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Tuning Nuclear Quadrupole Resonance: A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents

Christian Gösweiner, Perttu Lantto, Roland Fischer, Carina Sampl, Evrim Umut, Per-Olof Westlund, Danuta Kruk, Markus Bödenler, Stefan Spirk, Andreas Petrovič, and Hermann Scharfetter
Phys. Rev. X 8, 021076 – Published 25 June 2018
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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 QNH1, 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 Bi209 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.

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  • Received 16 January 2018
  • Revised 6 April 2018

DOI:https://doi.org/10.1103/PhysRevX.8.021076

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied PhysicsInterdisciplinary Physics

Authors & Affiliations

Christian Gösweiner1,*, Perttu Lantto2, Roland Fischer3, Carina Sampl3, Evrim Umut4, Per-Olof Westlund5, Danuta Kruk4, Markus Bödenler1, Stefan Spirk6,7, Andreas Petrovič1, and Hermann Scharfetter1

  • 1Institute of Medical Engineering, Graz University of Technology, 8010 Graz, Austria
  • 2NMR Research Unit, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland
  • 3Institute of Inorganic Chemistry, Graz University of Technology, 8010 Graz, Austria
  • 4Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, 10-719 Olsztyn, Poland
  • 5Departement of Chemistry, Umeå University, 901 87 Umeå, Sweden
  • 6Institute for Chemistry and Technology of Materials, Graz University of Technology, 8010 Graz, Austria
  • 7Institute of Paper, Pulp and Fibre Technology, Graz University of Technology, 8010 Graz, Austria

  • *Corresponding author. christian.goesweiner@tugraz.at

Popular Summary

Magnetic resonance imaging (MRI) is one of the most powerful diagnostic imaging tools in modern medicine, achieving high spatial resolution, tissue contrast, and penetration depth without the use of ionizing radiation. Tissue contrast is based in part on how long it takes protons in the body (placed in a magnetic field) to return to their normal state after being excited by a radio-frequency pulse. Contrast agents are often administered to patients to increase these relaxation times—and hence improve tissue contrast. Here, we aim to develop a novel type of contrast agent that avoids some of the shortcomings of current approaches and improves image contrast in a particularly smart way.

Our idea is based on quadrupole relaxation enhancement, a quantum-mechanical effect where nuclei in certain molecules interact with proton spins from nearby water molecules. This interaction transfers frequency-selective magnetization from the proton spins to the neighboring nuclei, which leads to a speed-up of the proton relaxation and, subsequently, to a contrast enhancement in the image. The frequency selectivity of this effect enables practical features such as the ability to activate or inactivate the contrast enhancement by modulating the magnetic field or by chemical modification. Specifically, we find that a class of organometallic compounds containing bismuth as the quadrupole nucleus fulfills many requirements for this type of contrast agent.

The results of our work point to “Bi-aryl” compounds as promising candidates for a new type of contrast agent that, because of their frequency-selective character, may provide interesting new options for MRI diagnostics in the future.

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Vol. 8, Iss. 2 — April - June 2018

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