Wideband Self‐Grounded Bow‐Tie Antenna for Thermal MR

The objective of this study was the design, implementation, evaluation and application of a compact wideband self-grounded bow-tie (SGBT) radiofrequency (RF) antenna building block that supports anatomical proton ((1) H) MRI, fluorine ((19) F) MRI, MR thermometry and broadband thermal intervention integrated in a whole-body 7.0 T system. Design considerations and optimizations were conducted with numerical electromagnetic field (EMF) simulations to facilitate a broadband thermal intervention frequency of the RF antenna building block. RF transmission (B1 (+) ) field efficiency and specific absorption rate (SAR) were obtained in a phantom, and the thigh of human voxel models (Ella, Duke) for (1) H and (19) F MRI at 7.0 T. B1 (+) efficiency simulations were validated with actual flip-angle imaging measurements. The feasibility of thermal intervention was examined by temperature simulations (f = 300, 400 and 500 MHz) in a phantom. The RF heating intervention (Pin = 100 W, t = 120 seconds) was validated experimentally using the proton resonance shift method and fiberoptic probes for temperature monitoring. The applicability of the SGBT RF antenna building block for in vivo (1) H and (19) F MRI was demonstrated for the thigh and forearm of a healthy volunteer. The SGBT RF antenna building block facilitated (19) F and (1) H MRI at 7.0 T as well as broadband thermal intervention (234-561 MHz). For the thigh of the human voxel models, a B1 (+) efficiency >/=11.8 muT/ radicalkW was achieved at a depth of 50 mm. Temperature simulations and heating experiments in a phantom demonstrated a temperature increase DeltaT >7 K at a depth of 10 mm. The compact SGBT antenna building block provides technology for the design of integrated 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).