| Zugriffsnummer | 35879 |
| Dokumenttyp | Zeitschriftenartikel |
| Peer Review | unbekannt |
| Sprache | Englisch |
| Titel | Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T |
| Autor(in); Institution |
Weidemann, Gerd; 8.1, Medizinische Messtechnik, PTB-Berlin
Seifert, Frank; 8.1, Medizinische Messtechnik, PTB-Berlin
Hoffmann, Werner; 8.1, Medizinische Messtechnik, PTB-Berlin
Pfeiffer, Harald; 8.1, Medizinische Messtechnik, PTB-Berlin
Seemann, Reiner; 8.1, Medizinische Messtechnik, PTB-Berlin
Ittermann, Bernd; 8.1, Medizinische Messtechnik, PTB-Berlin
|
| Quelle/Jahr | Magnetic Resonance Materials in Physics, Biology and Medicine: 29 (2016), 3, 371 - 378 |
| ISSN | 0968-5243 (PRINT) ; 1352-8661 (ONLINE) |
| DOI | |
| Verlag | Heidelberg [u.a.]: Elsevier |
| Freie Schlagworte | Magnetic resonance imaging ; Parallel transmission ; Power balance ; Radiated power ; RF safety |
| Zusammenfassung | Objective The power balance of multichannel transmit coils is a central consideration in assessing performance and safety issues. At ultrahigh fields, in addition to absorption and reflection, radiofrequency (RF) radiation into the far field becomes a concern. Materials and methods We engineered a system for in situ measurement of complex-valued scattering parameter (S-parameter) matrices of multichannel transmit coils that allows for the calculation of the reflected and accepted power for arbitrary steering conditions. The radiated power from an RF coil inside a large single-mode waveguide couples to that mode. Finite-difference time-domain simulations were used for the calculations, and E-field probes were used to measure the electric field distribution, and hence the radiated power, in the waveguide. To test this concept, an eight-channel shielded-loop array for 7T imaging was studied inside a 280-cm-long cylindrical waveguide with a 60-cm diameter. Results For a 7T parallel-transmit coil, the S-parameters were measured and the reflected power calculated as a function of steering conditions. Maximum radiated power was observed for the circularly polarized mode. Conclusion A system was developed for in situ S-parameter measurements combined with a method for determining radiated power, allowing a complete assessment of the power balance of multichannel transmit coils at 7T. |
Zitierung
Weidemann, G., Seifert, F., Hoffmann, W., Pfeiffer, H., Seemann, R., & Ittermann, B. (2016). Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T. Magnetic Resonance Materials in Physics, Biology and Medicine, 29(3), 371–378. https://doi.org/10.1007/s10334-016-0551-6