Journal ArticleDOI
On T2-shortening by weakly magnetized particles: the chemical exchange model.
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TLDR
The CE equation is shown to be identical to these theories in the respective limits and appropriate parameter relationships are derived for spherical particles, and the model reproduces the essential relaxation characteristics in the intermediate range.Abstract:
Chemical exchange (CE) theory is compared with two theories of T2-shortening caused by microscopic magnetic centers: inner- and outer-sphere relaxation theory (long-echo limit) and mean gradient diffusion theory (short-echo limit). The CE equation is shown to be identical to these theories in the respective limits and appropriate parameter relationships are derived for spherical particles. The theories are then compared with computer simulations of spherical particles and with a recent general theory, with good agreement in the asymptotic regions. The CE model also reproduces the essential relaxation characteristics in the intermediate range. Finally, good agreement of a CE model with simulations for magnetized cylinders is also demonstrated. The discussion is limited to weakly magnetized particles such that the maximum phase shift during an echo interval is less than one radian, permitting the use of the Luz-Meiboom CE equation. Published 2001 Wiley-Liss, Inc.read more
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Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications
Sophie Laurent,Delphine Forge,Marc Port,Alain Roch,Caroline Robic,Luce Vander Elst,Robert N. Muller +6 more
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MRI R2 and R2* mapping accurately estimates hepatic iron concentration in transfusion-dependent thalassemia and sickle cell disease patients
John C. Wood,John C. Wood,Cathleen Enriquez,Cathleen Enriquez,Nilesh R. Ghugre,Nilesh R. Ghugre,J. Michael Tyzka,J. Michael Tyzka,Susan Carson,Susan Carson,Marvin D. Nelson,Marvin D. Nelson,Thomas D. Coates,Thomas D. Coates +13 more
TL;DR: Both R2 and R2* can accurately measure hepatic iron concentration throughout the clinically relevant range of HIC with appropriate MRI acquisition techniques, despite significant differences in technique and instrumentation.
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Designed synthesis of uniformly sized iron oxide nanoparticles for efficient magnetic resonance imaging contrast agents.
Nohyun Lee,Taeghwan Hyeon +1 more
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Iron Oxide Based Nanoparticles for Multimodal Imaging and Magnetoresponsive Therapy.
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Size and surface effects on the MRI relaxivity of manganese ferrite nanoparticle contrast agents.
Ulrich I. Tromsdorf,Nadja C. Bigall,Michael G. Kaul,Oliver T. Bruns,Marija Nikolic,Birgit Mollwitz,Ralph A. Sperling,Rudolph Reimer,Heinz Hohenberg,Wolfgang J. Parak,Stephan Förster,Ulrike Beisiegel,Gerhard Adam,Horst Weller +13 more
TL;DR: Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches and an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystal is observed.
References
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Effects of Diffusion on Free Precession in Nuclear Magnetic Resonance Experiments
H. Y. Carr,Edward M. Purcell +1 more
TL;DR: In this paper, the effect of diffusion on free precession in nuclear resonance has been studied, and a new scheme for measuring the transverse relaxation time is described, which largely circumvents the diffusion effect.
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Theory of NMR signal behavior in magnetically inhomogeneous tissues: the static dephasing regime.
TL;DR: An approach is developed that analytically describes the NMR signal in the static dephasing regime where diffusion phenomena may be ignored and the signal decays exponentially with an argument which depends quadratically on TE.
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Oxygenation dependence of the transverse relaxation time of water protons in whole blood at high field
TL;DR: It is shown that the increase in T-1(2) with increasing blood deoxygenation arises from diffusion of water through these field gradients, which increases the volume magnetic susceptibility within the erythrocytes and thus creates local fieldgradients around these cells.
Journal ArticleDOI
Mr contrast due to intravascular magnetic susceptibility perturbations
TL;DR: A novel Monte Carlo model is developed with which the authors quantified the relationship between microscopic tissue parameters, NMR imaging parameters, and susceptibility contrast in vivo and demonstrated that spin echo functional images have greater microvascular sensitivity than gradient echo images, and that the specifics of the volume fraction and concentration dependence of transverse relaxivity change should allow for robust mapping of relative blood volume.
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Intravascular susceptibility contrast mechanisms in tissues
TL;DR: The factors affecting the rate of loss of transverse magnetization in gradient echo and spin‐echo pulse sequences have been quantified using computer modeling for media containing arrays of susceptibility variations and the implications for functional imaging based on the effects of deoxyhemoglobin in brain tissue are considered.