Journal ArticleDOI
Transverse relaxation of solvent protons induced by magnetized spheres: application to ferritin, erythrocytes, and magnetite
Pierre Gillis,Seymour H. Koenig +1 more
TLDR
On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low‐density polymer‐coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin, it appears that diffusion through intracellular gradients determines 1/T2.Abstract:
Since 1/T2 of protons of tissue water is generally much greater than 1/T1 at typical imaging fields, small single-ion contrast agents--such as Gd(DTPA), which make comparable incremental contributions and therefore smaller fractional contributions to 1/T2 compared to 1/T1--are not as desirable for contrast-enhancement as agents that could enhance 1/T2 preferentially. In principle, such specialized agents will only be effective at higher fields because the field dependence (dispersion) of 1/T1 is such that it approaches zero at high fields whereas 1/T2 approaches a constant value. The residual 1/T2 is called the "secular" contribution and arises from fluctuations in time--as sensed by the protons of diffusing solvent or tissue water molecules--of the component of the magnetic field parallel to the static applied field. For solutions or suspensions of sufficiently large paramagnetic or ferromagnetic particles (greater than or equal to 250 A diameter), the paramagnetic contributions to the relaxation rates satisfy 1/T2 much greater than 1/T1 at typical imaging fields. We examine the theory of secular relaxation in some detail, particularly as it applies to systems relevant to magnetic resonance imaging, and then analyze the data for solutions, suspensions, or tissue containing ferritin, erythrocytes, agar-bound magnetite particles, and liver with low-density composite polymer-coated magnetite. In most cases we can explain the relaxation data, often quantitatively, in terms of the theory of relaxation of protons (water molecules) diffusing in the outer sphere environments of magnetized particles. The dipolar field produced by these particles has a strong spatial dependence, and its apparent fluctuations in time as seen by the diffusing protons produce spin transitions that contribute to both 1/T1 and /T2 comparably at low fields; for the larger particles, because of dispersion, the secular term dominates at fields of interest. On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low-density polymer-coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin--for which 1/T2 is unexpectedly large--the source of its large relaxivity must reside in nonideal chemistry of the ferritin core. For blood, it appears that diffusion through intracellular gradients determines 1/T2.read more
Citations
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Journal ArticleDOI
Medical Application of Functionalized Magnetic Nanoparticles
TL;DR: The applications of these functionalized magnetic nanoparticles with their unique features will further improve medical techniques and enhance medical techniques.
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Perfusion imaging with NMR contrast agents
TL;DR: The use of MR contrast agents to measure tissue perfusion is reviewed, and the potential of contrast‐enhanced NMR for high resolution in vivo mapping of both physiology and anatomy is suggested.
Journal ArticleDOI
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.
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.
Journal ArticleDOI
Imaging iron stores in the brain using magnetic resonance imaging.
E. Mark Haacke,Norman Y.C. Cheng,Michael J. House,Qiang Liu,Jaladhar Neelavalli,Robert J. Ogg,Adnan Khan,Muhammad Ayaz,Wolff M. Kirsch,Andre Obenaus +9 more
TL;DR: This review examines the response of the magnetic resonance visible iron in tissue that produces signal changes in both magnitude and phase images that seem to correlate with brain iron content, but still have not been successfully exploited to accurately and precisely quantify brain iron.
References
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Journal ArticleDOI
Spin diffusion measurements : spin echoes in the presence of a time-dependent field gradient
E. O. Stejskal,J. E. Tanner +1 more
TL;DR: In this article, a derivation of the effect of a time-dependent magnetic field gradient on the spin-echo experiment, particularly in the presence of spin diffusion, is given.
Journal ArticleDOI
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.
Journal ArticleDOI
Modified Spin‐Echo Method for Measuring Nuclear Relaxation Times
S. Meiboom,D. Gill +1 more
TL;DR: In this article, a spin echo method adapted to the measurement of long nuclear relaxation times (T2) in liquids is described, and the pulse sequence is identical to the one proposed by Carr and Purcell, but the rf of the successive pulses is coherent, and a phase shift of 90° is introduced in the first pulse.
Journal ArticleDOI
Relaxation Effects in Nuclear Magnetic Resonance Absorption
TL;DR: In this article, the authors studied the effect of the thermal motion of the magnetic nuclei upon the spin-spin interaction in a rigid lattice and the line width of the absorption line.
Journal ArticleDOI
NMR‐Relaxation Mechanisms of O17 in Aqueous Solutions of Paramagnetic Cations and the Lifetime of Water Molecules in the First Coordination Sphere
T. J. Swift,Robert E. Connick +1 more
TL;DR: In this paper, an investigation was made of the temperature and frequency dependence of T2 for O17 in aqueous solutions containing Mn2+, Fe2+, Co2+, Ni2+, and Cu2+.