Triple-quantum filtered NMR imaging of sodium in the human brain

Abstract

In the past multiple-quantum filtered imaging of biexponential relaxation sodium-23 nuclei in the human brain ,has been limited by low signal to noise ratios; this thesis demonstrates that such imaging is feasible when using a modified gradient-selected triple-quantum filter at a repetition time which maximizes the signal to noise ratio.Nuclear magnetic resonance imaging of biexponential relaxation nuclei in the human brain may be useful for detecting ischemia, cancer, and. patho-

Comprehensive Account of Sodium Imaging and Spectroscopy for Brain Research

“…47,48 Earlier studies reported that extracellular sodium acts as mentioned in case 2 (T 2s ≈ T 2f ) and produces only T 2s ≈ T 2f single quantum coherence in biological systems. 28,47,48 This difference in the behavior of intracellular and extracellular sodium has been detected by the pulse sequence (designed for a triple-quantum filter) to separate intracellular and extracellular sodium ions in human skeletal muscles and human brain studies. 49−51 With extensive experimentation and further exploration, recent studies have shown contribution of the extracellular sodium in the multiquantum filtered signal.…”

“…The mono-and biexponential relaxation behavior in varying media further hinders the detection of sodium signals. 10 In the biological environment, fluctuations of EFG are random and exist with three types of interactions: 47 (1) interaction between sodium nucleus and dipole moment of protons in hydration sphere, (2) interaction between the quadruple moment of sodium nucleus with EFG from hydration sphere, and (3) interaction between sodium nuclear quadruple moment with EFG from outside hydration sphere. Extracellular sodium is surrounded by a hydration sphere (dipole−dipole interactions with protons), whereas intracellular sodium ions are attached to proteins (macromolecules).…”

“…Studies have shown that intracellular sodium behaves as mentioned in case 1. 47,48 This asymmetric relaxation time between energy levels (T 2s ≠ T 2f ) has been used to support that intracellular sodium ions produce triple quantum coherence (TQC). 47,48 Earlier studies reported that extracellular sodium acts as mentioned in case 2 (T 2s ≈ T 2f ) and produces only T 2s ≈ T 2f single quantum coherence in biological systems.…”

“…47,48 This asymmetric relaxation time between energy levels (T 2s ≠ T 2f ) has been used to support that intracellular sodium ions produce triple quantum coherence (TQC). 47,48 Earlier studies reported that extracellular sodium acts as mentioned in case 2 (T 2s ≈ T 2f ) and produces only T 2s ≈ T 2f single quantum coherence in biological systems. 28,47,48 This difference in the behavior of intracellular and extracellular sodium has been detected by the pulse sequence (designed for a triple-quantum filter) to separate intracellular and extracellular sodium ions in human skeletal muscles and human brain studies.…”

“…Spectral density for the motion of EFG with respect to ion is given as follows: where τ c corresponds to the correlation time of EFG describing the reorientation of quadrupolar interaction between 23 Na nucleus and EFG, and ω is the Larmor frequency of sodium ions in eq , from which the following conclusions can be drawn: Case 1: If τ c is comparable to the Larmor precession time, then T 2s ≠ T 2f . Sodium ions start having biexponential decay, resulting in multiquantum coherence (MQC). Case 2: If τ c is higher than the Larmor precession time, then T 2s ≈ T 2f .…”