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Interventional MRI: Tapering improves the distal sensitivity of the loopless antenna
Author(s) -
Qian Di,
ElSharkawy AbdElMonem M.,
Atalar Ergin,
Bottomley Paul A.
Publication year - 2010
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.22152
Subject(s) - sensitivity (control systems) , antenna (radio) , signal (programming language) , signal to noise ratio (imaging) , noise (video) , imaging phantom , acoustics , conductor , physics , detector , nuclear magnetic resonance , materials science , optics , mathematics , computer science , telecommunications , geometry , electronic engineering , engineering , artificial intelligence , image (mathematics) , programming language
The “loopless antenna” is an interventional MRI detector consisting of a tuned coaxial cable and an extended inner conductor or “whip”. A limitation is the poor sensitivity afforded at, and immediately proximal to, its distal end, which is exacerbated by the extended whip length when the whip is uniformly insulated. It is shown here that tapered insulation dramatically improves the distal sensitivity of the loopless antenna by pushing the current sensitivity toward the tip. The absolute signal‐to‐noise ratio is numerically computed by the electromagnetic method‐of‐moments for three resonant 3‐T antennae with no insulation, uniform insulation, and with linearly tapered insulation. The analysis shows that tapered insulation provides an ∼400% increase in signal‐to‐noise ratio in trans‐axial planes 1 cm from the tip and a 16‐fold increase in the sensitive area as compared to an equivalent, uniformly insulated antenna. These findings are directly confirmed by phantom experiments and by MRI of an aorta specimen. The results demonstrate that numerical electromagnetic signal‐to‐noise ratio analysis can accurately predict the loopless detector's signal‐to‐noise ratio and play a central role in optimizing its design. The manifold improvement in distal signal‐to‐noise ratio afforded by redistributing the insulation should improve the loopless antenna's utility for interventional MRI. Magn Reson Med 63:797–802, 2010. © 2010 Wiley‐Liss, Inc.