²⁰⁹Bi quadrupole relaxation enhancement in solids as a step towards new contrast mechanisms in magnetic resonance imaging

Abstract

Motivated by the possibility of exploiting species containing high spin quantum number nuclei (referred to as quadrupole nuclei) as novel contrast agents for Magnetic Resonance Imaging, based on Quadrupole Relaxation Enhancement (QRE) effects, 1H spin-lattice relaxation has been investigated for tris(2-methoxyphenyl)bismuthane and tris(2,6-dimethoxyphenyl)bismuthane in powder. The relaxation experiment has been performed in the magnetic field range of 0.5 T to 3 T (the upper limit corresponds to the field used in many medical scanners). A very rich QRE pattern (several frequency specific 1H spin-lattice relaxation rate maxima) has been observed for both compounds. Complementary Nuclear Quadrupole Resonance experiments have been performed in order to determine the quadrupole parameters (quadrupole coupling constant and asymmetry parameters) for 209Bi. Knowing the parameters, the QRE pattern has been explained on the basis of a quantum-mechanical picture of the system including single and double-quantum coherences for the participating nuclei (1H and 209Bi). In this way the quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained.

Sn‐Based Alloys Synthesized in an Ionic Liquid at Room Temperature: Cu6Sn5 as a Case Study

“…When the 1 H resonance frequency (the transition frequency between the 1 H energy levels) matches one of the 14 N transition frequencies, the 1 H polarization can be taken over by 14 N, as a result of the mutual magnetic dipole‐dipole coupling between the participating nuclei, leading to a frequency‐specific enhancement of the 1 H spin‐lattice relaxation rate referred to as QRE; the 1 H spin‐lattice relaxation maxima are called quadrupole peaks. The positions of the quadrupole peaks depend on the quadrupole parameters which are determined by the electric field gradient tensor at the 14 N position and appear when (as already pointed out) the dynamic is sufficiently slow . For 14 N there are three quadrupole peaks at the frequencies of , and where is the quadrupolar coupling constant of 14 N, and η the asymmetry parameter of the electric field gradient at the position of the 14 N nucleus.…”

“…The positions of the quadrupole peaks depend on the quadrupole parameters which are determined by the electric field gradient tensor at the 14 N position and appear when (as already pointed out) the dynamic is sufficiently slow. [15,[26][27][28] For 14 N there are three quadrupole 14 N, and η the asymmetry parameter of the electric field gradient at the position of the 14 N nucleus. The positions of the quadrupole peaks can be treated as markers of the 14 N chemical environment as a Q and η values are sensitive to the electric field gradient.…”

Predicting quadrupole relaxation enhancement peaks in proton R1-NMRD profiles in solid Bi-aryl compounds from NQR parameters

“…The evolution field can typically be varied to create proton Larmor frequencies from as low as 10 kHz to about 40 MHz. The experiments presented later in this article, however, are conducted between 20 and 128 MHz by the use of an additional superconducting 3 T magnet [2]. An early detailed description of the method can be found in the work of F. Noack [3], a more recent review is given in reference [1].…”

“…Field cycling MRI has also been successfully demonstrated at clinical field strengths of 1.5 T [21-23] and 3 T [24]. Recently, strong and pronounced QRE peaks have been observed in NMRD measurements of different Bi-aryl compounds [2]. The experimental data of this article will be used to evaluate the herein presented simulation.…”

“…Assumption (2): QRE can only occur at magnetic fields B ev at which ν L (B ev ) matches a QN transition frequency ν Q (B ev ).…”