FDTD Analysis of a Radiofrequency Knee Coil for Low-Field MRI: Sample-Induced Resistance and Decoupling Evaluation
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Applied Magnetic Resonance
FDTD Analysis of a Radiofrequency Knee Coil for Low-Field MRI: Sample-Induced Resistance and Decoupling Evaluation Maria Sole Morelli • Valentina Hartwig • Stefano Tassano • Nicola Vanello • Vincenzo Positano • Maria Filomena Santarelli Alessandro Carrozzi • Luigi Landini • Giulio Giovannetti
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Received: 1 August 2013 / Revised: 19 September 2013 / Published online: 9 October 2013 Ó Springer-Verlag Wien 2013
Abstract Magnetic resonance imaging (MRI) using high static field ([3T) generates high-quality images, thanks to high homogeneity in transmission as well as high signal-to-noise ratio (SNR) in reception. On the other hand, biological effects are proportional to the magnetic field strength and moreover the diagnostic accuracy is not always linked to high-quality imaging. For these reasons, the interest in lowfield imaging becomes greater, also because of cheaper setting, greater patients comfort and more safety profile. In simple cases, as for surface coil, the coil performance is evaluated using classical electromagnetic theory, but for more complex geometry and in presence of a sample, is more difficult to evaluate the solution and often is necessary to follow a trial-and-error approach. Numerical methods represent a solution to this problem. In this work, we performed numerical simulation on a two-channel knee coil for low-field (0.5 T) MRI scanner. We are interested in seeing the effect of a sample placed inside the coil on the sample-induced resistance and decoupling between channels. In particular, we observe how the position of the sample inside the channel influences the resistance value and for performing this we compared an innovative method based on the exponential fitting on voltage M. S. Morelli (&) Scuola Superiore Sant’Anna, Piazza Martiri della Liberta` 33, 56127 Pisa, Italy e-mail: [email protected] V. Hartwig N. Vanello V. Positano M. F. Santarelli L. Landini G. Giovannetti Institute of Clinical Physiology, National Council of Research, Pisa, Italy V. Hartwig V. Positano M. F. Santarelli L. Landini G. Giovannetti Fondazione G. Monasterio CNR-Regione Toscana, Pisa, Italy S. Tassano A. Carrozzi Paramed s.r.l, Genoa, Italy N. Vanello L. Landini Department of Information Engineering, University of Pisa, Pisa, Italy
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oscillation damping with a validated method (estimation using quality factor). Finally, for the complete coil, the scatter parameters were calculated in loaded and unloaded conditions.
1 Introduction Magnetic resonance imaging (MRI) is a technique that can produce high-quality images, using static and radiofrequency (RF) fields. To obtain high-quality images, high-field MR ([3T) generates high field of view (FOV) and high homogeneity in transmission as well as high signal-to-noise ratio (SNR) in reception [1]. Despite this, it is important to consider biological effects due to the strength of the field: in fact, the static magnetic field (B0), time-varying gradient field (dB/dt) and RF magnetic fiel
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