Wideband self-grounded bow-tie antenna for thermal MR


  • T.W. Eigentler
  • L. Winter
  • H. Han
  • E. Oberacker
  • A. Kuehne
  • H. Waiczies
  • S. Schmitter
  • L. Boehmert
  • C. Prinz
  • H.D. Trefna
  • T. Niendorf


  • NMR in Biomedicine


  • NMR Biomed 33 (5): e4274


  • The objective of this study was the design, implementation, evaluation and applica-tion of a compact wideband self-grounded bow-tie (SGBT) radiofrequency(RF) antenna building block that supports anatomical proton (1H) MRI, fluorine (19F)MRI, MR thermometry and broadband thermal intervention integrated in a whole-body 7.0 T system.Design considerations and optimizations were conducted with numerical electromag-netic field (EMF) simulations to facilitate a broadband thermal intervention frequencyof the RF antenna building block. RF transmission (B1+) field efficiency and specificabsorption rate (SAR) were obtained in a phantom, and the thigh of human voxelmodels (Ella, Duke) for1H and19F MRI at 7.0 T. B1+efficiency simulations were vali-dated with actual flip-angle imaging measurements. The feasibility of thermal inter-vention was examined by temperature simulations (f = 300, 400 and 500 MHz) in aphantom. The RF heating intervention (Pin= 100 W, t = 120 seconds) was validatedexperimentally using the proton resonance shift method and fiberoptic probes fortemperature monitoring. The applicability of the SGBT RF antenna building block forin vivo1H and19F MRI was demonstrated for the thigh and forearm of a healthyvolunteer.The SGBT RF antenna building block facilitated19F and1H MRI at 7.0 T as well asbroadband thermal intervention (234-561 MHz). For the thigh of the human voxelmodels, a B1+efficiency≥11.8μT/√kW was achieved at a depth of 50 mm. Tempera-ture simulations and heating experiments in a phantom demonstrated a temperatureincreaseΔT >7 K at a depth of 10 mm.The compact SGBT antenna building block provides technology for the design ofintegrated high-density RF applicators and for the study of the role of temperature in (patho-) physiological processes by adding a thermal intervention dimension to an MRI device (Thermal MR).