Abstract
Improvements to the signal-to-noise ratio of magnetic resonance detection lead to a strong reduction in measurement time, yet as a sole optimization goal for resonator design, it would be an oversimplification of the problem at hand. Multiple constraints, for example for field homogeneity and sample shape, suggest the use of numerical optimization to obtain resonator designs that deliver the intended improvement. Here we consider the 2D Lenz lens to be a sufficiently broadband flux transforming interposer between the sample and a radiofrequency (RF) circuit and to be a flexible and easily manufacturable device family with which to mediate different design requirements. We report on a method to apply topology optimization to determine the optimal layout of a Lenz lens and demonstrate realizations for both low- (45 MHz) and high-frequency (500 MHz) nuclear magnetic resonance.
Highlights
1.1 Signal-to-noise ratio (SNR) in magnetic resonance (MR)Nuclear MR spectroscopy and imaging are powerful tools for determining the molecular structure of chemical substances or for studying the anatomy of organisms
If the region of interest is reduced such that the variation lies below 10 %, the optimized lens (OL) at higher frequencies can still be used; depending on the application, one can use the magnetic lens designed for 45 MHz at 500 MHz to get a higher amplification if maintaining uniformity is not a concern or a smaller sample volume can be used
Topology optimization offers a feasible pathway with which to reach optimal designs that goes beyond mere intuition, and we could show, using a commercial finite-element tool, that it is possible to find practical Lenz lens arrangements that, when implemented, achieve their set goals
Summary
Nuclear MR spectroscopy and imaging are powerful tools for determining the molecular structure of chemical substances or for studying the anatomy of organisms. If we focus our attention on the LL, its design needs to be further investigated to improve the amplified field uniformity and to increase the field amplification for cases where the geometrical space for the LL is limited It was shown by Jouda et al (2017) that tuning and matching the LL at the frequency of operation improved the signal acquired significantly, even for those cases where the design space is constrained, it comes at the cost of losing the broadband nature of the LL and adds the difficulty in maintaining the Q factor of the coil/lens arrangement due to the resonance splitting effect. The design will depart considerably from the Lenz lens topology and may require additional constraints to ensure manufacturability
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