcium indicators for magnetic resonance imaging (MRI), formed by combining a powerful iron oxide nanoparticle-based contrast mechanism with the versatile calciumsensing protein calmodulin and its targets. Calcium-dependent protein-protein interactions drive particle clustering and produce up to 5-fold changes in T2 relaxivity, an indication of the sensors' potency. A variant based on conjugates of wild-type calmodulin and the peptide M13 reports concentration changes near 1 M Ca 2؉ , suitable for detection of elevated intracellular calcium levels. The midpoint and cooperativity of the response can be tuned by mutating the protein domains that actuate the sensor. Robust MRI signal changes are achieved even at nanomolar particle concentrations (<1 M in calmodulin) that are unlikely to buffer calcium levels. When combined with technologies for cellular delivery of nanoparticulate agents, these sensors and their derivatives may be useful for functional molecular imaging of biological signaling networks in live, opaque specimens. magnetic resonance ͉ T2 relaxation ͉ signal transduction ͉ molecular imaging ͉ neuroimaging C alcium ions (Ca 2ϩ ) have been a favorite target in molecular imaging studies because of the important role of calcium as a second messenger in cellular signaling pathways. Fluorescent calcium sensors are used widely in optical imaging, both at the cellular level and at the cell population level. Calcium-sensitive dyes have recently been used in conjunction with laser scanning microscopy to follow neural network activity in small, threedimensional brain areas (1) and to characterize patterns of interaction among cells in developing vertebrate embryos (2). Because of the scattering properties of dense tissue, highresolution optical approaches like these are usually limited to superficial regions of specimens and to restricted fields of view (3). To probe calcium dynamics more globally in living systems, a different imaging modality must be used.Magnetic resonance imaging (MRI) is an increasingly accessible technique for imaging opaque subjects at fairly high spatial resolution, and MRI studies of calcium dynamics could, in principle, complement optical approaches by offering both greatly expanded coverage and depth penetration in vivo (4). Calcium isotopes are unsuitable for direct imaging by magnetic resonance, so attempts to sensitize MRI to calcium have focused around the use of molecular imaging agents. Fluorinated derivatives of the bivalent cation chelator 1,2-bis(2-aminophenoxy)ethane-N,N,NЈ,NЈ-tetraacetic acid (BAPTA) have permitted calcium measurements in vivo by 19 F MRI but only at Ϸ10 Ϫ5 the sensitivity of standard MRI methods (5, 6). Two potentially more powerful proton T1 relaxation-promoting contrast agents were subsequently introduced. The paramagnetic ion manganese (Mn 2ϩ ) mimics calcium by entering cells through calcium channels. Because it accumulates much faster than it is removed, Mn 2ϩ produces an ''integral'' of calcium signaling history that can be d...

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Section: Mri Signal Changes In Response Tomentioning

confidence: 72%

Calcium-sensitive MRI contrast agents based on superparamagnetic iron oxide nanoparticles and calmodulin

Atanasijević¹,

Shusteff

Fam

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

231

169

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“…Under this condition, the relaxation rate R 2 * can be ascribed to the dephasing of motionless magnetic moments in a nonuniform field created by randomly distributed magnetic particles. [24][25][26][27][28][29] The value of R 2 * is then given by eq 4: Here, f ) υN is the volume fraction occupied by the particles (υ is the volume of a single particle and N is the number of particles per m 3 ) and R 2 0 is the contribution due to other relaxation mechanisms, such as the diamagnetic relaxation and a contribution as the result of chemical exchange of protons between the surface of the particles and the bulk water protons. Equation 4 was developed for spherical particles.…”

Section: Resultsmentioning

confidence: 99%

NMR Transversal Relaxivity of Suspensions of Lanthanide Oxide Nanoparticles

et al. 2007

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Aqueous suspensions of paramagnetic lanthanide oxide nanoparticles have been studied by NMR relaxometry. The observed R 2 * relaxivities are explained by the static dephasing regime (SDR) theory. The corresponding R 2 relaxivities are considerably smaller and are strongly dependent on the interval between the two refocusing pulses. The experimental data are rationalized by assuming the value of the diffusion correlation time, τ D , to be very long in a layer with adsorbed xanthan on the particle's surface. In this layer, the refocusing pulses are fully effective and R 2 ≈ 0. Outside this layer, the diffusion model for weakly magnetized particles was applied. From the fit of the experimental relaxation data with this model, both the particle radii (r p ) and the radii of the spheres, within which the refocusing pulses are fully effective (r diff ), were estimated. The values of r p obtained are in agreement with those determined by dynamic light scattering. Because the value of r diff depends on the external magnetic field B and on the magnetic moment of the lanthanide of interest (µ eff 2 ), the R 2 relaxivity was found to be proportional to B and to µ eff 2 .

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“…PROTON T2 RELAXATION MECHANISMS caused by superparamagnetic iron oxide (SPIO) particles are influenced by the strength of magnetic field, particle size, magnetic property of the core, and echo time (1)(2)(3)(4)(5). In addition, it has been reported that the T2 relaxation effect of SPIO strongly depends on its spatial distribution (6 -8).…”

mentioning

confidence: 99%

Relaxation effects of clustered particles

Tanimoto

Oshio

Suematsu

et al. 2001

Magnetic Resonance Imaging

108

111

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Relations between spatial distribution of superparamagnetic iron oxide (SPIO) particles and the image contrast caused by SPIO were investigated. Actual clustering pattern of particles was measured in the liver and spleen of animals using intravital laser confocal microscopy. SPIOdoped phantoms with and without Sephadex beads were made to simulate these patterns, and relaxation parameters were measured using a 1.5-T clinical scanner. Finally, these results were compared to clinical image data using SPIO particulate agent. Intravital microscopy indicated that the clustering of latex beads was more predominant in hepatic Kupffer cells than in splenic macrophages (P < 0

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Transverse relaxivity of particulate MRI contrast media: From theories to experiments

Cited by 159 publications

References 4 publications

Calcium-sensitive MRI contrast agents based on superparamagnetic iron oxide nanoparticles and calmodulin

Calcium-sensitive MRI contrast agents based on superparamagnetic iron oxide nanoparticles and calmodulin

NMR Transversal Relaxivity of Suspensions of Lanthanide Oxide Nanoparticles

Relaxation effects of clustered particles

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