Modular Coils with Low Hydrogen Content Especially for MRI of Dry Solids.
BACKGROUND
Recent advances have enabled fast magnetic resonance imaging (MRI) of solid materials. This development has opened up new applications for MRI, but, at the same time, uncovered new challenges. Previously, MRI-invisible materials like the housing of MRI detection coils are now readily depicted and either cause artifacts or lead to a decreased image resolution. In this contribution, we present versatile, multi-nuclear single and dual-tune MRI coils that stand out by (1) a low hydrogen content for high-resolution MRI of dry solids without artifacts; (2) a modular approach with exchangeable inductors of variable volumes to optimally enclose the given object; (3) low cost and low manufacturing effort that is associated with the modular approach; (4) accurate sample placement in the coil outside of the bore, and (5) a wide, single- or dual-tune frequency range that covers several nuclei and enables multinuclear MRI without moving the sample.


METHODS
The inductors of the coils were constructed from self-supporting copper sheets to avoid all plastic materials within or around the resonator. The components that were mounted at a distance from the inductor, including the circuit board, coaxial cable and holder were manufactured from polytetrafluoroethylene.


CONCLUSIONS
Residual hydrogen signal was sufficiently well suppressed to allow 1H-MRI of dry solids with a minimum field of view that was smaller than the sensitive volume of the coil. The SNR was found to be comparable but somewhat lower with respect to commercial, proton-rich quadrature coils, and higher with respect to a linearly-polarized commercial coil. The potential of the setup presented was exemplified by 1H/23Na high-resolution zero echo time (ZTE) MRI of a model solution and a dried human molar at 9.4 T. A full 3D image dataset of the tooth was obtained, rich in contrast and similar to the resolution of standard cone-beam computed tomography.
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Timon
T
Eichhorn
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Ute
U
Ludwig
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Elmar
E
Fischer
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Jens
J
Gröbner
Biological Anthropology, University Medical Center Freiburg, Freiburg, Germany.
Michael
M
Göpper
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany; Department of Craniomaxillofacial Surgery, University Medical Center Freiburg, Freiburg, Germany.
Anne-Katrin
AK
Eisenbeiss
Department of Craniomaxillofacial Surgery, University Medical Center Freiburg, Freiburg, Germany.
Tabea
T
Flügge
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Jürgen
J
Hennig
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Dominik
D
von Elverfeldt
Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany.
Jan-Bernd
JB
Hövener
D000818:Animals; D002138:Calibration; D004560:Electricity; D006793:Houseflies; D006859:Hydrogen / Q000737:chemistry*; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D012815:Signal Processing, Computer-Assisted; D059629:Signal-To-Noise Ratio; D013997:Time Factors
D006859:Hydrogen