Wideband Self‐Grounded Bow‐Tie Antenna for Thermal MR

Abstract

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 wholebody 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 (B 1 + ) 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. B 1 + 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 (P in = 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 B 1 + efficiency ≥11.8 μT/√kW was achieved at a depth of 50 mm. Temperature simulations and heating experiments in a phantom demonstrated a temperature increase ΔT >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

Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment

“…For this purpose, eight arbitrary RF channels (four from each module of the signal generator) were used to generate 400 MHz RF signals using tailored amplitude and phase settings. The RF signals were connected to eight wideband self-grounded bow-tie (SGBT) antennae [ 23 ] immersed in deionized water. The SGBT antennae were arranged in a circular array.…”

“…HT devices are increasingly capable of the personalized radio frequency (RF)-induced heating of target tissue volumes guided by sophisticated treatment planning procedures and thermal dose control [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. Thermal Magnetic Resonance (ThermalMR) is an HT variant that accommodates RF-induced heating [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ], temperature mapping using MR thermometry (MRT) [ 26 , 27 , 28 , 29 ], anatomic and functional imaging and the option for x-nuclei MR imaging (MRI) in a single, multi-purpose RF applicator.…”

Dipole-Fed Rectangular Dielectric Resonator Antennas for Magnetic Resonance Imaging at 7 T: The Impact of Quasi-Transverse Electric Modes on Transmit Field Distribution

“…Later, Ipek et al [14] found that the optimal transmit field efficiency can be achieved for a block with 150 mm × 50 mm × 50 mm and ε r between 90 and 110. Recently, Eigentler et al [15] developed a self-grounded bowtie antenna, which was immersed in a small volume filled with deuterium oxide (D 2 O), but they used quite a large water bolus to ensure a direct contact with a cuboid phantom.…”

“…All these reports [6,[13][14][15] assumed there was a direct contact between the dielectric block and the human body (or a phantom with a flat surface). Yet, such a contact is rather difficult to achieve for a solid, rectangular geometry, and it may not always be feasible in clinical settings.…”

Controlled Release of Therapeutics from Thermoresponsive Nanogels: A Thermal Magnetic Resonance Feasibility Study

“…To apply heat into a target site, controlled manipulation of temperature is required while concomitantly characterizing its outcome in vivo. Here, we used thermal magnetic resonance (ThermalMR) that provides RF-induced temperature modulation, temperature monitoring using MR thermometry, anatomic reference, functional imaging, and (nano)molecular probing in an integrated RF applicator [ 29 , 30 , 33 ].…”