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

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, H-1 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 H-1 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 Bi-209. 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 (H-1 and Bi-209). In this way the quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained

A mass-conserving fast algorithm to parameterize gravitational transport and deposition using digital elevation models

Many natural phenomena such as snow avalanches, debris flows, or lahars involve gravitational transport and deposition that is largely governed by topography. This paper describes a fast and mass-conserving algorithm to parameterize mass transport and deposition (MTD) over a digital elevation model. The algorithm is an extension to existing flow-routing and terrain parameterization techniques. Its fast execution allows application over large areas or its incorporation into other models, e.g., distributed glacier mass balance in mountain topography. The proposed method does not include effects of kinetic energy and thus neglects potential uphill flow of fast-moving mass. The application of MTD is described at the example of small and frequent snow avalanches in steep terrain for which the required parameters are approximated from published data. The algorithm MTD has been developed and is described for the gravitational redistribution of snow, but it is also applicable to other types of mass movements

Tuning nuclear quadrupole resonance:a novel approach for the design of frequency-selective MRI contrast agents

Abstract The interaction between water protons and suitable quadrupolar nuclei (QN) can lead to quadrupole relaxation enhancement (QRE) of proton spins, provided the resonance condition between both spin transitions is fulfilled. This effect could be utilized as a frequency selective mechanism in novel, responsive T₁ shortening contrast agents (CAs) for magnetic resonance imaging (MRI). In particular, the proposed contrast mechanism depends on the applied external flux density—a property that can be exploited by special field-cycling MRI scanners. For the design of efficient CA molecules, exhibiting narrow and pronounced peaks in the proton T₁ relaxation dispersion, the nuclear quadrupole resonance (NQR) properties, as well as the spin dynamics of the system QN−¹H, have to be well understood and characterized for the compounds in question. In particular, the energy-level structure of the QN is a central determinant for the static flux densities at which the contrast enhancement appears. The energy levels depend both on the QN and the electronic environment, i.e., the chemical bonding structure in the CA molecule. In this work, the NQR properties of a family of promising organometallic compounds containing ²⁰⁹Bi as QN have been characterized. Important factors like temperature, chemical structure, and chemical environment have been considered by NQR spectroscopy and ab initio quantum chemistry calculations. The investigated Bi-aryl compounds turned out to fulfill several crucial requirements: NQR transition frequency range applicable to clinical 1.5- and 3 T MRI systems, low temperature dependency, low toxicity, and tunability in frequency by chemical modification