A Model for the Dynamics of Spins 3/2 in Biological Media: Signal Loss during Radiofrequency Excitation in Triple-Quantum-Filtered Sodium MRI

Magnetic Resonance in Med

Boada

2001

Self Cite

A new method for selectively detecting sodium ions in anisotropic environments is presented. A spin-lock (SL) sequence, followed by a coherence transfer pulse, generates rank-two zero-quantum coherences, and converts them into observable transverse magnetization. The quadrupolar polarization is only generated when there are residual quadrupolar couplings in the sample, and provided the SL field strength is comparable to these couplings. This filter has proved to be more efficient than a double-quantum magic-angle (DQ-MA) filter in generating observable signal from ions in anisotropic media in both a nasal bovine cartilage sample and a liquid crystalline DNA sample. In living tissues, sodium ions are distributed in a multitude of local environments (1,2). These environments can be loosely classified in three different categories: 1) The liquid-like environments, wherein the sodium ions are inside the extreme narrowing limit (ENL), yielding an NMR spectrum comprised of a single Lorentzian line.2) The more viscous, isotropic environments, wherein the quadrupolar interaction is still averaged to zero on a time scale less than the inverse of the Larmor frequency, but with the ions involved in slow molecular motion outside the ENL. The ions in such an environment yield a single NMR resonance, consisting of a superposition of two Lorentzians with different widths.3) The liquid-crystalline, or anisotropic environments, wherein the quadrupolar interaction is not entirely averaged out on a time scale less than the inverse of the Larmor frequency, yielding sodium spectra consisting of a central line and two satellites. The study of the distribution of sodium ions in these environments is very useful for understanding the pathophysiology of many diseases, since a redistribution of ions is associated with any pathological condition affecting normal cell function (3).Sodium single-quantum NMR is nonselective with regard to the motional properties of the ions in different environments (it contains contributions from all three types of environments mentioned above). A multitude of sequences have been developed to increase the selectivity of sodium NMR, and thereby improve its sensitivity to changes associated with disease. For example, the signal obtained with a triple-quantum (TQ) sequence does not have contributions from sodium ions inside the ENL, and has successfully been employed as a sensitive indicator for pathologic conditions in animal models and humans (4 -7). However, further selectivity may still be desired, since certain diseases, such as cartilage degenerative diseases, are known to correlate well with a loss of sodium-ion ordering in the affected tissue (8). A sequence that does not discern between sodium ions in more viscous, isotropic, and liquid-crystalline anisotropic environments (such as a TQ filter) produces an unnecessary baseline, which can eventually mask small changes taking place in the pool of ordered ions. Consequently, NMR pulse sequences that yield signal only from 23 Na ions in anisotropic enviro...

Section: Resultsmentioning

confidence: 87%

Section: Theorymentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Section: A Modeling Of the Biological Samplementioning

confidence: 99%

See 3 more Smart Citations

Detection of sodium ions in anisotropic environments through spin‐lock NMR

Hancu

Magnetic Resonance in Med

Boada

2001

Self Cite

Thermal relaxation and coherence dynamics of spin 3/2. I. Static and fluctuating quadrupolar interactions in the multipole basis

Concepts Magnetic Resonance

2003

Self Cite

178

ABSTRACT:The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed.

Thermal relaxation and coherence dynamics of spin 3/2. II. Strong radio‐frequency field

Concepts Magnetic Resonance

2003

Self Cite

ABSTRACT:The relaxation dynamics of the spin-3/2 density operator under strong, on-resonance radio-frequency (RF) irradiation and in the presence of fluctuating and static quadrupolar interactions is reviewed. The evolution under the lock is analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. For isotropic systems, relaxation under offresonance spin-locking conditions and in the multiple-pulse quadrupolar echo (QE) experiment is reviewed also. Spin-lock pulse sequences optimized for the selective detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part I, the classical relaxation dynamics of spin 3/2 was reviewed.