Power balance and loss mechanism analysis in RF transmit coil arrays. Issue 4 (16th October 2014)

• Record Type: Journal Article
• Authors: Kuehne, Andre; Goluch, Sigrun; Waxmann, Patrick; Seifert, Frank; Ittermann, Bernd; Moser, Ewald; Laistler, Elmar
• Is Part Of: Magnetic resonance in medicine. Volume 74:Issue 4(2015:Oct.)
• Page Start: 1165
• Page End: 1176
• Publication Date: 2014-10-16
• Subjects: Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.25493
• Languages: English
• ISSNs: 0740-3194

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="mrm25493-sec-0001" sec-type="section"> <title>Purpose</title> <p>To establish a framework for transmit array power balance calculations based on power correlation matrices to accurately quantify the loss contributions from different mechanisms such as coupling, lumped components, and radiation.</p> </sec> <sec id="mrm25493-sec-0002" sec-type="section"> <title>Theory and Methods</title> <p>Starting from Poynting's theorem, power correlation matrices are derived for all terms in the power balance, which is formulated as a matrix equation. Finite‐difference time‐domain simulations of two 7 T eight‐channel head array coils at 297.2 MHz are used to verify the theoretical considerations and demonstrate their application. Care is taken to accurately incorporate all loss mechanisms. The power balance for static B<sub>1</sub> phase shims as well as two‐dimensional spatially selective transmit SENSE pulses is shown.</p> </sec> <sec id="mrm25493-sec-0003" sec-type="section"> <title>Results</title> <p>The simulated power balance shows an excellent agreement with theory, with a maximum power imbalance of less than 0.11%. Power loss contributions from the different loss mechanisms vary significantly between the investigated setups, and depending on the excitation mode imposed on the coil.</p> </sec> <sec id="mrm25493-sec-0004" sec-type="section"> <title>Conclusion</title> <p>The presented approach enables a straightforward loss evaluation for an arbitrary excitation of transmit coil arrays. Worst‐case power imbalance and losses are calculated in a straightforward manner. This allows for deeper insight into transmit array loss mechanisms, incorporation of radiated power components in specific absorption rate calculations and verification of electromagnetic simulations. Magn Reson Med 74:1165–1176, 2015. © 2014 Wiley Periodicals, Inc.</p> </sec> </abstract>